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Sökning: WFRF:(CEDERWALL Bo) > (2005-2009)

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1.
  • Khaplanov, Anton, 1980- (författare)
  • Applications of Pulse Shape Analysis Techniques for Segmented Planar Germanium Detectors
  • 2007
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The application of pulse shape analysis (PSA) and γ-ray tracking techniques has attracted a great deal of interest in the recent years in fields ranging from nuclear structure studies to medical imaging. These new data analysis methods add position sensitivity as well as directional information for the detected γ-rays to the excellent energy resolution of germanium detectors. This thesis focuses on the application of PSA on planar segmented germanium detectors, divided into three separate studies. The pulse shape analysis technique known as the matrix method was chosen due to its ability to treat events with arbitrary number and combinations of interactions within a single detector. It has been applied in two experiments with the 25-fold segmented planar pixel detector -- imaging and polarization measurements -- as well as in a simulation of upcoming detectors for DESPEC at NuSTAR/FAIR. In the first experiment, a point source of 137Cs was imaged. Events where the 662 keV γ-rays scattered once and were then absorbed in a different segment were treated by the PSA algorithm in order to find the locations of these interactions. The Compton scattering formula was then used to determine the direction to the source. The experiment has provided a robust test of the performance of the PSA algorithm on multiple interaction events, in particular those with interactions in adjacent segments, as well as allowed to estimate the realistically attainable position resolution. In the second experiment, the response of the detector to polarized photons of 288 keV was studied. The polarization of photons can be measured through the observation of the angular distribution of Compton-scattered photons, Hence the ability to resolve the interaction locations had once again proven useful. The third study is focused on the performance of the proposed planar germanium detectors for the DESPEC array. As these detectors have not yet been manufactured at the time of this writing, a set of data simulated in GEANT4 was used. The detector response was calculated for two of the possible segmentation patterns -- that with a single pixelated contact and one where both contacts are segmented into mutually orthogonal strips. In both cases, PSA was applied in order to reconstruct the interaction locations from this response. It was found that the double-sided strip detector can achieve an over-all better position resolution with a given number of readout channels. However, this comes at the expense of a small number of complex events where the reconstruction fails. These results have also been compared to the performance of the 25-fold pixelated detector.
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2.
  • Al-Khatib, A., et al. (författare)
  • Competition between collective and noncollective excitation modes at high spin in Ba-124
  • 2006
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 74:1
  • Tidskriftsartikel (refereegranskat)abstract
    • High-spin states in Ba-124 were investigated in two experiments using the Ni-64(Ni-64, 4n)Ba-124 reaction at three different beam energies. In-beam gamma-ray coincidences were measured with the Euroball and Gammasphere detector arrays. In the experiment with Euroball, the CsI detector array Diamant was employed to discriminate against charged-particle channels. Six new rotational bands were observed in Ba-124, and previously known bands were extended to higher spins. One of the bands shows a transition from collective to noncollective behavior at high spins. Configuration assignments are suggested on the basis of comparison with cranked shell model and cranked Nilsson-Strutinsky calculations.
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3.
  • Al-Khatib, A., et al. (författare)
  • High-spin states in Ba-124
  • 2005
  • Ingår i: Acta Physica Polonica B. - 0587-4254 .- 1509-5770. ; 36:4, s. 1029-1032
  • Tidskriftsartikel (refereegranskat)abstract
    • High-spin states in Ba-124 were populated using the Ni-64 (Ni-64,4n) Ba-124 reaction at beam energies of 255 and 261 MeV. Gamma-ray coincidences were measured using the EUROBALL detector array. The charged-particle detector array DIAMANT provided channel selection. The previously known rotational bands are extended to higher spins. Five new hands are observed, one of them extends up to the spin 40h region.
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4.
  • Andgren, Karin, et al. (författare)
  • Excited states in the neutron-deficient nuclei Rn-197,Rn-199,Rn-201
  • 2008
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 77:5, s. 054303-1-054303-7
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states of the extremely neutron-deficient radon isotopes with N = 111, 113, 115 have been studied for the first time in a series of in-beam experiments performed at the Accelerator Laboratory of the University of Jyvaskyla. The reactions used were: Sn-118(Kr-82, 3n)Rn-197, Sn-120(Kr-82, 3n)Rn-199, Sm-150(Cr-52, 3n)Rn-199, and Sn-122(Kr-82, 3n)Rn-201. The gamma rays emitted from excited states in the different isotopes were identified using the recoil-alpha-decay tagging technique. The estimated cross section for the production of Rn-197(m) was 7(3) nb, which is the lowest cross section reported so far for an in-beam study. The energies of the (17/2(+)) levels built on the isomeric (13/2(+)) states in Rn-197,Rn-199,Rn-201 indicate a transition from an anharmonic vibrational structure toward a rotational structure at low spins for these nuclei. However, the transition is not as sharp as predicted by theory.
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5.
  • Andgren, Karin, et al. (författare)
  • gamma-ray spectroscopy of At-197
  • 2008
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 78:4, s. 044328-1-044328-8
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states of the extremely neutron-deficient nucleus At-197 have been studied in an in-beam experiment using the fusion-evaporation reaction Sn-118(Kr-82,p2n)At-197. gamma rays belonging to At-197 feeding the I-pi=(9/2(-)) ground state, as well as gamma rays feeding the 311-keV I-pi=(13/2(+)) isomer, decaying via the emission of gamma rays, and the 52-keV I-pi=(1/2(+)) alpha-decaying isomer have been identified using the recoil-alpha-decay tagging technique. Total Routhian surface calculations predict a near-spherical shape for the (9/2(-)) ground state and oblate shapes with beta(2) around -0.2 for the (1/2(+)) and the (13/2(+)) states. These predictions agree with our experimental findings.
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6.
  • Andgren, Karin, 1979- (författare)
  • Lifetime measurements of excited states in 165Lu and 107Cd
  • 2006
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Measuring lifetimes of excited nuclear states can give important information on the internal structure of the nucleus. This thesis is based on two experiments performed in Italy and in the USA in order to deduce the lifetimes of excited states in 165Lu and 107Cd. The lifetimes were measured using the Recoil Distance Method and the reduced transition probabilities between states have been calculated from the lifetimes in a model independent way. In the analysis of the data from the experiment on 165Lu, the shape of the nucleus is investigated using a collective rotational model to describe the observed excited states. A possibility of a triaxial shape of this nucleus is discussed. In the second experiment the obtained reduced transition probabilities for the nucleus 107Cd are compared to theoretical predictions for vibrational and rotational excitation modes
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7.
