Novel Penning-trap techniques reveal isomeric states in 128 In and 130 In for the first time
D.A. Nesterenko, A. Kankainen, J. Kostensalo, C.R. Nobs, A.M. Bruce, O. Beliuskina, L. Canete, T. Eronen, E.R. Gamba, S. Geldhof, R. de Groote, A. Jokinen, J. Kurpeta, I.D. Moore, L. Morrison, Zs. Podolyák, I. Pohjalainen, S. Rinta-Antila, A. de Roubin, M. Rudigier, J. Suhonen, M. Vilén, V. Virtanen, J. Äystö
aa r X i v : . [ nu c l - e x ] M a y Novel Penning-trap techniques reveal isomeric statesin
In and
In for the first time
D.A. Nesterenko a , A. Kankainen a , J. Kostensalo a , C.R. Nobs b , A.M. Bruce b , O. Beliuskina a , L. Canete a , T. Eronen a ,E.R. Gamba b , S. Geldhof a , R. de Groote a , A. Jokinen a , J. Kurpeta d , I.D. Moore a , L. Morrison c , Zs. Podoly´ak c ,I. Pohjalainen a , S. Rinta-Antila a , A. de Roubin a , M. Rudigier c , J. Suhonen a , M. Vil´en a , V. Virtanen a , J. ¨Ayst¨o a a University of Jyvaskyla, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland b School of Computing, Engineering and Mathematics, University of Brighton, Brighton BN2 4GJ, United Kingdom c Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom d Faculty of Physics, University of Warsaw, ulica Pasteura 5, PL-02-093 Warsaw, Poland
Abstract
Isomeric states in
In and
In have been studied with the JYFLTRAP Penning trap at the IGISOL facility. Byemploying novel ion manipulation techniques, different states were separated and masses of six beta-decaying stateswere measured. JYFLTRAP was also used to select the ions of interest for identification at a post-trap decay spec-troscopy station. A new beta-decaying high-spin isomer feeding the 15 − isomer in Sn has been discovered in
Inat 1797 . + spin-trap isomer. In In, the lowest-lying (10 − ) isomeric stateat 58 . − and 1 − states in In, stemming from parallel/antiparallel coupling of ( π g − / ) ⊗ ( ν h − / ),has been found to be around 200 keV lower than predicted by the shell model. Precise information on the energies ofthe excited states determined in this work is crucial for producing new improved effective interactions for the nuclearshell model description of nuclei near Sn.
Keywords:
Isomers, Penning trap, beta-decay spectroscopy, shell modelNeutron-rich indium isotopes provide essential data totest the nuclear shell model [1, 2] and to further developnucleon-nucleon interactions and related potentials [3, 4].This is important for example to obtain better predic-tions for the astrophysical rapid neutron capture process[5] traversing through the N = 82 isotones and forming itssecond abundance peak at A ≈ A ≈
130 region [6, 7, 8, 9, 10, 11, 12], and given evidencee.g. for a reduction of the Z = 40 proton subshell gapwhen approaching N = 82 [6, 11]. Despite these advances,excitation energies for many long-living beta-decaying iso-meric states have remained unknown although they canprovide crucial information on the nucleon-nucleon inter-actions close to Sn.Isomers have a different spin, shape, or structurecompared to the lower-lying states in the nucleus (seee.g. [13]), hindering their de-excitation and prolongingthe lifetimes. High-spin isomers in odd-odd nuclei, suchas
In studied in this work, cannot be populated via theground-state beta decay of their even-even parent nucleus.The fission yields of high-spin isomers can also be lowerthan for the ground states, making it possible to miss re-lated beta decays or even the existence of such isomers.For example the isomeric yield fraction of the (21 / − ) iso- mer in In has been measured to be less than 30 % inproton-induced fission on uranium [14]. In this work, weemploy novel Penning-trap techniques to study the beta-decay of isomeric states in background-free conditions giv-ing key information on the excited states they populate inthe daughter nucleus.The pioneering work on the isomeric states of neutron-rich indium isotopes done by Fogelberg et al. [15, 16]focused on the even- A isotopes − In. These stud-ies have recently been extended, at RIKEN, to
In [9]and
In [8] studied via the beta decay of , Cd usingthe EURICA detector setup and to
In [12] populated inthe in-flight fission of
U. Penning-trap mass spectrom-etry offers a way to determine the excitation energies oflong-living isomeric states as has been done for the odd- A In and
