Spectroscopic studies of neutron-rich ^{129}In and its β-decay daughter, ^{129}Sn, using the GRIFFIN spectrometer
F.H. Garcia, C. Andreoiu, G.C. Ball, N. Bernier, H. Bidaman, V. Bildstein, M. Bowry, D.S. Cross, M.R. Dunlop, R. Dunlop, A.B. Garnsworthy, P.E. Garrett, J. Henderson, J. Measures, B. Olaizola, K. Ortner, J. Park, C.M. Petrache, J.L. Pore, K. Raymond, J.K. Smith, D. Southall, C.E. Svensson, M. Ticu, J. Turko, K. Whitmore, T. Zidar
SSpectroscopic studies of neutron-rich
In and its β -decay daughter, Sn, using theGRIFFIN spectrometer
F.H. Garcia, ∗ C. Andreoiu, G.C. Ball, N. Bernier,
2, 3, † H. Bidaman, V. Bildstein, M. Bowry, ‡ D.S. Cross, M.R. Dunlop, R. Dunlop, A.B. Garnsworthy, P.E. Garrett, J. Henderson, § J. Measures,
2, 5
B. Olaizola, K. Ortner, J. Park,
2, 3, ¶ C.M. Petrache, J.L. Pore, ∗∗ K. Raymond, J.K. Smith, †† D. Southall, ‡‡ C.E. Svensson, M. Ticu, J. Turko, K. Whitmore, and T. Zidar Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada Department of Physics, University of Guelph, Guelph, Ontario N1G 2W1, Canada University of Surrey, Guildford GU2 7XH, United Kingdom Centre de Sciences Nucléaire et Sciences de la Matière,CNRS/IN2P3, Université Paris-Saclay, Orsay, France (Dated: January 15, 2021)The β -decay of neutron-rich In into
Sn was studied using the GRIFFIN spectrometer atthe ISAC facility at TRIUMF. The study observed the half-lives of the ground state and each ofthe β -decaying isomers. The level scheme of Sn has been expanded with thirty-one new γ -raytransitions and nine new excited levels, leading to a re-evaluation of the β -branching ratios and levelspin assignments. The observation of the β -decay of the (29/2 + ) 1911-keV isomeric state in In isreported for the first time, with a branching ratio of 2.0(5) % . I. INTRODUCTION
The region around the doubly magic Sn nucleusis replete with critical information required for nuclearstructure models and astrophysical applications [1, 2].This isotope region is a key input to the nuclear shellmodel and the theoretical frameworks required to estab-lish a working predictive and descriptive model of nuclei,and as a result it has been the focus of a series of theo-retical studies [3–5].In nuclear astrophysics there is also a need for informa-tion on this region due to the importance of the A = 130 elemental abundance peak [6, 7]. The rapid neutron-capture process ( r -process) is responsible for the genera-tion of isotopes heavier than iron in stellar environments[8, 9], and is shown to have key waiting points at themagic shell closures in the vicinity of the tin isotopes[10, 11].The Sn nucleus, three neutrons removed from the ∗ [email protected] † Present address: Department of Physics, University of the West-ern Cape, P/B X17, Bellvill, ZA-7535, South Africa ‡ Present address: School of Computing, Engineering and PhysicalSciences, University of the West of Scotland, Paisley PA1 2BE,United Kingdom § Present address: Lawrence Livermore National Laboratory, Liv-ermore, California 94550, USA ¶ Present address: Department of Physics, Lund University, 22100Lund, Sweden ∗∗ Present address: Lawrence Berkeley National Laboratory, Berke-ley, California 94720, USA †† Present Address: Department of Physics, Pierce College,Puyallup, Washington 98374, USA ‡‡ Present address: Department of Physics, University of Chicago,Chicago, IL 60637, USA N = 82 shell closure, is important for studying the ef-fects of single neutron excitations and other shell effects,as evidenced by the sixty years of study it has undergone.Several production mechanisms have been used in orderto study In, and its β − daughter, Sn, including fis-sion [12], β − -decay [13–17], β n-decay [18, 19] and internaltransition decay [20, 21]. Though the information on thetransitions and energy levels in this daughter nucleus isplentiful, there are virtually no definitive spin or parityassignments for the levels above the 3/2 + ground state,the 11/2 − + Sn, high-efficiency γ -ray spec-troscopy and coincidence techniques were used to uncovernew transitions, new decay patterns and new levels, pro-viding more input information for state-of-the-art theo-retical models. II. EXPERIMENT
