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論文

Competition between allowed and first-forbidden $$beta$$ decays of $$^{208}$$At and expansion of the $$^{208}$$Po level scheme

Brunet, M.*; Podoly$'a$k, Zs.*; Berry, T. A.*; Brown, B. A.*; Carroll, R. J.*; Lica, R.*; Sotty, Ch.*; Andreyev, A. N.; Borge, M. J. G.*; Cubiss, J. G.*; et al.

Physical Review C, 103(5), p.054327_1 - 054327_13, 2021/05

https://doi.org/10.1103/PhysRevC.103.054327
 被引用回数：4 パーセンタイル：57.13(Physics, Nuclear)

The structure of $$^{208}$$Po populated through the EC/$$beta^{+}$$ decay of $$^{208}$$At is investigated using $$gamma$$-ray spectroscopy at the ISOLDE Decay Station. The presented level scheme contains 27 new excited states and 43 new transitions, as well as a further 50 previously observed $$gamma$$ rays which have been (re)assigned a position. Through the analysis using the shell model calculations approximately half of the $$beta$$-decay strength of $$^{208}$$At is found to proceed via allowed decay and half via first-forbidden decay. The first-forbidden transitions predominantly populate core excited states at high excitation energies, which is qualitatively understood using shell model considerations.

論文

Competition between allowed and first-forbidden $$beta$$ decay; The Case of $$^{208}$$Hg $$rightarrow$$ $$^{208}$$Tl

Carroll, R. J.*; Podoly$'a$k, Zs.*; Berry, T.*; Grawe, H.*; Alexander, T.*; Andreyev, A. N.; Ansari, S.*; Borge, M. J. G.*; Brunet, M.*; Creswell, J. R.*; et al.

Physical Review Letters, 125(19), p.192501_1 - 192501_6, 2020/11

https://doi.org/10.1103/PhysRevLett.125.192501
 被引用回数：9 パーセンタイル：62.22(Physics, Multidisciplinary)

The $$beta$$ decay of $$^{208}$$Hg into the one-proton hole, one neutron-particle $$^{208}_{81}$$Tl$$_{127}$$ nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the $$N > 126$$, $$Z < 82$$ quadrant of neutron-rich nuclei. While both negative and positive parity states with spin 0 and 1 are expected within the $$Q_{beta}$$ window, only three negative parity states are populated directly in the $$beta$$ decay. The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden $$beta$$ decays, essential for the understanding of the nucleosynthesis of heavy nuclei in the rapid neutron capture process. Furthermore, the observation of the parity changing $$0^{+} rightarrow 0^{-} beta$$ decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators.

論文

Detailed spectroscopy of doubly magic $$^{132}$$Sn

Benito, J.*; Fraile, L. M.*; Korgul, A.*; Piersa, M.*; Adamska, E.*; Andreyev, A. N.; $'A$lvarez-Rodr$'i$guez, R.*; 他81名*

Physical Review C, 102(1), p.014328_1 - 014328_18, 2020/07

https://doi.org/10.1103/PhysRevC.102.014328
 被引用回数：14 パーセンタイル：84.12(Physics, Nuclear)

The structure of the doubly magic $$^{132}_{50}$$Sn$$_{82}$$ has been investigated at the ISOLDE facility at CERN, populated both by the $$beta$$-decay of $$^{132}$$In and $$beta$$-delayed neutron emission of $$^{133}$$In. The level scheme of $$^{132}$$Sn is greatly expanded with the addition of 68 $$gamma$$-ray transitions and 17 levels. The identification of particle-hole multiplets both for protons and neutrons and the transition rates connecting different particle-hole configurations may provide input on the two-body matrix elements and single-particle states for state-of-the-art calculations.

論文

In-source laser spectroscopy of dysprosium isotopes at the ISOLDE-RILIS

Chrysalidis, K.*; Barzakh, A. E.*; Ahmed, R.*; Andreyev, A. N.; Ballof, J.*; Cubiss, J. G.*; Fedorov, D. V.*; Fedosseev, V. N.*; Fraile, L. M.*; Harding, R. D.*; et al.

