| 1. |
- Desidera, S., et al.
(författare)
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The SPHERE infrared survey for exoplanets (SHINE) I. Sample definition and target characterization
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 651
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Tidskriftsartikel (refereegranskat)abstract
- Context. Large surveys with new-generation high-contrast imaging instruments are needed to derive the frequency and properties of exoplanet populations with separations from ~5 to 300 au. A careful assessment of the stellar properties is crucial for a proper understanding of when, where, and how frequently planets form, and how they evolve. The sensitivity of detection limits to stellar age makes this a key parameter for direct imaging surveys.Aims. We describe the SpHere INfrared survey for Exoplanets (SHINE), the largest direct imaging planet-search campaign initiated at the VLT in 2015 in the context of the SPHERE Guaranteed Time Observations of the SPHERE consortium. In this first paper we present the selection and the properties of the complete sample of stars surveyed with SHINE, focusing on the targets observed during the first phase of the survey (from February 2015 to February 2017). This early sample composed of 150 stars is used to perform a preliminary statistical analysis of the SHINE data, deferred to two companion papers presenting the survey performance, main discoveries, and the preliminary statistical constraints set by SHINE.Methods. Based on a large database collecting the stellar properties of all young nearby stars in the solar vicinity (including kinematics, membership to moving groups, isochrones, lithium abundance, rotation, and activity), we selected the original sample of 800 stars that were ranked in order of priority according to their sensitivity for planet detection in direct imaging with SPHERE. The properties of the stars that are part of the early statistical sample wererevisited, including for instance measurements from the Gaia Data Release 2. Rotation periods were derived for the vast majority of the late-type objects exploiting TESS light curves and dedicated photometric observations.Results. The properties of individual targets and of the sample as a whole are presented.
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| 2. |
- Osborn, H. P., et al.
(författare)
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The PDS 110 observing campaign - photometric and spectroscopic observations reveal eclipses are aperiodic
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 485:2, s. 1614-1625
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Tidskriftsartikel (refereegranskat)abstract
- PDS 110 is a young disc-hosting star in the Orion OB1A association. Two dimming events of similar depth and duration were seen in 2008 (WASP) and 2011 (KELT), consistent with an object in a closed periodic orbit. In this paper, we present data from a ground-based observing campaign designed to measure the star both photometrically and spectroscopically during the time of predicted eclipse in 2017 September. Despite high-quality photometry, the predicted eclipse did not occur, although coherent structure is present suggesting variable amounts of stellar flux or dust obscuration. We also searched for radial velocity (RV) oscillations caused by any hypothetical companion and can rule out close binaries to 0.1Ms. Asearch of Sonneberg plate archive data also enabled us to extend the photometric baseline of this star back more than 50 yr, and similarly does not re-detect any deep eclipses. Taken together, they suggest that the eclipses seen in WASP and KELT photometry were due to aperiodic events. It would seem that PDS 110 undergoes stochastic dimmings that are shallower and of shorter duration than those of UX Ori variables, but may have a similar mechanism.
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| 3. |
- Plompen, A. J. M., et al.
(författare)
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The joint evaluated fission and fusion nuclear data library, JEFF-3.3
- 2020
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 56:7
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Forskningsöversikt (refereegranskat)abstract
- The joint evaluated fission and fusion nuclear data library 3.3 is described. New evaluations for neutron-induced interactions with the major actinides 235U, 238U and 239Pu, on 241Am and 23Na, 59Ni, Cr, Cu, Zr, Cd, Hf, W, Au, Pb and Bi are presented. It includes new fission yields, prompt fission neutron spectra and average number of neutrons per fission. In addition, new data for radioactive decay, thermal neutron scattering, gamma-ray emission, neutron activation, delayed neutrons and displacement damage are presented. JEFF-3.3 was complemented by files from the TENDL project. The libraries for photon, proton, deuteron, triton, helion and alpha-particle induced reactions are from TENDL-2017. The demands for uncertainty quantification in modeling led to many new covariance data for the evaluations. A comparison between results from model calculations using the JEFF-3.3 library and those from benchmark experiments for criticality, delayed neutron yields, shielding and decay heat, reveals that JEFF-3.3 performes very well for a wide range of nuclear technology applications, in particular nuclear energy.
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| 4. |
- Pastorello, A., et al.
(författare)
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INTERACTING SUPERNOVAE AND SUPERNOVA IMPOSTORS : SN 2009ip, IS THIS THE END?
- 2013
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 767:1, s. 1-
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Tidskriftsartikel (refereegranskat)abstract
- We report the results of a three-year-long dedicated monitoring campaign of a restless luminous blue variable (LBV) in NGC 7259. The object, named SN 2009ip, was observed photometrically and spectroscopically in the optical and near-infrared domains. We monitored a number of erupting episodes in the past few years, and increased the density of our observations during eruptive episodes. In this paper, we present the full historical data set from 2009 to 2012 with multi-wavelength dense coverage of the two high-luminosity events between 2012 August and September. We construct bolometric light curves and measure the total luminosities of these eruptive or explosive events. We label them the 2012a event (lasting similar to 50 days) with a peak of 3x10(41) erg s(-1), and the 2012b event (14 day rise time, still ongoing) with a peak of 8 x 1042 erg s(-1). The latter event reached an absolute R-band magnitude of about -18, comparable to that of a core-collapse supernova (SN). Our historical monitoring has detected high-velocity spectral features (similar to 13,000 km s(-1)) in 2011 September, one year before the current SN-like event. This implies that the detection of such high-velocity outflows cannot, conclusively, point to a core-collapse SN origin. We suggest that the initial peak in the 2012a event was unlikely to be due to a faint core-collapse SN. We propose that the high intrinsic luminosity of the latest peak, the variability history of SN 2009ip, and the detection of broad spectral lines indicative of high-velocity ejecta are consistent with a pulsational pair-instability event, and that the star may have survived the last outburst. The question of the survival of the LBV progenitor star and its future fate remain open issues, only to be answered with future monitoring of this historically unique explosion.
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| 5. |
- Biller, B. A., et al.