The Isotope Separator and ACcelerator (ISAC) facil-ity of TRIUMF [22] employs the Isotope Separation On-Line (ISOL) technique in order to produce radioactiveisotope beams [23]. Isotopes are generated by bombard-ing a uranium carbide (UC x ) target with a 9.8 µ A beamof 480 MeV protons, provided by the main 520-MeV cy-clotron [24]. The relevant isotopes are selectively ion-ized for extraction using the Ion-Guide Laser Ion Source(IGLIS) [25], in order to reduce any isobaric contamina-tion. The ionized species are then passed through thehigh-resolution mass spectrometer (
M/δM ∼ ) [26],in order to produce an isotopically clean beam. Onceextracted, the desired In radioactive isotope beam is a r X i v : . [ nu c l - e x ] J a n transported to the experimental station. The β − de-cay of the In isotope to
Sn was observed using theGamma-Ray Infrastructure For Fundamental Investiga-tions of Nuclei (GRIFFIN) [27–29]The GRIFFIN array is a state-of-the-art, high-resolution γ -ray spectrometer, equipped with sixteenhigh-purity germanium (HPGe) clover detectors for theidentification of γ -rays [30]. Each of the sixteen HPGeclover detectors contains four crystals, making a total of64 crystals that can detect γ -rays, allowing for analy-ses to be carried out in single crystal or addback modes[28, 30]. For this experiment, the SCintillating Electron-Positron Tagging ARray (SCEPTAR) [28] was placed atthe centre of GRIFFIN, in order to provide tagging for β particles. A cycling mylar tape station, the focus of whichis at the centre of SCEPTAR, provides a continuous im-plantation spot and aids in the removal of contaminants.An implantation cycle can be set to optimize observationof the decay of interest. During the course of this exper-iment, a mix of the β − decaying isomers of In wereimplanted at a rate of ∼ + ground state, In gs , 54% in the (1/2 − ) 459-keV In m isomer, 3% in the (23/2 − ) 1630-keV In m isomer and1% in the (29/2 + ) 1911-keV In m isomer, neglectingthe uncertainty in the ground state branch of the (1/2 − )isomer.The GRIFFIN array was arranged in its high-efficiencyconfiguration, where the HPGe clover detectors were po-sitioned 11 cm away from the implantation spot [28]. A20 mm Delrin shield was put in place around SCEPTARto minimize Bremsstrahlung radiation from high energy β − particles. The experimental campaign for In con-sisted of running the tape system in consecutive 21.5-second cycles, with 1.5 s for tape move, 5 s for back-ground collection, 10 s for isotope implantation and 5 sfor isotope decay. The total run duration was 2.75 hrs,for a total of 460 cycles with 6.29 × addback singlesevents, and 1.81 × coincidence events collected duringthe run time. The combination of GRIFFIN and SCEP-TAR allowed for the correlated observation of γ -rays incoincidence with the emitted β particles, in a 500 ns co-incidence window, in order to tag on the specific Indecays. Furthermore, γ - γ coincidences, with a 500 ns co-incidence window, were used for the verification of tran-sitions and decay patterns through the excited levels ofthe Sn daughter.The energy and efficiency calibrations for GRIFFINwere done using a series of standard sources of Co, Co,
Ba,
Eu, allowing for a calibration to be madein the range between 81 keV and 3.6 MeV. Coincidencesumming corrections were done by constructing a γ - γ matrix with detectors positioned at 180 ◦ of each otherto correct for real coincidence summing, a methodologyestablished for GRIFFIN in Ref. [29]. Transitions werealso verified to be real transitions rather than sum orescape peaks. III. RESULTSA. Transitions and Levels in Sn Energy (keV) C oun t s ( k e V / b i n ) Sn Sb Sn Figure 1. β -gated γ -ray spectrum, in addback mode, showingvarious known transitions in Sn (red squares). Transitionsin
Sb ( β decay daughter of Sn; green circles) and
Sn( β n daugther of In; blue triangles) are also observed.