In isotopes at JYFLTRAP [17]. In additionto low-spin isomers, high-spin isomers with spin parities23 / − and 21 / − have been observed in the , In iso-topes [18, 19]. Recently, several indium isotopes were mea-sured with the TITAN Penning trap [20] but some isomericstates were not fully resolved.For even- A nuclei the high-spin states of , , Inhave been recently studied using the nuclear shell model[21]. A good agreement between the shell-model calcu-lations and the experiment was found using the effective
Preprint submitted to Journal of L A TEX Templates May 20, 2020 nteraction jj45pna. On the other hand, restrictions tothe model space had to be used for the lighter isotopeswhich needed to be compensated by re-adjusting the ef-fective charges of the nucleons. As computational powerincreases, calculations in the full relevant model space be-come possible. Information on the spins, parities, energies,and reduced transition probabilities are vital for fittingnew effective interactions for these previously computa-tionally problematic model spaces. The present paper is astep towards understanding the properties of nuclei south-west of
Sn.In this work, we have studied long-living beta-decayingstates in
In and
In by applying novel ion-trappingmethods to measure their masses and decay properties.The neutron-rich indium isotopes were produced with a30-MeV proton beam impinging into a uranium target atthe Ion Guide Isotope Separator On-Line (IGISOL) facil-ity [22]. The fission fragments were thermalized in heliumgas, extracted from the IGISOL gas cell and guided to-wards the high-vacuum region of the mass separator usinga sextupole ion guide [23]. Most of the fragments end upas singly-charged ions, which were accelerated to 30 keV,and mass-separated with a dipole magnet. The continuous
A/q beam was cooled and bunched employing the radiofre-quency quadrupole cooler and buncher (RFQ) [24] beforeinjecting into the JYFLTRAP double Penning trap massspectrometer [25]. A dedicated post-trap spectroscopysetup was prepared after JYFLTRAP to identify the stateswhose masses had been studied. The isomerically purifiedion bunches from JYFLTRAP were implanted into a mov-able mylar tape surrounded by a scintillator detector, two70 % coaxial and a broad-energy range Ge detector.At JYFLTRAP, the ions were first cooled and purifiedusing the buffer-gas cooling technique [27] in the first trap.It allowed to clean the ions from isobaric contaminants. Toresolve the isomeric states from each other and from theground state an additional purification step employing aRamsey dipolar cleaning [28] pattern with two 5-ms excita-tion fringes, separated by either 40 ms ( In m and In)or 90 ms (
In and In m ) waiting time in between, wasapplied in the second trap. This was further followed bya cooling period in the first trap before the actual massmeasurements using the time-of-flight ion cyclotron reso-nance (TOF-ICR) [29, 30] technique in the second trap todetermine the ion’s cyclotron frequency ν c = qB/ (2 πm ),where q and m are the charge and the mass of the ion and B is the magnetic field strength. The measurements wereperformed using time-separated oscillatory fields [26, 31]with 25 ms (On) - 350 ms (Off) - 25 ms (On) pattern for In (see Fig. 1.(a)) and 25 ms (On) - 150 ms (Off) - 25 ms(On) pattern for
In. The magnetic field strength wasdetermined using
Te (mass excess ∆ = − . Te (∆ = − . In and
In, respectively. The use of iso-baric references had the benefit that possible systematicuncertainties due to imperfections in the trap cancel out[33]. Time-dependent fluctuations in the magnetic field
Figure 1: (Color online) Typical measurements performed atJYFLTRAP. (a) TOF-ICR spectrum for In m with 25-350-25ms (On-Off-On) Ramsey excitation pattern. The isomeric state wasselected by using a Ramsey dipolar cleaning method before the ac-tual measurement. The black points with error bars represent themean time-of-flight for each scanned frequency. The solid red lineis a fit of the theoretical curve to the data points [26]. The blueshading around the data points indicates the number of ions in eachtime-of-flight bin. (b) Projection of the cyclotron motion of In + ions onto the position-sensitive detector obtained with the PI-ICRtechnique using a 320 ms phase accumulation time. strength [34] were also taken into account in the analysis.Count-rate class analysis [35] was performed to accountfor ion-ion interactions in the trap. For the final result,a weighted mean and its inner and