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Beta-delayed proton emission from nuclides in the neighborhood of 100Sn was
studied at the National Superconducting Cyclotron Laboratory. The nuclei were
produced by fragmentation of a 120 MeV/nucleon 112Sn primary beam on a Be
target. Beam purification was provided by the A1900 Fragment Separator and the
Radio Frequency Fragment Separator. The fra...
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... Fig. 4 and Fig. 5 are presented the energy spectra and βp-decay curves, respectively, for several implanted nuclei. The deduced half-lives and b βp values are summarized in Table I. The decay properties of these nuclides are discussed in detail in the following ...
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... emission from 92 Rh is reported here for the first time [ Fig. 4(a)]. A b βp value of 1.9(1)% was deduced, and a γ -ray spectrum coincident with βp events is presented in Fig. 6. The γ rays with energies of 394.4(2), 893.1(2), and 1097.5(5) keV originate from the deexcitation of known levels in 91 Tc and have relative intensities of 97(20)%, 100%, and 14(9)%, respectively. 93 Pd is predicted to be a ...
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... to be 7.5(5)%, similar to the upper limit of 5% reported in Ref. [27]. By taking the statistical model calculations [37] at face value, this new result is more consistent with a 7/2 + ground state for 93 Pd (b βp = 4.8%) as opposed to the previously proposed 9/2 + ground state (b βp = 1.7%). The energy spectrum of β-delayed protons, shown in Fig. 4(b), agrees with that in Ref. [27], confirming the absence of significant isobaric contamination in the ...
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... βp-energy spectrum [ Fig. 4(d)] and the βp-decay half-life of 1.80(8) s obtained in the present work [ Fig. 5(e)] agree with the results reported in Ref. [2], resolving the discrepancy with the earlier βp-decay data Ref. [28] and supporting the conclusions of Ref. [2]. A b βp value of 2.5(3)% was also measured. No evidence was found here for βp decay of the 21/2 + ...
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... βp-energy spectrum [ Fig. 4(j)] has a structure similar to that reported in Ref. [47], but it has considerably more statistics. Nevertheless, it was not possible to draw a strong conclusion concerning the expectation of the statistical βp decay for the two alternative spins within the shell-model framework. While the experimental spectrum in Fig. 4(j) shows little ...
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... βp-energy spectrum [ Fig. 4(j)] has a structure similar to that reported in Ref. [47], but it has considerably more statistics. Nevertheless, it was not possible to draw a strong conclusion concerning the expectation of the statistical βp decay for the two alternative spins within the shell-model framework. While the experimental spectrum in Fig. 4(j) shows little structure, in line with the prediction for a 5/2 + ground state, there are events above 3 MeV that may be considered as a separate high-energy proton group that is expected to be present for the 7/2 + decay based again on the shell-model results ...
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... calculated composition of the burst ashes obtained without any βp emission (which corresponds to previous cal- culations where this decay mode was neglected) was compared with calculations that took into account the experimentally determined βp branches, including the ones indicated in Fig. 13 [see Fig. 14(a)]. Noticeable effects occur for mass A = 83, 87, 93, 97, and in particular for mass A = 101, because of the sizable b βp values of 83 Zr, 87 Mo, 93 Pd, 97 Cd, and 101 Sn [see Fig. 14(b)]. However, these effects are not dramatic due to the small b βp values involved. In the simplest picture, βp emission should only play a role late in ...
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... mode was neglected) was compared with calculations that took into account the experimentally determined βp branches, including the ones indicated in Fig. 13 [see Fig. 14(a)]. Noticeable effects occur for mass A = 83, 87, 93, 97, and in particular for mass A = 101, because of the sizable b βp values of 83 Zr, 87 Mo, 93 Pd, 97 Cd, and 101 Sn [see Fig. 14(b)]. However, these effects are not dramatic due to the small b βp values involved. In the simplest picture, βp emission should only play a role late in the freezeout, when proton capture rates are slow owing to lower temperature or hydrogen exhaustion, as otherwise an emitted proton would tend to be recaptured. As shown in Fig. 14(b), ...
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... 101 Sn [see Fig. 14(b)]. However, these effects are not dramatic due to the small b βp values involved. In the simplest picture, βp emission should only play a role late in the freezeout, when proton capture rates are slow owing to lower temperature or hydrogen exhaustion, as otherwise an emitted proton would tend to be recaptured. As shown in Fig. 14(b), the increase in A = 100 yield was about four times larger than what one would expect from a simple transfer of A = 101 nuclei to A = 100 after freezeout due to the βp branching. This indicates that βp emission also plays a role during the rp process because of inefficient recapturing of emitted protons. This leads to an increase of A ...