  • Andgren, Karin, et al. (författare)
  • Lifetime measurements of normal deformed states in Lu-165(71)
  • 2005
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 71:1, s. 121-127
  • Tidskriftsartikel (refereegranskat)abstract
    • Picosecond lifetimes of medium spin states in Lu-165 were measured for the first time. The reaction used to populate the nucleus of interest was La-139(Si-30,4n)Lu-165 at a beam energy of 135 MeV. The beam was provided by the XTU-tandem accelerator of Laboratori Nazionali di Legnaro, Italy. By using the differential decay curve method, lifetimes of 19 states in four different rotational bands were obtained. Therefrom the B(E2) values and the transitional quadrupole moments were deduced. The obtained Q(t) for the different bands are compared with total Routhian surface (TRS) calculations and particle-rotor-model calculations. The TRS calculations predict different axial symmetric shapes for the bands built on the 9/2(-)[514], 9/2(+)[404], and 1/2(-)[541] configurations, with a gamma softness for the 9/2(-)[514] configuration. This band has also been studied using the particle-rotor model, the results of which, however, are consistent with a triaxial shape with a gamma value of -15(p).
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8.
  • Andgren, Karin, et al. (författare)
  • Low-spin collective behavior in the transitional nuclei Mo-86,Mo-88
  • 2007
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 76:1, s. 014307-
  • Tidskriftsartikel (refereegranskat)abstract
    • Low-spin structures in Mo-86,Mo-88 were populated using the Ni-58(Ar-36, x alpha yp) heavy-ion fusion-evaporation reaction at a beam energy of 111 MeV. Charged particles and gamma rays were emitted in the reactions and detected by the DIAMANT CsI ball and the EXOGAM Ge array, respectively. In addition to the previously reported low-to-medium spin states in these nuclei, new low-spin structures were observed. Angular correlation and linear polarization measurements were performed in order to unambiguously determine the spins and parities of intensely populated states in Mo-88. Quasiparticle Random Phase Approximation (QRPA) calculations were performed for the first and second excited 2(+) states in Mo-86 and Mo-88. The results are in qualitative agreement with the experimental results, supporting a collective interpretation of the low-spin states for these transitional nuclei.
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9.
  • Andgren, Karin, 1979- (författare)
  • Studies of collective phenomena in neutron deficient nuclei : by means of lifetime measurements, angular correlation measurements and the recoil-decay tagging technique
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The nucleus is a mesoscopic system that retains features from both the quantum and macroscopic worlds. A basic property of a macroscopic body is its shape. Nuclear shapes can be deduced from experimental data as they influence the excitation mode of the nucleus and hence the energies and lifetimes of its excited levels. Various short-lived nuclei were created in fusion-evaporation experiments performed at international heavy-ion accelerator facilities. The emitted γ rays and, in some experiments, also the charged particles and neutrons emitted in the reactions were detected. The studied neutron-deficient isotopes were either selected by the type and number of particles emitted in the reactions, or by using their characteristic decays. The excited states of the different isotopes were extracted from the γ-ray analyses. Spectroscopic properties, such as the lifetimes of the excited states or the angular distribution of the emitted γ rays were measured when possible. The experimentally obtained level schemes together with the other spectroscopic information were used to deduce the excitation modes and the shapes of the studied nuclei. The detector systems are described in the first chapter and in the second chapter some techniques used to extract information from the experimental data are explained. Finally, a brief theoretical overview on the nuclear models which were used to interpret the experimental results is given.
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10.
  • Bianco, L., et al. (författare)
  • alpha-Decay branching ratios measured by gamma-ray tagging
  • 2008
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 597:2-3, s. 189-191
  • Forskningsöversikt (refereegranskat)abstract
    • The nuclides Pt168-170 were produced by bombarding isotopically enriched Mo-92,Mo-94 targets with 336, 348 MeV Kr-78 ions. Prompt gamma rays were detected at the target position and provided a selection criterion for the Pt168-170 nuclei. This technique enables the problem of the background from higher-energy alpha decays in the spectrum to be circumvented. The Pt nuclei were separated in flight using the gas-filled separator RITU and implanted into the GREAT spectrometer, which was used to study subsequent alpha decays. The alpha-decay branching ratios of Os164-166 were deduced from the fraction of selected Pt168-170 nuclei correlated with a decays Of Os164-166. The resulting branching ratios agree with the literature values but can have improved precision.
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11.
  • Caceres, L., et al. (författare)
  • Spherical proton-neutron structure of isomeric states in Cd-128
  • 2009
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 79:1, s. 011301-
  • Tidskriftsartikel (refereegranskat)abstract
    • The gamma-ray decay of isomeric states in the even-even nucleus Cd-128 has been observed. The nucleus of interest was produced both by the fragmentation of Xe-136 and the fission of U-238 primary beams. The level scheme was unambiguously constructed based on.. coincidence relations in conjunction with detailed lifetime analysis employed for the first time on this nucleus. Large-scale shell-model calculations, without consideration of excitations across the N = 82 shell closure, were performed and provide a consistent description of the experimental level scheme. The structure of the isomeric states and their decays exhibit coexistence of proton, neutron, and strongly mixed configurations due to p. interaction in overlapping orbitals for both proton and neutron holes.
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12.