outer errors [36] werecalculated, and the larger of the errors was adopted. Theresults from the TOF-ICR measurements are summarizedin Table 1 and noted with a .For In, it is interesting to compare the results ob-tained in this work with clean samples of In + statesat JYFLTRAP, to the combined ground state and isomermeasurements performed with In ions using the TI-TAN Penning trap at TRIUMF [20]. Whereas the massesfor In m agree well between the two measurements, theground-state mass determined from the two-state fit on In [20] is 20(10) keV higher than the seven times2ore precise JYFLTRAP value. As a result, the excita-tion energy obtained at TITAN is 23(13) keV lower thanthe JYFLTRAP value (see Table 1).For In, the TOF-ICR measurement was not able toresolve the 1 ( − ) ground state from the (10 − ) isomeric statelying at 50(50) keV [37]. The TOF-ICR resonances col-lected with 400 ms and 600 ms excitation times showed asimilar production ratio between the (5 + ) isomer and thelower-mass state. This suggests that the lower-mass statewas the (10 − ) level which has a similar half-life to the(5 + ) isomeric state (see Table 1) whereas the 1 ( − ) groundstate has a much shorter half-life of 290(20) ms [37]. Thisis consistent with the non-observation of the most promi-nent gamma lines from the beta decay of the 1 ( − ) state inthe collected beta-gated gamma-ray spectra for the stud-ied lower-mass state. We conclude that the (10 − ) and (5 + )isomers in In were measured with the TOF-ICR tech-nique, however, the result for the (10 − ) state might stillcontain a small contribution from the weakly producedground state.To resolve all three states in In, a novel phase-imagingion cyclotron resonance (PI-ICR) technique [39, 40, 41]was employed at JYFLTRAP. The cyclotron frequency wasdetermined based on the phase difference after a phaseaccumulation time t acc . With the PI-ICR technique, allthree states were resolved (see Fig. 1.(b)). The In m isomer was measured using Cs (∆ = − . t acc = 250 ms), and the other twostates were measured against In m with t acc =320 ms.The data analysis followed otherwise the same proceduresas described for TOF-ICR measurements. The PI-ICRfrequency ratio results are highlighted with b in Table 1.The shorter-living ground state of In was the leastpopulated in the PI-ICR spectra and supports the con-clusion that the lower-mass state in the TOF-ICR mea-surements was predominantly the (10 − ) state. The mass-excess values determined from the TOF-ICR and PI-ICR measurements of In m and In m agree witheach other (see Table 1). The recent measurement atthe TITAN Penning trap [20] reports mass-excess val-ues of − ( − ) ground state and − + ) isomer in In. The valuereported for the 1 ( − ) ground state from TITAN [20] is wellabove the value from this work and it actually fits betterwith the (10 − ) state measured in this work. The ground-state mass determined in this work, − . − In at an excitation energy of1797 . In, and both had trap cycles of around 0.75 s. There-fore, it is estimated that the new isomeric state In m has to have a half-life longer than 0.3 s. Since the statewas previously unknown, a pure beam of In m was pre-pared with the trap, and implanted on a tape which wasmoved after every 1000 seconds ( ≈
17 mins). For com-parison, a spectrum employing only first-trap purification not sufficient to resolve the three states, was also collected.Figure 2 shows the two beta-gated gamma-ray spectra ob-tained with these settings.Most of the observed beta-delayed gamma transitionsfrom the new In m and their intensities match withthe transitions observed from the 15 − isomer with T / = 220(30) ns in Sn in Refs. [42, 43]. Therefore, the newisomeric state in
In has to populate the (15 − ) isomerin Sn either directly or indirectly. We also observe twogamma transitions (1280 keV and 1779 keV) not observedin [42, 43]. Of these, the strong 1779 keV transition has anintensity similar to the 15 − → − transition, suggestingit feeds the 15 − isomer. The 1779 keV transition has beenalready observed in [16] where it was not assigned becauseit was not coincident with other gamma transitions withinthe used time window of 2-20 ns. Therefore, coincidencesbetween the transitions above and below the 15 − statewith a half-life of 220(30) ns could not have been observedin Ref. [16]. The resulting level scheme for Sn is shownleft in Fig. 3.
