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![Spectra of γ-rays which have been detected in the time interval 50 ns-1µs after the detection of two fragments by SAPhIR. (a) γ-rays in prompt coincidence with the 241/242 keV transition ( 120 Sn and 122 Sn). The 458-and 648keV transitions are pollutions (they belong to the decay of the isomeric 7 + state of 88 Rb [22]). (b) γ-rays in prompt coincidence with the 253 keV transition, which is a doublet. The 1050-and 1230-keV γ-rays are the first two transitions of 118 Sn and the 241-, 661-, and 1494-keV ones are assigned to 120 Sn. (c) γ-rays in prompt coincidence with the 264 keV transition ( 122 Sn).](profile/Olivier-Stezowski/publication/235595038/figure/fig3/AS:667830659842051@1536234645237/Spectra-of-g-rays-which-have-been-detected-in-the-time-interval-50-ns-1s-after-the.png)
Spectra of γ-rays which have been detected in the time interval 50 ns-1µs after the detection of two fragments by SAPhIR. (a) γ-rays in prompt coincidence with the 241/242 keV transition ( 120 Sn and 122 Sn). The 458-and 648keV transitions are pollutions (they belong to the decay of the isomeric 7 + state of 88 Rb [22]). (b) γ-rays in prompt coincidence with the 253 keV transition, which is a doublet. The 1050-and 1230-keV γ-rays are the first two transitions of 118 Sn and the 241-, 661-, and 1494-keV ones are assigned to 120 Sn. (c) γ-rays in prompt coincidence with the 264 keV transition ( 122 Sn).
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The 119–126Sn nuclei have been produced as fission fragments in two reactions induced by heavy ions: 12C+238U at a bombarding energy of 90 MeV and 18O+208Pb at 85 MeV. Their level schemes have been built from γ rays detected using the Euroball array. High-spin states located above the long-lived isomeric states of the even- and odd-A 120–126Sn nucl...
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... III B 5. Using the data from the SAPhIR experiment, the tran- sitions involved in the de-excitation of the 4890-keV level have been found to be delayed. The spectrum of γ-rays which have been detected in the time interval 50 ns-1µs after the detection of two fragments by SAPhIR and in prompt coincidence with the 241/242 keV transition is drawn in Fig. 4(a). As this γ line is a triplet, the spec- trum exhibits transitions emitted by the isomeric states of three fission fragments, 88 Rb [22], 120 Sn and 122 Sn. The spectrum shown in Fig. 4(b) is gated by the 253 keV γ-ray. This line is a doublet, as this energy occurs both in the decay of the 7 − isomeric state of 118 Sn (associ- ated ...
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... detected in the time interval 50 ns-1µs after the detection of two fragments by SAPhIR and in prompt coincidence with the 241/242 keV transition is drawn in Fig. 4(a). As this γ line is a triplet, the spec- trum exhibits transitions emitted by the isomeric states of three fission fragments, 88 Rb [22], 120 Sn and 122 Sn. The spectrum shown in Fig. 4(b) is gated by the 253 keV γ-ray. This line is a doublet, as this energy occurs both in the decay of the 7 − isomeric state of 118 Sn (associ- ated with the 1050-and 1230-keV transitions) and in the decay of the isomeric state at 4890 keV, newly estab- lished in 120 Sn. The statistics of this spectrum is too low to show the 1253-keV ...
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... branches which are placed above the the 10 + and 7 − isomeric states of 122 Sn, since two parallel decay paths located just below the 242 keV transition, 609+1103 on the one hand and 264+680+1125 on the other hand, exactly fits their difference in energy (see Fig. 6). Examples of coin- cidence spectra of γ lines belonging to 122 Sn are given in Fig. 4(a) and (c), which demonstrate that all the transi- tions involved in the de-excitation of the 4720-keV level are delayed. The time distribution between the detec- tion of two fragments by SAPhIR and the emission of the 1103-keV γ-ray gives T 1/2 = 146(15) ns. In order to reduce the background we have selected the events con- taining ...