The Q β value for the In β -decay to Sn is7.769(19) MeV and the neutron separation energy, S n ,for Sn is 5.316(26) MeV [31]. Gamma-ray transitionswere investigated up to the neutron separation energy.From the analysis of this data set, all but two of thetransitions currently reported for the
Sn nucleus wereobserved [31]. There were also 31 newly observed tran-sitions and 9 newly observed excited states in the
Snnucleus, never observed through the β − decay of its Inparent or otherwise. Figure 1 shows a portion of the β -gated γ -ray spectrum observed in this work; transitionsin the Sn of interest, along with transitions in the β granddaughter, Sb, and in the In β n daughter, Sn are identified. Figures 2 and 3 demonstrate themechanism used to establish new transitions. Figure 2shows the gating from below method used to determineseveral intensities, in this case that of the 1071-keV tran-sition. The intensity of this transition required gatingfrom below on the 1047-keV transition, while Figure 3shows the γ -ray spectrum resulting from a gate placedon the 1054-keV transition, where coincident transitionsat 1257, 1271 and 1302 keV were observed.Table I summarizes the energy levels observed in thiswork, along with the transitions from each level, the finalstate, the relative intensity with respect to the highestintensity 2118-keV γ -ray, and the γ -ray branching ratio.The table also compares the branching ratios for each ofthe known γ -rays appearing in the evaluation by Timar,Elekes and Singh [31]. With the exception of seven γ -rays at 146, 278, 280, 1071, 1096, 1586, and 2371 keV,all transition intensities were obtained from the addbacksingles spectrum. The seven γ -rays mentioned requireddirectly gating from below in order to fit their energy andintensity values, as demonstrated in Figure 2. The othernew transitions were observed in the γ -ray spectrum andtheir placement confirmed through coincidence gating, as Energy (keV) C oun t s / k e V Energy (keV) C oun t s / k e V × k e V Figure 2. A γ -ray spectrum, in addback mode, showing ev-idence for the 1071-keV γ -ray, depopulating the 2118-keVstate, in coincidence with the 1047-keV γ -ray, depopulatingthe 1047-keV state of Sn. The 1071-keV transition lies onthe shoulder of a much more intense transition at 1075-keV,necessitating gating from below to obtain its relative inten-sity. The inset shows the gate on 1047 keV used to producethe spectrum.
Energy (keV) C oun t s / k e V k e V k e V k e V k e V C oun t s / k e V Energy (keV)
Figure 3. A γ -ray spectrum, in addback mode, showing evi-dence for the 1271-keV γ -ray, depopulating the new state at2326-keV, in coincidence with the 1054-keV γ -ray, depopulat-ing the 1054-keV state in Sn. Though weak, this transitionis visible in the ungated γ -ray spectrum, but it is much moreclear in the 1054-keV coincidence spectrum. This coincidencealso confirms its placement in the level scheme. The transi-tion at 1257 keV is also newly observed, while those at 1289and 1302 keV are known in Sn. The inset shows the gateon 1054 keV used to produce the spectrum. in shown in Figure 3.Though most of the branching ratios observed in thecourse of this work are in good agreement with the workof Gausemel et al. [17], there are some notable discrepan-cies. These are attributed to major differences in the con-ditions of the two experiments. The work by Gausemel etal. utilized three germanium detectors, while the presentwork made use of all 16 HPGe clover detectors avail-able