200 400 600 800 1000 12000200400600800100012001400 C oun t s / k e V Energy (keV) ** * * * * ** * C oun t s / k e V Energy (keV)
In all In m2 Figure 2: (Color online) Beta-gated gamma-ray spectrum obtainedwith the trap purification set to
In (including all three states, inblack) and to the new high spin isomer In m at 1.8 MeV (in red).The peaks tabulated in Table 2 are shown with an asterisk (*). Thestrong 1779-keV transition is shown in the inset. To further investigate the studied states and the newhigh-spin isomer in
In, shell-model calculations wereperformed in a valence space consisting of the proton or-bitals 1 p / , 0 f / , 1 p / , and 0 g / , and the neutron or-bitals 0 g / , 1 d / , 1 d / , 2 s / , and 0 h / using the shellmodel code NuShellX@MSU [47] with the effective inter-action jj45pna [45]. The interaction jj45pna is a CD-Bonnpotential re-normalized with the perturbative G-matrixapproach. Interestingly, the calculations predict that thefirst isomeric state in In would be 10 − (see Fig. 4), sim-ilar to In, but in disagreement with experiments sug-gesting it is (8 − ) [46] based on the observed feeding to a(7 − ) state in the daughter. However, the feeding mightalso be explained by the missed transitions from higher-lying levels. The excitation energy determined here for the3 able 1: Isomeric states in In and
In studied in this work together with their spins, parities J π , and half-lives T / from literature[37, 38]. The frequency ratios r = ν c,ref /ν c determined using the TOF-ICR ( a ) and PI-ICR ( b ) techniques in this work, correspondingmass-excess values ∆ and excitation energies E x are tabulated and compared to the literature values from [20, 37]. The reference nuclideshave been listed for each measurement. The TOF-ICR measurement of In m (marked with c ) was done as an admixture with the groundstate, and hence the PI-ICR value is recommended. Nuclide J π T / Ref. r = ν c,ref /ν c ∆ ∆ lit. E x E x,lit. (s) (keV) (keV) (keV) (keV) In (3) + Te 1 . a − . − . In m (8 − ) 0.72(10) Te 1 . a − . − . . In m (16 + ) ≥ . Te 1 . a − . . In 1 ( − ) In m . b − . − In m (10 − ) 0.54(1) Te 1 . a,c − . . In m . b − . − . In m (5 + ) 0.54(1) Te 1 . a − . Cs 0 . b − . . − . − . Table 2: Observed γ transitions following the beta decay of In m and their relative intensities. The conversion coefficients α from theBrIcc calculator [44] were used to obtain the total intensity I tot =(1 + α ) I γ . This mainly concerns the 119.5-keV ( α = 0 . α = 0 . E α < .
01. Due to the used coincidence gate of 1.5 µ s, the γ transitionsfollowing the 10 + ( T / = 3 µ s) and 7 − ( T / = 6 . ∗ ). For comparison, intensitiesobtained within 1.5 µ s after the Sn implantation in Ref. [42] aregiven, renormalized to the 119-keV transition. E γ I tot (%) I tot (%) [42] J πi → J πf − → − − → − ∗ + → − − → + − → − ∗ + → + − → − + → + ∗ + → + − → + )1779.1(3) 85(8) ((15 + ) → − ) Figure 3: Levels in
Sn fed by the beta decay of In m ( J π =(16 + ), Q β = 10970(18) keV) studied in this work (left). For com-parison, level scheme based on shell-model calculations using theeffective interaction jj45pna [45] is given (right). Only transitionsdown to the 7 − isomer are shown. The 79 keV transition marked inparentheses was not detected. first isomeric state in In, 285 . In is 16 + since no other spin-trap statesare located at around 2 MeV (see Fig. 4). The 16 + state consists 92 % of the configuration ( π g / ) − ⊗ ( ν d − / h − / ). The 16 + assignment is further supportedby the systematics of high-spin isomers in the N = 79 iso-tones Sn,
Sb and
Te (see Fig. 5). They all havehigh-spin isomers with similar leading neutron configura-4 xp. jj45pna (3) + + + + - - - - - + - + - - + + + - + - - - + (16 + )(1 + )(1 - )(8 - )(1 - ) In Figure 4: Experimental level scheme of
In based on this workand [46] (left). The lowest excited states for each spin-parity werecalculated with the shell model using the effective interaction jj45pna[45] (right). The calculated excitation spectrum contains also manyother states with the same spin-parities but they are too numerousto be presented in this figure. In fact, the 16 + -state is the 71st statein In. tions ν d − / h − / , located at 1803 keV ((23 / + ) in Sn[48, 18]), 1545 keV ((13 + ) in Sb [48]) and 1940 keV((23 / + ) in Te [49]). In addition, similar high-spin iso-mers are also found in neighbouring indium isotopes, suchas the (21 / − ) state in In and (23 / − ) in In [18].Allowed beta decay from the new (16 + ) isomer wouldpopulate 15 + and 16 + states in Sn. The four neu-tron holes in