(författare)
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Dynamical masses for two M1 + mid-M dwarf binaries monitored during the SPHERE-SHINE survey
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 658
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Tidskriftsartikel (refereegranskat)abstract
- We present orbital fits and dynamical masses for HIP 113201AB and HIP 36985AB, two M1 + mid-M dwarf binary systems monitored as part of the SPHERE-SHINE survey. To robustly determine the age of both systems via gyrochronology, we undertook a photometric monitoring campaign for HIP 113201 and GJ 282AB, the two wide K star companions to HIP 36985, using the 40 cm Remote Observatory Atacama Desert telescope. Based on this monitoring and gyrochronological relationships, we adopt ages of 1.2 ± 0.1 Gyr for HIP 113201AB and 750 ± 100 Myr for HIP 36985AB. These systems are sufficiently old that we expect that all components of these binaries have reached the main sequence. To derive dynamical masses for all components of the HIP 113201AB and HIP 36985AB systems, we used parallel-tempering Markov chain Monte Carlo sampling to fit a combination of radial velocity, direct imaging, and Gaia and HIPPARCOS astrometry. Fitting the direct imaging and radial velocity data for HIP 113201 yields a primary mass of 0.54 ± 0.03 M⊙, fully consistent with its M1 spectral type, and a secondary mass of 0.145 ± M⊙. The secondary masses derived with and without including HIPPARCOS-Gaia data are all considerably more massive than the 0.1 M⊙ mass estimated from the photometry of the companion. Thus, the dynamical impacts of this companion suggest that it is more massive than expected from its photometry. An undetected brown dwarf companion to HIP 113201B could be a natural explanation for this apparent discrepancy. At an age >1 Gyr, a 30 MJup companion to HIP 113201B would make a negligible (<1%) contribution to the system luminosity but could have strong dynamical impacts. Fitting the direct imaging, radial velocity, and HIPPARCOS-Gaia proper motion anomaly for HIP 36985AB, we find a primary mass of 0.54 ± 0.01 M⊙ and a secondary mass of 0.185 ± 0.001 M⊙, which agree well with photometric estimates of component masses, the masses estimated from MK– mass relationships for M dwarf stars, and previous dynamical masses in the literature.
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| 6. |
- Gatera, A., et al.
(författare)
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Prompt-fission γ -ray spectral characteristics from Pu 239 (nth,f)
- 2017
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 95:6
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present new results for prompt fission γ-ray spectral characteristics from the thermal neutron induced fission of Pu∗240. The measured spectra were unfolded by using the detectors' response functions, simulated with geant4. We obtained in average per fission a γ-ray multiplicity Mγ=(7.35±0.12), a mean photon energy ϵγ=(0.85±0.02) MeV, and an average total energy released in fission Ēγ,tot=(6.27±0.11) MeV. Our results are in good agreement with historical data measured in the 1970s by Verbinski et al. and results from recent calculations in the framework of Monte Carlo Hauser-Feshbach models. Our measured average total energy is slightly smaller than the one deduced previously and present in evaluated data. From this we conclude that the Pu239(nth,f) reaction may be ruled out as possible source of γ heating underestimation, when compared with benchmark calculations based on existing nuclear data.
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| 7. |
- Munari, U., et al.
(författare)
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The GALAH survey and symbiotic stars - I. Discovery and follow-up of 33 candidate accreting-only systems
- 2021
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 505:4, s. 6121-6154
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Tidskriftsartikel (refereegranskat)abstract
- We have identified a first group of 33 new candidates for symbiotic stars (SySt) of the accreting-only variety among the 600 255 stars so far observed by the GALactic Archaeology with HERMES (GALAH) high-resolution spectroscopic survey of the Southern hemisphere, more than doubling the number of those previously known. GALAH aims to high latitudes and this offers the possibility to sound the Galaxy for new SySt away from the usual plane and bulge hunting regions. In this paper, we focus on SySt of the M spectral type, showing an Hα emission with a peak in excess of 0.5 above the adjacent continuum level, and not affected by coherent radial pulsations. These constraints will be relaxed in future studies. The 33 new candidate SySt were subjected to an array of follow-up confirmatory observations [X-ray/ultraviolet (UV) observations with the Swift satellite, search for optical flickering, presence of a near-UV upturn in ground-based photometric and spectroscopic data, radial velocity changes suggestive of orbital motion, and variability of the emission-line profiles]. According to Gaia Early Data Release 3 (EDR3) parallaxes, the candidate new SySt are located at the tip of the giant branch, sharing the same distribution in M(Ks) of the well-established SySt. The accretion luminosities of the candidate new SySt are in the range 1-10 L⊙, corresponding to mass accretion rates of 0.1-1 × 10-9 M⊙ yr-1 for white dwarfs of 1 M⊙. The M giant of one of them presents a large lithium overabundance.
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| 8. |
- Billnert, Robert, 1981, et al.
(författare)
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Novel Scintillation Detectors for Prompt Fission γ-Ray Measurements
- 2012
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3884 .- 1875-3892. ; 31, s. 29-34
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Konferensbidrag (refereegranskat)abstract
- In this work we present first results from measurements of prompt fission γ-rays from the spontaneous fission in 252Cf. New and accurate data on corresponding γ-rays from the reactions 235U(nth,f) and 239Pu(nth,f) are highly demanded for the modeling of new Generation-IV nuclear reactor systems. For these experiments we employed scintillation detectors made out of new materials (LaBr3, LaCl3 and CeBr3), whose properties were necessary to know in order to obtain reliable results. Hence, we have characterized these detectors. In all the important properties these detectors outshine sodium-iodine detectors that where used in the 1970s, when the existing data had been acquired. Our finding is that the new generation of scintillation detectors is indeed promising, as far as an improved precision of the demanded data is concerned.
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| 9. |
- Göök, A., et al.
(författare)
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Photo-fission at the S-DALINAC
- 2009
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Ingår i: 4th international workshop on nuclear fission and fission-product spectroscopy. - : American Institute of Physics (AIP). - 9780735407145 ; , s. 351-354
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Experiments on photo-induced fission of 238U and 234U using bremsstrahlung with endpoint energies between 6 MeV and 9 MeV have been carried out at the superconducting Darmstadt electron linear accelerator S-DALINAC. A twin Frisch grid ionization chamber has been used to determine energy and mass distributions via the 2E-technique. The fission fragment emission angle, which is used to correct for energy loss in the target and backing material for a correct determination of fragment energy and mass, is deduced from the time difference between cathode and anode signals. The research program including the foreseen search for parity violation in photo-induced fission and first experimental results will be presented. © 2009 American Institute of Physics.
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| 10. |
- Hambsch, F.-J., F. Tovesson, S. Oberstedt, V. Frisch, A. Oberstedt, B. Fogelberg, and E. Ramström
(författare)
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First measurement of the 233Pa Fission Cross Section.
- 2003
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Ingår i: 10th International Seminar on Interaction of Neutrons with Nuclei. Neutron Spectroscopy, Nuclear Structure, Related Topics, 2003 202. ; , s. 202-
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Konferensbidrag (refereegranskat)
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| 11. |
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| 12. |
- Hambsch, F.-J., Tovesson, F., Oberstedt, S., Oberstedt, A., Fogelberg, B. and Ramström, E.
(författare)
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First Direct Measurements of the 233Pa Fission Cross Section up to 8.5 MeV
- 2002
-
Konferensbidrag (refereegranskat)
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| 13. |
- Makii, H., et al.