  • Cederwall, Bo, et al. (författare)
  • Evidence for enhanced collectivity in Te-I-Xe nuclei near the N=Z=50 double shell closure
  • 2007
  • Ingår i: PROTON EMITTING NUCLEI AND RELATED TOPICS. - MELVILLE, USA : AMER INST PHYSICS. - 9780735404755 ; , s. 156-162
  • Konferensbidrag (refereegranskat)abstract
    • Gamma-ray transitions have been identified for the first time in the extremely neutron-deficient T-z = 1 nuclide Xe-110 and the energies of the three lowest excited states in the ground-state band have been deduced. A level scheme has also been constructed for the proton-unbound, T-z = 3/2 nuclide I-109, exhibiting band structures built on g(7/2) and h(11/2) states in a weakly deformed, triaxial nucleus. In addition, a third band is proposed to be bui It oil a g(7/2) orbital coupled to an octupole-vibrational phonon of the Te-108 core. The results were obtained in a recoil-decay tagging experiment using the Ni-58(Fe-54,2n/p2n) reaction at a beam energy of 195 MeV. The experiment was performed using the highly efficient JUROGAM y-ray spectrometer in conjunction with the RITU gas-filled recoil separator and the GREAT focal -plane spectrometer. The results on Xe-110 establish a breaking of the normal trend of increasing first excited 2(+) and 4(+) level energies as a function of decreasing neutron number as the N = 50 major shell gap is approached for the neutron-deficient Xe isotopes. This unusual feature is suggested to be an effect of enhanced collectivity, possibly arising from isoscalar n-p interactions becoming increasingly important close to the N = Z line. Features in the low-lying levels of Te-106 and I-109, showing similar trends, are also discussed.
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13.
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14.
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15.
  • Garnsworthy, A. B., et al. (författare)
  • Spectroscopy of Po-212 and At-213 using a He-8 radioactive beam and EXOGAM
  • 2005
  • Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 31:10, s. S1851-S1854
  • Tidskriftsartikel (refereegranskat)abstract
    • A beam of 28 MeV He-8 particles with an average intensity 2 x 10(5) ions s(-1), produced by the SPIRAL facility at GANIL, was used to initiate fusion-evaporation reactions in thick targets of Pb-201 and Bi-209. Excited states of Po-212 and At-213 were populated in (He-8,4n) reactions. The emitted gamma-rays were detected using the EXOGAM array composed of four Compton suppressed germanium Clover detectors in a close geometry configuration. Preliminary results show that Po-212 has been populated to high spin (I similar or equal to 14) with a significantly increased yield compared with our previous He-8 beam experiment. An apparently increased relative population of states up to 12(+) was observed compared with published results from a Pb-208(Be-9,alpha n)(212) Po reaction at 48 MeV. Evidence is presented for a previously unreported de-excitation pathway: 69 keV (13(-) -> 12(+)). States up to I-pi = (39/2(-)) have also been observed in At-213.
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16.
  • Gorska, M., et al. (författare)
  • Evolution of the N=82 Shell Gap below 132Sn Inferred from Core Excited States in 131In
  • 2009
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 672:4-5, s. 313-316
  • Tidskriftsartikel (refereegranskat)abstract
    • The gamma-ray decay of ail excited state in In-131, the one proton hole neighbor of the doubly magic (132)sn has been measured. A high-spin, core-excited isomer with T-1/2 = 630(60) us was identified following production by both relativistic fragmentation of a Xe-136 beam and fission Of a U-238 beam. This state deexcites by a single gamma-ray branch of 3782(2) keV from which direct evidence for the size of the N = 82 shell gal) is inferred. The results are discussed in comparison to a shell-model Calculation including configurations across the closed shells at N = 82 and Z = 50. (C) 2009 Elsevier B.V. All rights reserved.
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17.
  • Hadinia, Baharak, et al. (författare)
  • First identification of excited states in 106Te and evidence for isoscalar-enhanced vibrational collectivity
  • 2005
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 72:4, s. 041303-1-041303-5
  • Tidskriftsartikel (refereegranskat)abstract
    • Gamma-ray transitions in the extremely neutron-deficient nucleus Te-106 have been identified for the first time. The experiment utilized the Fe-54(Fe-54,2n)Te-106(*) reaction, and the gamma-ray transitions from excited states in Te-106 were selected by use of the recoil-decay-tagging technique. The production cross section was estimated at 25 nb, a new limit for in-beam gamma-ray spectroscopy. A ground-state band tentatively extending up to I-pi=10(+) is proposed. The systematics of low-lying yrast states in the Te isotopes is discussed within the context of vibrational excitations and residual nucleon-nucleon interactions.
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18.
  • Hadinia, Baharak, et al. (författare)
  • First identification of gamma-rays in Te-106 using recoil decay tagging technique
  • 2006
  • Ingår i: Frontiers in Nuclear Structure Astrophysics, and Reactions: FINUSTAR. - MELVILLE, NY : AMER INST PHYSICS. - 0735403236 - 9780735403239 ; , s. 457-459
  • Konferensbidrag (refereegranskat)abstract
    • Gamma-ray transitions from excited states in Te-106 have been identified using the recoil decay tagging technique. The experiment which was the reaction Fe-54(Fe-54,2n)Te-106* was performed at the JYFL accelerator facility at the University of Jyvaskyla, Finland. The production cross section was estimated at 25 nb, a new limit for in-beam gamma-ray spectroscopy. A tentative level structure for the ground state band of Te-106 is proposed.
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19.
  • Hadinia, Baharak, et al. (författare)
  • Identification of gamma rays from Au-172 and alpha decays of Au-172, Ir-168, and Re-164
  • 2009
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 80:6, s. 064310-
  • Tidskriftsartikel (refereegranskat)abstract
    • The very neutron deficient odd-odd nucleus Au-172 was studied in reactions of 342 and 348 MeV Kr-78 beams with an isotopically enriched Ru-96 target. The alpha decays previously reported for Au-172 were confirmed and the decay chain extended down to Tm-152 through the discovery of a new alpha-decaying state in Re-164 [E-alpha=5623(10) keV; t(1/2)=864(-110)(+150) ms; b(alpha)=3(1)%]. Fine structure in these alpha decays of Au-172 and Ir-168 were identified. A new alpha-decaying state was also observed and assigned as the ground state in Au-172 [E-alpha=6762(10) keV; t(1/2)=22(-5)(+6) ms]. This decay chain was also correlated down to Tm-152 through previously reported alpha decays. Prompt gamma rays from excited states in Au-172 have been identified using the recoil-decay tagging technique. The partial level scheme constructed for Au-172 indicates that it has an irregular structure. Possible configurations of the alpha-decaying states in Au-172 are discussed in terms of the systematics of nuclei in this region and total Routhian surface calculations.