Sn can maximally couple to spin 16 + as ν h − / , and hence there are no 17 + states within theused model space. According to the shell-model calcu-lations, the first 15 + and 16 + states in Sn would lie1200 keV and 1020 keV above the 15 − state, which theshell model places at 4017 keV. The shell model predictsthat the first 15 + state in Sn consists 97.1 % of the ν g − / d − / h − / configuration. Therefore, the beta de-cay from the 16 + isomer to the 15 + state would convertthe 0 g / proton hole into 0 g / neutron hole, in agreementwith an allowed beta decay. The calculated 16 + state in Sn is 99.5 % ( ν h / ) − and so not likely to be fed inthis beta decay. Although the observed 1280 keV transi-tion would match in energy with the shell-model predictionfor the 15 + → − transition, the intensity is rather lowto explain the observed intensities below the 15 − state.We therefore assume that the 1779 keV transition feedsthe 15 − isomer (based on its intensity and non-coincidence with other gamma transitions as reported in [16]) and orig-inates from a (15 + ) level directly fed in the beta decay of In m . This would place the new (15 + ) state at 5878keV. The right of Fig. 3 shows that the shell model pre-dicts the 15 + and 16 + states at somewhat lower energies.However, the next 15 + and 16 + states are calculated atenergies greater than 7.2 MeV.For In (see Fig. 6), the shell model predicts a low-lying isomeric 10 − state but at 264 keV. This is around 200keV higher than the experimental value of 58 . − isomeric state has the ( π g − / ) ⊗ ( ν h − / ) con-figuration which is also the largest component for the1 − ground state with ≈
80% contribution. The othertwo significant contributions to the ground state comefrom the configurations ( π p − / ) ⊗ ( ν d − / ), ≈ π p − / ) ⊗ ( ν s − / ), ≈ + and 5 + states at 457 keV and 550 keV. Theexcitation energy for the (5 + ) isomer, 385 . + ) state at 388.3(2) keV [50, 51]. Al-though the (5 + ) state is around 200 keV lower than pre-dicted, the experimental and theoretical spectra are in arelatively good agreement indicating that the current the-oretical understanding of this mass region is reasonable.Therefore, one can expect that the theoretical predictions,such as the spin-parity of the new In isomer, are reli-able.In this work isomeric states in
In and
In were stud-ied with the JYFLTRAP Penning trap at the IGISOLfacility. Furthermore, more accurate ground-state massvalues, important for the astrophysical rapid neutron cap-ture process and mass models, were obtained. Employingnovel ion manipulation techniques, different states wereresolved and masses of six beta-decaying states were mea-sured. JYFLTRAP was also used to select the ions of inter-est for post-trap decay spectroscopy enabling background-free studies of the states in question. A new isomeric statein
In feeding indirectly the 15 − isomer in Sn was dis-covered. Large-scale shell-model calculations suggest thatthis new isomeric state has a spin-parity of 16 + follow-ing well the systematics in the region. The shell-modelcalculations predict that the first isomeric state in Inwould be 10 − , similar to In, but in disagreement withexperiments suggesting it is (8 − ). The excitation energydetermined here for the (8 − ) isomer in In (285 . In, the energy difference for the (10 − ) and1 ( − ) states, stemming from parallel/antiparallel couplingof ( π g − / ) ⊗ ( ν h − / ) has been found to be 58.6(82) keV,which is around 200 keV lower than predicted by the shellmodel. Precise information on the energies of excitedstates determined in this work is crucial for producing newimproved effective interactions for the nuclear shell modeldescription of nuclei near Sn. Here we have demon-strated that such previously challenging isomeric statescan be studied, or even new isomers discovered, using anovel combination of ion-trapping techniques and decay5 igure 5: Systematics of the isomeric states in the investigated region. Data are taken from ENSDF and XUNDL (marked with (*)) [46] andinclude the excitation energies of the isomeric states in
In and
In from this work. spectroscopy. This provides new possibilities for futurestudies of isomeric states.
Acknowledgments
This work has been supported by the EU Horizon2020 research and innovation program under grant No.771036 (ERC CoG MAIDEN). The support from theAcademy of Finland under the Finnish Centre of Ex-cellence Programme 2012-2017 (Nuclear and Accelera-tor Based Physics Research at JYFL) and projects No.306980, 312544, 275389, 284516, 295207 is greatfully ac-knowledged. UK authors were supported by STFC GrantNos. ST/L005840/1, ST/P003982/1 and ST/P005314/1.
