SwePub - search: WFRF:(Wyss Ramon A.)

Enumeration	Reference	Cover	Find
1.	Reifarth, R., et al. (author) Nuclear astrophysics with radioactive ions at FAIR 2016 In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1 Conference paper (peer-reviewed)abstract The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.
2.	Aktas, Özge, 1987-, et al. (author) First observation of γ-ray transitions in 111Mo In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. Journal article (peer-reviewed)abstract Excited states in the extremely neutron-rich nuclei 109Mo and 111Mo have been studied following nucleon knock-out reactions. Seven $\gamma$-ray transitions, some of them in prompt mutual coincidence, have been identified for the first time in 11Mo using the DALI2 and MINOS detector systems at the BigRIPS and ZeroDegree electromagnetic fragments separator at the RIBF, RIKEN, Japan. Total Routhian surface (TRS) and Particle- Plus Rotor calculations have been performed to investigate the predicted shape coexistence and its effect on the structure of nuclei in this region of the nuclear chart. Following the results of the calculations, theoretical level schemes are proposed for positive and negative parity states and compared with the experimental findings.
3.	Liu, Xiaoyu, et al. (author) Evidence for enhanced neutron-proton correlations from the level structure of theN = Z + 1 nucleus 87Tc In: PHYSICAL REVIEW C. Journal article (other academic/artistic)abstract The low-lying excited states in the neutron-deficient N = Z + 1 nucleus 8743 Tc 44 have been studiedvia the fusion-evaporation reaction 54 Fe( 36 Ar, 2n1p) 87 Tc at the Grand Accélérateur National d’IonsLourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliaryNEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt γ-rays, neutrons, and charged particles emitted in the reaction. A level scheme of 87 Tc from the (9/2 +g.s. ) state to the (33/2 +)statewasestablishedbasedon6mutuallycoincidentγ-ray transitions. The con-1structed level structure exhibits a rotational behavior with a sharp back bending at ~ω ≈ 0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N = 44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N = Z line.
4.	Liu, X., et al. (author) Evidence for enhanced neutron-proton correlations from the levelstructure of the N= Z+ 1 nucleus 8743Tc44 2021 In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 104:2 Journal article (peer-reviewed)abstract The low-lying excited states in the neutron-deficient N = Z + 1 nucleus (87)(43)Tcc(44) have been studied via the fusion-evaporation reaction Fe-54(Ar-36, 2n1p)Tc-87 at the Grand Accelerateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt gamma rays, neutrons, and charged particles emitted in the reaction. A level scheme of Tc-87 from the (9/2(g.s.)(+)) state to the (33/2(1)(+)) state was established based on six mutually coincident gamma-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at (h) over bar omega approximate to 0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N = 44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N = Z line.
5.	Liu, Xiaoyu, et al. (author) Evidence for spherical-oblate shape coexistence in Tc-87 2022 In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 106:3 Journal article (peer-reviewed)abstract Excited states in the neutron-deficient nucleus Tc-87 have been studied via the fusion-evaporation reaction 54Fe(36Ar, 2n1p) Tc-87 at 115 MeV beam energy. The AGATA gamma-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of gamma rays and light particles. Six transitions from the deexcitation of excited states belonging to a new band in Tc-87 were identified by comparing gamma-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in 87Tc is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band.
6.	Perries, S, et al. (author) Decay-out of the yrast superdeformed band in Nd-136 : Towards an experimental extraction of the neutron pairing gap at large deformation 1999 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 60:6 Journal article (peer-reviewed)abstract A study of the Nd-136 nucleus has been performed with the EUROBALL III multidetector to establish the decay-out of the yrast superdeformed (SD) band. Three discrete linking transitions (754, 1456, and 1493 keV) have been discovered, establishing the position of the SD band at 7.03 MeV excitation energy with proposed spin and parity 17((-)) for the lowest observed SD state. Neutron pairing gap parameters for SD shapes have been extracted in Nd isotopes, using the strong-coupling model and odd-even mass difference formulas. The major conclusion of our phenomenological analysis is that the pairing correlations do subsist in the SD configurations of nuclei in the A = 130 mass region. [S0556-2813(99)01312-6].
7.	Algora, A., et al. (author) Pronounced Shape Change Induced by Quasiparticle Alignment 2000 In: Physical Review C (Nuclear Physics). - 0556-2813 .- 1089-490X. ; 61:3 Journal article (peer-reviewed)abstract Mean lifetimes of high-spin states of Kr-74 have been determined using the Doppler-shift attenuation method. The high-spin states were studied using the Ca-40(Ca-40, alpha 2p) reaction at a beam energy of 160 MeV with the GASP gamma-ray spectrometer. The ground-state band and negative parity side band show the presence of three different configurations in terms of transitional quadrupole deformations. A dramatic shape change was found along the ground-state band after the S-band crossing. The deduced quadrupole deformation changes are well reproduced by cranked Woods-Saxon Strutinsky calculations.
8.	Andreyev, A. N., et al. (author) New microsecond isomers in Bi-189,Bi-190 2001 In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 10:2, s. 129-133 Journal article (peer-reviewed)abstract New microsecond isomers in the neutron-deficient isotopes Bi-189g,Bi-190 have been identified after in-flight separation by the velocity filter SHIP. The evaporation residues were identified on the basis of delayed recoil-gamma /X-ray, recoil-gamma /X-ray-alpha and excitation function measurements. The systematics of the [pi 1i(13/2)]13/2(+) excited states in the odd-mass Bi nuclei is discussed.