(författare)
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Effects of the nuclear structure of fission fragments on the high-energy prompt fission γ -ray spectrum in U 235 (nth,f)
- 2019
-
Ingår i: Physical Review C. - 2469-9985. ; 100:4
-
Tidskriftsartikel (refereegranskat)abstract
- The prompt fission γ-ray energy spectrum for cold-neutron-induced fission of U235 was measured in the energy range Eγ=0.8-20MeV, by gaining a factor of about 105 in statistics compared to the measurements performed so far. The spectrum exhibits local bump structures at Eγ≈4MeV and ≈6MeV, and also a broad one at ≈15MeV. In order to understand the origins of these bumps, the γ-ray spectra were calculated using a statistical Hauser-Feshbach model, taking into account the deexcitation of all the possible primary fission fragments. It is shown that the bump at ≈4MeV is created by the transitions between the discrete levels in the fragments around Sn132, and the bump at ≈6MeV mostly comes from the complementary light fragments. It is also indicated that a limited number of nuclides, which have high-spin states at low excitation energies, can contribute to the bump structure around Eγ≈15MeV, induced by the transition feeding into the low-lying high-spin states.
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| 14. |
- Oberstedt, Andreas, et al.
(författare)
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Characterization of LaCl3:Ce detectors for prompt fission gamma-ray measurements
- 2009
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Ingår i: 4th international workshop on nuclear fission and fission-product spectroscopy. - : American Institute of Physics (AIP). - 9780735407145 ; , s. 257-260
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The properties of cylindrical 1.5//×1.5//LaCl3:Cescintillation detectors were determined. For the energy resolution values between 3.8 and 4.2% at 662 keV were observed, following the expected E-1/2 behavior. The intrinsic full peak efficiency was determined to be more than 50% higher than for NaI:Tl detectors of same size. The observed intrinsic timing resolution for 60Co was estimated to 441 ps and the intrinsic activity of the lanthanum crystals was assessed. © 2009 American Institute of Physics.
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| 15. |
- Oberstedt, Andreas, 1960-, et al.
(författare)
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Identification of prompt fission gamma-rays with lanthanum-chloride scintillation detectors
- 2012
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 668, s. 14-20
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we demonstrate the employment of LaCl3 : Ce scintillation detectors for the identification of prompt fission gamma-rays from gamma-radiation in contrast to other reactions. We present the properties of cylindrical 1.5 in. x 1.5 in. detectors in terms of intrinsic activity, energy resolution, intrinsic full peak efficiency and intrinsic timing resolution. In addition, we show results from the measurement of gamma-rays emitted in coincidence with the spontaneous fission of Cf-252, which lead us to the conclusion that the properties of the detectors used in this work, in particular the good timing resolution and a reasonably good energy resolution, are more than just sufficient for the assessment of prompt gamma-heat in future nuclear reactors as requested by the OECD. Hence, in our opinion, LaCl3 : Ce detectors, compared to those made out of LaBr3 : Ce crystals, represent an appropriate and quasi low-cost choice for the above mentioned applications.
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| 16. |
- Oberstedt, Andreas, 1961, et al.
(författare)
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Identification of prompt fission γ-rays with lanthanum-chloride scintillation detectors
- 2012
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 668:0, s. 14--20-20
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we demonstrate the employment of LaCl3:Ce scintillation detectors for the identification of prompt fission γ-rays from γ-radiation in contrast to other reactions. We present the properties of cylindrical 1.5 in.×1.5 in. detectors in terms of intrinsic activity, energy resolution, intrinsic full peak efficiency and intrinsic timing resolution. In addition, we show results from the measurement of γ-rays emitted in coincidence with the spontaneous fission of 252Cf, which lead us to the conclusion that the properties of the detectors used in this work, in particular the good timing resolution and a reasonably good energy resolution, are more than just sufficient for the assessment of prompt γ-heat in future nuclear reactors as requested by the OECD. Hence, in our opinion, LaCl3:Ce detectors, compared to those made out of LaBr3:Ce crystals, represent an appropriate and quasi low-cost choice for the above mentioned applications.
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| 17. |
- Oberstedt, Andreas, 1961, et al.
(författare)
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Prompt fission gamma-ray spectra characteristics - systematics and predictions
- 2015
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3884 .- 1875-3892. ; 64, s. 91-100
-
Konferensbidrag (refereegranskat)abstract
- Revised systematics for prompt fission gamma-ray spectra (PFGS) characteristics as function of both atomic and mass number of the compound system, derived from recent experiments on thermal-neutron induced and spontaneous fission, is presented and applied to fission induced by fast neutrons. Results from these calculations for U-238(n, f) and U-235(n, f) for incident neutron energies from 0 to 20 MeV are compared to new experimental results, exhibiting nice agreement. Very recent PFGS measurements for Pu-240(sf) and Pu-242(sf) have been evaluated and the determined PFGS characteristics are shown to also fit well with the systematics. From this we conclude that the obtained systematics, although purely empirical, is indeed a useful tool for the prediction of average total gamma-ray energy released in prompt fission, mean energy per photon as well as average photon multiplicity for fissioning systems, which are difficult or even impossible to study experimentally. (C) 2015 The Authors. Published by Elsevier B.V.
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| 18. |
- Oberstedt, S., et al.
(författare)
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Correlation measurements of fission-fragment properties
- 2010
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X.
-
Konferensbidrag (refereegranskat)abstract
- For the development of future nuclear fission applications and for a responsible handling of nuclear waste the a-priori assessment of the fission-fragments' heat production and toxicity is a fundamental necessity. The success of an indispensable modelling of the fission process strongly depends on a good understanding of the particular mechanism of scission, the mass fragmentation and partition of excitation energy. Experimental observables are fission-fragment properties like mass- and energy-distributions, and the prompt neutron as well as γ-ray multiplicities and emission spectra. The latter quantities should preferably be known as a function of fragment mass and excitation energy. Those data are highly demanded as published by the OECD-NEA in its high priority data request list. With the construction of the double (v, E) spectrometer VERDI we aim at measuring pre- and post-neutron masses directly and simultaneously to avoid prompt neutron corrections. From the simultaneous measurement of pre- and post-neutron fission-fragment data the prompt neutron multiplicity may then be inferred fully correlated with fragment mass yield and total kinetic energy. Using an ultra-fast fission event trigger spectral prompt fission γ-ray measurements may be performed. For that purpose recently developed lanthanum-halide detectors, with excellent timing characteristics, were coupled to the VERDI spectrometer allowing for a very good discrimination of fission γ-rays and prompt neutrons due to their different time-of-flight.
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| 19. |
- Oberstedt, S., et al.
