| 1. |
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| 2. |
- Di Nitto, A., et al.
(författare)
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Study of Non-fusion Products in the 50Ti+249Cf Reaction
- 2018
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 784, s. 199-205
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Tidskriftsartikel (refereegranskat)abstract
- The isotopic distribution of nuclei produced in the 50Ti + 249Cf reaction has been studied at the gas-filled recoil separator TASCA at GSI Darmstadt, which separates ions according to differences in magnetic rigidity. The bombardment was performed at an energy around the Bass barrier and with the TASCA magnetic fields set for collecting fusion-evaporation reaction products. Fifty-three isotopes located “north-east” of 208Pb were identified as recoiling products formed in non-fusion channels of the reaction. These recoils were implanted with energies in two distinct ranges; besides one with higher energy, a significant low-energy contribution was identified. The latter observation was not expected to occur according to kinematics of the known types of reactions, namely quasi-elastic, multi-nucleon transfer, deep-inelastic collisions or quasifission. The present observations are discussed within the framework of two-body kinematics passing through the formation of a composite system.
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| 3. |
- Düllmann, Ch. E., et al.
(författare)
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Production and Decay of Element 114: High Cross Sections and the New Nucleus 277Hs
- 2010
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Ingår i: Physical Review Letters. - 1079-7114. ; 104:25
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Tidskriftsartikel (refereegranskat)abstract
- The fusion-evaporation reaction 244Pu(48Ca, 3-4n)288,289114 was studied at the new gas-filled recoil separator TASCA. Thirteen correlated decay chains were observed and assigned to the production and decay of 288,289114. At a compound nucleus excitation energy of E* = 39.8-43.9 MeV, the 4n evaporation channel cross section was 9.8(-3.1)(+3.9) pb. At E* = 36.1-39.5 MeV, that of the 3n evaporation channel was 8.0-(+7.4)(4.5) pb. In one of the 3n evaporation channel decay chains, a previously unobserved alpha branch in 281Ds was observed ( probability to be of random origin from background: 0.1%). This alpha decay populated the new nucleus 277Hs, which decayed by spontaneous fission after a lifetime of 4.5 ms.
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| 4. |
- Espegren, Fredrik, 1989, et al.
(författare)
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Tellurium transport in the RCS under conditions relevant for severe nuclear accidents
- 2021
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Ingår i: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 139
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Tidskriftsartikel (refereegranskat)abstract
- In the case of a severe nuclear power plant accident, tellurium is one of the more problematic and volatile fission products. If released it could become a health issue as it decays to iodine which accumulates in the thyroid gland. Research exists, that indicates tellurium likely interacts with caesium under severe accident conditions, thus it is important to further explore related phenomenon. In this work, tellurium was exposed to high temperature under oxidizing and inert conditions simulating severe accident conditions with and without airborne caesium iodide to determine the effect on the tellurium source term. The effect of caesium iodide was noticeable on tellurium transport behaviour in the gas phase under oxidizing and inert conditions. Under humid oxidizing conditions with caesium iodide, no significant impact on the total aerosol mass transport was noticed. However, less tellurium was transported through the model primary circuit and a potentially new compound was observed on the filter located after this model. Comparing inert dry to humid with caesium iodide showed an increase in the total aerosol mass transport whereas there was a decrease noticed of the tellurium reaching the filter after the model primary circuit. In the latter case, new unidentified compound(s) correlated to caesium, iodine and tellurium were observed on the filter located after the model. In this work, evidence was found that tellurium behaviour will be affected by caesium iodide under the investigated conditions. Moreover, it seems that under inert conditions the formed compounds may be stable at close to ambient temperatures. Unlike under oxidizing conditions, where dissociation likely occurred.
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| 5. |
- Forsberg, Ulrika, et al.
(författare)
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First Experiment at TASCA Towards X-Ray Fingerprinting of Element 115 Decay Chains
- 2012
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Ingår i: Acta Physica Polonica. Series B: Elementary Particle Physics, Nuclear Physics, Statistical Physics, Theory of Relativity, Field Theory. - 0587-4254. ; 43:2, s. 305-311
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Tidskriftsartikel (refereegranskat)abstract
- To identify the atomic number of superheavy nuclei produced in Ca-48-induced fusion-evaporation reactions, an experiment aiming at measuring characteristic X-rays is being prepared at GSI, Darmstadt, Germany. The gas-filled separator TASCA will be employed, sending the residues towards the multi-coincidence detector setup TASISpec. Two ion-optical modes relying on differing magnetic polarities of the quadrupole magnets can be used at TASCA. New simulations and experimental tests of transmission and background suppression for these two focusing modes into TASISpec are presented.