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20.
  • Hadinia, Baharak, et al. (författare)
  • In-beam gamma-ray and alpha-decay spectroscopy of 170Ir
  • 2007
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 76:4, s. 044312-1-044312-8
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states in the highly neutron deficient odd-odd nucleus Ir-170 have been investigated. The experiment was performed using the Sn-112(Ni-60, pn)Ir-170 reaction and employing the recoil-decay tagging technique. Gamma rays were detected using the JUROGAM gamma-ray spectrometer and those belonging to Ir-170 were selected based on recoil identification provided by the RITU gas-filled recoil separator and the GREAT spectrometer at the RITU focal plane. A partial level scheme of Ir-170 is presented for the first time. New alpha-decay branches are assigned to Ir-170 and a tentative level structure for Re-166 is deduced from a study of the alpha-decay fine structure and the associated alpha-gamma correlations.
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21.
  • Hadinia, Baharak (författare)
  • In-beam study of 106Te and 107Te using the recoil decay tagging technique
  • 2006
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Atomic nuclei are complex many-body systems and exhibit an interplay between single-particle and collective degrees of freedom. In order to describe and predict the “behavior” of nucleons inside the nuclei a variety of theoretical models have been created, each applicable to their own domain of nuclear phenomena. Experimental information is needed in order to test and improve the various theoretical models with the ultimate goal of creating unified theory of nuclear structure. In-beam γ-ray spectroscopy is one way of probing the inner structure of nuclei and it is the subject of this thesis, which describes the first identification of excited states in the extremely neutron deficient nuclei 106Te and 107Te. The experiments were performed at the Accelerator Laboratory of the University of Jyväskylä, Finland, using the recoil-decay tagging technique. Prompt γ rays emitted following fusion evaporation reactions were detected by the Jurogam detector array and the selection of the γ rays of interest was based on the recoil identification provided by the RITU gas-filled recoil separator and the GREAT focal plane spectrometer. The production cross sections were estimated to be 25nb and 1μb for 106Te and 107Te, respectively. In case of the nucleus 106Te, several γ rays have been observed. A vibrational-like yrast band has been suggested. For 107Te a number of γ rays have been assigned and a tentative partial level scheme has been suggested. The experimental data have been compared to shell model calculations.
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22.
  • Hadinia, Baharak, 1975- (författare)
  • In-beam Study of Extremely Neutron deficient Nuclei Using the Recoil-Decay Tagging Technique
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The low-lying structures of the extremely neutron-deficient nuclei 106Te, 107Te, 110Xe, 170Ir and 172Au have been investigated experimentally. Prompt gamma rays emitted in fusion-evaporation reactions were detected by the Jurogam HPGe array. The gamma rays were assigned to specific reaction channels using the recoil-decay tagging technique provided by the gas-filled separator RITU and the GREAT focal-plane spectrometer. The experimental set-up and the technique used to extract the information from the experimental data are described in detail. Results were interpreted in terms of the nuclear shell model and Total Routhian Surface calculations. In addition, decay studies on 170Ir, 172Au and 164Re led to the discovery of new alpha-decay branches in these nuclei.
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23.
  • Herskind, B., et al. (författare)
  • Charged particle feeding of hyperdeformed nuclei in the A=118-126 region
  • 2006
  • Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T125, s. 108-114
  • Tidskriftsartikel (refereegranskat)abstract
    • A breakthrough was recently obtained in the analysis of the so-called Hyper-Long-HyperDeformed (HLHD) experiment made at the EUROBALL-IV gamma-detector array (EB). The Ni-64 + Ni-64 double right arrow Ba-128* fusion reaction was studied at E-beam = 255 and 261 MeV, reaching the highest angular momentum that the compound nuclei can accommodate. To date no discrete HD rotational bands have been identified. However, rotational patterns in the form of ridge-structures in three-dimensional (3D) rotational mapped spectra are identified with dynamic moments of inertia J((2)) ranging from 71 to 111h(2) MeV-1 in 12 different nuclei selected by charged particle- and/or gamma-gating. The four nuclei, Te-118, Cs-124, Cs-125 and Xe-124 found with moment of inertia J((2)) >= 100h(2) MeV-1, are most likely hyperdeformed, the remaining nuclei with smaller values of J((2)), are considered to be superdeformed, in qualitative agreement with recent theoretical calculations.
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24.
  • Herskind, B., et al. (författare)
  • Light charged particles as gateway to hyperdeformation
  • 2007
  • Ingår i: Acta Physica Polonica B. - 0587-4254 .- 1509-5770. ; 38:4, s. 1421-1430
  • Tidskriftsartikel (refereegranskat)abstract
    • The Euroball-IV gamma-detector array, equipped with the ancillary charged particle detector array DIAMANT was used to study the residues of the fusion reaction Ni-64 + Ni-64 double right arrow Ba-128 at E-beam. = 255 and 261 MeV, in an attempt to reach the highest angular momentum and verify the existence of predicted hyperdeformed rotational bands. No discrete hyperdeformed bands were identified, but nevertheless a breakthrough was obtained through a systematic search for rotational ridge structures with very large moments of inertia J(2) >= 100 h(2) MeV((-1)), in agreement with theoretical predictions for hyperdeformed shapes. Evidence for hyperdeformation was obtained by charged particle + gamma-ray gating, selecting triple correlated ridge structures in the continuum of each of the nuclei, Te-118, Xe-124 and Cs-124,Cs-125. In 7 additional nuclei, rotational ridges were also identified with J(2) = 71-77h(2) MeV((-1)), which most probably correspond to superdeformed shape. The angular distributions of the emitted charged particles show an excess in forward direction over expectations from pure compound evaporation, which may indicate that in-complete fusion plays an important role in the population of very elongated shapes.
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25.