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... and 175-keV transitions of the yrast cascade is drawn in Fig. 13 the complementary fragments, 100−98 Zr, it exhibits new peaks at 1070, 1083, 1171, 1212, and 1457 keV. In a sec- ond step, we have analyzed the coincidence relationships of these new γ-lines and placed all these transitions in three cascades above the 27/2 − state at 2833 keV (see Fig. 14). In addition two other lines were observed in coincidence with a part of the yrast transitions, thus the 889 keV transition defines a new state at 3076 keV and the 1152 keV one a new state at 3809 keV. The two most intense transitions of the new cascade assigned to 121 Sn thanks to their coincidences with their complementary fragments ...
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Citations
... The results obtained using this experimental setup will be illustrated based on the case of well studied 132 Te [55][56][57][58][59][60][61][62]. Figure 9(a) shows the partial level scheme of 132 Te (below 4.3 MeV). Several different isomeric Fig. 9 (a) The partial level scheme of 132 Te (below 4.3 MeV). ...
\gamma$-ray spectroscopy of fission fragments is a powerful method for studies of nuclear structure properties. Recent results on the spectroscopy of fission fragments, using the combination of the AGATA $\gamma$-ray tracking array and the VAMOS++ large acceptance magnetic spectrometer at GANIL, are reported. A comparison of the performance of the large germanium detector arrays EXOGAM and AGATA illustrates the advances in $\gamma$-ray spectroscopy of fission fragments. Selected results are highlighted for prompt $\gamma$-ray spectroscopy studies, measurements of short lifetimes of excited states with the Recoil Distance Doppler-Shift method, using both AGATA and VAMOS++ and prompt-delayed $\gamma$-ray spectroscopy studies using AGATA, VAMOS++ and EXOGAM.
... The involved nuclei are close to the N = 82 shell, while the shell effects are generally neglected in the phenomenological formulas [72]. Recent studies showed that a high-spin structure exists in the nuclei near 132 Sn, including Xe [57,74,75] and Ba [76] isotopes. Therefore, the spin cut-off parameter should be larger than the predicted values derived without shell effects. ...
Nuclear level density is important for evaluating nuclear reaction processes, but its microscopic investigation is not frequently performed. The present work applies a recently developed shell-model-based method to estimate the level density of fission products Xe133–137 and Ba135–138. The monopole-based universal interaction, VMU, and the M3Y type spin-orbit interaction are combined to construct the shell-model Hamiltonian. The model space is truncated based on the binding energy of each configuration, estimated from the monopole interaction. The calculated level densities of Xe133–137 and Ba135–138 are in good agreement with available experimental data. The effects of spin-orbit and tensor forces on the nuclear level density and the shell effects in the spin distribution are discussed.
... The first 2 + states in semi-magic nuclei have a nearly particle number independent energy variation, which has long been recognized [7]. The Sn isotope chain, which extends from the doubly magic 100 Sn to the doubly magic 132 Sn and beyond [27,29,30,44], is the traditional place to illustrate seniority. Sn exists in 41 different known isotopes, ranging from 99 Sn to 139 Sn. ...
... The other v = 3, 19/2 + , 23/2 + isomers with significant mixing from d 3/2 ⊗ s 1/2 orbitals are also known in these odd-A Sn isotopes [2]. The identification of a higher seniority v = 4, 15 − isomer in Sn isotopes [24,[28][29][30] has been of great interest due to its potential to probe effective interactions in many-body problems. The generalized seniority scheme, with a multi-j configuration h 11/2 ⊗ d 3/2 ⊗ s 1/2 (pair degeneracy of Ω = 9) [18], could explain the measured B(E1) rates for the v = 4, 13 − isomers, and the B(E2) rates for the v = 4, 15 − isomers in the Sn isotopes [29,30]. ...