(författare)
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Future research program on prompt gamma-ray emission in nuclear fission
- 2015
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-601X .- 1434-6001. ; 51:12, s. 1-9
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Forskningsöversikt (refereegranskat)abstract
- In recent years the measurement of prompt fission gamma-ray spectra (PFGS) has gained renewed interest, after about forty years since the first comprehensive studies of the reactions U-235(n(th), f), Pu-239(n(th), f) and Cf-252(sf). The renaissance was initiated by requests for new values especially for.-ray multiplicity and average total energy release per fission in neutron-induced fission of U-235 and Pu-239. Both isotopes are considered the most important ones with respect to the modeling of innovative cores required for the Generation-IV reactors, the majority working with fast neutrons. During the last 5 years we have conducted a systematic study of spectral data for thermal-neutron-induced fission on U-235 and Pu-241 as well as for the spontaneous fission of Cf-252 with unprecedented accuracy. From the new data we conclude that those reactions do not considerably contribute to the observed heat excess and suspect other reactions playing a significant role. Possible contributions may originate from fast-neutron-induced reactions on U-238, which is largely present in the fuel, or from gamma-induced fission from neutron capture in the construction material. A first experiment campaign on prompt gamma-ray emission from fast-neutron-induced fission on U-235,U-238 was successfully performed in order to test our assumptions. In the following we attempt to summarize, what has been done in the field to date, and to motivate future measurement campaigns exploiting dedicated neutron and photon beams as well as upcoming highly efficient detector assemblies.
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| 20. |
- Oberstedt, S., et al.
(författare)
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Prompt fission gamma-ray spectra characteristics - a first summary
- 2015
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3884 .- 1875-3892. ; 64, s. 83-90
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Konferensbidrag (refereegranskat)abstract
- In this work we give an overview of our investigations of prompt gamma-ray emission in nuclear fission. This work was conducted during the last five years in response to a high priority nuclear data request formulated by the OECD/NEA. The aim was to reveal data deficiencies responsible for a severe under-prediction of the prompt gamma heating in nuclear reactor cores. We obtained new prompt fission gamma-ray spectral (PFGS) data for Cf-252(SF) as well as for thermal-neutron induced fission on U-235(nth,f) and Pu-241(nth,f). In addition, first PFGS measurements with a fast-neutron beam were accomplished, too. The impact of the new data and future data needs are discussed.
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| 21. |
- Oberstedt, S., et al.
(författare)
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Prompt fission γ -rays from the reactions 252Cf(SF) and 235U(nth, f) - New data
- 2013
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 62, s. Art. no. 02003-
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Konferensbidrag (refereegranskat)abstract
- We present new spectral data of prompt γ-ray emission from the spontaneous fission of 252Cf. This work was performed in direct response to an OECD/NEA high priority data request. We discuss the impact of our new data on evaluated nuclear data tables not only for this nuclide, but also for 238U and 241Pu, which are always produced in a reactor. Furthermore, we will show results from our investigation of prompt γ-ray emission from the reaction 235 U(nth, f), measured in at the Centre for Energy Research of the Hungarian Academy of Sciences in Budapest, Hungary. Spectral data obtained with three different detectors are consistent and led to an uncertainty on total energy and multiplicity considerably smaller than requested by the OECD/NEA.
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| 22. |
- Peck, M., et al.
(författare)
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Pulse-height defect of Ar+CF4 mixtures as a counting gas for fission-fragment detectors
- 2019
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier B.V.. - 0168-9002 .- 1872-9576. ; 919, s. 105-112
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Tidskriftsartikel (refereegranskat)abstract
- For the detection of energetic charged particles, gaseous ionization detectors use a variety of counting gases. We studied the properties of non-flammable, high stopping-power Ar+CF4 as counting gas. We assess the usability of different mixtures for compact, high-luminosity fast ionization chambers for future applications in nuclear photonics. The pulse-height defect (PHD) of Ar+CF4 mixtures at different pressures has been extracted in comparison to P-10 gas (90%Ar+10%CH4) for fragments from 252Cf spontaneous fission in a twin Frisch-grid ionization chamber. For the different mixtures of Ar+CF4 (P-10), a PHD of 4.5–11MeV (4MeV) and 6–12MeV (5.5MeV) for light and heavy fragments, respectively, have been measured. Based on these findings, reconstructed 252Cf mass and total kinetic energy distributions are consistent with literature, which demonstrates success in the PHD correction procedure.
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| 23. |
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| 24. |
- Tovesson, F., Hambsch, F.-J., Oberstedt, A., Fogelberg, B., Ramström, E. and Oberstedt, S.
(författare)
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Determination of the 233Pa(n,f) reaction cross section for thorium fueled reactors
- 2002
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Ingår i: Proceedings of Workshop on Advanced Reactors with Innovative Fuels ARWIF 2001, Chester, UK, Oct 22-24,2001, Nuclear Energy Agency, 2002 461.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 25. |
- Tovesson, F., Hambsch, F.-J., Oberstedt, A., Fogelberg, B., Ramström, E. and Oberstedt, S.
(författare)
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The Pa-233 Fission Cross Section
- 2002
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Ingår i: Proc.of the Int.conf. on Nuclear Data for Science and Technology, Oct.7-12, 2001, Tsukuba, Japan. Journal of Nuclear Science and Technology, Supplement 2, (August 2002) 210.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 26. |
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| 27. |
- Tovesson, F., V.Fritsch, F.-J.Hambsch, S.Oberstedt, A.Oberstedt, B.Fogelberg, E.Ramstrom
(författare)
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The 233Pa fission cross-section
- 2003
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Ingår i: IRMM Neutron Physics Unit 2002 Scientific Report; EUR 20684 EN.
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 28. |
- Vladuca, G., et al.
(författare)
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Calculation of the neutron-induced fission cross section of 233Pa up to 20 MeV
- 2004
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Ingår i: Nuclear Physics A. - : Elsevier BV. - 0375-9474 .- 1873-1554. ; 740:1-2, s. 3-19
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Tidskriftsartikel (refereegranskat)abstract
- Since very recently, direct measurements of the 233Pa(n,f) cross-section are available in the energy range from 1.0 to 8.5 MeV. This has stimulated a new, self-consistent, neutroncross-section evaluation for the n+233Pa system, in the incident neutron energy range 0.01–20MeV. Since higher fission chances are involved also the lighter Pa-isotopes had to be re-evaluated in a consistent manner. The results are quite different compared to earlier evaluation attempts. Since 233Pa is a key isotope in the thorium based fuel cycle the quality of its reaction cross-sections is important for the modeling of future advanced fuel and reactor concepts. The present status of the evaluated libraries is that they differ by a factor of two in the absolute fissioncross-section and also in the threshold energy value.
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| 29. |
- Al-Adili, Ali, et al.
(författare)
-
Analysis of prompt fission neutrons in U-235(nth,f) and fission fragment distributions for the thermal neutron induced fission of U-234
- 2016
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Ingår i: CNR*15 - 5th International Workshop On Compound-Nuclear Reactions And Related Topics. - : EDP Sciences.