  • Hidvegi, Attila, et al. (författare)
  • A high-speed data acquisition system for segmented Ge-detectors
  • 2007
  • Ingår i: 2007 IEEE Nuclear Science Symposium Conference Record. - : IEEE. - 1424409233 - 9781424409235 - 9781424409228 ; , s. 536-537
  • Konferensbidrag (refereegranskat)abstract
    • When using segmented Ge-detectors for gamma ray tracking it is necessary to determine the segment pulse shapes with high accuracy. A high-speed data acquisition system with many channels, high precision and with high sampling rate is required. There are also many other applications for such a system. Our system uses high performance FPGAs (Xilinx Virtex-V [2]) to cope with the data rates delivered by the high speed ADC chosen (Atmel 2Gsps, 10 bits) and to make all the data processing onboard in real time. Each board contains four such ADCs, which can either handle four channels up to full speed, or achieve higher sampling rates with interleaving. The boards can communicate with each other over different types of high-speed communication links. Control and monitoring is implemented with embedded processors. The processed result will be transmitted over Ethernet to final storage. The project introduces many challenging issues: signal integrity, ADC performance, interfacing ADCs to the FPGA, synchronisation of ADCs across the entire system, implementing flexible processing algorithms, high speed interconnection between boards and managing the significant heat generation. This is an ongoing project with interesting potentials for the future.
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26.
  • Hidvegi, Attila, et al. (författare)
  • A high-speed data acquisition system for segmented Ge-detectors
  • 2007
  • Ingår i: 2006 IEEE Nuclear Science Symposium Conference Record, Vol 1-6. - : IEEE. - 1424405610 - 9781424405619 - 1424405602 ; , s. 999-1001
  • Konferensbidrag (refereegranskat)abstract
    • When using segmented Ge-detectors for gamma ray tracking it is necessary to determine the segment pulse shapes with high accuracy. A high-speed data acquisition system with many channels, high precision and with high sampling rate is required. To find the optimum performance, we are investigating what can be achieved by a system with extremely high sampling rates, 10 bits @2GS/s. There are many other applications for such a system. Higher sampling rates usually mean lower bit resolution of the ADC, but with oversampling we expect to achieve a very good energy and time resolution. The system uses high performance FPGAs (Xilinx Virtex-IV) to cope with the data rates delivered by the high speed ADCs and to make all the data processing onboard in real time. Control and monitoring is implemented in an embedded soft processor. This processor is also in charge of the offboard gigabit Ethernet communication. The final system will consist of several separate boards, each with a number of input channels that will have to communicate with each other in real time over a high-speed communication link. The processed result will be transmitted over Ethernet to final storage. The project introduces many challenging issues, which are being addressed in turn with different prototype designs. These issues are: the ADC performance, interfacing the ADCs to the FPGA, implementing the flexible processing algorithms and high speed interconnection between the boards.
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27.
  • Hornillos, M. B. G., et al. (författare)
  • gamma-ray spectroscopy approaching the limits of existence of atomic nuclei : A study of the excited states of Pt-168 and Pt-169
  • 2009
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 79:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states in the N=90 and N=91 Pt nuclei have been investigated using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator. These nuclei were populated via the reactions Mo-92(Kr-78,2n) and Mo-94(Kr-78,3n) at 335 and 348 MeV, respectively. The recoil-decay tagging technique has been used to correlate prompt gamma radiation with the characteristic alpha decays of Pt-168 and Pt-169. A gamma-gamma analysis has allowed a level scheme for Pt-168 to be reported for the first time and the level scheme for Pt-169 to be extended. The excitation energies of the proposed positive-parity yrast states of Pt-168 are compared with calculations based on the interacting boson model and found to be in excellent agreement. These data show a continuation of the trend toward vibrational nuclei as the N=82 shell gap is approached. In addition, new excited states constituting two decay paths have been discovered in Pt-169. .  
  •  
28.
  • Ideguchi, E., et al. (författare)
  • Study of high-spin states in 48Ca region induced by secondary fusion reactions
  • 2005
  • Konferensbidrag (refereegranskat)abstract
    • A new method of in-beam gamma-ray spectroscopy induced by secondary fusion reactions, 37P+9Be and 46Ar+9Be is presented. Low-energy secondary beams of 37P and 46Ar ions of ∼5 MeV/A were developed in order to induce fusion evaporation reactions. Excited states of nuclei in the vicinity of 48Ca, 49-52Ti and 46Ca, were studied by the method as well as β decay of the secondary beam 46Ar. Gamma-gamma coincidence and excitation function analysis were performed to study high-spin states of Ti isotopes.
  •  
29.
  • Ideguchi, E, et al. (författare)
  • Study of high-spin states in the Ca-48 region by using secondary fusion reactions
  • 2005
  • Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 25, s. 429-430
  • Tidskriftsartikel (refereegranskat)abstract
    • An in-beam gamma-ray spectroscopy study, following a fusion reaction induced by a neutronrich secondary beam, Ar-46 + Be-9, is presented. A low-energy secondary beam of Ar-46 at similar to 5 MeV/A was developed in order to induce fusion reactions. Gamma-gamma coincidence and excitation function analysis was performed to study high-spin states in the vicinity of Ca-48, Ti49-52.
  •  
30.
  • Joss, D. T., et al. (författare)
  • Probing structural changes in the very neutron-deficient Os isotopes with recoil-decay tagging
  • 2005
  • Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 31:10, s. S1593-S1598
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent years, the exploitation of the iecoil-decay tagging (RDT) technique with,large arrays of germanium detectors has revealed much information about the structure of heavy nuclei approaching the proton drip line. The yrast bands of the N <= 93 osmium isotopes have been identified in a campaign of tagging experiments using various spectrometer arrays coupled to the RITU gas-filled separator based at the University of Jyvaskyla. Trends in the yrast state excitation energies have indicated a transition from gamma-soft triaxial to near-spherical shapes with decreasing neutron number. Recent experimental results for Os-162 obtained with the JUROGAM and GREAT spectrometers also indicate the importance of configurations involving the h(9/2) neutron states as the N = Z 82 shell gaps are approached.
  •  
31.
  • Joss, D. T., et al. (författare)
  • Yrast states and band crossings in the neutron-deficient platinum isotopes Pt169-173
  • 2006
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 74:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The yrast states in the light platinum isotopes Pt169-173 have been investigated in a recoil-decay tagging experiment using the JUROGAM gamma-ray spectrometer in conjunction with the RITU gas-filled recoil separator and the GREAT tagging spectrometer. Gamma-ray transitions have been established for the first time in the odd-N isotopes, Pt-169 and Pt-173, and the yrast sequences in Pt-170 and Pt-172 have been extended. We discuss the possibility that the weakly deformed yrast structures of Pt-170, Pt-172, and Pt-173 are crossed by a deformed intruder configuration at spin similar to 8h.