to the GRIFFIN array, allowing for more efficientcoincidence detection. Furthermore, some of the transi-tions were observed with branching ratios down to − ,pushing the limits of the detection mechanisms availableto the previous experiment. The β -decay of the (29/2 + )1911-keV isomer in In to the (27/2 − ) 2552-keV state in Sn was observed for the first time. This 2552-keVstate was previously observed in the fission study doneby Lozeva et al. [21]. The transitions from the isomericstates at 1762 keV and 1803 keV to lower-lying statesin the level scheme, 19.7 keV and 41.0 keV, respectively,were not observed. However transitions feeding into thesestates were present in the data, confirming the placementof the levels, within uncertainty. able I: Energy levels and transitions observed in
Sn, following the β − decay of In. All intensities are normalized tothe most intense transition at 2118 keV, from the (7/2 + ) 2118-keV state to the 3/2 + ground state. The values calculated inthis experiment are compared to those present in the Evaluated Nuclear Structure Data File search (ENSDF) database of theNational Nuclear Data Center (NNDC). The level spins and parities are adopted from Ref. [31], unless otherwise stated.This work ENSDF E level (keV) E γ (keV) J πi J πf E f (keV) Relative I γ BR γ BR γ + − + ) 3/2 + − ) 11/2 − + ) 3/2 + † (7/2 − ) (9/2 − ) 763.7(1) 0.0068(8) 3.6(5) 4.3(6)1008.5(2) (7/2 − ) 11/2 − † (7/2 + ) (5/2 + ) 769.1(1) 0.0080(10) 95(7) 68(16)1047.4(2) (7/2 + ) 3/2 + + ) (5/2 + ) 769.1(1) 0.036(2) 34(1) 33(2)1054.4(2) (7/2 + ) 3/2 + − ) 11/2 − + ) (7/2 + ) 1047.0(2) 0.0025(6) 5(1) 2.2(13)907.3(2) (3/2 + ) (1/2 + ) 315.1(2) 0.0394(7) 86(1) 74(5)1222.6(2) (3/2 + ) 3/2 + + ) (5/2 + ) 769.1(1) 0.007(3) 32(14) 36(6) § + ) (1/2 + ) 315.1(2) 0.0193(9) 88(4) 80(5) § + ) 3/2 + § − ) 11/2 − + ) 3/2 + − , 9/2 + ) (7/2 + ) 1054.3(2) 0.0137(11) 100(8) 100(9)765.0(3) (7/2 − , 9/2 + ) (5/2 + ) 769.1(1) 0.0037(11) 27(8) 69(6)1499.1(2) (7/2 − , 9/2 + ) 11/2 − ∗ (7/2 + ) 1054.3(2) 0.0037(6) 58(9)843.4(3) (7/2 – 11/2) ∗ (7/2 + ) 763.7(1) 0.0064(5) 100(7)1613.6(3) 1613.4(2) (7/2 + ) ‡ + − , 9/2 + ) ∗ (5/2 + ) 769.1(1) 0.0027(2) 100(9)1653.0(3) (7/2 − , 9/2 + ) ∗ − − ) (7/2 − ) 1043.9(1) 0.0043(3) 45(4) 75(6) § − ) (5/2 + ) 769.1(1) 0.0094(4) 100(4) 100(9) § − ) (9/2 − ) 763.7(1) 0.0075(5) 79(6) 95(9) § − ) 11/2 − + ) (13/2 − ) 1359.5(3) 0.1235(12) 77.2(6) 75(4)570.4(2) (15/2 + ) (15/2 − ) 1171.5(3) 0.160(2) 100.0(7) 100(6)1853.3(2) 318.0(6) (7/2, 9/2) (7/2 − , 9/2 + ) 1534.4(2) 0.0073(3) 48(2) 32(4)799.4(2) (7/2, 9/2) (7/2 + ) 1054.3(2) 0.0153(9) 100(6) 100(8)806.3(4) (7/2, 9/2) (7/2 + ) 1047.0(2) 0.0016(4) 11(3)1085.7(6) (7/2, 9/2) (5/2 + ) 769.1(1) 0.0046(3) 30(2)1865.1(1) 330.9(3) (7/2 + ) (7/2 − , 9/2 + ) 1534.4(2) 0.0060(14) 0.7(2) 0.66(5) Table I: (Continued).
This work ENSDF E level (keV) E γ (keV) J πi J πf E f (keV) Relative I γ BR γ BR γ + ) (5/2 + ) 1455.2(2) 0.0083(5) 1.03(6) 0.34(4)576.1(3) (7/2 + ) (3/2 + ) 1288.6(2) 0.0009(2) 0.11(3) 0.39(3)821.4(2) (7/2 + ) (7/2 − ) 1043.9(1) 0.0173(5) 2.14(5) 2.22(1)1095.9(2) † (7/2 + ) (5/2 + ) 769.1(1) 0.081(5) 9.9(6) 8.5(11)1101.4(2) (7/2 + ) (9/2 − ) 763.7(1) 0.0435(7) 5.36(7) 5.7(4)1830.6(3) (7/2 + ) 11/2 − + ) 3/2 + + ∗ (7/2 + ) 1054.3(2) 0.0123(7) 1002118.3(1) 212.2(3) (7/2 + ) (7/2) 1906.2(2) 0.0045(6) 0.45(6) 0.64(5)253.1(3) (7/2 + ) (7/2 + ) 1865.1(1) 0.0057(4) 0.57(4) 0.08(2)265.5(3) (7/2 + ) (7/2, 9/2) 1853.3(2) 0.0036(4) 0.36(4) 0.35(5)583.6(2) (7/2 + ) (7/2 − , 9/2 + ) 1534.4(2) 0.0144(7) 