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the ongoing analysis of two fission experiments. Both projects are part of the collaboration between the nuclear reactions group at Uppsala and the JRC-IRMM. The first experiment deals with the prompt fission neutron multiplicity in the thermal neutron induced fission of U-235(n,f). The second, on the fission fragment properties in the thermal fission of U-234(n,f). The prompt fission neutron multiplicity has been measured at the JRC-IRMM using two liquid scintillators in coincidence with an ionization chamber. The first experimental campaign focused on U-235(nth,f) whereas a second experimental campaign is foreseen later for the same reaction at 5.5 MeV. The goal is to investigate how the so-called saw-tooth shape changes as a function of fragment mass and excitation energy. Some harsh experimental conditions were experienced due to the large radiation background. The solution to this will be discussed along with preliminary results. In addition, the analysis of thermal neutron induced fission of U-234(n,f) will be discussed. Currently analysis of data is ongoing, originally taken at the ILL reactor. The experiment is of particular interest since no measurement exist of the mass and energy distributions for this system at thermal energies. One main problem encountered during analysis was the huge background of U-235(nth, f). Despite the negligible isotopic traces in the sample, the cross section difference is enormous. Solution to this parasitic background will be highlighted.
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| 30. |
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| 31. |
- Al-Adili, Ali, et al.
(författare)
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Prompt fission neutron yields in thermal fission of U-235 and spontaneous fission of Cf-252
- 2020
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Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 102:6
-
Tidskriftsartikel (refereegranskat)abstract
- Background: The sharing of excitation energy between the fission fragments is one of the key issues in studying nuclear fission. One way to address this is by studying prompt-fission neutron multiplicities as a function of other fission observables such as the mass, (nu) over bar (A). These are vital benchmark data for both fission and nuclear deexcitation models, putting constrains on the fragment excitation energy and hence on the competing prompt neutron/gamma-ray emission. Despite numerous detailed studies, recent measurements done at JRC-Geel with the SCINTIA array in the epithermal region show surprisingly strong discrepancies to earlier thermal fission data and the Wahl systematics. Purpose: The purpose was to perform measurements of the prompt-fission neutron multiplicity, as a function of fragment mass and total kinetic energy (TKE), in U-235(n(th), f) and Cf-252(sf), to verify and extend the SCINTIA results. Another goal was to validate the analysis methods, and prepare for planned investigations at excitation energies up to 5.5 MeV. Methods: The experiments were conducted at the former 7 MV Van de Graaff facility in JRC-Geel, using a Twin Frisch-Grid Ionization Chamber and two liquid scintillation detectors. A neutron beam with an average energy of 0.5 MeV was produced via the Li-7(p,n) reaction. The neutrons were thermalized by a 12 cm thick block of paraffin. Digital data acquisition systems were utilized. Comprehensive simulations were performed to verify the methodology and to investigate the role of the mass and energy resolution on measured (nu) over bar (A) and (nu) over bar (TKE) values. The simulation results also revealed that the partial derivative(nu) over bar/partial derivative A and partial derivative(TKE) over bar/partial derivative(nu) over bar are affected by the mass and energy resolution. However, the effect is small for the estimated resolutions of this work. Detailed Fluka simulations were performed to calculate the fraction of thermal neutron-induced fission, which was estimated to be about 98%. Results: The experimental results on (nu) over bar (A) are in good agreement with earlier data for Cf-252(sf). For U-235(n(th), f), the (nu) over bar (A) data is very similar to the data obtained with SCINTIA, and therefore we verify these disclosed discrepancies to earlier thermal data and to the Wahl evaluation. The experimental results on (nu) over bar (TKE) are also in agreement with the data at epithermal energies. For Cf-252(sf) a slope value of partial derivative(TKE) over bar/partial derivative(nu) over bar = (-12.9 f 0.2) MeV/n was obtained. For U-235(n(th), f) the value is (-12.0 +/- 0.1) MeV/n. Finally, the neutron spectrum in the center-of-mass system was derived and plotted as a function of fragment mass. Conclusions: This work clearly proves the lack of accurate correlation between fission fragment and neutron data even in the best-studied reactions. The new results highlight the need of a new evaluation of the prompt-fission multiplicity for U-225(n(th), f).
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| 32. |
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| 33. |
- Al-Adili, Ali, et al.
(författare)
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Sensitivity of Measured Fission Yields on Prompt-neutron Corrections
- 2014
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Ingår i: Nuclear Data Sheets. - : Elsevier BV. - 0090-3752 .- 1095-9904. ; 119, s. 342-345
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Tidskriftsartikel (refereegranskat)abstract
- Although the number of emitted prompt neutrons from the fission fragments increases as a function of excitation energy, it is not fully understood whether the increase in (nu) over bar (A) as a function of E-n is mass dependent. The share of excitation energies among the fragments is still under debate, but there are reasons to believe that the excess in neutron emission originates only from the heavy fragments, leaving (nu) over bar (light) (A) almost unchanged. We have investigated the consequences of a mass-dependent increase in (nu) over bar (A) on the final mass and energy distributions. The analysis have been performed on experimentally measured data on U-234(n, f). The assumptions concerning (nu) over bar (A) are essential when analysing measurements based on the 2E-technique, and impact significantly on the measured observables. For example, the post-neutron emission mass yield distribution revealed changes up to 10-30 %. The outcome of this work pinpoints the urgent need to determine (nu) over bar (A) experimentally, and in particular, how (nu) over bar (A) changes as a function of incident neutron energy. Many fission yields in the data libraries could be largely affected, since their analysis is based on a different assumption concerning the neutron emission.
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| 34. |
- Bevilacqua, Riccardo, et al.
(författare)
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A procedure for the characterization of electron transmission through Frisch grids
- 2015
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 770, s. 64-67
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Tidskriftsartikel (refereegranskat)abstract
- In Frisch grid ionization chambers special attention must be paid to the operating voltages in order to avoid unwanted collection of electrons on the Frisch grid. Collection of electrons on the grid will lead to a decreased signal to noise ratio and consequently a deteriorated energy resolution. Furthermore, systematic errors in the determination of the angular distribution will be introduced. Theoretical formulas for minimized collection of electrons on the grid were derived by Bunemann et al. [3] in the special case of a Frisch grid consisting of a plane of parallel wires. No such formulas exist for other grid geometries and a careful calibration procedure is needed. We describe here a procedure for characterizing the Frisch grid in terms of its transparency to electrons for a grid consisting of a mesh of crossed wires.
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| 35. |
- Billnert, Robert, 1981, et al.