9.	Andreyev, A. N., et al. (author) The discovery of a prolate-oblate-spherical shape triple of spin 0(+) states in the atomic nucleus Pb-186 2001 In: Nuclear Physics A. - : Elsevier BV. - 0375-9474 .- 1873-1554. ; 682, s. 482C-486C Journal article (peer-reviewed)abstract Two excited J(pi)=0(+) states in Pb-186 populated in the a-decay of Po-190 have been identified through alpha -particle/conversion electron coincidences in an experiment at the velocity filter SHIP. The parent Po-190 nuclei have been produced in the Nd-142(Cr-52,4n)Po-190 complete fusion reaction, alpha -particle energies and branching ratios have been measured and hindrance factors were deduced. The observed states have been interpreted as the band heads of the known prolate and (yet unobserved) oblate rotational bands in Pb-186.
10.	de Angelis, G., et al. (author) Coherent proton-neutron contribution to octupole correlations in the neutron-deficient Xe-114 nucleus 2002 In: Physics Letters B. - 0370-2693 .- 1873-2445. ; 535:04-jan, s. 93-102 Journal article (peer-reviewed)abstract Gamma ray linear polarization and picosecond lifetimes have been measured for levels in the neutron deficient nucleus Xe-114 using the EUROBALL IV spectrometer and the Cologne plunger device. The EUCLIDES Si-ball was used to improve the reaction channel selectivity. The linear polarization results have, for the first time, unambiguously determined the electromagnetic character of the dipole transitions de-exciting the negative parity level sequence, providing clear evidence for enhanced octupole collectivity. The discovery of two E3 transitions and the measurement of the lifetimes of the states depopulated by these transitions have allowed a quantitative determination of the octupole collectivity in the A approximate to 112 mass region. The large measured B(E3) values, close to approximate to 70 W.u., are among the strongest observed hitherto and indicate a coherent proton-neutron contribution to the octupole moment.
11.	Jeppesen, H. B., et al. (author) Multi-quasiparticle states in (256)Rf 2009 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 79:3, s. 031303- Journal article (peer-reviewed)abstract Excited states in (256)Rf were populated via the Pb-208(Ti-50,2n) fusion-evaporation reaction. Delayed gamma-ray and electron decay spectroscopy was performed and three isomeric states in (256)Rf have been identified. A fourth low-energy nonyrast state was identified from the gamma-ray decay of one of the higher lying isomers. The states are interpreted as multi-quasiparticle excitations.
12.	Karlgren, Daniel, et al. (author) High-angular-momentum structures in Zn-64 2004 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 69, s. 1-034330 Journal article (peer-reviewed)abstract High-angular-momentum states in Zn-64 were populated in the Ca-40(Si-28,4p) reaction at a beam energy of 122 MeV. Evaporated, light, charged particles were identified by the Microball, while gamma rays were detected using the Gammasphere array. The main focus of this paper is on two strongly coupled, collective bands. The yrast band, which was previously known, has been linked to lower-lying states establishing the excitation energies and angular momenta of in-band states for the first time. The newly identified excited band decays to the yrast band but firm angular-momentum assignments could not be made. In order to interpret these structures cranked-Nilsson-Strutinsky calculations have been performed. The calculations have been extended to account for the distribution of nucleons within a configuration. The yrast collective band is interpreted as based on the pi(f(7/2))(-1)(p(3/2)f(5/2))(2)(g(9/2))(1)nu(p(3/2)f(5/2))(4)(g(9/2))(2) configuration. There are several possible interpretations of the second band but it is difficult to distinguish between the different possibilities.
13.	Kelsall, N. S., et al. (author) Testing mean-field models near the N=Z line : gamma-ray spectroscopy of the T-z=1/2 nucleus Kr-73 2002 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 65:4 Journal article (peer-reviewed)abstract Excited states in the N=Z+1 nucleus Kr-73 have been investigated using the Ca-40(Ar-36,2pn) and Ca-40(Ca-40,alpha2pn) reactions at 145 and 160 MeV, respectively. gamma rays were detected using the Gammasphere array and events were recorded in coincidence with charged-particle and neutron detectors. The three previously observed bands were extended to high spin, and a new unfavored positive-parity band has been observed. The alignment characteristics and decay properties of the bands are all consistent with large-deformation prolate rotation, with no clear evidence for oblate bands or shape coexistence. This is quite different from neighboring Kr-72,Kr-74, indicating a strong shape-stabilizing role for the valence neutron. The experimental results are compared to extended total Routhian surface, cranked Nilsson Strutinsky, and cranked relativistic mean-field calculations. The results suggest that the paired calculations lack some important physics. Neutron-proton correlations may be the missing ingredient. There is also evidence for an unusual band crossing in the negative-parity bands, which may indicate the presence of T=0 pairing correlations. At high spin all the models can reproduce the experimental data.
14.	Lagergren, K, et al. (author) Coexistence of superdeformed shapes in Er-154 2001 In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 8702:2 Journal article (peer-reviewed)abstract A new superdeformed rotational band has been observed in Er-154 using the Euroball Ge detector array. The new band and the one previously observed can be understood as based on coexisting superdeformed structures at prolate and triaxial shapes, respectively. The observation resolves long-standing difficulties in the theoretical interpretation of superdeformed states in Er-154.