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| 6. |
- Forsberg, U., et al.
(författare)
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Recoil-α-fission and recoil-α-α-fission events observed in the reaction 48Ca + 243Am
- 2016
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Ingår i: Nuclear Physics, Section A. - : Elsevier BV. - 0375-9474. ; 953, s. 117-138
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Tidskriftsartikel (refereegranskat)abstract
- Products of the fusion-evaporation reaction 48Ca + 243Am were studied with the TASISpec set-up at the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. Amongst the detected thirty correlated α-decay chains associated with the production of element Z=115, two recoil-α-fission and five recoil-α-α-fission events were observed. The latter five chains are similar to four such events reported from experiments performed at the Dubna gas-filled separator, and three such events reported from an experiment at the Berkeley gas-filled separator. The four chains observed at the Dubna gas-filled separator were assigned to start from the 2n-evaporation channel 289115 due to the fact that these recoil-α-α-fission events were observed only at low excitation energies. Contrary to this interpretation, we suggest that some of these recoil-α-α-fission decay chains, as well as some of the recoil-α-α-fission and recoil-α-fission decay chains reported from Berkeley and in this article, start from the 3n-evaporation channel 288115.
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| 7. |
- Forsberg, Ulrika, et al.
(författare)
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Spectroscopic Tools Applied to Element Z = 115 Decay Chains
- 2014
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X .- 2101-6275. - 9782759811755 - 9782759811762 ; 66, s. 02036-02036
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Konferensbidrag (refereegranskat)abstract
- Nuclides that are considered to be isotopes of element Z = 115 were produced in the reaction 48Ca + 243Am at the GSI Helmholtzzentrum für Schwerionenforschung Darmstadt. The detector setup TASISpec was used. It was mounted behind the gas-filled separator TASCA. Thirty correlated α-decay chains were found, and the energies of the particles were determined with high precision. Two important spectroscopic aspects of the offline data analysis are discussed in detail: the handling of digitized preamplified signals from the silicon strip detectors, and the energy reconstruction of particles escaping to upstream detectors relying on pixel-by-pixel dead-layer thicknesses.
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| 8. |
- Gates, J. M., et al.
(författare)
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First Superheavy Element Experiments at the GSI Recoil Separator TASCA: The Production and Decay of Element 114 in the 244Pu(48Ca,3-4n) Reaction
- 2011
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 83:5
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Tidskriftsartikel (refereegranskat)abstract
- Experiments with the new recoil separator, Transactinide Separator and Chemistry Apparatus (TASCA), at the GSI were performed by using beams of Ca-48 to irradiate targets of Pb206-208, which led to the production of No252-254 isotopes. These studies allowed for evaluation of the performance of TASCA when coupled to a new detector and electronics system. By following these studies, the isotopes of element 114 ((288-291)114) were produced in irradiations of Pu-244 targets with Ca-48 beams at compound nucleus excitation energies around 41.7 and 37.5 MeV, demonstrating TASCA's ability to perform experiments with picobarn-level cross sections. A total of 15 decay chains were observed and were assigned to the decay of 288-291114. A new a-decay branch in (281)Ds was observed, leading to the new nucleus (277)Hs.
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| 9. |
- Gausemel, H., et al.
(författare)
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Decay of 127In and 129In.
- 2004
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Ingår i: Phys. Rev. C. ; 69:054307
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Tidskriftsartikel (refereegranskat)
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| 10. |
- Graeger, R., et al.
(författare)
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Experimental Study of the 238U(36S,3-5n)269-271Hs Reaction Leading to the Observation of 270Hs
- 2010
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 81:6
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Tidskriftsartikel (refereegranskat)abstract
- The deformed doubly magic nucleus (270)Hs has so far only been observed as the four-neutron (4n) evaporation residue of the reaction Mg-26+Cm-248, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of (270)Hs in the 4n evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict that the reactions Ca-48+Ra-226 and S-36+U-238 result in higher cross sections due to lower reaction Q values, in contrast to simple arguments based on the reaction asymmetry, which predict opposite trends. Calculations using HIVAP predict cross sections for the reaction S-36+U-238 that are similar to those of the Mg-26+Cm-248 reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction S-36+U-238 and the observation of (270)Hs, which is produced in the 4n evaporation channel, with a measured cross section of 0.8(-0.7)(+2.6) pb at 51-MeV excitation energy. The one-event cross-section limits (68% confidence level) for the 3n, 4n, and 5n evaporation channels at 39-MeV excitation energy are 2.9 pb, while the cross-section limits of the 3n and 5n channel at 51 MeV are 1.5 pb. This is significantly lower than the 5n cross section of the Mg-26+Cm-248 reaction at similar excitation energy.