Nuclear Instruments and Methods in Physics Research B, 463, p.472 - 475, 2020/01

https://doi.org/10.1016/j.nimb.2019.04.021
 被引用回数：3 パーセンタイル：36.4(Instruments & Instrumentation)

放射壊変によって生成された多数のジスプロシウム同位体について、ISOLDEのレーザー共鳴イオン源(RILIS)を用いてイオン源内レーザー分光法によって研究した。$$^{152}$$Dyに対する相対的な同位体シフトを$$4f^{10}6s^{2}~^{5}I_{8}$$ (gs) $$rightarrow$$ $$4f^{10}6s6p~(8,1)^{o}_{8}$$共鳴遷移を用いて測定した。電子的因子Fとマスシフト因子Mを導出し、それらを使って$$^{rm 145m}$$Dyと$$^{rm 147m}$$Dyの平均自乗荷電半径の変化を初めて決定した。

論文

Electromagnetic properties of low-lying states in neutron-deficient Hg isotopes; Coulomb excitation of $$^{182}$$Hg, $$^{184}$$Hg, $$^{186}$$Hg and $$^{188}$$Hg

Wrzosek-Lipska, K.*; Rezynkina, K.*; Bree, N.*; Zieli$'n$ska, M.*; Gaffney, L. P.*; Petts, A.*; Andreyev, A. N.; Bastin, B.*; Bender, M.*; Blazhev, A.*; et al.

European Physical Journal A, 55(8), p.130_1 - 130_23, 2019/08

https://doi.org/10.1140/epja/i2019-12815-2
 被引用回数：11 パーセンタイル：74.44(Physics, Nuclear)

The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass $$^{182-188}$$Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of 0$$^{+}_{1,2}$$, 2$$^{+}_{1,2}$$, and 4$$^{+}_{1}$$ states was observed in all nuclei under study. Reduced $$E2$$ matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions.

論文

Investigation of the $$Delta$$$$n$$ = 0 selection rule in Gamow-Teller transitions; The $$beta$$-decay of $$^{207}$$Hg

Berry, T. A.*; Podoly$'a$k, Zs.*; Carroll, R. J.*; Lic$u{a}$, R.*; Grawe, H.*; Timofeyuk, N. K.*; Alexander, T.*; Andreyev, A. N.; Ansari, S.*; Borge, M. J. G.*; et al.

Physics Letters B, 793, p.271 - 275, 2019/06

https://doi.org/10.1016/j.physletb.2019.04.039
 被引用回数：5 パーセンタイル：47.88(Astronomy & Astrophysics)

Gamow-Teller $$beta$$ decay is forbidden if the number of nodes in the radial wave functions of the initial and final states is different. This $$Delta$$$$n$$ = 0 requirement plays a major role in the $$beta$$ decay of heavy neutron-rich nuclei, affecting the nucleosynthesis through the increased half-lives of nuclei on the astrophysical $$r$$-process pathway below both $$Z$$ = 50 (for $$N >$$ 82) and $$Z$$ = 82 (for $$N >$$ 126). The level of forbiddenness of the $$Delta$$$$n$$ = 1 $$nu$$1$$g_{9/2} rightarrow pi$$0$$g_{7/2}$$ transition has been investigated from the $$beta^{-}$$ decay of the ground state of $$^{207}$$Hg into the single-proton-hole nucleus $$^{207}$$Tl in an experiment at the ISOLDE Decay Station. From statistical observational limits on possible $$gamma$$-ray transitions depopulating the $$pi$$0$$g^{-1}_{7/2}$$ state in $$^{207}$$Tl, an upper limit of 3.9$$times$$10$$^{-3}$$ % was obtained for the probability of this decay, corresponding to log$$ft >$$ 8.8 within a 95% confidence limit. This is the most stringent test of the $$Delta$$$$n$$ = 0 selection rule to date.

論文

EXILL; A High-efficiency, high-resolution setup for $$gamma$$-spectroscopy at an intense cold neutron beam facility

Jentschel, M.*; Blanc, A.*; de France, G.*; K$"o$ster, U.*; Leoni, S.*; Mutti, P.*; Simpson, G.*; Soldner, T.*; Ur, C.*; Urban, W.*; et al.

Journal of Instrumentation (Internet), 12(11), p.P11003_1 - P11003_33, 2017/11

https://doi.org/10.1088/1748-0221/12/11/P11003
 被引用回数：38 パーセンタイル：84.92(Instruments & Instrumentation)

A highly efficient array of high-purity germanium (HPGe) detectors was developed and operated at the cold neutron beam facility PF1B of the Institut Laue-Langevin (ILL) to carry out nuclear structure studies, via measurements of $$gamma$$-rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent flux of about 10$$^8$$ns$$^{-1}$$cm$$^{-2}$$ at the target position and negligible neutron halo. The target was surrounded by an array of eight to ten anti-Compton shielded EXOGAM Clover detectors, four to six anti-Compton shielded large coaxial GASP detectors and two standard Clover detectors. For a part of the campaign the array was combined with 16 LaBr$$_{3}$$:(Ce) detectors from the FATIMA collaboration.