15.	Lieder, R. M., et al. (author) Investigations of the level scheme of Gd-144 and lifetimes in the quadrupole bands 2004 In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 21:1, s. 37-55 Journal article (peer-reviewed)abstract For a level scheme investigation of Gd-144 an experiment with the gamma-spectrometer EUROBALL III has been carried out and lifetimes have been measured with the gamma-spectrometer GASP using the Doppler-shift attenuation method. The high-spin states have been populated in these experiments by means of the Mo-100(Ti-48,4n) reaction at 215 MeV and the Cd-114(S-36,6n) reaction at E = 182 MeV, respectively. The known quadrupole band has been modified and a new one has been established. Reduced E2 transition probabilities B(E2) were determined for seven members of these quadrupole bands. They show values between approximate to60 and 130 W.u. and this considerable enhancement gives evidence for a significant nuclear deformation. A (pih(11/2))(2) circle times (vh(11/2))(-2) configuration may be assigned to one of the quadrupole bands according to total Routhian surface calculations. The spin dependence of the B(E2) values has been explained by IBM calculations involving high-spin quasiparticle excitations.
16.	Bruce, A. M., et al. (author) Two-neutron alignment and shape changes in As-69 2000 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 6202:2 Journal article (peer-reviewed)abstract The nucleus As-69 was Studied using the Ca-40(S-32,3p)As-69 reaction at a beam energy of 105 MeV. An extension of the band built on the g(9/2) orbital was observed to exhibit a band crossing at a rotational frequency of 0.511 MeV with an associated alignment of 7 (h) over bar. This alignment is interpreted as being due to a pair of g(9/2) neutrons. Total Routhian surface calculations have been carried out which confirm that the shape of this nucleus changes from oblate at low spin to a triaxial prolate shape at intermediate spin.
17.	Bäck, Torbjörn, et al. (author) Lifetime measurement of the first excited 2(+) state in (108)Te 2011 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 84:4, s. 041306- Journal article (peer-reviewed)abstract The lifetime of the first excited 2(+) state in the neutron deficient nuclide (108)Te has been measured for the first time, using a combined recoil decay tagging and recoil distance Doppler shift technique. The deduced reduced transition probability is B(E2;0(g.s.)(+) -> 2(+)) = 0.39(-0.04)(+0.05)e(2)b(2). Compared to previous experimental data on neutron deficient tellurium isotopes, the new data point constitutes a large step (six neutrons) toward the N = 50 shell closure. In contrast to what has earlier been reported for the light tin isotopes, our result for tellurium does not show any enhanced transition probability with respect to the theoretical predictions and the tellurium systematics including the new data is successfully reproduced by state-of-the-art shell model calculations.
18.	Fischer, S. M., et al. (author) Alignment delays in the N = Z nuclei Kr-72, Sr-76, and Zr-80 2001 In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 8713:13 Journal article (peer-reviewed)abstract The ground state rotational bands of the N = Z nuclei Kr-72, Sr-76, and Zr-80 have been extended into the angular momentum region where rotation alignment of particles is normally expected. By measuring the moments of inertia of these bands we have observed a consistent increase in the rotational frequency required to start pair breaking, when compared to neighboring nuclei. Kr-72 shows the most marked effect. It has been widely suggested that these delayed alignments arise from np-pairing correlations. However, alignment frequencies are very sensitive to shape degrees of freedom and normal pairing, so the new experimental observations are still open to interpretation.
19.	Gueorguieva, E., et al. (author) High-spin states in Au-191 : Evidence for triaxial shape? 2003 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 68:5, s. 543081-5430814 Journal article (peer-reviewed)abstract The level scheme of Au-191 was considerably extended to high spin using gamma spectroscopy with the Eurogam-II array and internal conversion measurements with the Orsay electron spectrometer. Several bands that appear as strongly coupled were associated with low- Omega configurations in Au-191 . Using total routhian surface and cranked shell model calculations it was shown that these bands have a rotation-aligned nature and are most likely generated by the nonaxiallity of the nucleus induced by the odd proton. The predictions for the presence of such bands in Au-191 and in the oblate nuclei in the Pt-Au-Hg region found excellent agreement with the experimental data, as well as the predictions for their alignments and band-crossing frequencies in Au-191 .
20.	Gueorguieva, E., et al. (author) Sets of rotation-aligned bands indicating nonaxiality in Au-190 2004 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 69:4, s. 044320- Journal article (peer-reviewed)abstract The level scheme of Au-190 was extended up to high spin using gamma spectroscopy with the Eurogam-II array and internal conversion measurements with the electron- gamma spectrometer of Orsay. Several sets of rotation-aligned bands were found and associated with high- j, low- K configurations. According to the total Routhian surface and cranked shell model calculations these bands are caused by the nonaxiality of the nuclear deformation (gammaless than or equal to-70degrees). Furthermore, very good agreement was obtained between the experimental data and the theoretical predictions for the properties of these bands, such as alignments, band-crossing frequencies, and signature inversion, thus supporting the suggested nonaxial shapes.
21.	Joss, D. T., et al. (author) Yrast spectroscopy in the neutron-deficient nucleus Os-169 2002 In: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 66:5 Journal article (peer-reviewed)abstract Excited states in the neutron-deficient isotope Os-169 have been identified for the first time in an experiment using the Jurosphere gamma-ray spectrometer in conjunction with the Ritu gas-filled recoil separator. The problems associated with identifying neutron-deficient isotopes produced with low fusion cross sections against a high background of competing channels, including fission, have been overcome by using the recoil-decay tagging technique. The band structures observed in Os-169 are interpreted in the context of the systematics of neighboring nuclei and the predictions of cranked Woods-Saxon calculations. The systematics of the second (i(13/2))(2) neutron alignment in this region are discussed.