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| 11. |
- Khuyagbaatar, J., et al.
(författare)
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48Ca+249Bk Fusion Reaction Leading to Element Z=117: Long-Lived α-Decaying 270Db and Discovery of 266Lr
- 2014
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Ingår i: Physical Review Letters. - 1079-7114. ; 112:17
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Tidskriftsartikel (refereegranskat)abstract
- The superheavy element with atomic number Z=117 was produced as an evaporation residue in the 48Ca+249Bk fusion reaction at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. The radioactive decay of evaporation residues and their α-decay products was studied using a detection setup that allowed measuring decays of single atomic nuclei with half-lives between sub-μs and a few days. Two decay chains comprising seven α decays and a spontaneous fission each were identified and are assigned to the isotope 294-117 and its decay products. A hitherto unknown α-decay branch in 270Db (Z=105) was observed, which populated the new isotope 266Lr (Z=103). The identification of the long-lived (T1/2=1.0+1.9−0.4 h) α-emitter 270Db marks an important step towards the observation of even more long-lived nuclei of superheavy elements located on an “island of stability.”
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| 12. |
- Khuyagbaatar, J., et al.
(författare)
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Fusion reaction 48Ca + 249Bk leading to formation of the element Ts (Z=117)
- 2019
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Ingår i: Physical Review C. - 2469-9985. ; 99:5
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Tidskriftsartikel (refereegranskat)abstract
- The heaviest currently known nuclei, which have up to 118 protons, have been produced in 48Ca induced reactions with actinide targets. Among them, the element tennessine (Ts), which has 117 protons, has been synthesized by fusing 48Ca with the radioactive target 249Bk, which has a half-life of 327 d. The experiment was performed at the gas-filled recoil separator TASCA. Two long and two short α decay chains were observed. The long chains were attributed to the decay of 294Ts. The possible origin of the short-decay chains is discussed in comparison with the known experimental data. They are found to fit with the decay chain patterns attributed to 293Ts. The present experimental results confirm the previous findings at the Dubna Gas-Filled Recoil Separator on the decay chains originating from the nuclei assigned to Ts.
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| 13. |
- Khuyagbaatar, J., et al.
(författare)
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Search for elements 119 and 120
- 2020
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Ingår i: Physical Review C. - 2469-9985. ; 102:6
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Tidskriftsartikel (refereegranskat)abstract
- A search for production of the superheavy elements with atomic numbers 119 and 120 was performed in the 50Ti+249Bk and 50Ti+249Cf fusion-evaporation reactions, respectively, at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. Over four months of irradiation, the 249Bk target partially decayed into 249Cf, which allowed for a simultaneous search for both elements. Neither was detected at cross-section sensitivity levels of 65 and 200 fb for the 50Ti+249Bk and 50Ti+249Cf reactions, respectively, at a midtarget beam energy of Elab = 281.5 MeV. The nonobservation of elements 119 and 120 is discussed within the concept of fusion-evaporation reactions including various theoretical predictions on the fission-barrier heights of superheavy nuclei in the region of the island of stability.
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| 14. |
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| 15. |
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| 16. |
- Kučera, Jan, et al.
(författare)
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Tellurium determination by three modes of instrumental neutron activation analysis in aerosol filters and trap solutions for the simulation of a severe nuclear accident
- 2020
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Ingår i: Microchemical Journal. - : Elsevier BV. - 0026-265X. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- Tellurium belongs to the elements not frequently determined by neutron activation analysis (NAA) or other analytical methods. We present results of a new methodological study using three independent modes of instrumental NAA (INAA) using the 123mTe, 131Te and 131I radionuclides. We compare the results obtained in terms of accuracy, precision and limits of detection (LOD). We utilized the INAA procedures tested for the tellurium determination in aerosol filters and trap solutions in a model experiment aimed at reducing the knowledge gap concerning the behaviour of 132Te, a radiologically significant fission product, which constitutes a considerable health risk towards the public in case of its release in a severe nuclear power plant accident. We found that the nuclear reaction 130Te(n,γ)131Te and gamma-ray spectrometric measurement of 131I, a descendant of 131Te, is the most sensitive way of Te determination by INAA providing as low LOD values as 0.15 µg of Te in the Teflon aerosol filters and 0.22 µg mL-1 in the 0.1 M NaOH trap solutions. The three independent INAA modes allowed employing the self-verification principle of INAA for increasing the trustworthiness of our results. Finally, we also point to the indispensable role of the non-destructive feature of INAA for assay of samples, such as Teflon aerosol filters, that are difficult to be analysed by other analytical methods requiring complete sample destruction without analyte losses.