(författare)
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New prompt spectral gamma-ray data from the reaction Cf-252(sf) and its implication on present evaluated nuclear data files
- 2013
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 87:2
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Tidskriftsartikel (refereegranskat)abstract
- We present results from new spectral prompt gamma-ray measurements from the spontaneous fission of Cf-252. Apart from one recent experiment, about four decades have passed since the last dedicated experiments were reported in the literature. Hence, there was a need for a revision. We have measured prompt fission. rays with both cerium-doped LaBr3 and CeBr3 scintillation detectors, both of which exhibit excellent timing and good energy resolution. The emission yield was determined to be nu(gamma) = (8.30 +/- 0.08)/fission and nu(gamma) = (8.31 +/- 0.10)/fission, with the average energy of is an element of(gamma) = (0.80 +/- 0.01) MeV and is an element of(gamma) = (0.80 +/- 0.01) MeV and total energy of E-gamma,E-tot = (6.64 +/- 0.08) MeV and E-gamma,E-tot = (6.65 +/- 0.12) MeV, with the LaBr3 and CeBr3 detectors, respectively. Since the results from the two detectors are in excellent agreement and confirm the historical data, but not those in the present evaluated nuclear data files, we strongly recommend an update.
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| 36. |
- Carlson, A. D., et al.
(författare)
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A new evaluation of the neutron data standards
- 2017
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Ingår i: ND 2016. - : EDP Sciences. - 9782759890200
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Konferensbidrag (refereegranskat)abstract
- Evaluations are being done for the H(n,n), 6Li(n,t), 10B(n,αγ), 10B(n,α), C(n,n), Au(n,γ), 235U(n,f) and 238U(n,f) standard cross sections. Evaluations are also being done for data that are not traditional standards including: the Au(n,γ) cross section at energies below where it is considered a standard; reference cross sections for prompt gamma-ray production in fast neutron-induced reactions; reference cross sections for very high energy fission cross sections; the 235U thermal neutron fission spectrum and the 252Cf spontaneous fission neutron spectrum and the thermal constants.
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| 37. |
- Carlson, A. D., et al.
(författare)
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Evaluation of the Neutron Data Standards
- 2018
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Ingår i: Nuclear Data Sheets. - : Elsevier BV. - 0090-3752 .- 1095-9904. ; 148, s. 143-188
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Tidskriftsartikel (refereegranskat)abstract
- With the need for improving existing nuclear data evaluations, (e.g., ENDF/B-VIII.0 and JEFF-3.3 releases) the first step was to evaluate the standards for use in such a library. This new standards evaluation made use of improved experimental data and some developments in the methodology of analysis and evaluation. In addition to the work on the traditional standards, this work produced the extension of some energy ranges and includes new reactions that are called reference cross sections. Since the effort extends beyond the traditional standards, it is called the neutron data standards evaluation. This international effort has produced new evaluations of the following cross section standards: the H(n,n), Li-6(n,t), B-10(n, alpha), B-10(n,alpha(1)gamma), C-nat(n,n), Au(n,gamma), U-235(n,f) and U-238(n,f). Also in the evaluation process the U-238(n,gamma) and Pu-239(n,f) cross sections that are not standards were evaluated. Evaluations were also obtained for data that are not traditional standards: the Maxwellian spectrum averaged cross section for the Au(n,gamma) cross section at 30 keV; reference cross sections for prompt gamma-ray production in fast neutron-induced reactions; reference cross sections for very high energy fission cross sections; the Cf-252 spontaneous fission neutron spectrum and the U-235 prompt fission neutron spectrum induced by thermal incident neutrons; and the thermal neutron constants. The data and covariance matrices of the uncertainties were obtained directly from the evaluation procedure.
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| 38. |
- Göök, Alf, et al.
(författare)
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A position-sensitive twin ionization chamber for fission fragment and prompt neutron correlation experiments
- 2016
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier B.V.. - 0168-9002 .- 1872-9576. ; 830, s. 366-374
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Tidskriftsartikel (refereegranskat)abstract
- A twin position-sensitive Frisch grid ionization chamber, intended as a fission fragment detector in experiments to study prompt fission neutron correlations with fission fragment properties, is presented. Fission fragment mass and energies are determined by means of the double kinetic energy technique, based on conservation of mass and linear momentum. The position sensitivity is achieved by replacing each anode plate in the standard twin ionization chamber by a wire plane and a strip anode, both readout by means of resistive charge division. This provides information about the fission axis orientation, which is necessary to reconstruct the neutron emission process in the fully accelerated fragment rest-frame. The energy resolution compared to the standard twin ionization chamber is found not to be affected by the modification. The angular resolution of the detector relative to an arbitrarily oriented axis is better than 7° FWHM. Results on prompt fission neutron angular distributions in 235U(n,f) obtained with the detector in combination with an array of neutron scintillation detectors is presented as a proof of principle.
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| 39. |
- Göök, A., et al.
(författare)
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Application of the ShockleyRamo theorem on the grid inefficiency of Frisch grid ionization chambers
- 2012
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 664:1, s. 289-293
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Tidskriftsartikel (refereegranskat)abstract
- The concept of grid inefficiency in Frisch grid ionization chambers and its influence on the anode pulse shape is explained in terms of the ShockleyRamo theorem for induced charges. The grid inefficiency correction is deduced from numerically calculated weighting potentials. A method to determine the correction factor experimentally is also presented. Experimental and calculated values of the correction factor are shown to be in good agreement.
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| 40. |
- Göök, A., et al.
(författare)
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Prompt neutron multiplicity in correlation with fragments from spontaneous fission of Cf 252
- 2014
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Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 90:6
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Tidskriftsartikel (refereegranskat)abstract
- The spontaneous fission of Cf252 serves as an excellent benchmark of prompt emission in fission since experimental data can be obtained without the need of an incident beam. With the purpose of providing experimental data on the prompt fission neutron properties in correlation with fission-fragment characteristics, an experiment on Cf252(SF) has been performed. In addition, the experiment serves as a benchmark of setup and analysis procedures for measurements of fluctuations in the prompt-neutron properties as a function of incident neutron energy in fission of the major actinides U235 and Pu239. The experiment employs a twin Frisch grid ionization chamber as fission-fragment detector while neutrons were counted by using a liquid scintillator placed along the symmetry axis of the ionization chamber. Average neutron multiplicity has been obtained as a function of fission-fragment mass and total kinetic energy (TKE). The average multiplicity as a function of mass agrees well with available data in the literature in the mass range from 80 to 170 u. The existence of additional sawtooth structures in the far asymmetric mass region could not be confirmed, although the statistical accuracy of the present experiment is as good as the previous study where such structures have been reported [Nucl. Phys. A 490, 307 (1988).NUPABL0375-947410.1016/0375-9474(88)90508-8]. The available data in the literature on the TKE dependence of the multiplicity show strong deviations. Therefore, effort was focused on investigating experimental factors in low-efficiency neutron-counting experiments that may lead to faulty determination of this dependence. Taking these factors into account, a result that agrees well with data from high-efficiency neutron-counting experiments is obtained. The experimental arrangement allows determination of the angle between the detected neutron and the fission axis, which permits the neutron properties to be transformed into the fission-fragment rest frame. Fission neutron emission spectra in the fragment center-of-mass frame have thereby been obtained as a function of the fission-fragment mass and TKE.