22.	Spolaore, P., et al. (author) Identification and study of the very neutron deficient nuclide I-111 : search for octupole correlations in the region of N approximate to Z approximate to 56 2001 In: Nuclear Physics A. - 0375-9474 .- 1873-1554. ; 682, s. 387C-393C Journal article (peer-reviewed)abstract High-spin states in the neutron-deficient nuclide I-111 have been populated with the fusion reaction Ni-58 + Ni-58 at a beam energy of 210 MeV, in an experiment performed at the Tandem Accelerator of the Laboratori Nazionali di Legnaro. The gamma spectrometer GASP was used in time coincidence with the ISIS Si-ball and the CAMEL recoil mass spectrometer for the positive identification of the nuclide. Gamma transitions and structure details previously attributed to I-111 by Other authors are only partially confirmed. The obtained level scheme includes new rotational bands and a new low lying structure which suggests the presence of octupole correlations at predicted rotational frequency values.
23.	Stefanova, E. A., et al. (author) Four-quasiparticle alignments in Ge-66 2003 In: Acta Physica Polonica B. - 0587-4254 .- 1509-5770. ; 34:4, s. 2237-2240 Journal article (peer-reviewed)abstract Above angular momentum 10(+), we found two positive-parity sequences, connected by energetically staggered DeltaI = 1 M1 transitions. The total Routhian surface calculations predict a strong triaxial deformation for them. To our knowledge, this is the first observation of staggered M1 transitions in a deformed four-quasiparticle pi(g(9/2)(2))v(g(9/2)(2)) regime.
24.	Stefanova, E. A., et al. (author) Four-quasiparticle alignments in Ge-66 2003 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 67:5 Journal article (peer-reviewed)abstract The neutron-deficient nucleus Ge-66 was populated at high spin in two experiments using the reaction Ca-40(S-32,alpha2p) at beam energies of 105 and 95 MeV. In the first experiment, a self-supporting Ca-40 target was used, while a gold-backed target of similar thickness was used in the second experiment. gamma rays were detected with the EUROBALL array, combined with the charged-particle detector array EUCLIDES and the Neutron Wall. The level scheme of Ge-66 was extended up to Eapproximate to18 MeV and I-pi=(23(-)). Above angular momentum 10(+), we found two sequences, connected by energetically staggered DeltaI=1 M1 transitions. The total Routhian surface calculations describe Ge-66 at lower spins as a gamma-soft nucleus having a moderate deformation of beta(2)approximate to0.23, while a triaxial deformation is predicted for the band structures above I-pi=10(+). To our knowledge, this is the first observation of staggered M1 transitions in a deformed four-quasiparticle pi(g(9/2)(2))nu(g(9/2)(2)) structure.
25.	Stefanova, E. A., et al. (author) Observation of negative-parity high-spin states of As-68 2005 In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 24:1, s. 1-4 Journal article (peer-reviewed)abstract The neutron-deficient nucleus As-68 was populated at high spin in two experiments using the reaction Ca-40(S-32, 3pn) at beam energies of 105 and 95 MeV. A self-supporting and a gold-backed, highly enriched Ca-40 target were used. Gamma rays were detected with the EUROBALL array, combined with the charged-particle detector array EUCLIDES and the Neutron Wall. The As-68 level scheme was considerably extended, especially at negative parity and many previous spin-parity assignments were confirmed or rejected. The total-Routhian-surface (TRS) calculations find shape coexistence and γ softness for the negative- and positive-parity states, respectively.
26.	Van De Vel, K., et al. (author) In-beam gamma-ray spectroscopy of Po-190 : First observation of a low-lying prolate band in Po isotopes 2003 In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 17:2, s. 167-171 Journal article (peer-reviewed)abstract Gamma rays from excited states of Po-190 have been observed using I the Jurosphere Ge-detector array coupled to the RITU gas-filled separator. They were associated with a collective band which from spin 4h onwards resembles the prolate rotational bands known in the isotones Pb-188 and Hg-186. This indicates that in Po-190 the prolate configuration becomes yrast above I = 2h. The experimental results are interpreted in a two-band mixing calculation and are in agreement with a-decay data and potential energy surface calculations.
27.	Andreyev, A. N., et al. (author) alpha decay of the new isotopes Rn-193,Rn-194 2006 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 74:6, s. 064303- Journal article (peer-reviewed)abstract The new neutron-deficient isotopes Rn-193,Rn-194 have been identified in the complete fusion reaction Cr-52+Sm-144 -> Rn-196(*) at the velocity filter SHIP. The alpha-decay energy and half-life value of Rn-194 were determined to be E-alpha=7700(10) keV and T-1/2=0.78(16) ms, respectively. For Rn-193 the half-life of T-1/2=1.15(27) ms and two alpha lines at E-alpha 1=7685(15) keV, I-alpha 1=74(20)% and E-alpha 2=7875(20) keV, I-alpha 2=26(12)% were found. The decay pattern of Rn-193, which is substantially different from that of the heavier odd-A Rn isotopes, provides first experimental evidence for the long-predicted deformation in the very neutron-deficient Rn nuclei.
