1. |
- Andreyev, A. N., et al.
(author)
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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
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In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 66:1
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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.
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2. |
- Bäck, Torbjörn, et al.
(author)
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First observation of gamma-rays from the proton emitter Au-171
- 2003
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In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 16:4, s. 489-494
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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.
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3. |
- Bäck, Torbjörn, et al.
(author)
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Spectroscopy of the neutron-deficient nuclide Pt-171
- 2003
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In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 17:1, s. 1-5
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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.
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4. |
- Van De Vel, K., et al.
(author)
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In-beam gamma-ray spectroscopy of Po-190 : First observation of a low-lying prolate band in Po isotopes
- 2003
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In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 17:2, s. 167-171
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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.
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5. |
- Nieminen, P., et al.
(author)
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gamma-ray spectroscopy of Bi-191,Bi-193
- 2004
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In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 69:6, s. 064326-
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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.
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6. |
- Van de Vel, K., et al.
(author)
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Identification of low-lying proton-based intruder states in Pb189-193
- 2002
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In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 65:6
-
Journal article (peer-reviewed)abstract
- Low-lying proton-based intruder states have been observed in the odd-mass isotopes Pb-189,Pb-191,Pb-193 in experiments at the RITU gas-filled recoil separator. The identification has been performed by observing the fine structure in the alpha decay of the parent Po-193,Po-195,Po-197 nuclei in prompt coincidence with conversion electrons and gamma rays in the daughter lead isotopes. Along with the literature data these results establish a systematics of intruder states in the odd-mass lead isotopes from Pb-197 down to Pb-185. Interpretation of these states involves the coupling of the 1i(13/2) or 3p(3/2) odd neutron to the 0(+) state in the oblate minimum in the even-mass lead core. Conversion coefficients have been determined for some of the transitions, revealing mixing between the coexisting states. The experimental results are compared to potential energy surface calculations.
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7. |
- Bark, R A, et al.
(author)
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Coexistence of triaxial and prolate shapes in Ir-171
- 1999
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In: Nuclear Physics A. - 0375-9474 .- 1873-1554. ; 657:2, s. 113-133
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Journal article (peer-reviewed)abstract
- Excited states in Ir-171 have been observed for the first time. Gamma-rays were assigned to the nucleus by the recoil-decay tagging method, The ground-state band has a structure consistent with an h(11/2) proton coupled to a core of large triaxial deformation. At high spins, a bandcrossing occurs which is interpreted as a change in shape to a prolate deformation, Band-mixing calculations are performed for Ir171-175. These show that shape-coexistence between triaxial and prolate states in these nuclei follows the same systematics found in their Pt and Os neighbours. The systematics are also compared with deformations calculated for Ir171-179 using the code "Ultimate Cranker". Dipole bands were also observed, but tilted axis cranking calculations suggest that they are associated with a collective rotation.
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8. |
- King, S L, et al.
(author)
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First observation of excited states in the neutron deficient nuclei (PT)-P-168 and Pt-170
- 1998
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In: Physics Letters B. - 0370-2693 .- 1873-2445. ; 443:1-4, s. 82-88
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Journal article (peer-reviewed)abstract
- Excited states have been observed for the first time in (XPt)-X-168 and Pt-170 using the alpha-decay recoil-tagging technique. The trend of decreasing deformation moving away from the N = 104 mid-shell continues far Pt-170 but the structure of Pt-168 is significantly different. The low spin level energy systematics in Pt168-184 are presented and discussed within the framework of the interacting boson model. (C) 1998 Elsevier Science B.V. All rights reserved.
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9. |
- Kirsebom, O. S., et al.