ReferencesReferences [1] M. G. Mayer, On closed shells in nuclei. ii, Phys. Rev. 75 (1949)1969–1970. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [2] O. Haxel, J. H. D. Jensen, H. E. Suess, On the ”magic num-bers” in nuclear structure, Phys. Rev. 75 (1949) 1766–1766. doi:10 . . . . .URL https://link . aps . org/doi/10 . . . . [3] E. Caurier, G. Mart´ınez-Pinedo, F. Nowacki, A. Poves,A. P. Zuker, The shell model as a unified view ofnuclear structure, Rev. Mod. Phys. 77 (2005) 427–488. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [4] L. Coraggio, A. Covello, A. Gargano, N. Itaco, T. Kuo,Shell-model calculations and realistic effective interac-tions, Progr. Part. Nucl. Phys. 62 (1) (2009) 135 – 182. doi:https://doi . org/10 . . ppnp . . . .URL . sciencedirect . com/science/article/pii/S0146641008000410 [5] C. J. Horowitz, et al., r-process nucleosynthesis: con-necting rare-isotope beam facilities with the cosmos, xp. jj45pna + - + - - + )(10 - )(5 + )1 (-) In Figure 6: The experimental level scheme of
In based on this work,together with the 3 + state from [46], compared with the shell-modelcalculations using the effective interaction jj45pna [45]. The calcu-lated level scheme contains only the lowest excited states for eachspin-parity. There are also many other states with the same spin-parities but they are too numerous to be presented in this figure.J. Phys. G: Nucl. Part. Phys. 46 (8) (2019) 083001. doi:10 . .URL https://doi . org/10 . [6] J. Taprogge, et al., 1 p / proton-hole state in Sn andthe shell structure along N=82, Phys. Rev. Lett. 112 (2014)132501. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [7] J. Taprogge, et al., β decay of Cd and excitedstates in
In, Phys. Rev. C 91 (2015) 054324. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [8] A. Jungclaus, et al., First observation of γ rays emittedfrom excited states south-east of Sn: The πg − / N νf / multiplet of In , Phys. Rev. C 93 (2016) 041301. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [9] A. Jungclaus, et al., β decay of semi-magic Cd: Revision andextension of the level scheme of
In, Phys. Rev. C 94 (2016)024303. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [10] C. Lorenz, et al., β decay of Cd and excitedstates in
In, Phys. Rev. C 99 (2019) 044310. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [11] Z. Q. Chen, et al., Proton shell evolution below Sn: First measurement of low-lying β -emitting iso-mers in , Ag, Phys. Rev. Lett. 122 (2019) 212502. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [12] V. H. Phong, et al., Observation of a µ s isomer in In , Phys.Rev. C 100 (2019) 011302. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [13] P. Walker, G. Dracoulis, Energy traps in atomic nuclei, Nature 399 (1999) 35–40. doi:10 . .URL https://doi . org/10 . [14] V. Rakopoulos, M. Lantz, S. Pomp, A. Solders, A. Al-Adili,L. Canete, T. Eronen, A. Jokinen, A. Kankainen, A. Mattera,I. D. Moore, D. A. Nesterenko, M. Reponen, S. Rinta-Antila,A. de Roubin, M. Vil´en, M. ¨Osterlund, H. Penttil¨a, Isomericfission yield ratios for odd-mass Cd and In isotopes using thephase-imaging ion-cyclotron-resonance technique, Phys. Rev. C99 (2019) 014617. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [15] B. Fogelberg, T. Nagarajan, B. Grapengiesser, Levels andtransition probabilities in In as observed in the de-cay of
Cd, Nucl. Phys. A 230 (2) (1974) 214 – 220. doi:http://dx . doi . org/10 . .URL . sciencedirect . com/science/article/pii/0375947474903030 [16] B. Fogelberg, P. Carl, Levels and transition probabil-ities in , , , , Sn studied in the decay ofIn isotopes, Nucl. Phys. A 323 (2) (1979) 205 – 252. doi:http://dx . doi . org/10 . .URL . sciencedirect . com/science/article/pii/0375947479901088 [17] A. Kankainen, et al., Isomeric states close to doubly magic Snstudied with the double Penning trap JYFLTRAP, Phys. Rev.C 87 (2013) 024307. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [18] H. Gausemel, B. Fogelberg, T. Engeland, M. Hjorth-Jensen,P. Hoff, H. Mach, K. A. Mezilev, J. P. Omtvedt, De-cay of In and