28.	Andreyev, A. N., et al. (author) Signatures of the Z=82 shell closure in alpha-decay process 2013 In: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 110:24 Journal article (peer-reviewed)abstract In recent experiments at the velocity filter Separator for Heavy Ion reaction Products (SHIP) (GSI, Darmstadt), an extended and improved set of α-decay data for more than 20 of the most neutron-deficient isotopes in the region from lead to thorium was obtained. The combined analysis of this newly available α-decay data, of which the Po186 decay is reported here, allowed us for the first time to clearly show that crossing the Z=82 shell to higher proton numbers strongly accelerates the α decay. From the experimental data, the α-particle formation probabilities are deduced following the Universal Decay Law approach. The formation probabilities are discussed in the framework of the pairing force acting among the protons and the neutrons forming the α particle. A striking resemblance between the phenomenological pairing gap deduced from experimental binding energies and the formation probabilities is noted. These findings support the conjecture that both the N=126 and Z=82 shell closures strongly influence the α-formation probability.
29.	Antalic, S., et al. (author) The new isotopes in Po-Rn region 2007 In: Acta Physica Polonica B. - 0587-4254 .- 1509-5770. ; 38:4, s. 1557-1560 Journal article (peer-reviewed)abstract This contribution reviews the results of the recent experiments at the velocity filter SHIP in GSI Darmstadt obtained in the region of neutron deficient isotopes from lead to radon. The data for new very neutron-deficient isotopes Po-187, Rn-193,Rn-194 and their decay properties are presented. The isotopes were produced and identified in the complete fusion reactions Ti-46+Sm-144 -> Po-187+3n and Cr-52+Sm-144 -> Rn-194,Rn-193+2,3n.
30.	Bhagwat, A., et al. (author) Microscopic-Macroscopic Mass Calculations with Wigner-Kirkwood expansion 2011 In: International EFES-IN2P3 Conference on "Many Body Correlations from Dilute to Dense Nuclear Systems", MBC 2011. - : IOP Publishing. - 1742-6588. ; 321:1, s. 012053- Journal article (peer-reviewed)abstract The systematic study and calculation of ground state nuclear masses continues to be one of the active and important areas of research in nuclear physics. The present work is an attempt to determine the ground state masses of nuclei spanning the entire periodic table, using the Microscopic-Macroscopic approach. The semi-classical Wigner-Kirkwood (WK) expansion method is used to calculate shell corrections for spherical and deformed nuclei. The expansion is achieved upto the fourth order in . The shell corrections, along with the pairing energies obtained by using the Lipkin-Nogami scheme, constitute the microscopic part of the nuclear masses. The macroscopic part is obtained from a liquid drop formula with six adjustable parameters. It is shown that the Microscopic-Macroscopic mass calculation thus achieved, yields reliable description of ground state masses of nuclei across the periodic table. The present status of the WK mass calculations and the possible future perspectives are discussed.
31.	Cederwall, Bo, et al. (author) Collective rotational-vibrational transition in the very neutron-deficient nuclei (171,172)-Pt 1998 In: Physics Letters B. - AMSTERDAM, NETHERLANDS : ELSEVIER SCIENCE. - 0370-2693 .- 1873-2445. ; 443:1-4, s. 69-76 Journal article (peer-reviewed)abstract Excited states have been identified for the first time in very neutron deficient Pt-171.172 nuclei using the recoil-or-decay tagging technique. The ground-state band in Pt-172 has been established up to I-pi = 8+. A similar level sequence, presumably built on the I-pi = 13/2(+) state, is observed for Pt-171. The data are compared with theoretical calculations based on the mean field approach and the random phase approximation and are put into the context of the systematics of platinum isotopes. (C) 1998 Elsevier Science B.V. All rights reserved.
32.	Ideguchi, E., et al. (author) High-spin intruder band in In-107 2010 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 81:3, s. 034303- Journal article (peer-reviewed)abstract High-spin states in the neutron-deficient nucleus In-107 were studied via the Ni-58(Cr-52,3p) reaction. In-beam gamma rays were measured using the JUROGAM detector array. A rotational cascade consisting of ten gamma-ray transitions, which decays to the 19/2(+) level at 2.002 MeV, was observed. The band exhibits the features typical for smooth terminating bands that also appear in rotational bands of heavier nuclei in the A similar to 100 region. The results are compared with total Routhian surface and cranked Nilsson-Strutinsky calculations.
33.	Joss, D. T., et al. (author) The influence of quasineutron configurations on 161Ta and nearby odd-A nuclei 2011 In: AIP Conf. Proc.. - : AIP. - 9780735409835 ; , s. 43-48 Conference paper (peer-reviewed)abstract Several strongly coupled bands in the neutron-deficient nucleus 161Ta have been identified and quasiparticle configuration assignments have been made on the basis of rotational alignments and cranked shell model calculations. The level scheme elucidated for 161Ta highlights the competition between the ν(h 9/2) and ν(i 13/2) orbitals to form the yrast spectrum. The band structures in 161Ta also provide new insights into the structural features of other heavy odd-A nuclei populated with much lower reaction cross sections in this region at the proton drip line.