Citations
... The models have difficulties describing both the isomer excitation energies and ground-state electromagnetic moments along the indium chain. Considerable experimental and theoretical efforts have concentrated on the region around 100 Sn [1], the heaviest known self-conjugate and doubly magic nucleus (N ¼ Z ¼ 50), including decay spectroscopy [2][3][4][5][6][7][8][9], laser spectroscopy [10][11][12], Coulomb excitation studies [13][14][15], and mass measurements [16][17][18][19]. The similar valence orbitals that the protons and neutrons occupy are expected to enhance the effect of proton-neutron pairing, while the proximity of the double shell closure and proton drip line make it a unique laboratory to test our understanding of the strong interaction. ...
The excitation energy of the 1/2− isomer in 99In at N=50 is measured to be 671(37) keV and the mass uncertainty of the 9/2+ ground state is significantly reduced using the ISOLTRAP mass spectrometer at ISOLDE/CERN. The measurements exploit a major improvement in the resolution of the multireflection time-of-flight mass spectrometer. The results reveal an intriguing constancy of the 1/2− isomer excitation energies in neutron-deficient indium that persists down to the N=50 shell closure, even when all neutrons are removed from the valence shell. This trend is used to test large-scale shell model, ab initio, and density functional theory calculations. The models have difficulties describing both the isomer excitation energies and ground-state electromagnetic moments along the indium chain.
... [395][396][397]). Recent decay studies have focused on β-delayed particle emission probabilities (e.g., [379,[398][399][400][401][402]). Modifications of β-decay rates in the astrophysical environment, for example due to continuum electron capture, have been calculated and are significant in some cases [403]. ...
Nuclear astrophysics is a field at the intersection of nuclear physics and astrophysics, which seeks to understand the nuclear engines of astronomical objects and the origin of the chemical elements. This white paper summarizes progress and status of the field, the new open questions that have emerged, and the tremendous scientific opportunities that have opened up with major advances in capabilities across an ever growing number of disciplines and subfields that need to be integrated. We take a holistic view of the field discussing the unique challenges and opportunities in nuclear astrophysics in regards to science, diversity, education, and the interdisciplinarity and breadth of the field. Clearly nuclear astrophysics is a dynamic field with a bright future that is entering a new era of discovery opportunities.
... Efforts continue at NSCL (National Superconducting Cyclotron Laboratory, Michigan, USA) to contribute to the region [58], e.g., with spectroscopy using knock-out reactions [59], or the recent mass measurement of 80 Zr [60]. At GSI, revisited isomeric decay in 102 Sn and resulting effective neutron and proton charges based on state-of-the-art shellmodel calculations were published [61], 13 years after the RISING [62] experiment. ...
... Efforts continue at NSCL (National Superconducting Cyclotron Laboratory, Michigan, USA) to contribute to the region [58], e.g., with spectroscopy using knock-out reactions [59], or the recent mass measurement of 80 Zr [60]. At GSI, revisited isomeric decay in 102 Sn and resulting effective neutron and proton charges based on state-of-the-art shell-model calculations were published [61], 13 years after the RISING [62] experiment. ...
Inevitable progress has been achieved in recent years regarding the available data on the structure of 100Sn and neighboring nuclei. Updated nuclear structure data in the region is presented using selected examples. State-of-the-art experimental techniques involving stable and radioactive beam facilities have enabled access to those exotic nuclei. The analysis of experimental data has established the shell structure and its evolution towards N = Z = 50 of the number of neutrons, N, and the atomic number, Z, seniority conservation and proton–neutron interaction in the g9/2 orbit, the super-allowed Gamow–Teller decay of 100Sn, masses and half-lives along the rapid neutron-capture process (r-process) path and super-allowed α decay beyond 100Sn. The status of theoretical approaches in shell model and mean-field investigations are discussed and their predictive power assessed. The calculated systematics of high-spin states for N = 50 isotopes including the 5− state and N = Z nuclei in the g9/2 orbit is presented for the first time.
... Ten single-sided segmented strip detectors (SSSSDs) were placed farther downstream for Q β measurements. Events accompanying proton emission were separated from positron events by requiring a minimum of 1500 keV energy deposited in a single pixel of a DSSSD as described in Ref. [31]. ...