論文

Ground-state configuration of neutron-rich $$^{35}$$Al via Coulomb breakup

Chakraborty, S.*; Datta, U.*; Aumann, T.*; Beceiro-Novo, S.*; Boretzky, K.*; Caesar, C.*; Carlson, B. V.*; Catford, W. N.*; Chartier, M.*; Cortina-Gil, D.*; et al.

Physical Review C, 96(3), p.034301_1 - 034301_9, 2017/09

https://doi.org/10.1103/PhysRevC.96.034301
 被引用回数：4 パーセンタイル：27.61(Physics, Nuclear)

GSIのLAND-FRSセットアップを用いて、$$^{35}$$Alの基底状態配位をクーロン分解反応によって調べた。そこで得られた包括的断面積は78(13)mbとなった。単一粒子模型によるクーロン分解反応断面積を大規模殻模型計算による$$^{34}$$Al+1中性子系の分光学的因子と組み合わせることによって得られた理論計算の断面積を実験値と比較した。その結果、殻模型計算では$$f$$軌道の寄与をいくらか過大評価し、$$p$$軌道の寄与を過小評価していることがわかった。これは、$$^{35}$$Alの基底状態において中性子数28の殻ギャップが著しく縮まっており、それによって、$$pf$$殻を占める最後の2個の中性子軌道が$$p$$軌道をより多く占有しているためであると考えられる。

論文

Identification of the crossing point at $$N$$ = 21 between normal and intruder configurations

Lic$u{a}$, R.*; Rotaru, F.*; Borge, M. J. G.*; Gr$'e$vy, S.*; Negoita, F.*; Poves, A.*; Sorlin, O.*; Andreyev, A. N.; Borcea, R.*; Costache, C.*; et al.

Physical Review C, 95(2), p.021301_1 - 021301_6, 2017/02

https://doi.org/10.1103/PhysRevC.95.021301
 被引用回数：18 パーセンタイル：79.42(Physics, Nuclear)

The $$beta^{-}$$ decay of $$^{34}$$Mg was used to study the $$^{34}$$Al nucleus through $$gamma$$ spectroscopy at the Isotope Separator On-Line facility of CERN. Previous studies identified two $$beta$$-decaying states in $$^{34}$$Al having spin-parity assignments $$J^{pi}$$=4$$^{-}$$ dominated by the normal configuration $$pi$$(d5/2)$$^{-1}$$ $$bigoplus$$ $$nu$$(f7/2) and $$J^{pi}$$ = 1$$^{+}$$ by the intruder configuration $$pi$$(d5/2)$$^{-1}$$ $$bigoplus$$ $$nu$$(d3/2)$$^{-1}$$(f7/2)$$^{2}$$. Their unknown ordering and relative energy have been the subject of debate for the placement of $$^{34}$$Al inside or outside the $$N$$ = 20 "island of inversion". We report here that the 1$$^{+}$$ intruder lies only 46.6 keV above the 4$$^{-}$$ ground state. In addition, a new half-life of $$T_{1/2}$$=44.9(4)ms, that is twice as long as thepreviously measured 20(10) ms, has been determined for $$^{34}$$Mg. Large-scale shell-model calculations with the recently developed SDPF-U-MIX interaction are compared with the new data and used to interpret the mechanisms at play at the very border of the $$N$$ = 20 island of inversion.

論文

Beta-delayed proton emission from $$^{20}$$Mg

Lund, M. V.*; Andreyev, A. N.; Borge, M. J. G.*; Cederk$"a$ll, J.*; De Witte, H.*; Fraile, L. M.*; Fynbo, H. O. U.*; Greenlees, P. T.*; Harkness-Brennan, L. J.*; Howard, A. M.*; et al.

European Physical Journal A, 52(10), p.304_1 - 304_14, 2016/10

https://doi.org/10.1140/epja/i2016-16304-x
 被引用回数：17 パーセンタイル：75.78(Physics, Nuclear)

Beta-delayed proton emission from $$^{20}$$Mg has been measured at ISOLDE, CERN, with the ISOLDE Decay Station setup including both charged-particle and $$gamma$$-ray detection capabilities. A total of 27 delayed proton branches were measured including seven so far unobserved. An updated decay scheme, including three new resonances above the proton separation energy in $$^{20}$$Na and more precise resonance energies, is presented. Beta-decay feeding to two resonances above the Isobaric Analogue State in $$^{20}$$Na is observed. This may allow studies of the 4032.9(2.4) keV resonance in $$^{19}$$Ne through the beta decay of $$^{20}$$Mg, which is important for the astrophysically relevant reaction $$^{15}$$O($$alpha$$,$$gamma$$)$$^{19}$$Ne. Beta-delayed protons were used to obtain a more precise value for the half-life of $$^{20}$$Mg, 91.4(1.0) ms.