34.	Lagergren, Karin, et al. (author) Isospectral superdeformed bands in the N=46 nuclei Mo-88 and Tc-89 2004 In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 21:3, s. 375-381 Journal article (peer-reviewed)abstract Superdeformed bands in Mo-88 and Tc-89 were populated Using Ca-40-induced fusion-evaporation reactions on Ni-58 at a beam energy of 185 MeV. Gamma-rays emitted in the reactions were detected using the Gammasphere spectrometer, in coincidence with charged particles detected by the Microball array. A new superdeformed band was assigned to the nucleus Mo-88, leading to a revisit of earlier configuration assignments for superdeformed structures in this nucleus. In particular, the theoretical interpretation of a pair of identical (isospectral) superdeformed bands in Mo-88/Tc-89 is discussed. The configurations that are assigned to the four SD bands belonging to Mo-88 have properties that are predicted to be significantly affected by pair correlations.
35.	Lagergren, Karin, et al. (author) Shape evolution in the superdeformed A approximate to 80-90 mass region 2003 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 68:6, s. 643091-643095 Journal article (peer-reviewed)abstract Superdeformed bands in Mo-88, Tc-89, and Tc-91 were populated using a Ca-40 beam with an energy of 185 MeV, impinging on a backed Ni-58 target. gamma rays and charged particles emitted in the reactions were detected using the Gammasphere Ge detector array and the CsI(TI) array Microball. Average transition quadrupole moments Q(t) with significantly improved accuracy compared to earlier work, were deduced for the bands using the residual doppler shift technique. The experimental results were included into a systematic study of the Q(t) values throughout the superdeformed mass 80-90 region. The superdeformed shell gaps are predicted to move towards larger deformations with increasing Z and N in this mass region. This trend is confirmed by the experimental Q(t) values.
36.	Lieder, R. M., et al. (author) From highly to superdeformed shapes : study of Gd-143 2000 In: Nuclear Physics A. - 0375-9474 .- 1873-1554. ; 671:04-jan, s. 52-70 Journal article (peer-reviewed)abstract A superdeformed band has been discovered in Gd-143 consisting Of 15 transitions. It does not show the band crossing observed in the neighbouring heavier Gd isotopes and it is degenerate with the superdeformed band in Eu-143. In contrast to other degenerate bands at superdeformed shape, the configurations of the bands are quite different here. They result from the exchange of a nu 6(4) with a pi[404]9/2 configuration. In addition, a collective band has been observed which adopts a well-deformed triaxial shape at high spins according to calculations. The transition from highly to superdeformed shapes proceeds via triaxial shapes.
37.	Nieminen, P., et al. (author) gamma-ray spectroscopy of Bi-191,Bi-193 2004 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 69:6, s. 064326- Journal article (peer-reviewed)abstract Prompt and delayed gamma rays from Bi-191,Bi-193 have been identified using the recoil-decay tagging, isomer tagging, and recoil gating techniques, resulting in extensive level schemes for both nuclei. Excitation energies of the isomeric 13/2(+) states have been established and oblate strongly coupled bands built on them have been observed. The nearly spherical 9/2(-) ground-state bands appear to be crossed by more oblate-deformed low-lying structures. The properties of the bands feeding the 1/2(+) intruder states indicate some structural change between Bi-193 and Bi-191. The deformation associated with each of these states has been extracted from total Routhian surface calculations which also reveal the development of prolate minima with decreasing neutron number. B(M1)/B(E2) ratios have been measured for the observed strongly coupled bands in order to resolve the intrinsic excitations. The observed quasiparticle structures in Bi-193 and high-spin isomers both in Bi-193 and Bi-191 are interpreted based on the coupling of the odd proton to the even-even Pb core.
38.	Qi, Chong, et al. (author) Abrupt changes in alpha-decay systematics as a manifestation of collective nuclear modes 2010 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 81:6, s. 064319- Journal article (peer-reviewed)abstract An abrupt change in alpha-decay systematics around the N = 126 neutron shell closure is discussed. It is explained as a sudden hindrance of the clustering of the nucleons that eventually form the a particle. This is because the clustering induced by the pairing mode acting upon the four nucleons is inhibited if the configuration space does not allow a proper manifestation of the pairing collectivity.
39.	Weiszflog, M., et al. (author) High-spin spectroscopy of Ga-63(31)32 and Ga-65(31)34 2001 In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 11:1, s. 25-38 Journal article (peer-reviewed)abstract High-spin states in the nuclei Ga-63 and Ga-65 were studied following the reaction S-32 + Ca-40 at a reaction energy of 125 MeV and using the GASP gamma -ray spectrometer in combination with the ISIS charged-particle detector system. In addition to low-lying negative-parity states with single-particle character, rotational-like cascades built on the 9/2(+) and 19/2(-) states have been observed in both nuclei. Sidebands with negative parity in Ga-63 and positive parity in Ga-65 could be established. The experimental results are compared with Total Routhian Surface calculations which describe the nuclei as moderately deformed (beta (2) approximate to 0.25) and gamma soft at low rotational frequencies. The highest experimentally observed positive-parity state in Ga-65 (41/2(+)) is in good agreement with the calculated crossing of the collective band with a non-collective one terminating at this spin.
40.	Andgren, Karin, et al. (author) Low-spin collective behavior in the transitional nuclei Mo-86,Mo-88 2007 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 76:1, s. 014307- Journal article (peer-reviewed)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.