  •  
32.
  • Joss, D. T., et al. (författare)
  • Yrast structures in the light Pt isotopes Pt169-173
  • 2005
  • Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 31:10, s. S1715-S1718
  • Tidskriftsartikel (refereegranskat)abstract
    • The exploitation of the recoil-decay tagging (RDT) technique has reinvigorated experimental investigations of the shape coexistence phenomenon in heavy neutron-deficient nuclei. In a recent experiment using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator, excited states have been investigated in the light platinum isotopes. In addition to extending the yrast sequences in Pt-170 and Pt-172, the first observation of excited states in the odd-N isotopes, Pt-169 and Pt-173, is reported. The bands are discussed in terms of trends in level excitation energies as a function of neutron number.
  •  
33.
  • Jungclaus, A., et al. (författare)
  • Observation of isomeric decays in the r-process waiting-point nucleus Cd-130(82)
  • 2007
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:13
  • Tidskriftsartikel (refereegranskat)abstract
    • The gamma decay of excited states in the waiting-point nucleus Cd-130(82) has been observed for the first time. An 8(+) two-quasiparticle isomer has been populated both in the fragmentation of a Xe-136 beam as well as in projectile fission of U-238, making Cd-130 the most neutron-rich N=82 isotone for which information about excited states is available. The results, interpreted using state-of-the-art nuclear shell-model calculations, show no evidence of an N=82 shell quenching at Z=48. They allow us to follow nuclear isomerism throughout a full major neutron shell from Cd-98(50) to Cd-130(82) and reveal, in comparison with Ni-76(48) one major proton shell below, an apparently abnormal scaling of nuclear two-body interactions.
  •  
34.
  • Khaplanov, Anton, et al. (författare)
  • A gamma-ray polarimeter based on a single segmented planar HPGe detector
  • 2008
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 593:3, s. 459-465
  • Tidskriftsartikel (refereegranskat)abstract
    • The polarization sensitivity of a segmented planar HPGe detector has been measured. For this purpose 662 keV photons from a Cs-137 source which were Compton scattered at approximate to 90 degrees in a coaxial germanium detector were utilized as a source of partially linearly polarized gamma radiation of the energy; approximate to 288 keV. The detector has a 50 x 50 x 21 mm sensitive volume and 5 x 5 electrical segmentation of the cathode contact. The degree of linear polarization is determined through the analysis of the directions of Compton scatterings inside the detector. The locations of the Compton scattering interactions and of the subsequent photo-absorption interactions have been determined with the help of pulse shape analysis (PSA), provided that these interactions are in two different segments of the planar detector. A comparison with a polarization analysis using the position resolution defined by the physical segmentation (without the use of PSA) was also performed. It is demonstrated that the use of PSA enables a much higher polarization sensitivity for events where the 288 keV photons scatter between adjacent pixels. Such events constitute 90% of the data for the 288 keV photons and are even more important for gamma-rays of lower energies.
  •  
35.
  • Khaplanov, Anton, et al. (författare)
  • Compton imager based on a single planar segmented HPGe detector
  • 2007
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 580, s. 1075-1078
  • Tidskriftsartikel (refereegranskat)abstract
    • A collimator-free Compton imaging system has been developed based on a single high-purity germanium detector and used to generate images of radioactive sources emitting gamma rays. The detector has a planar crystal with one pixellated contact with a total of 25 segments. Pulse shape analysis has been applied to achieve a 3D-position sensitivity of the detector. The first imaging results from this detector are presented, based on the reconstruction of events where a gamma ray is fully absorbed after scattering between adjacent segments.
  •  
36.
  • Khaplanov, Anton, et al. (författare)
  • Position sensitivity of segmented planar HPGe detectors for the DESPEC project at FAIR
  • 2008
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 592, s. 325-333
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the proposed germanium detector systems for the upcoming DESPEC array at the FAIR facility consists of triple modules of electrically segmented planar high-purity germanium detectors. In this work, the position sensitivity obtained by means of pulse shape analysis (PSA) for simulated gamma-ray interactions has been studied for the possible segmentation patterns for such detectors-the double-sided strip detector (DSSD) and the one-sided pixelated geometry. An over-all similar number of readout channels has been considered for each case, resulting in 8 + 8 strips and 16 pixels. It has been found that the higher physical granularity of the DSSD results in a significantly higher position resolution, as well as in a somewhat lower probability of merging multiple interaction points. A drawback of the DSSD geometry is the inability to assign the interactions to the correct voxels for certain complex multiple interaction patterns. This effect has been studied in detail. Finally, a comparison has been made with the existing 25-pixel planar detector at KTH [A. Khaplanov, et al., Nucl. Instr. and Meth. A 580 (2007) 1075; L. Milechina, B. Cederwall, Nucl. Instr. and Meth. A 550 (2005) 278)].
  •  
37.
  • Khaplanov, Anton, et al. (författare)
  • Position sensitivity of the proposed segmented germanium detectors for the DESPEC project
  • 2009
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 604:1/2, s. 56-59
  • Tidskriftsartikel (refereegranskat)abstract
    • The DESPEC HPGe array is a part of the NuSTAR project at FAIR, Germany. It is aimed at the spectroscopy of the stopped decaying exotic nuclei. Segmented gamma-ray tracking detectors are proposed for this array in order to maximize detection efficiency and background suppression when searching for very rare events. Two types of detector modules-stacks of three 16-fold segmented planar crystals and 12- and 16-fold segmented clover detectors-have been investigated and compared from the point of view of the achievable position resolution using pulse shape analysis (PSA). To this end, detector signals from realistic gamma-ray interactions have been calculated. These signals were treated by PSA in order to reconstruct the photon interaction locations. Comparing the initial interaction locations to the reconstructed ones, it was found that the double-sided strip planar detector yielded position reconstruction errors at least a factor 2 lower than the other detectors considered
  •  
38.