In, Phys. Rev. C 69 (2004) 054307. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [19] B. Fogelberg, et al., Decays of In,
Sn, and the positionof the h neutron hole state, Phys. Rev. C 70 (2004) 034312. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [20] C. Babcock, et al., Mass measurements of neutron-rich indiumisotopes toward the N=82 shell closure, Phys. Rev. C 97 (2018)024312. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [21] M. Rejmund, et al., Electromagnetic proper-ties of neutron-rich nuclei adjacent to the Z=50shell closure, Phys. Lett. B 753 (2016) 86 – 90. doi:http://doi . org/10 . . physletb . . . .URL . sciencedirect . com/science/article/pii/S0370269315009417 [22] I. Moore, et al., Towards commissioning the new IGISOL-4facility 317 (2013) 208 – 213, XVIth International Conferenceon ElectroMagnetic Isotope Separators and Techniques Relatedto their Applications, December 27, 2012 at Matsue, Japan. doi:http://dx . doi . org/10 . . nimb . . . .URL . sciencedirect . com/science/article/pii/S0168583X13007143 [23] P. Karvonen, I. Moore, T. Sonoda, T. Kessler, H. Penttil¨a,K. Per¨aj¨arvi, P. Ronkanen, J. ¨Ayst¨o, A sextupole ion beamguide to improve the efficiency and beam quality at IGISOL,Nucl. Instrum. Meth. Phys. Res. B 266 (21) (2008) 4794 – 4807. doi:DOI:10 . . nimb . . . .[24] A. Nieminen, J. Huikari, A. Jokinen, J. ¨Ayst¨o, P. Campbell,E. Cochrane, Beam cooler for low-energy radioactive ions,Nucl. Instrum. Meth. Phys. Res. A 469 (2) (2001) 244 – 253. doi:http://dx . doi . org/10 . .URL . sciencedirect . com/science/article/pii/S0168900200007506 [25] T. Eronen, et al., JYFLTRAP: a Penning trap for precisionmass spectroscopy and isobaric purification, Eur. Phys. J. A48 (4) (2012) 46. doi:10 . .URL http://dx . doi . org/10 . [26] M. Kretzschmar, The Ramsey method in high-precisionmass spectrometry with Penning traps: Theoretical foun-dations, Int. J. Mass Spectrom. 264 (23) (2007) 122 – 145. doi:http://dx . doi . org/10 . . ijms . . . . RL . sciencedirect . com/science/article/pii/S1387380607001649 [27] G. Savard, S. Becker, G. Bollen, H. J. Kluge, R. B. Moore,T. Otto, L. Schweikhard, H. Stolzenberg, U. Wiess, A new cool-ing technique for heavy ions in a Penning trap, Phys. Lett. A158 (5) (1991) 247 – 252. doi:10 . .[28] T. Eronen, V.-V. Elomaa, U. Hager, J. Hakala, A. Joki-nen, A. Kankainen, S. Rahaman, J. Rissanen, C. Weber,J. ¨Ayst¨o, Preparing isomerically pure beams of short--lived nuclei at JYFLTRAP, Nucl. Instrum. Meth. Phys.Res. B 266 (1920) (2008) 4527 – 4531, Proceedings of theXVth International Conference on Electromagnetic IsotopeSeparators and Techniques Related to their Applications. doi:http://dx . doi . org/10 . . nimb . . . .URL . sciencedirect . com/science/article/pii/S0168583X08007696 [29] G. Gr¨aff, H. Kalinowsky, J. Traut, A direct determination ofthe proton electron mass ratio, Z. Phys. A 297 (1) (1980) 35–39. doi:10 . .URL http://dx . doi . org/10 . [30] M. K¨onig, G. Bollen, H. J. Kluge, T. Otto, J. Szerypo,Quadrupole excitation of stored ion motion at the true cyclotronfrequency, Int. J. Mass Spectrom. Ion Processes 142 (1-2) (1995)95 – 116. doi:10 . .[31] S. George, K. Blaum, F. Herfurth, A. Herlert, M. Kret-zschmar, S. Nagy, S. Schwarz, L. Schweikhard, C. Yazid-jian, The Ramsey method in high-precision mass spec-trometry with Penning traps: Experimental results,Int. J. Mass Spectrom. 264 (23) (2007) 110 – 121. doi:http://dx . doi . org/10 . . ijms . . . .URL . sciencedirect . com/science/article/pii/S1387380607001662 [32] M. Wang, G. Audi, F. Kondev, W. Huang, S. Naimi, X. Xu,The AME2016 atomic mass evaluation (II). Tables, graphs andreferences, Chin. Phys. C 41 (3) (2017) 030003.URL http://stacks . iop . org/1674-1137/41/i=3/a=030003 [33] C. Roux, et al., Data analysis of Q-value measurements for dou-ble-electron capture with SHIPTRAP, Eur. Phys. J. D 67 (7)(2013) 1–9. doi:10 . .URL http://dx . doi . org/10 . [34] L. Canete, et al., High-precision mass measurements of Aland P at JYFLTRAP, Eur. Phys. J. A 52 (5) (2016) 1–8. doi:10 . .URL http://dx . doi . org/10 . [35] A. Kellerbauer, K. Blaum, G. Bollen, F. Herfurth, H.