... The identification of a higher seniority v = 4, 15 − isomer in Sn isotopes [24,[28][29][30] has been of great interest due to its potential to probe effective interactions in many-body problems. The generalized seniority scheme, with a multi-j configuration h 11/2 ⊗ d 3/2 ⊗ s 1/2 (pair degeneracy of Ω = 9) [18], could explain the measured B(E1) rates for the v = 4, 13 − isomers, and the B(E2) rates for the v = 4, 15 − isomers in the Sn isotopes [29,30]. Both the B(E2) and B(E1) rates support a parabolic trend for these neutron-rich Sn isotopes, irrespective of the odd or even nature of the involved electric tensor [18]. ...
Nuclear isomers are the metastable excited states of nuclei. The isomers can be categorized into a few classes including spin, seniority, K, shape and fission isomers depending upon the hindrance mechanisms. In this paper, we aim to present an overview of seniority isomers, which is a category related to the seniority quantum number. The discussion is mainly based on the concepts of seniority and generalized seniority. Various aspects of seniority isomers and their whereabouts have been covered along with the situations where seniority mixing prevents the isomerism.
... [16] In neutron-rich In (Z = 49) and Sb (Z = 51) isotopes, the valence proton hole and particle occupy the adjacent spinorbit partners g 9/2 and g 7/2 , respectively, while the valence neutron holes dominantly occupy the h 11/2 orbital. Even-A 118−130 Sn isotopes possess 7 − and 10 + isomers with dominant neutron νh −1 11/2 d −1 3/2 and νh −2 11/2 configurations, respectively [3][4][5][6]. Odd-A 121−131 Sb isotopes have 19/2 − and 23/2 + isomers with dominant π g 7/2 νh −1 11/2 d −1 3/2 and π g 7/2 νh −2 11/2 configurations [7][8][9][10][11], with an additional proton particle in g 7/2 coupled to the 7 − and 10 + isomers in even-A Sn isotopes, respectively. It should be noted that the 23/2 + isomers in Sb isotopes do not correspond to maximally aligned configurations (I π Max = 27/2 + ) but rather to I π Max − 2 = 23/2 + , illustrating the influence of spin and seniority mixing in these isotopes. ...
... The results of the calculations are shown in Fig. 8. The 10 + seniority isomer in even-A 120-130 Sn isotopes is known to be dominantly arising from νh −2 11/2 configuration [3][4][5][6]. Stretched angular momentum coupling of π g 7/2 particle in 121-131 Sb (π g 9 (b) Energies of the 19/2 + (black), 23/2 + (red), and 27/2 + (blue) level in Z = 51 121-131 Sb isotopes. The evolution of the 10 + states in Z = 50 120-130 Sn isotopes are also shown in green in these panels. ...
The low-lying states of Eu146 populated in the decay of the 9+ isomer were studied. The γ-ray intensities were reanalyzed employing germanium detectors, and the lifetimes of the 61− and 62− states were measured using the mirror symmetric centroid difference (MSCD) method with fast-timing LaBr3(Ce) scintillator detectors. The B(M1) values of the 61−→51− and 62−→51− transitions were deduced, and all observed states were interpreted as members of the πd5/2−1νf7/2 and πg7/2−1νf7/2 multiplets. In particular, the 51− level is shown to be dominated by the πd5/2−1νf7/2 configuration, solving the discrepancy in its configuration assignment proposed in previous works. These experimental results were compared with the shell model calculations using several different effective interactions. The systematics of low-lying structure in the N=83 isotones Pr142, Pm144, and Eu146 was established.
... Such studies suggested modifications of several components of the twobody matrix elements to reach a consistent agreement with excitation energies and B(E2) transition probabilities. In particular, 118−128 Sn were investigated with GAM-MASPHERE employing heavy-ion-induced fusion-fission reactions with different projectile-target combinations (e.g., 48 Ca and 64 Ni beams at ∼ 7 MeV/u on 208 Pb and 238 U targets) [98], and with EUROBALL coupled to the fission fragment detector SAPhIR, using 12 C+ 238 U and 18 O+ 208 Pb heavy-ion reactions at ∼ 7 MeV/u [99]. In the same EUROBALL experiments, odd A 115−121 In nuclei were also studied [100]. ...