(author)
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Measurement of the 2+→0+ ground-state transition in the β decay of F 20
- 2019
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In: Physical Review C. - 2469-9985. ; 100:6
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Journal article (peer-reviewed)abstract
- We report the first detection of the second-forbidden, nonunique, 2+→0+, ground-state transition in the β decay of F20. A low-energy, mass-separated F+20 beam produced at the IGISOL facility in Jyväskylä, Finland, was implanted in a thin carbon foil and the β spectrum measured using a magnetic transporter and a plastic-scintillator detector. The β-decay branching ratio inferred from the measurement is bβ=[0.41±0.08(stat)±0.07(sys)]×10-5 corresponding to logft=10.89(11), making this one of the strongest second-forbidden, nonunique β transitions ever measured. The experimental result is supported by shell-model calculations and has significant implications for the final evolution of stars that develop degenerate oxygen-neon cores. Using the new experimental data, we argue that the astrophysical electron-capture rate on Ne20 is now known to within better than 25% at the relevant temperatures and densities.
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10. |
- Andreyev, A. N., et al.
(author)
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alpha-decay of the new isotope Po-187 : Probing prolate structures beyond the neutron mid-shell at N=104
- 2006
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In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 73:4, s. 044324-
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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.
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11. |
- Andreyev, A. N., et al.
(author)
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Signatures of the Z=82 shell closure in alpha-decay process
- 2013
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In: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 110:24
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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.
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12. |
- Bark, R A, et al.
(author)
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Bandcrossings in Os-171
- 1999
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In: Nuclear Physics A. - 0375-9474 .- 1873-1554. ; 646:4, s. 399-413
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Journal article (peer-reviewed)abstract
- The nucleus Os-171 has been populated using the reaction Sn-116(Ni-58,2pn). Four new bands are identified, and the previously known bands are extended in spin, to a maximum of 53/2 (h) over bar. One- and three-quasiparticle configurations are identified, and beta, gamma, and octupole configurations are assigned tentatively. The effects of a possible intruder configuration on the negative parity bands are tested using band-mixing calculations.
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13. |
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14. |
- Cederwall, Bo, et al.
(author)
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Collective rotational-vibrational transition in the very neutron-deficient nuclei (171,172)-Pt
- 1998
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In: Physics Letters B. - AMSTERDAM, NETHERLANDS : ELSEVIER SCIENCE. - 0370-2693 .- 1873-2445. ; 443:1-4, s. 69-76
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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.
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15. |
- Joss, D. T., et al.
(author)
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Identification of excited states in Os-167 and Os-168 : shape coexistence at extreme neutron deficiency
- 2001
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In: Nuclear Physics A. - : Elsevier. - 0375-9474 .- 1873-1554. ; 689:04-mar, s. 631-654
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Journal article (peer-reviewed)abstract
- Excited states in the very neutron-deficient isotopes Os-167 and Os-168 have been observed using the reaction Sn-112(Ni-58, 2pxn). The JUROSPHERE gamma -ray spectrometer array was used in conjunction with the RITU gas-filled recoil separator to collect prompt gamma radiation in coincidence with recoils implanted in a silicon strip detector located at the focal plane of RITU. Using a selective recoil decay tagging technique it has been possible to unambiguously assign gamma -ray transitions to Os-167 and Os-168 through the characteristic a radioactivity of these nuclides. The high-spin structure of the bands is discussed in terms of quasiparticle configurations within the framework of the cranked shell model. The role of shape coexistence in Os-168 is examined with phenomenological three-band mixing calculations.
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16. |
- Joss, D. T., et al.
(author)
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Strongly coupled bands in the neutron-deficient nucleus Re-167
- 2003
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In: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 68:1
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Journal article (peer-reviewed)abstract
- Excited states in the neutron-deficient nucleus Re-167 have been observed in a recoil-tagging experiment performed with the Jurosphere gamma-ray spectrometer in conjunction with the RITU gas-filled recoil separator. The low-spin yrast band, based on a proton h(11/2) orbital, comprises a strongly coupled band and exhibits significant signature splitting, indicative of a triaxial shape with gamma<0degrees. At higher spin the rotational alignment of a pair of i(13/2) neutrons induces a transition to an axial prolate shape resulting in a drastic reduction of the signature splitting. Two other strongly coupled bands have been established and their structures are discussed in terms of quasiparticle configurations.
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17. |
- Joss, D. T., et al.
(author)
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Yrast spectroscopy in the neutron-deficient nucleus Os-169
- 2002
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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.
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