41.	Andreyev, A. N., et al. (author) alpha-decay of the new isotope Po-187 : Probing prolate structures beyond the neutron mid-shell at N=104 2006 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 73:4, s. 044324- Journal article (peer-reviewed)abstract The new neutron-deficient isotope Po-187 has been identified in the complete fusion reaction Ti-46+Sm-144 -> Po-187+3n at the velocity filter SHIP. Striking features of the Po-187 alpha decay are the strongly-hindered decay to the spherical ground state and unhindered decay to a surprisingly low-lying deformed excited state at 286 keV in the daughter nucleus Pb-183. Based on the potential energy surface calculations, the Po-187 ground state and the 286 keV excited state in Pb-183 were interpreted as being of prolate origin. The systematic deviation of the alpha-decay properties in the lightest odd-A Po isotopes relative to the smooth behavior in the even-A neighbors is discussed. Improved data for the decay of Bi-187(m,g) were also obtained.
42.	Andreyev, A. N., et al. (author) In-beam and alpha-decay spectroscopy of Po-191 and evidence for triple shape coexistence at low energy in the daughter nucleus Pb-187 2002 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 66:1 Journal article (peer-reviewed)abstract Prompt gamma rays have been observed for the first time from the neutron-deficient nucleus Po-191 using the recoil-decay tagging technique at the RITU gas-filled separator. In addition improved alpha decay data have been measured for Po-191 and its daughter product Pb-187. The complementary gamma- and alpha-decay data point to the onset of oblate deformation in the light odd-mass Po nuclei by approaching the neutron midshell at N=104. The pattern of the favored and unfavored states observed on top of the 13/2(+) isomer in Po-191 indicates a change from the weak-coupling towards the strong-coupling scheme in Po-191m. In the daughter nucleus Pb-187, the 13/2(+) and 3/2(-) isomeric states become degenerate within the experimental accuracy. Evidence for triple shape coexistence at low energy has been found in the high-spin isomer in Pb-187. The results are supported by potential-energy surface calculations and by particle-plus-rotor calculations.
43.	Andreyev, A. N., et al. (author) Shape-changing particle decays of Bi-185 and structure of the lightest odd-mass Bi isotopes 2004 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 69:5, s. 054308- Journal article (peer-reviewed)abstract Proton and alpha decay of the proton-rich nuclide Bi-185 has been restudied in more detail in the complete fusion reaction Nb-93(Mo-95, 3n)Bi-185 at the velocity filter SHIP. The observed decay pattern of Bi-185 and of the heavier odd-mass isotopes Bi-187,Bi-189,Bi-191,Bi-193 are interpreted based on potential-energy surface calculations. It is shown that the experimental systematics of the particle decays and of the excited states in these nuclei (where known) can be explained by the prolate-oblate shape co-existence at low excitation energy. The observed state in Bi-185 is proposed to be of prolate nature, which is in contrast with the previously proposed oblate interpretation.
44.	Bhagwat, A., et al. (author) Investigation of band termination in the lower fp shell within the cranked relativistic mean field model 2013 In: International Conference on Recent Trends in Nuclear Physics-2012 (ICRTNP 2012). - : AIP. - 9780735411470 ; , s. 105-108 Conference paper (peer-reviewed)abstract The excitation energy difference (ΔE) between the terminating states built on the f7/2 n and d3/2 -1f 7/2 n+1 configurations (here, 'n' denotes the number of valence particles outside the 40Ca core and the particle hole excitation across the magic gap 20 is of proton type) in the lower fp shell are studied systematically within the framework of the cranked relativistic mean field model. The ΔE thus defined, depends predominantly on the f 7/2 - d3/2 shell gap, and its evolution as a function of neutron - proton asymmetry. The latter, in turn, depends on the isoscalar - isovector balance in the spin - orbit potential. Therefore, a systematic investigation of the difference ΔE is expected to test quantitatively the predicted shell gaps as a function of isospin. We find that: 1) the conventional NL3 parameter set over estimates the ΔE values, implying that the said shell gap is over - estimated in this parametrization and 2) the largest deviation between the calculated and the experimental values of ΔE is obtained for the nucleus with the smallest asymmetry value in the set of nuclei considered, and that the deviation decreases with increasing asymmetry, indicating that the in RMF parametrization considered, the isoscalar - isovector balance in the spin - orbit potential requires improvement. We carry out a re - fit of the RMF parameters to attempt a remedy to these two problems. We find that in addition to the binding energies and charge radii, if a constraint is put on the f7/2 - d3/2 shell gap in the fit to the Lagrangian parameters, the overall agreement of ΔE with the experiment improves significantly, without disturbing the agreement already achieved for the bulk properties of the nuclei spanning the entire periodic table. At a finer level, however, it is found that the isoscalar - isovector balance in the spin orbit interaction is required to be improved further. A detailed work in this direction is in progress.
45.	Bhagwat, A., et al. (author) Mic–Mac model based on the Wigner–Kirkwood method 2023 In: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 59:12 Journal article (peer-reviewed)abstract About a decade ago we proposed a new Microscopic–Macroscopic (Mic–Mac) model where the semiclassical Wigner–Kirkwood expansion of the energy up to fourth-order in ħ is used to compute the shell corrections in a deformed Woods-Saxon potential instead of the usual Strutinsky averaging scheme [1, 2]. For a set of 551 even-even nuclei computed with this new model, we found a rms deviation of 610 keV from the experimental masses, similar to the value obtained using the well-known Finite Range Droplet Model and the Lublin–Strasbourg Drop Model for the same set of nuclei. In a next step, we compute the ground-state properties of these 551 nuclei with the same method but using the mean-field provided by the Gogny forces within an Extended Thomas-Fermi approximation. We find that this Mic–Mac model using the Gogny D1S (D1M) force gives a fairly good description of the ground-state energies with a rms deviation of 834 keV (819 keV). This implies that Mic–Mac models based on effective two-body forces, for example Gogny D1S and D1M interactions, perform practically as well as the most efficient Mic–Mac models regarding ground-state properties.