... The level structure above these isomers is instead expected to give information on the involvement of the h 11/2 orbital in generating high-spin states above the isomeric states. By using prompt-delayed coincidence techniques of various types [98,99], the level schemes of Sn isotopes have been extended to 8 MeV excitation energy (see Fig. 13a). Additional 15 − and 13 − isomeric states (with half-lives of the order of 5-250 ns) were established around 4.5 MeV in even-even Sn, and states located above 3 MeV were found to be ascribed to several broken pairs of neutrons occupying the νh 11/2 orbit. ...
... Lower part: complete set of E2 transition amplitudes known for the (h 11/2 ) n isomers in Sn isotopes. The smooth variation with Z of the B(E2) reduced transition probabilities reflects the filling of the proton h 11/2 subshell, which is found to be half-filled at N = 73 (i.e., 123 Sn) [98,99,106]. Experimental data from heavy-ion-induced fusion-fission reactions and GAMMASPHERE. ...
The paper reviews recent developments in $$\gamma $$ γ -ray spectroscopy of the neutron-rich fragments produced in nuclear fission. This subject has been an intensive area of study spanning more than five decades. Here we highlight key results and describe the evolution of the associated experimental techniques since the last review papers in 1995 (I. Ahmad and W.R. Phillips, Rep. Prog. Phys. 58(11), 1415 (1995); J. H. Hamilton et al., Prog. Part. Nucl. Phys. 35, 635(1995)). Research themes in nuclear structure will be explored along with the fission reaction mechanism and the links to nuclear astrophysics and applications.
... Our result corresponding to isomeric states for the Rn chain shows the importance of h 9/2 , f 7/2 and i 13/2 orbitals. Several recent articles are available in the literature to explain seniority isomer for different nuclei within the framework of the nuclear shell-model [20,58,59]. ...
... Sn isotopes are long known to present an interesting ground for pairing correlations of nucleons in both experimental and theoretical studies. Experimental groups [24,25] recently reported the measurements of the higher seniority v = 4, 15 − and 13 − isomers in the Sn-isotopes. In particular, the surprisingly similar trends of the experimental B(E2) values in the 15 − isomers and the B(E1) values in the 13 − isomers were highlighted by Iskra et al. [25] without any justification. ...
... [16] In neutron-rich In (Z = 49) and Sb (Z = 51) isotopes, the valence proton hole and particle occupy the adjacent spinorbit partners g 9/2 and g 7/2 , respectively, while the valence neutron holes dominantly occupy the h 11/2 orbital. Even-A 118−130 Sn isotopes possess 7 − and 10 + isomers with dominant neutron νh −1 11/2 d −1 3/2 and νh −2 11/2 configurations, respectively [3][4][5][6]. Odd-A 121−131 Sb isotopes have 19/2 − and 23/2 + isomers with dominant π g 7/2 νh −1 11/2 d −1 3/2 and π g 7/2 νh −2 11/2 configurations [7][8][9][10][11], with an additional proton particle in g 7/2 coupled to the 7 − and 10 + isomers in even-A Sn isotopes, respectively. It should be noted that the 23/2 + isomers in Sb isotopes do not correspond to maximally aligned configurations (I π Max = 27/2 + ) but rather to I π Max − 2 = 23/2 + , illustrating the influence of spin and seniority mixing in these isotopes. ...
... The results of the calculations are shown in Fig. 8. The 10 + seniority isomer in even-A 120-130 Sn isotopes is known to be dominantly arising from νh −2 11/2 configuration [3][4][5][6]. Stretched angular momentum coupling of π g 7/2 particle in 121-131 Sb (π g 9 (b) Energies of the 19/2 + (black), 23/2 + (red), and 27/2 + (blue) level in Z = 51 121-131 Sb isotopes. The evolution of the 10 + states in Z = 50 120-130 Sn isotopes are also shown in green in these panels. ...