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| 41. |
- Göök, A., et al.
(författare)
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Prompt neutrons in correlation with fission fragments from U 235 (n,f)
- 2018
-
Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 98:4
-
Tidskriftsartikel (refereegranskat)abstract
- Improved knowledge of prompt emission in fission has significant implications for our understanding of the fission process. It is also important for improving nuclear data evaluation, with impact on applications. The correlation between prompt neutrons and fragments emitted in binary neutron induced fission of U235 has been studied at the GELINA facility. The experiment employs an array of proton recoil scintillators and a position-sensitive twin ionization chamber. This experimental arrangement permits measurement of the correlations between neutron emission, fragment angle, and mass and energy of the fission fragments. In this article, we present results on prompt fission neutron energy and multiplicity correlations with mass and total kinetic energy of the fission fragments. Results from the present measurement shows distinct differences compared to earlier studies of the correlated fission fragment and prompt neutron emission quantities. The differences with respect to earlier investigations are interpreted as improved fission fragment energy resolution in the present measurement. The present result supports several recent model calculations of prompt neutron and fission fragment correlations.
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| 42. |
- Hambsch, F. -J, et al.
(författare)
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Fission Fragment Yield, Cross Section and Prompt Neutron and Gamma Emission Data from Actinide Isotopes
- 2014
-
Ingår i: Nuclear Data Sheets. - : Elsevier BV. - 0090-3752 .- 1095-9904. ; 119, s. E38-E41
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Tidskriftsartikel (refereegranskat)abstract
- Recent experimental investigations on major and minor actinides at the JRC-IRMM are presented. Fission-fragment distributions of isotopes with vibrational resonances in the sub-threshold fission cross section, i. e. U-234,U-238, have been measured. For U-234, the impact of an increased neutron multiplicity for the heavy fragments with higher incident neutron energies has been studied as observed in experiment and also recently theoretically predicted. The impact is found to be noticeable on post-neutron mass yields, which are the relevant quantities for a-priori waste assessments. The fission cross sections for Pu-240,Pu-242 at threshold and in the plateau region are being investigated within the ANDES project. The results show some discrepancies to the ENDF/B-VII. 1 evaluation mainly for Pu-242 around 1 MeV, where the evaluation exhibits a resonance-like structure not observed so clearly in the present work. The requested target accuracy in design studies of innovative reactor concepts like Gen-IV is in the range of a few percent. In order to be able to respond to requests for measurements of prompt neutron and gamma-ray emission in fission JRC-IRMM has also invested in setting up a neutron and gamma-ray detector array. The neutron array is called SCINTIA and has so far been tested with Cf-252(SF). For gamma-ray multiplicity and spectrum measurements of Cf-252(SF) and U-235(n(th), f) lanthanum- and cerium-halide detectors were successfully used.
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| 43. |
- Hambsch, F. -J, et al.
(författare)
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Investigation of the Fission Process at IRMM
- 2011
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Ingår i: Journal of the Korean Physical Society. - : Korean Physical Society. - 0374-4884 .- 1976-8524. ; 59:2, s. 1654-1659
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Tidskriftsartikel (refereegranskat)abstract
- The investigation of the fission process is and has been a major undertaking at IRMM. The most recent investigations concerned the reaction (234)U(n,f) and (238)U(n,f) around vibrational resonances at the barrier of the fission cross-section. Furthermore prompt neutron emission of (252)Cf(SF) has been investigated understanding for the first time the prompt neutron multiplicity as a function of total kinetic energy (TKE). Theoretical modelling of reaction cross sections as well as prompt neutron multiplicity and spectra has been performed using the experimental data as input parameters. Also instrument developments for correlation measurements of fission fragment properties has been pursued in recent years with the time-of-flight spectrometer VERDI and detectors for prompt fission gamma-ray.
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| 44. |
- Hambsch, F. -J, et al.
(författare)
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Prompt Neutron Emission Correlations with Fission Fragment Properties
- 2018
-
Ingår i: Fission And Properties Of Neutron-Rich Nuclei. - : World Scientific. - 9789813229433 ; , s. 503-512
-
Konferensbidrag (refereegranskat)abstract
- The investigation of the dynamics of the nuclear fission process has been a standing research topic at the JRC-Geel during the past decades. Recently the focus was put on the de-excitation of fission fragments through the emission of prompt neutrons and gamma-rays. To this end new detector systems were developed at JRC-Geel, e.g. a position sensitive ionization chamber used in conjunction with the neutron scintillator array SCINTIA. The array has been tested using the spontaneous fission of Cf-252. The goal is to study correlations of fission fragments with prompt neutron emission in the resolved resonance region. No strong fluctuations of the average prompt neutron multiplicity for the strongest resonances in U-235 were observed. From the present data the mass-dependent neutron multiplicity, v(A), was generated. The v(A) distribution shows a more pronounced dip around the doubly magic mass A = 132 and at very low masses around A similar to 80 compared to the literature. In addition, a steeper slope for v(TKE) is observed. Cross checking with fragment data clearly shows a narrower mass and total kinetic energy (TKE) distribution. The 2E-2v spectrometer VERDI (VElocity foR Direct mass Identification) became operational. For Cf-252(sf) superior mass resolution is observed compared to a twin Frisch-grid ionization chamber. For post-neutron mass distributions still some issues need to be solved and v(A), being the difference of pre- and post-neutron mass distributions, is still deviating from literature data. Eventually, VERDI will provide a complementary measurement technique to assess v(A) and v(TKE). In addition, an experimental campaign to measure v(A) as a function of incident neutron energy for different actinides has been started. First tests show promising results.
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| 45. |
- Oberstedt, Andreas, 1961, et al.
(författare)
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Impact of low-energy photons on the characteristics of prompt fission gamma-ray spectra
- 2015
-
Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 92:1
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we report on a new study of prompt gamma-rays from the spontaneous fission of Cf-252. Photons were measured in coincidence with fission fragments by employing four different lanthanide halide scintillation detectors. Together with results from a previous work of ours, we determined characteristic parameters with high precision, such as the average gamma-ray multiplicity (nu) over bar (gamma) = (8.29 +/- 0.13), the average energy per photon is an element of(gamma) = (0.80 +/- 0.02) MeV, and the total gamma-ray energy release per fission E-gamma,(tot) = (6.65 +/- 0.10) MeV. The excellent agreement between the individual results obtained in all six measurements proves the good repeatability of the applied experimental technique. The impact of low-energy photons, i.e., below 500 keV, on prompt fission gamma-ray spectra characteristics has been investigated as well by comparing our results with those taken with the DANCE detector system, which appears to suffer from absorption effects in the low-energy region. Correction factors for this effect were estimated, giving results comparable to ours as well as to historical ones. From this we demonstrate that the different techniques of determining the average gamma-ray multiplicity, either from a properly measured and normalized spectrum or a measured multiplicity distribution, give equivalent and consistent results.