46.	Bhagwat, A., et al. (author) Microscopic-macroscopic approach for binding energies with the Wigner-Kirkwood method. II. Deformed nuclei 2012 In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 86:4, s. 044316- Journal article (peer-reviewed)abstract The binding energies of deformed even-even nuclei have been analyzed within the framework of a recently proposed microscopic-macroscopic model. We have used the semiclassical Wigner-Kirkwood (h) over bar expansion up to fourth order, instead of the usual Strutinsky averaging scheme, to compute the shell corrections in a deformed Woods-Saxon potential including the spin-orbit contribution. For a large set of 561 even-even nuclei with Z >= 8 and N >= 8, we find an rms deviation from the experiment of 610 keV in binding energies, comparable to the one found for the same set of nuclei using the finite range droplet model of Moller and Nix (656 keV). As applications of our model, we explore its predictive power near the proton and neutron drip lines as well as in the superheavy mass region. Next, we systematically explore the fourth-order Wigner-Kirkwood corrections to the smooth part of the energy. It is found that the ratio of the fourth-order to the second-order corrections behaves in a very regular manner as a function of the asymmetry parameter I = (N - Z)/A. This allows us to absorb the fourth-order corrections into the second-order contributions to the binding energy, which enables us to simplify and speed up the calculation of deformed nuclei.
47.	Bhagwat, A., et al. (author) Recent developments in the Wigner - Kirkwood mass formula 2013 In: International Conference on Recent Trends in Nuclear Physics-2012 (ICRTNP-2012). - : AIP. - 9780735411470 ; , s. 20-24 Conference paper (peer-reviewed)abstract The recently proposed microscopic - macroscopic model for nuclear masses, based on the shell corrections obtained by using the semi - classical Wigner - Kirkwood (WK) ℏ expansion of one body quantal partition function, has been extended to the even - even deformed nuclei. The nuclear potential is assumed to be deformed Woods - Saxon with spin - orbit contribution. The Coulomb potential is obtained by folding charge densities. The resulting partition function is expanded upto the fourth order in ℏ to obtain averaged energies. The shell corrections thus obtained along with pairing energies determined within the framework of the Lipkin - Nogami scheme constitute microscopic part of the model. The macroscopic part is obtained from a liquid drop formula, with nine adjustable parameters. These parameters are fitted by considering a large set of 561 even - even nuclei with Z ≥ 8 and N ≥ 8. The fit yields rms deviation of merely 610 keV from the corresponding experimental masses. A few applications of the mass formula are presented and discussed in this paper.
48.	Bhagwat, A., et al. (author) WIGNER-KIRKWOOD METHOD FOR MICROSCOPIC-MACROSCOPIC CALCULATION OF BINDING ENERGIES 2010 In: International Journal of Modern Physics E. - 0218-3013. ; 19:4, s. 747-758 Journal article (peer-reviewed)abstract We propose to use the semi-classical Wigner-Kirkwood (h) over bar expansion to calculate shell corrections for spherical and deformed nuclei. The expansion is carried out up to fourth order in (h) over bar. A systematic study of Wigner-Kirkwood averaged energies is presented as a function of the deformation degrees of freedom. The shell corrections, along with the pairing energies obtained by using the Lipkin-Nogami scheme are used in the microscopic-macroscopic approach to calculate binding energies. The macroscopic part is obtained from a liquid drop formula with six adjustable parameters. Considering a set of 367 spherical nuclei, the liquid drop parameters are adjusted to reproduce the experimental binding energies, which yields a rms deviation of 630 keV.
49.	Bäck, Torbjörn, et al. (author) First observation of gamma-rays from the proton emitter Au-171 2003 In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 16:4, s. 489-494 Journal article (peer-reviewed)abstract Gamma-rays from the alpha- and proton-unstable nuclide Au-171 have been observed for the first time. The gamma-rays were correlated with both a proton- and an alpha-particle decay branch, confirming that the nucleus decays by alpha and proton emission from a single (11/2(-)) state. The measurement confirms the previously determined half-lives for these particle decays but the present values are of higher precision. In addition, a longer half-life than determined in previous work was measured for the proton-unstable tentative ground state. The results are discussed in relation to structures in neighbouring nuclei and compared with a Strutinsky-type TRS calculation.
50.	Bäck, Torbjörn, et al. (author) Spectroscopy of the neutron-deficient nuclide Pt-171 2003 In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 17:1, s. 1-5 Journal article (peer-reviewed)abstract A number of previously unobserved gamma-rays emitted from the neutron-deficient nuclide Pt-171 have been identified using the recoil decay tagging technique. The level scheme has been updated using information from gamma-gamma coincidences and angular distribution measurements. To further confirm the assignments of the gamma-rays to Pt-171, the events were correlated with the alpha-decay of the daughter nucleus Os-167.

Skapa referenser, mejla, bekava och länka

Permalink

Träfflista för sökning "WFRF:(Wyss Ramon A.) "

Refine your search

Year