We report on new or more precise half-lives, β-decay endpoint energies, and β-delayed proton emission branching ratios of Pd91, Cd95, In97, and Sn99. The measured values are consistent with known mirror transitions in lighter Tz=−1/2 nuclei, shell-model calculations, and various mass models. In addition to the β-decaying (9/2+) ground state, circumstantial evidence for a short-lived, proton-emitting isomer with spin (1/2−) was found in In97. Based on the experimental data, a semiempirical theory on proton emission, and shell-model calculations, the proton separation energy of the In97 ground state was determined to be −0.10±0.19 MeV. The existence of the short-lived, proton-unstable (1/2−) isomer in In97 establishes Cd96 as an rp-process waiting point.
... Many of the topics listed above are manifest in numerous isomeric states of N,Z 50 nuclei [7], which offer important insights into their structure: E2 seniority isomers in N = 50 isotones 92 Mo, 94 Ru, 96 Pd, and 98 Cd [8][9][10][11]; a high-spin, negative-parity isomer in 94 Pd [48] with = 1,3 electric transitions (E1, E3); multiple isomers in 95 Ag [12] decaying via = 3,4 electric transitions (E3, E4); N = Z spin-gap isomers in 94 Ag, 96 Cd, and 98 In [3,[13][14][15][16][17][18][19]; and core-excited isomers in 96 Ag and 98 Cd [20][21][22]. This is by no means an exhaustive list. ...
... The majority of the ions were implanted in the middle module of the three 1-mm-thick double-sided silicon strip detectors (DSSSDs) of WAS3ABi, where each DSSSD was segmented into 60 × 40 1-mm-wide strips in the x and y directions, respectively. Particle decay events were correlated to ion implantation events as described in Ref. [19], which used a similar set of segmented Si detectors. γ rays following decay events were detected with the Euroball-RIKEN Cluster Array (EURICA) [44], featuring a total of 84 HPGe crystals that surrounded WAS3ABi in a 4π geometry. ...
DOI:https://doi.org/10.1103/PhysRevC.96.049901
... Many of the topics listed above are manifest in numerous isomeric states of N,Z 50 nuclei [7], which offer important insights into their structure: E2 seniority isomers in N = 50 isotones 92 Mo, 94 Ru, 96 Pd, and 98 Cd [8][9][10][11]; a high-spin, negative-parity isomer in 94 Pd [48] with = 1,3 electric transitions (E1, E3); multiple isomers in 95 Ag [12] decaying via = 3,4 electric transitions (E3, E4); N = Z spin-gap isomers in 94 Ag, 96 Cd, and 98 In [3,[13][14][15][16][17][18][19]; and core-excited isomers in 96 Ag and 98 Cd [20][21][22]. This is by no means an exhaustive list. ...
... The majority of the ions were implanted in the middle module of the three 1-mm-thick double-sided silicon strip detectors (DSSSDs) of WAS3ABi, where each DSSSD was segmented into 60 × 40 1-mm-wide strips in the x and y directions, respectively. Particle decay events were correlated to ion implantation events as described in Ref. [19], which used a similar set of segmented Si detectors. γ rays following decay events were detected with the Euroball-RIKEN Cluster Array (EURICA) [44], featuring a total of 84 HPGe crystals that surrounded WAS3ABi in a 4π geometry. ...
Half-lives and energies of γ rays emitted in the decay of isomeric states of nuclei in the vicinity of the doubly magic Sn100 were measured in a decay spectroscopy experiment at Rikagaku Kenkyusho (The Institute of Physical and Chemical Research) of Japan Nishina Center. The measured half-lives, some with improved precision, are consistent with literature values. Three new results include a 55-keV E2γ ray from a new (4+) isomer with T1/2=0.23(6)μs in Rh92, a 44-keV E2γ ray from the (15+) isomer in Ag96, and T1/2(6+)=13(2) ns in Cd98. Shell-model calculations of electromagnetic transition strengths in the (p1/2,g9/2) model space agree with the experimental results. In addition, experimental isomeric ratios were compared to the theoretical predictions derived with an abrasion-ablation model and the sharp cutoff model. The results agreed within a factor of 2 for most isomers. From the nonobservation of time-delayed γ rays in Sn100, new constraints on the T1/2, γ-ray energy, and internal conversion coefficients are proposed for the hypothetical isomer in Sn100.