1.44(7)662.9(2) (7/2 + ) (5/2 + ) 1455.2(2) 0.0125(3) 1.25(3) 1.22(8)829.9(2) (7/2 + ) (3/2 + ) 1288.6(2) 0.0048(3) 0.48(3) 0.6(10)1071.0(2) † (7/2 + ) (7/2 + ) 1047.0(2) 0.0006(1) 0.06(1) 0.2(10)1074.7(2) (7/2 + ) (7/2 − ) 1043.9(1) 0.0666(7) 6.66(7) 6.1(4)1349.5(2) (7/2 + ) (5/2 + ) 769.1(1) 0.0511(8) 5.11(8) 4.6(3)1354.7(2) (7/2 + ) (9/2 − ) 763.7(1) 0.0417(11) 4.2(1) 2.9(3)2083.0(3) (7/2 + ) 11/2 − + ) 3/2 + + + + ) ∗ (7/2 + ) 1054.3(2) 0.0012(3) 82(21)1558.1(4) (7/2, 9/2 + ) ∗ (5/2 + ) 769.1(1) 0.0015(3) 100(18)2406(1) 604.4(5) (23/2 − ) (23/2 + ) 1803(1) 0.0090(4) 100 1002552(1) 145.5(3) † (27/2 − ) (23/2 − ) 2406(1) 0.0011(2) 100 1002568.0(3) 2252.9(3) (1/2, 3/2) ∗ (1/2) + ∗ + ∗ (5/2 + ) 1455.2(2) 0.0002(2) 6(4)1384.2(3) (1/2, 3/2) ∗ (3/2 + ) 1222.4(2) 0.0035(4) 90(11)2290.5(3) (1/2, 3/2) ∗ (1/2) + ∗ + + ) (7/2 + ) 1054.3(2) 0.0018(3) 22(3) 36(24)2021.9(2) (7/2, 9/2 + ) (5/2 + ) 769.1(1) 0.0082(3) 100(3) 100(7)2836.0(2) 718.0(3) (7/2 + , 9/2 + ) (7/2 + ) 2118.3(1) 0.0026(5) 5(1)1301.8(2) (7/2 + , 9/2 + ) (7/2 − , 9/2 + ) 1534.4(2) 0.0058(8) 12(2) 10.2(8)1781.4(2) (7/2 + , 9/2 + ) (7/2 + ) 1054.3(2) 0.0490(6) 100(1) 100(7)1791.4(3) (7/2 + , 9/2 + ) (7/2 − ) 1043.9(1) 0.0031(4) 6.3(7) 7.2(7)2066.5(2) (7/2 + , 9/2 + ) (5/2 + ) 769.1(1) 0.0299(6) 61(1) 57(4)2072.9(3) (7/2 + , 9/2 + ) (9/2 − ) 763.7(1) 0.0003(1) 0.6(2) 3.5(9)2981.9(2) 863.8(4) (7/2 + ) (7/2 + ) 2118.3(1) 0.0007(3) 3(1) Table I: (Continued).
This work ENSDF E level (keV) E γ (keV) J πi J πf E f (keV) Relative I γ BR γ BR γ + ) (7/2, 9/2) 1853.3(2) 0.0036(8) 18(4)1927.6(3) (7/2 + ) (7/2 − ) 1054.3(2) 0.0015(3) 8(1)2212.6(2) (7/2 + ) (5/2 + ) 769.1(1) 0.0201(5) 100(2) 100(6)2980.7(7) (7/2 + ) 3/2 + − ) (7/2 − ) 1043.9(1) 0.0045(7) 79(11) 90(9)2764.0(2) (3/2 − ) (1/2) + + ) (7/2 + ) 1613.6(3) 0.0020(5) 17(4)2094.0(3) (7/2 + ) (7/2 + ) 1047.0(2) 0.0041(4) 34(3)2371.1(3) † (7/2 + ) (5/2 + ) 769.1(1) 0.0045(3) 37(3) 16.2(18)2376.4(3) (7/2 + ) (9/2 − ) 763.7(1) 0.0025(6) 20(5) 30(3)3140.1(2) (7/2 + ) 3/2 + + ∗ (9/2 − ) 763.7(1) 0.0005(2) 1003581.8(3) 1257.0(6) (7/2, 9/2 + ) ∗ (7/2, 9/2) 2326.1(4) 0.0013(2) 90(17)2527.1(3) (7/2, 9/2 + ) ∗ (7/2 + ) 1054.3(2) 0.0013(3) 93(23)2812.7(8) (7/2, 9/2 + ) ∗ (5/2 + ) 769.1(1) 0.0014(4) 100(25)2818.4(5) (7/2, 9/2 + ) ∗ (9/2 − ) 763.7(1) 0.0010(4) 69(27)3590.4(1) 1889.5(2) (3/2 − ) (7/2 − ) 1701.0(2) 0.0106(5) 23(1) 23(2)1977.0(2) (3/2 − ) (7/2 + ) 1613.6(3) 0.0113(5) 24(1) 21(2)2301.7(2) (3/2 − ) (3/2 + ) 1288.6(2) 0.0178(3) 38.0(5) 30(2)2367.9(2) (3/2 − ) (3/2 + ) 1222.4(2) 0.0292(4) 62.3(7) 51(4)2546.2(2) (3/2 − ) (7/2 − ) 1043.9(1) 0.0469(5) 100(1) 100(7)3276.0(2) (3/2 − ) (1/2) + − ) 3/2 + † (21/2 − ) (23/2 − ) 2406(1) 0.011(6) 7.2(1)1715.9(2) (21/2 − ) (21/2) 2277(1) 0.0286(7) 17.6(4) 16.4(14)2189.8(2) (21/2 − ) (23/2 + ) 1803(1) 0.162(2) 100.0(7) 100(7)2230.8(2) (21/2 − ) (19/2 + ) 1762(1) 0.0577(9) 35.5(5) 41(2)4136.6(3) 2847.8(2) (1/2, 3/2) ∗ (3/2 + ) 1288.6(2) 0.0026(1) 100(3)2915.5(5) (1/2, 3/2) ∗ (3/2 + ) 1222.4(2) 0.0019(3) 73(12) ∗ Spin assignment for new levels, based on β and γ decay systematics. † Intensity calculated from coincidences. ‡ Revised spin assignment for known levels, based on β and γ decay systematics. § Based on ENSDF information: Weighted average between In gs and In m . B. Decay of the 9/2 + 129
In ground state
1. Half-life of In gs Plotting the intensity of a γ -ray as a function of cy-cle time allows for the measurement of isotope half-life;a spectrum can be generated and fit with a characteris-tic decay formula, from which the half-life can then beextracted. To improve statistics, background-corrected timing gates on 39 γ -rays — shown in Table II — associ-ated with the decay of the In ground state into