  • Lagergren, Karin, et al. (författare)
  • High-spin states in the proton-unbound nucleus Re-161
  • 2006
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 74:2, s. 024316-
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states in Re-161 were populated using the Cd-106(Ni-58, p2n) reaction at a beam energy of 270 MeV, resulting in the first observation of gamma rays emitted from this nucleus. The reaction products were separated from scattered beam and fission fragments by the gas-filled recoil separator RITU, and were implanted in the double-sided silicon strip detectors of the GREAT spectrometer. Prompt gamma rays were detected by the JUROGAM Ge detector array and were assigned to Re-161 based on alpha- and proton-decay tagging of the implanted reaction products. The near-yrast high-spin level structure, which was delineated to spins around 39/2, is discussed in the context of the total Routhian surface formalism. The level scheme is interpreted in terms of the alignment of h(9/2)/f(7/2) neutrons at lower spins, followed by excitations involving the pi h(11/2) subshell at higher spins.
  •  
39.
  • Lorente, A. Sanchez, et al. (författare)
  • Performance of HPGe detectors in high magnetic fields
  • 2007
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 573:3, s. 410-417
  • Tidskriftsartikel (refereegranskat)abstract
    • A new generation of high-resolution hypernuclear gamma-spectroscopy experiments with high-purity germanium detectors (HPGe) are presently designed at the FINUDA spectrometer at DA Phi NE, the Frascati phi-factory, and at (P) over bar ANDA, the (p) over barp hadron spectrometer at the future FAIR facility. Both, the FINUDA and (P) over bar ANDA spectrometers are built around the target region covering a large solid angle. To maximise the detection efficiency the HPGe detectors have to be located near the target, and therefore they have to be operated in strong magnetic fields (B approximate to I T). The performance of HPGe detectors in such an environment has not been well investigated so far. In the present work VEGA and EUROBALL Cluster HPGe detectors were tested in the field provided by the ALADiN magnet at GSI. No significant degradation of the energy resolution was found, and a change in the rise time distribution of the pulses from preamplifiers was observed. A correlation between rise time and pulse height was observed and is used to correct the measured energy, recovering the energy resolution almost completely. Moreover, no problems in the electronics due to the magnetic field were observed.
  •  
40.
  • Mach, H., et al. (författare)
  • Application of ultra-fast timing techniques to the study of exotic and weakly produced nuclei
  • 2005
  • Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 31:10, s. S1421-S1426
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultra-fast time-delayed techniques have been recently applied in a number of studies where exotic nuclei were identified using advanced selection techniques. These include large Compton-suppressed Ge arrays, in-flight separators or recoil separators. Some of the new results are discussed in this presentation. Besides the results for Mg-32 and Pd-96, they include the first determination of the half-life of the 8(+) state in Ge-80, T-1/2 = 2.95(6) ns, and significantly more precise results for Mn-51 (3680 keV level) and V-48 (421 keV level), T-1/2 = 1760(40) ps and T-1/2.
  •  
41.
  • Mason, P., et al. (författare)
  • Evidence for octupole correlations in Ba-124,Ba-125
  • 2005
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 72:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The gamma decay of the nuclei Ba-124,Ba-125 has been investigated by means of the EUROBALL spectrometer, coupled to the DIAMANT array of charged-particle detectors, using the reaction Ni-64 + Ni-64 at E-beam=255 and 261 MeV. In the nucleus Ba-125 six new E1 transitions have been found to link opposite-parity bands currently interpreted as nu d(5/2)(+g(7/2)),nu h(11/2) structures. The previously unknown J(pi) = 3(-) level in the nucleus Ba-124 has also been identified; its excitation energy is accurately reproduced by a microscopic calculation including octupole correlations. Both issues are bolstered by sizable B(E1)/B(E2) ratios.
  •  
42.
  • Mason, P, et al. (författare)
  • Octupole signatures in Ba-124,Ba-125
  • 2005
  • Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 31:10, s. S1729-S1733
  • Tidskriftsartikel (refereegranskat)abstract
    • The gamma decay of the nuclei Ba-121,Ba-125 has been investigated with the EUROBALL array, using the reaction Ni-64+Ni-64 at E-beam = 255 and 261 MeV. Six new E1 transitions have been found in the nucleus Ba-125, suggesting a significant role of octupole correlations in the origin of its parity doublets. The J(pi) = 3(-) level of the nucleus Ba-124 has been identified for the first time. Its excitation energy is in very good agreement with a prediction based on a microscopic model including octupole interactions.
  •  
43.
  • Milechina, L., et al. (författare)
  • 3D position sensitivity of a highly segmented Ge detector
  • 2005
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 550:02-jan, s. 278-291
  • Tidskriftsartikel (refereegranskat)abstract
    • The 3D position resolution of a planar HPGe detector with a 25-fold segmented cathode contact has been studied. The measurements were performed with a collimated Cs-137 gamma-ray pencil beam and a coincidence scattering technique that selects single interaction events at well-defined irradiation points. The gamma rays scattered at 90 degrees, depositing 374 keV energy in the detector, were registered and the pulse shapes from the irradiated segment and three neighboring segments were analyzed. The resulting average 3D position sensitivity for single gamma-ray interactions is estimated at 0.4 mm.
  •  
44.
  • Nyako, B. M., et al. (författare)
  • Search for hyperdeformation in light Xe nuclei
  • 2005
  • Ingår i: Acta Physica Polonica B. - 0587-4254 .- 1509-5770. ; 36:4, s. 1033-1038
  • Tidskriftsartikel (refereegranskat)abstract
    • The ultimate search for hyperdeformation (HD) at high spins with the EUROBALL spectrometer was performed for Ba-126 as a hyper long (HLHD) experiment. The DIAMANT ancillary detector was used to tag gamma-rays in coincidence with the emitted light charged particles. Using gamma-energy correlation methods, the particle-xn-gamma data have been analysed to search for hyperdeformed structures in the corresponding residual nuclei. Data in coincidence with one alpha particle indicate the presence of normal deformed collective bands up to very high spins and the possible occurrence of HD-like ridge structures in Xe-122.
  •  
45.