-J. Kluge,M. Kuckein, E. Sauvan, C. Scheidenberger, L. Schweikhard,From direct to absolute mass measurements: A study of theaccuracy of ISOLTRAP, Eur. Phys. J. D 22 (1) (2003) 53–64. doi:10 . .URL http://dx . doi . org/10 . [36] R. T. Birge, The calculation of errors by the methodof least squares, Phys. Rev. 40 (1932) 207–227. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [37] B. Singh, Nuclear Data Sheets for A = 130,Nucl. Data Sheets 93 (1) (2001) 33 – 242. doi:http://dx . doi . org/10 . . . .URL . sciencedirect . com/science/article/pii/S0090375201900122 [38] Z. Elekes, J. Timar, Nuclear Data Sheets for A= 128, Nucl. Data Sheets 129 (2015) 191 – 436. doi:http://dx . doi . org/10 . . nds . . . .URL . sciencedirect . com/science/article/pii/S0090375215000472 [39] S. Eliseev, K. Blaum, M. Block, C. Droese, M. Goncharov,E. Minaya Ramirez, D. A. Nesterenko, Y. N. Novikov,L. Schweikhard, Phase-Imaging Ion-Cyclotron-ResonanceMeasurements for Short-Lived Nuclides, Phys. Rev. Lett. 110(2013) 082501. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [40] S. Eliseev, et al., A phase-imaging technique for cyclotron-fre-quency measurements, Appl. Phys. B 114 (1) (2014) 107–128. doi:10 . .URL https://doi . org/10 . [41] D. A. Nesterenko, T. Eronen, A. Kankainen, L. Canete,A. Jokinen, I. D. Moore, H. Penttil¨a, S. Rinta-Antila,A. de Roubin, M. Vilen, Phase-Imaging Ion-Cyclotron-Res-onance technique at the JYFLTRAP double Penning trapmass spectrometer, Eur. Phys. J. A 54 (9) (2018) 154. doi:10 . .URL https://doi . org/10 . [42] S. Pietri, et al., First observation of the decay of a 15 − se-niority v = 4 isomer in Sn, Phys. Rev. C 83 (2011) 044328. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [43] L. W. Iskra, et al., Higher-seniority excitations in evenneutron-rich Sn isotopes, Phys. Rev. C 89 (2014) 044324. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [44] T. Kib´edi, T. Burrows, M. Trzhaskovskaya, P. Davidson,C. Nestor, Evaluation of theoretical conversion coefficients us-ing BrIcc, Nucl. Instr. Meth. Phys. Res. Sect. A 589 (2) (2008)202 – 229. doi:https://doi . org/10 . . nima . . . .URL . sciencedirect . com/science/article/pii/S0168900208002520 [45] R. Machleidt, High-precision, charge-dependent Bonn nu-cleon-nucleon potential, Phys. Rev. C 63 (2001) 024001. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [46] National Nuclear Data Center, Brookhaven National Labora-tory. [link].URL . nndc . bnl . gov [47] B. Brown, W. Rae, The shell-model code nushellx@msu,Nuclear Data Sheets 120 (2014) 115 – 118. doi:https://doi . org/10 . . nds . . . .URL . sciencedirect . com/science/article/pii/S0090375214004748 [48] J. Genevey, J. A. Pinston, C. Foin, M. Rejmund, H. Faust,B. Weiss, High spin isomers in Sn and
Sb, Phys. Rev. C65 (2002) 034322. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [49] C. Zhang, et al., Yrast excitations in A=126-131Te nuclei from deep inelastic Te+ Ni reac-tions, Nucl. Phys. A 628 (3) (1998) 386 – 402. doi:https://doi . org/10 . .URL . sciencedirect . com/science/article/pii/S0375947497006179 [50] I. Dillmann, et al., N = 82 Shell Quenching of the Classical r -Process “Waiting-Point” Nucleus Cd, Phys. Rev. Lett. 91(2003) 162503. doi:10 . . . .URL https://link . aps . org/doi/10 . . . [51] A. Scherillo, J. Genevey, J. A. Pinston, A. Covello, H. Faust,A. Gargano, R. Orlandi, G. S. Simpson, I. Tsekhanovich,N. Warr, Neutron-rich In and Cd isotopes close to thedoubly magic Sn, Phys. Rev. C 70 (2004) 054318. doi:10 . . . .URL https://link . aps . org/doi/10 . . .054318