Snwere summed and the counts as a function of cycle timefit using a standard exponential decay, as seen in Figure4. The fit returned a half-life of t / = 0 . s, in agree-ment with t / = 0 . s quoted in the evaluation byTimar, Elekes and Singh [31]. A chop analysis, which in-volved a change in the width of the timing window for thefit, was conducted to check for any rate dependent effectson the half-life; no discernible effects were observed. Theweighted average value between the evaluted half-life of0.611(5) s and the observed half-live of 0.60(1) s is cal-culated to be 0.609(4) s, where the uncertainty has beenincrease by the (cid:112) χ . Time (s) In gs t = 0.60(1) s C o un t s ( m s / b i n )
16 17 18 19 20 2110008006004002000
Figure 4. A spectrum of total counts as a function of cycletime, representing 39 transitions associated with the
Inground state decay into states in
Sn. The fit, seen in red,returned a value of t / = 0 . s. The reduced χ for thisfit is 1.3.Table II. Transitions used to build the half-life plot shownin Figure 4. These were identified as transitions from statespopulated by the ground state of In.Transitions (keV)212.2(3) 662.9(2) 1349.5(2) 2021.9(2)253.1(3) 765.0(3) 1354.7(2) 2066.5(2)265.5(3) 799.4(2) 1499.1(2) 2072.9(3)278.0(2) 821.4(2) 1613.4(2) 2083.0(3)285.2(2) 829.9(2) 1736.6(3) 2118.3(2)318.0(6) 1054.4(2) 1781.4(2) 2212.6(2)330.9(3) 1074.7(2) 1791.4(3) 2376.4(3)411.2(6) 1095.9(2) 1830.6(3) 2980.7(7)480.2(2) 1101.4(2) 1864.8(2) 3140.1(2)576.1(3) 1301.8(2) 1906.2(2) β -feeding and logft values Several new transitions and new levels from the β -decay of the ground state of In into excited states of
Sn were observed. Figure 5 shows the γ -rays observedin Sn due to this decay. Newly observed transitionsand levels are coloured (red), along with their proposedspin assignments.Table III lists the states that are populated by theground state along with the β -feeding intensities andthe log ft values calculated in this work, together witha comparison to the work of Gausemel et al. [17]. Theelectron conversion coefficients for low-energy γ -rays aretaken into account when doing these calculations, usingthe BrIcc utility available through the NNDC [32]. The data observed by Gausemel et al. showed direct β -feedingto the 35-keV isomeric state on the order of < . The β -feeding values obtained in the present work are nor-malized to reflect 100 % feeding to excited states.Spin assignments for the newly observed levels are pro-posed based on the β -decay selection rules and γ -raysystematics. The newly observed states at 1607 keV,2024 keV and 3447 keV are tentatively assigned spinsbetween (7/2) and (11/2), as they are observed to de-cay to states with proposed spins between 7/2 and 9/2,while decays to states with spins of 3/2 or lower were notobserved.The new state at 1688 keV decays to the 11/2 − + ) 769-keV levels such that the spin and parityof this state can be restricted to (7/2 − , 9/2 + ). The newstates at 2326 keV and 3582 keV are observed to decayto states with tentative spins between (5/2 + ) and 9/2 − ,such that their spins can be restricted to (7/2, 9/2 + ).The log ft values calculated between the (9/2 + ) In gs and the above mentioned states, shown in Table III, areall consistent with the allowed or first-forbidden decaysimplied