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| 46. |
- Oberstedt, Andreas, et al.
(författare)
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Improved values for the characteristics of prompt-fission gamma-ray spectra from the reaction U-235(n(th), f)
- 2013
-
Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X .- 2469-9985 .- 2469-9993. ; 87:5, s. 051602-
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present results from measurements of prompt gamma rays from the thermal neutron induced fission of U-235. Photons were measured in coincidence with fission fragments with cerium-doped LaCl3 and LaBr3 as well as CeBr3 scintillation detectors, which offer an intriguing combination of excellent timing resolution and good resolving power. The spectra measured with all employed detectors are in excellent agreement with respect to their shapes. Characteristic parameters were extracted for a gamma-energy range from 0.1 to 6.0 MeV and the results obtained with several detectors were averaged. From that, the average emission yield of prompt-fission gamma rays was determined to be (nu) over bar (gamma) = (8.19 +/- 0.11) per fission, the average energy per photon to be epsilon(gamma) = (0.85 +/- 0.02) MeV, and the total energy to be E-gamma,E-tot = (6.92 +/- 0.09) MeV. The uncertainties are much lower than the 7.5% requested for the modeling of advanced nuclear reactor cores. Estimating the influence of gamma rays with energies between 6 and 10 MeV on the values determined in this work revealed a negligible deviation of the order of the found uncertainties.
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| 47. |
- Oberstedt, Andreas, 1960-, et al.
(författare)
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New prompt fission gamma-ray spectral data and its implication on present evaluated nuclear data files
- 2013
-
Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892 .- 1875-3884. ; 47, s. 156-165
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we report on new spectral prompt gamma-ray measurements from the spontaneous fission of Cf-252 and thermal neutron-induced fission of U-236*. In both experiments, fission of U-236*. In both experiments, gamma-ray multiplicities, average and total gamma-energies were extracted. gamma-ray multiplicities, average and total.-energies were extracted. Apart from one recent measurement on Cf-252, about four decades have passed since the last dedicated experiments were reported in literature. Hence, there was a need for a revision, not only with respect to high priority nuclear data requests by the Nuclear Energy Agency (NEA). In the first mentioned experiment we have measured prompt fission gamma-rays with both cerium-doped LaBr3 and CeBr3 scintillation detectors, which both exhibit excellent timing and good energy resolution. The results from both detectors are in excellent agreement with each other and confirm the historical data. In the experiment on U-235(n(th), f) we employed cerium-doped LaCl3 detectors, together with the lanthanum bromide detectors mentioned above. Even here the first results indicate a good agreement with data from the early 1970' s. They are also in accordance with data in evaluated libraries like ENDF/B-VII.0, while this is not the case for Cf-252(SF). Hence, here an update is strongly recommended.
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| 48. |
- Oberstedt, S., et al.
(författare)
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Artificial diamonds as radiation-hard detectors for ultra-fast fission-fragment timing
- 2013
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 714, s. 31-37
-
Tidskriftsartikel (refereegranskat)abstract
- In the framework of the construction of the double time-of-flight spectrometer VERDI, where we aim at measuring pre- and post-neutron masses directly and simultaneously, ultra-fast time pick-up detectors based on artificial diamond material were investigated for the first time with fission fragments from Cf-252 (0.5 MeV/u < E/A < 2 MeV/u). Signal stability under a high radiation fluence was determined up to at least 10(9) fission-fragments/cm(2) together with more than 3.5 x 10(9) neutrons/cm(2) and 3 x 10(10) alpha-particles/cm(2). This fluence is characteristic for fission experiments. The pre-requisite for the observed signal stability is the application of priming of the diamond material with a strong beta-source for about 48 h. The intrinsic timing resolution of a 100 mu m thick polycrystalline CVD diamond detector with a size of 1 x 1 cm(2) was determined to sigma(int) = (283 +/- 41) ps by comparison with Monte-Carlo simulations. Using broadband pre-amplifiers, 4-fold segmented detectors of same total size and with a thickness of 180 mu m show an intrinsic timing resolution of sigma(int) = (106 +/- 21) ps. This is highly competitive with the best micro-channel plate detectors. Due to the limited and batch-dependent charge collection efficiency of poly-crystalline diamond material, the detection efficiency for fission fragments may be smaller than 100%.
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| 49. |
- Oberstedt, S., et al.
(författare)
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First results on the neutron-induced fission cross-section of Pa-231 for incident neutron energies E-n > 17 MeV
- 2012
-
Ingår i: Annals of Nuclear Energy. - : Elsevier. - 0306-4549 .- 1873-2100. ; 43, s. 26-30
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Tidskriftsartikel (refereegranskat)abstract
- First results on the neutron-induced fission cross-section of Pa-231 for incident neutron energies E-n > 17 MeV are presented. The experiments were carried out with quasi mono-energetic neutrons produced in the reaction T(d, n)He-4. Corrections for low-energy neutron background produced in this reaction at incident deuteron energies E-d > 2 MeV are taken into account and based on experimental data obtained by two different techniques. Despite the relatively large error bars at the higher neutron energies, the new cross-section values meet the accuracy requirements set by the IAEA and will allow to remove the hitherto existing large spread between different previously published data. Recent cross-section calculations describe well the new experimental results, which are in consistency with cross-section values obtained in a particle-transfer reaction at excitation energies corresponding to neutron energies E-n < 10 MeV.
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| 50. |
- Oberstedt, S., et al.
(författare)
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High-precision prompt-gamma-ray spectral data from the reaction Pu-241(n(th), f)
- 2014
-
Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 90:2, s. Art. no. 024618-
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present results from the first high-precision prompt-gamma-ray spectral measurements from the reaction Pu-241(n(th), f). Apart from one recent experiment, no data are reported in the literature for this fissioning system, which motivated a new dedicated experiment. We have measured prompt-fission gamma rays with three cerium-doped LaBr3 (two 5.08 cm x 5.08 cm and one 7.62 cm x 7.62 cm) and one CeBr3 (5.08 cm x 5.08 cm) scintillation detectors, which all exhibit excellent timing and good energy resolution. The average gamma-ray multiplicity was determined to be (nu) over bar (gamma) = (8.21 +/- 0.09) per fission, the average energy to be epsilon(gamma) = (0.78 +/- 0.01) MeV, and the total energy to be E-gamma,E-tot = (6.41 +/- 0.06) MeV as the weighted average from all detectors. Since the results from all detectors are in excellent agreement, and the total released gamma energy is modestly higher than the one in the present evaluated nuclear data files, we suspect that the underestimation of the prompt-gamma heating in nuclear reactors is due to fast-neutron-induced fission on U-238 or rather from fission induced by gamma rays from neutron capture in the construction material.
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