  • O'Donnell, D., et al. (författare)
  • Spectroscopy of the neutron-deficient nucleus Os-167(91)
  • 2009
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 79:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states of the nucleus Os-167 have been populated by the reaction Mo-92(Kr-78,2pn). The JUROGAM gamma-ray detector array has been used in conjunction with the RITU gas-filled separator and the GREAT spectrometer to observe prompt gamma rays in coincidence with recoiling fusion-evaporation residues and their subsequent decay by alpha particle emission. By correlating prompt gamma radiation with the characteristic alpha radioactivity of Os-167, it has been possible to extend the level scheme for this nucleus significantly. In particular, an extension of the yrast band and four previously unobserved bands are reported. In addition, the recoil distance Doppler-shift method was used to determine a lifetime of tau=20(4) ps for The I-pi=17/2(+) state in Os-167. Hence, the level of collectivity and magnitude of deformation of the low spin yrast band of this nucleus is established. .  
  •  
46.
  • Persson, Andreas, et al. (författare)
  • A prototype detector module for combined PET/CT or combined photon counting/standard CT based on SiPM technology
  • 2009
  • Ingår i: 2009 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE RECORD, VOLS 1-5. - 9781424439614 ; , s. 3503-3507
  • Konferensbidrag (refereegranskat)abstract
    • A method extending the functionality of silicon photomultipiers (SiPMs) has been developed. It enables the use of SiPMs for quantifying high radiation fluxes in current mode as well as in pulse mode measurements for counting and characterizing individual gamma-ray or X-ray photons when coupled to scintillators. This opens new possibilities for multimodal medical imaging by providing the means for producing common radiation sensors for PET, standard CT and photon counting CT. Currently, two separate detector systems are required for combined PET/CT. Similarly, standard current integrating CT and the novel concept of photon counting CT currently also requires separate detector systems. We here present a novel detector design featuring dual-mode readout of SiPM-based radiation sensors that enables imaging systems where conventional CT imaging is combined with PET, as well as in CT systems where both conventional integrating (high-flux) and photon counting (low-dose) operation can be selected. Such dual-mode SiPMs coupled to scintillators in medical imaging can be used to detect and characterize single primary X-ray or gamma-ray photons up to fluxes of millions of photons per mm(2) per second in pulse mode. Current mode operation allows the dynamic range to he extended to the much higher rates found in standard CT imagers and beyond. A prototype detector is being developed and studied from the point of view of the energy and timing resolution required for the photon-counting application as well as the flux-to-current characteristics, essential for the current mode.
  •  
47.
  • Petri, M., et al. (författare)
  • Nuclear levels in proton-unbound I-109 : Relative single-particle energies beyond the proton drip line
  • 2007
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 76:5
  • Tidskriftsartikel (refereegranskat)abstract
    • A level scheme has been constructed for the proton-unbound, T-z=3/2 nuclide I-109(53)56 following a recoil-decay-tagging experiment using the Ni-58(Fe-54, p2n gamma) reaction at a beam energy of 195 MeV. The experiment was performed using the highly efficient JUROGAM gamma-ray spectrometer in conjunction with the RITU gas-filled recoil separator and the GREAT focal-plane spectrometer. Cranking calculations are used to interpret band structures built on pi g(7/2) and pi h(11/2) states in a weakly deformed, triaxial nucleus.
  •  
48.
  • Robin, J., et al. (författare)
  • Discrete decay of the yrast superdeformed band in the Tb-151 nucleus
  • 2008
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 78:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The Euroball array has been used to search for linking transitions between the superdeformed (SD) and the normal deformed (ND) wells in Tb-151. Many. rays in the energy range 2-4 MeV have been observed in coincidence with the yrast SD band. It is proposed that the highest energy transition of 3748 keV and the strongest line (2818 keV) of the previously observed transitions both decay from the same SD level as their links with the ND states have been identified. The current spectra have insufficient statistics to completely identify the decay point in the SD band. Theoretical calculations covering SD bands in the A approximate to 150 region enable the two possible spin assignments to be compared with experimental data on proposed links in Gd-149 and Dy-152. It is concluded that the energy of the lowest SD band member in Tb-151 has an excitation energy of 12861 keV and a spin of 65/2(+).
  •  
49.
  • Robin, J., et al. (författare)
  • Extended investigation of superdeformed bands in Tb-151,Tb-152 nuclei
  • 2008
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 77:1
  • Tidskriftsartikel (refereegranskat)abstract
    • A detailed study of known and new SD bands in Tb isotopes has been performed with the use of the EUROBALL IV gamma-ray array. The high-statistics data set has allowed for the extension of known SD bands at low and high spins by new gamma-ray transitions. These transitions, as it turns out, correspond to the rotational frequencies where the principal superdeformed gaps (Z=66,N=86) close giving rise to up- or down-bending mechanisms. This enables to attribute the underlying theoretical configurations with much higher confidence as compared to the previous identifications. Five new SD bands have been discovered, three of them assigned to the Tb-152 and the two others to the Tb-151 nuclei. Nuclear mean-field calculations have been used to interpret the structure of known SD bands as well as of the new ones in terms of nucleonic configurations.
  •  
50.
  • Ruchowska, E., et al. (författare)
  • Nuclear structure of Th-229
  • 2006
  • Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 73:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Lifetimes of excited states in Th-229, populated in the beta decay of Ac-229, have been measured using the advanced time-delayed beta gamma gamma(t) method. Half-lives of 14 states have been determined including 11 of them for the first time. Twenty-seven new gamma lines have been introduced into the beta-decay scheme of Ac-229 based on results of gamma gamma coincidence measurements. Reduced transition probabilities have been determined for more than 70 gamma transitions in Th-229. Average parallel to D-0 parallel to values of 0.029(1), 0.077(3), and 0.024(5) e fm have been deduced for the lowest K-pi=1/2(+/-),3/2(+/-), and 5/2(+/-) parity partner bands, respectively. Excited states in Th-229 and experimental transition rates have been interpreted within the quasiparticle-plus-phonon model. The half-life of the 3.5-eV, 3/2(+) isomeric state is predicted to be about 10 h. Potential energy surfaces on the (beta(2),beta(3)) plane for the lowest single quasiparticle configurations in Th-229 have been calculated using the Strutinsky method.
  •  
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