by the proposed spin assignments.Previous work using γ -ray information [17, 31] as-signed a spin of between (1/2) and (7/2 + ) for the 1614-keV level, with no detectable β -feeding from the (1/2 − ) In m parent. Gausemel et al. observed a transition at1977 keV, from the (3/2 − ) 3590-keV state to the 1614-keV state, which was observed in the present work andis shown in Figure 7. A new transition, at 1526-keV,was also observed from the (7/2 + ) state at 3140 keV,casting doubt on the possibility of a 1/2 spin. Further-more, the 1614-keV level is observed to have a direct β -feeding component, equivalent to double the intensity ofthe 1977-keV transition from the 3590-keV state observedboth by Gausemel et al. and in this work, indicating thatthe 1614-keV level is most likely fed by the (9/2 + ) In gs and has a spin of (7/2 + ). This spin assignment is cor-roborated by the 6.54(2) log ft value shown in Table III,which is consistent with an allowed transition. C. Decay of (1/2 − ) In m
1. Half-life of In m The twelve γ -ray transitions used to generate the half-life spectrum shown in Figure 6 are listed in Table IV.The fit to the data returned a half-life of t / = 1 . s. A chop analysis was carried out and no systematiceffects were observed. The present result is a factor ofthree more precise than the value 1.23(3) s quoted inthe evaluation by Timar, Elekes and Singh [31]. Theweighted average of these two values is 1.17(2) s, with itsuncertainty increased by (cid:112) χ . In In β + − − ) 763.7(5/2 + ) 769.1(7/2 − ) 1043.9(7/2 + ) 1047.0(7/2 + ) 1054.3(3/2 + ) 1288.6(5/2 + ) 1455.2(7/2 − ,9/2 + ) 1534.4(7/2 + ) 1613.6(7/2,9/2) 1853.3(7/2 + ) 1865.1(7/2) 1906.2(7/2 + ) 2118.3(7/2,9/2 + ) 2326.1(7/2,9/2 + ) 2791.0(7/2 + ,9/2 + ) 2836.0(7/2 + ) 2981.9(7/2 + ) 3140.3(7/2 to 11/2) 3446.7(7/2,9/2 + ) 3581.8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . + − − ) 763.7(5/2 + ) 769.1(7/2 − ) 1043.9(7/2 + ) 1047.0(7/2 + ) 1054.3(3/2 + ) 1288.6(5/2 + ) 1455.2(7/2 − ,9/2 + ) 1534.4(7/2 to 11/2) 1607.3(7/2 + ) 1613.61688.3(7/2 − ) 1701.0(7/2,9/2) 1853.3(7/2 + ) 1865.1(7/2) 1906.2(7/2 to 11/2) 2023.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sn β (7/2 − ,9/2 + ( Figure 5. The level scheme of
Sn, populated through the β -decay of the ground state of In, showing the high-lying states(top) and the low-lying states (bottom). The colour (red) represents new transitions and levels found in this work. For the caseof the 1614-keV state, the coloured (7/2 + ) spin indicates a new spin assignment to a previously observed level. The half-livesof the ground state and the Sn m γ -ray intensity and their uncertainties can be found in Table I. β -feeding and logft values The In m isomer was observed to decay to knownstates in Sn, as well as to three newly observed states.Figure 7 shows the γ -rays observed in this decay; thespins of the three new levels populated in Sn were de-termined from β -feeding and γ -ray systematics. Table Vsummarizes the β -feeding intensities and the log ft valuesobtained in the present work, using the weighted half-lifevalue of 1.17(2) s, compared with the results of Gausemel et al. [17] who also observed a 77(15) % direct β -feedingto the 3/2 + ground state in Sn; the present β -feedingintensities have been scaled to represent the remaining23 % of observed β -feeding to excited states.The new states at 2568 keV and 2606 keV are observedto decay to the (1/2) + − ) In m . The 4137-keV state decays to the 1289-keV and 1222-keV states, both