... In [15], the γ-transition with energy 172 keV, observed in the α-decay measurements of the chain 109 Xe 105 Te 101 Sn, was assigned to the deexcitation of the first excited + 5 2 state to the + 7 2 ground state, while the opposite order was proposed in a previous experiment [16], where a γ-ray transition of similar energy was identified in an in-beam γ-ray experiment by tagging on β-delayed protons from 101 Sn. An attempt to establish the spin of the first excited state in 101 Sn was also performed in a β-delayed proton emission experiment [17], but unfortunately it was not possible to draw a definite conclusion, more precise mass measurements being required. Our prediction for 101 Sn is in line with [15], where the experimental finding was substantiated by SM calculations very similar to those presented in this paper. ...
This paper presents a short overview of a procedure we have recently introduced, dubbed the double-step truncation method, which is aimed to reduce the computational complexity of large-scale shell-model calculations. Within this procedure, one starts with a realistic shell-model Hamiltonian defined in a large model space, and then, by analyzing the effective single particle energies of this Hamiltonian as a function of the number of valence protons and/or neutrons, reduced model spaces are identified containing only the single-particle orbitals relevant to the description of the spectroscopic properties of a certain class of nuclei. As a final step, new effective shell-model Hamiltonians defined within the reduced model spaces are derived by way of a unitary transformation of the original large-scale Hamiltonian. A detailed account of this transformation is given and the merit of the double-step truncation method is illustrated by discussing few selected results for ⁹⁶Mo, described as four protons and four neutrons outside ⁸⁸Sr. Some new preliminary results for light odd-tin isotopes from A =101 to 107 are also reported.
... For a possible 2p capture process bypassing the 68 Se roadblock, the proton separation energy of proton-unbound 69 Br is critical and two complementary measurements of S Br p 69 ( ) have been performed [220,221] whose results restrict the reaction flow via the 68 Se(2p,γ) bypass to at most 20% [221]. Beta-decay halflives and βdelayed proton decay branchings in the 100 Sn region were measured and constrained the composition of the type I x-ray burst ashes [224][225][226]. The pioneering halflife measurement of 96 Cd, for example, excluded to possibility that x-ray bursts are the major source of 96 Ru in the solar system [226]. ...
The National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU) is a scientific user facility that offers beams of rare isotopes at a wide range of energies. This article describes the facility, its capabilities, and some of the experimental devices used to conduct research with rare isotopes. The versatile nuclear science program carried out by researchers at NSCL continues to address the broad challenges of the field, employing sensitive experimental techniques that have been developed and optimized for measurements with rare isotopes produced by in-flight separation. Selected examples showcase the broad program, capabilities, and the relevance for forefront science questions in nuclear physics, addressing, for example, the limits of nuclear existence; the nature of the nuclear force; the origin of the elements in the cosmos; the processes that fuel explosive scenarios in the Universe; and tests for physics beyond the standard model of particle physics. NSCL will cease operations in approximately 2021. The future program will be carried out at the Facility for Rare Isotope Beams, FRIB, presently under construction on the MSU campus adjacent to NSCL. FRIB will provide fast, stopped, and reaccelerated beams of rare isotopes at intensities exceeding NSCL's capabilities by three orders of magnitude. An outlook will be provided on the enormous opportunities that will arise upon completion of FRIB in the early 2020s.
The isomeric structure and properties in proton-rich nuclides are crucial for determining the path of the rapid proton capture process (rp-process). For example, bound nuclei inside the dripline can have unbound isomeric states and change the rp-process pathway. The configuration interaction shell model is used to investigate nuclei around the Z=N line at the southwest region of Sn100. The excitation mechanism of 1/21− isomers is identified as dominated by exciting one nucleon in the 1p1/2 orbit to the 0g9/2 orbit. The study explores the decay properties of both the ground and isomeric states. Remarkably, competitive β+ decay and proton emission are predicted in the unbound 1/21− isomer of Sn97, suggesting potential influences on the rp-process pathway.
The excitation energy of the 1/2$^-$ isomer in $^{99}$In at ${N=50}$ is measured to be 671(37) keV and the mass uncertainty of the 9/2$^+$ ground state is significantly reduced using the ISOLTRAP mass spectrometer at ISOLDE/CERN. The measurements exploit a major improvement in the resolution of the multi-reflection time-of-flight mass spectrometer. The results reveal an intriguing constancy of the $1/2^-$ isomer excitation energies in neutron-deficient indium that persists down to the $N = 50$ shell closure, even when all neutrons are removed from the valence shell. This trend is used to test large-scale shell model, \textit{ab initio}, and density functional theory calculations. The models have difficulties describing both the isomer excitation energies and ground-state electromagnetic moments along the indium chain.