論文

Fast-timing study of the $$l$$-forbidden 1/2$$^+$$ $$rightarrow$$ 3/2$$^+$$ $$M1$$ transition in $$^{129}$$Sn

Lic$u{a}$, R.*; Mach, H.*; Fraile, L. M.*; Gargano, A.*; Borge, M. J. G.*; M$u{a}$rginean, N.*; Sotty, C. O.*; Vedia, V.*; Andreyev, A. N.; Benzoni, G.*; et al.

Physical Review C, 93(4), p.044303_1 - 044303_7, 2016/04

https://doi.org/10.1103/PhysRevC.93.044303
 被引用回数：5 パーセンタイル：39.53(Physics, Nuclear)

The levels in $$^{129}$$Sn populated from the $$beta^-$$ decay of $$^{129}$$In isomers were investigated at the ISOLDE facility of CERN using the newly commissioned ISOLDE Decay Station. The lowest 1/2$$^+$$ state and the 3/2$$^+$$ ground state in $$^{129}$$Sn are expected to have configurations dominated by the neutron $$s_{1/2}$$ ($$l$$=0) and $$d_{3/2}$$ ($$l$$=2) single-particle states, respectively. Consequently, these states should be connected by a somewhat slow $$l$$-forbidden $$M1$$ transition. Using fast-timing spectroscopy we have measured the half-life of the 1/2$$^+$$ 315.3-keV state, $$T_{1/2}$$ = 19(10) ps, which corresponds to a moderately fast $$M1$$ transition. Shell-model calculations using the CD-Bonn effective interaction, with standard effective charges and $$g$$ factors, predict a 4-ns half-life for this level. We can reconcile the shell-model calculations to the measured $$T_{1/2}$$ value by the renormalization of the $$M1$$ effective operator for neutron holes.

論文

Shapes of $$^{192,190}$$Pb ground states from $$beta$$-decay studies using the total-absorption technique

Est$'e$vez Aguado, M. E.*; Algora, A.*; Agramunt, J.*; Rubio, B.*; Tain, J. L.*; Jord$'a$n, D.*; Fraile, L. M.*; Gelletly, W.*; Frank, A.*; Csatl$'o$s, M.*; et al.

Physical Review C, 92(4), p.044321_1 - 044321_8, 2015/10

https://doi.org/10.1103/PhysRevC.92.044321
 被引用回数：16 パーセンタイル：71.72(Physics, Nuclear)

The $$beta$$ decay of $$^{192,190}$$Pb has been studied using the total absorption technique at the ISOLDE (CERN) facility. The $$beta$$-decay strength deduced from the measurements, combined with QRPA theoretical calculations, allow us to infer that the ground states of the $$^{192,190}$$Pb isotopes are spherical. These results represent the first application of the shape determination method using the total absorption technique for heavy nuclei and in a region where there is considerable interest in nuclear shapes and shape effects.

論文

$$B(E2;2^+_1rightarrow 0^+_1)$$ value in $$^{90}$$Kr

R$'e$gis, J.-M.*; Jolie, J.*; Saed-Samii, N.*; Warr, N.*; Pfeiffer, M.*; Blanc, A.*; Jentschel, M.*; K$"o$ster, U.*; Mutti, P.*; Soldner, T.*; et al.

Physical Review C, 90(6), p.067301_1 - 067301_4, 2014/12

https://doi.org/10.1103/PhysRevC.90.067301
 被引用回数：23 パーセンタイル：80.23(Physics, Nuclear)

A smooth onset of collectivity in $$^{88,92,94,96}$$Kr has been determined from reported $$B(E2;2^+_1rightarrow 0^+_1)$$ and E(2$$^+_1$$) values. This is in contrast to the sudden onset in even-even Zr, Mo, and Sr isotopes. Our objective was to complete the systematics by determining the $$B(E2;2^+_1rightarrow 0^+_1)$$ value in $$^{90}$$Kr, which was produced by cold-neutron-induced fission of $$^{235}$$U. The lifetime of the 2$$^+_1$$ state in $$^{90}$$Kr was measured via the electronic $$gamma - gamma$$ timing technique using the EXILL and FATIMA spectrometers. Based on the measured mean lifetime of $$tau$$ = 15(10) ps, the $$B(E2;2^+_1rightarrow 0^+_1)$$ value of 13$$^{+26}_{-5}$$ W.u. in $$^{90}$$Kr is determined for the first time and the smooth onset of deformation in the even-even Kr isotopes beyond neutron number N=50 is confirmed.

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