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| 17. |
- Langrock, G., et al.
(författare)
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Digital liquid-scintillation counting and effective pulse-shape discrimination with artificial neural networks
- 2015
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 103:1, s. 15-25
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Tidskriftsartikel (refereegranskat)abstract
- A typical problem in low-level liquid scintillation (LS) counting is the identification of alpha particles in the presence of a high background of beta and gamma particles. Especially the occurrence of beta-beta and beta-gamma pile-ups may prevent the unambiguous identification of an alpha signal by commonly used analog electronics. In this case, pulse-shape discrimination (PSD) and pile-up rejection (PUR) units show an insufficient performance. This problem was also observed in own earlier experiments on the chemical behaviour of transactinide elements using the liquid-liquid extraction system SISAK in combination with LS counting alpha-particle signals from the decay of the transactinides could not be unambiguously assigned. However, the availability of instruments for the digital recording of LS pulses changes the situation and provides possibilities for new approaches in the treatment of LS pulse shapes. In a SISAK experiment performed at PSI, Villigen, a fast transient recorder, a PC card with oscilloscope characteristics and a sampling rate of 1 giga samples s(-1) (1 ns per point), was used for the first time to record LS signals. It turned out, that the recorded signals were predominantly alpha, beta-beta and beta-gamma pile up, and fission events. This paper describes the subsequent development and use of artificial neural networks (ANN) based on the method of "back-propagation of errors" to automatically distinguish between different pulse shapes. Such networks can "learn" pulse shapes and classify hitherto unknown pulses correctly after a learning period. The results show that ANN in combination with fast digital recording of pulse shapes can be a powerful tool in LS spectrometry even at high background count rates.
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| 18. |
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| 19. |
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| 20. |
- Rudolph, Dirk, et al.
(författare)
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Alpha-Photon Coincidence Spectroscopy Along Element 115 Decay Chains
- 2014
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Ingår i: Acta Physica Polonica. Series B: Elementary Particle Physics, Nuclear Physics, Statistical Physics, Theory of Relativity, Field Theory. - 0587-4254. ; 45, s. 263-272
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Tidskriftsartikel (refereegranskat)abstract
- Produced in the reaction 48Ca+243Am, thirty correlated α-decay chains were observed in an experiment conducted at the GSI Helmholzzentrum für Schwerionenforschung, Darmstadt, Germany. The decay chains are basically consistent with previous findings and are considered to originate from isotopes of element 115 with mass numbers 287, 288, and 289. A set-up aiming specifically for high-resolution charged particle and photon coincidence spectroscopy was placed behind the gas-filled separator TASCA. For the first time, γ rays as well as X-ray candidates were observed in prompt coincidence with the α-decay chains of element 115.
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| 21. |
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| 22. |
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| 23. |
- Rudolph, Dirk, et al.
(författare)
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Selected Spectroscopic Results on Element 115 Decay Chains
- 2015
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Ingår i: Journal of Radioanalytical and Nuclear Chemistry. - : Springer Science and Business Media LLC. - 0236-5731 .- 1588-2780. ; 303:2, s. 1185-1190
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Tidskriftsartikel (refereegranskat)abstract
- Thirty correlated alpha-decay chains were observed in an experiment studying the fusion-evaporation reaction 48Ca + 243Am at the GSI Helmholtzzentrum f¨ur Schwerionenforschung. The decay characteristics of the majority of these 30 chains are consistent with previous observations and interpretations of such chains to originate from isotopes of element Z = 115. High-resolution alpha-photon coincidence spectroscopy in conjunction with comprehensive Monte-Carlo simulations allow to propose excitation schemes of atomic nuclei of the heaviest elements, thereby probing nuclear structure models near the ‘Island of Stability’ with unprecedented experimental precision.
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| 24. |
- Rudolph, Dirk, et al.
(författare)
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Spectroscopy of Element 115 Decay Chains
- 2013
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Ingår i: Physical Review Letters. - 1079-7114. ; 111:11
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Tidskriftsartikel (refereegranskat)abstract
- A high-resolution , X-ray and gamma-ray coincidence spectroscopy experiment was conducted at the GSI Helmholtzzentrum für Schwerionenforschung. Thirty correlated alpha-decay chains were detected following the fusion-evaporation reaction 48Ca + 243Am. The observations are consistent with previous assignments of similar decay chains to originate from element Z = 115. For the first time, precise spectroscopy allows the derivation of excitation schemes of isotopes along the decay chains starting with elements Z > 112. Comprehensive Monte-Carlo simulations accompany the data analysis. Nuclear structure models provide a first level interpretation.
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| 25. |
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