Background: The Z=50 shell closure, near N=82, is unique in the sense that it is the only shell closure with the spin-orbit partner orbitals, πg9/2 and πg7/2, enclosing the magic gap. The interaction of the proton hole/particle in the above-mentioned orbitals with neutrons in the νh11/2 orbital is an important prerequisite to the understanding of the nuclear structure near N=82 and the νπ interaction.
... The Sn region is an important region, in which many experimental and theoretical studies, such as identification of different isomeric states in Sn isotopes [1][2][3][4][5][6][7][8][9], Gamow-Teller decay of the doubly magic nucleus 100 Sn [10], measurement of electromagnetic properties of different excited states [11], upcoming measurements for definite spin assignments [12], population of high-spin states [1], theoretical calculations of nuclear g factors [13], and ab initio study of lighter Sn isotopes [14], are going on. Recent studies report lowering of the νg 7/2 orbital in comparison with the νd 5/2 for 101 Sn [15]. ...
... The Sn region is an important region, in which many experimental and theoretical studies, such as identification of different isomeric states in Sn isotopes [1][2][3][4][5][6][7][8][9], Gamow-Teller decay of the doubly magic nucleus 100 Sn [10], measurement of electromagnetic properties of different excited states [11], upcoming measurements for definite spin assignments [12], population of high-spin states [1], theoretical calculations of nuclear g factors [13], and ab initio study of lighter Sn isotopes [14], are going on. Recent studies report lowering of the νg 7/2 orbital in comparison with the νd 5/2 for 101 Sn [15]. ...
... There are three different experimental groups that are working to identify seniority isomers in the Sn isotopes. The Fotiades [19] group at LBNL, the Astier [1] group at Legnaro and the IRes-Strasbourg and Iskra group [2,3] at Argonne have done different experiments to populate isomeric states in odd and even Sn isotopes using fusionfission reactions. The high-spin structure above the 10 + isomers in 118,120,122,124 Sn was reported by Fotiades et al. in Ref. [19]. ...
... Because of the special structure of the spectra, the Sn isotopes have been studied extensively [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Reference [28] shows that the excited states of heavy Sn for mass number A 120 are expected to be described by considering valence neutrons moving in a spherical well, while the excited levels above 3 MeV are ascribed to several broken pairs of valence neutrons occupying the νh 11/2 orbit. Therefore, in order to study the effect of noncollective pairs, the yrast band of 124,126,128 Sn will be considered as examples with noncollective pairs in the SDPSM, in which at most two noncollective pairs with I = 0, 2, 4, 6, 8, and 10 occupying the h 11/2 orbit are possible. ...
... The yrast states of the heavy Sn isotopes are expected to be only due to excitations of neutrons moving in a spherical well, particularly due to several broken pairs in the νh 11/2 orbit [28]. Therefore, to reveal the effect of the noncollective pairs, the excitation energies against angular momentum I are presented in Fig. 3, in which the results in the vibrational and rotational limits [42,43] are also provided. ...
... The calculated spectrum for 128,126,124 Sn. Experimental values are taken from Refs.[28,30]. ...
The effects of possible noncollective pairs in even-evenSn124–128 are studied in the nucleon-pair shell model, in which a few noncollective neutron pairs originating from the alignment of two neutrons in the νh11/2 orbit are considered. From the low-lying-level energies, B(E2) ratios, and excited states obtained from the model, it is shown that the yrast band structure can be explained as the evolution from vibrational to rotational type as a function of spin. The mechanism of the yrast band can be explained as band crossing between the ground-state band and the S band constructed from the neutron alignment in the νh11/2 orbit. The noncollective configurations may be crucial for describing the yrast states in even-evenSn124,126,128 in the SD-pair shell model.