of which have tentativespin assignments of (3/2 + ), indicating that this state islikely to have a 1/2 or 3/2 spin. The log ft values for these Table III. The β -feeding intensities and log ft values for statesin Sn, observed through the β -decay of the (9/2 + ) In gs state and calculated with the weighted average half-life of0.609(4) s. Columns denoted by Ref. [17] contain valuesestablished in the work of Gausemel et al. . The β -feedingvalues have been normalized to reflect 100% feeding of excitedstates. E x (keV) I β (%) log ft This work Ref. [17] This work Ref. [17]763.7(1) 2.03(8) 2.1(4) 6.43(2) 6.4(1)1043.9(1) 1.95(8) 2.0(4) 6.36(2) 6.4(1)1047.0(2) 0.30(4) 0.35(6) 7.17(6) 7.1(1)1054.3(2) 1.62(10) 2.1(3) 6.44(3) 6.33(7)1534.4(2) 0.60(9) 0.46(6) 6.73(7) 6.85(6)1607.3(3) 0.14(2) 7.33(7)1613.6(3) 0.88(3) 6.54(2)1688.2(3) 0.20(2) 7.15(4)1701.0(2) 0.52(5) 0.24(2) 6.74(5) 7.08(4)1853.3(2) 0.85(5) 0.76(6) 6.47(3) 6.53(4)1865.1(1) 37.6(3) 36(2) 4.83(1) 4.85(3)1906.2(2) 0.18(3) 0.13(3) 7.13(8) 7.3(1)2023.6(4) 0.48(3) 6.67(3)2118.3(1) 46.9(3) 49(3) 4.64(1) 4.63(3)2326.1(4) 0.06(2) 7.49(14)2791.0(3) 0.39(15) 0.47(9) 6.48(2) 6.4(1)2836.0(2) 3.53(5) 3.36(15) 5.51(1) 5.54(2)2981.9(2) 1.01(4) 0.74(5) 5.99(2) 6.14(3)3140.3(2) 0.99(4) 0.67(4) 5.94(2) 6.11(3)3446.7(4) 0.020(9) 7.5(2)3581.8(3) 0.19(3) 6.46(7)
Time (s)
16 17 18 19 20 21 In m1 t = 1.16(1) s C o un t s ( m s / b i n ) Figure 6. A spectrum of total counts as a function of cy-cle time, representing twelve transitions associated with thedecay of In m into states in Sn. The fit, seen in red,returned a value of t / = 1 . s. The reduced χ for thisfit is 1.2. states, shown in Table V, are consistent with either theallowed or first-forbidden transitions expected from the(1/2 − ) In m to the respective states in Sn.The excess feeding into the (5/2 + ) states at 769 keV Table IV. Transitions used to build the half-life plot shownin Figure 6. These were identified as transitions from statespopulated by the In m isomer.Transitions (keV)175.5(4) 1889.5(2) 2764.0(2)315.4(2) 2035.6(3) 3078.7(3)907.3(2) 2367.9(2) 3276.0(2)1222.6(2) 2546.2(2) 3589.7(3)Table V. The β -feeding intensities and log ft values, calcu-lated, for states in Sn, observed through the β -decay ofthe (1/2 − ) In m isomer and calculated with the weightedaverage half-life of 1.17(2) s. The values calculated in thiswork are compared to the values calculated by Gausemel etal. [17]. E x (keV) I β (%) log ft This work Ref. [17] This work Ref. [17]315.1(2) 14.3(2) 15.1(13) 6.10(1) 6.10(4)769.1(1) † † † Unique 1st forbidden and 1455 keV has been attributed to direct β -feeding fromthe (1/2 − ) In m to these states, rather than to unob-served transitions feeding these levels from higher levelspopulated by either the β -decay of the (9/2 + ) In gs or the (1/2 − ) In m . The log ft values for the 769-keV and 1455-keV states, calculated with feeding from In m are 9.31(9) and 9.55(5), respectively, consistentwith unique first-forbidden transitions, supporting thespin assignments for these states, given as (5/2 + ). D. Decay of (23/2 − ) In m
1. Half-life of In m Only four viable γ -ray transitions, at 382, 515, 2190and 2231 keV, could be used in the half-life fitting ofthe In m isomer. The spectrum and the fit are showin Figure 8. The adopted value for the half-life of the(23/2 − ) In m is t / = 0 . s. This result, which in-0 In β + + + ) 769.1(7/2 − ) 1043.9(7/2 + ) 1047.0(3/2 + ) 1222.4(3/2 + ) 1288.6(5/2 + ) 1455.4(7/2 + ) 1613.6(7/2 − ) 1701.0(1/2,3/2) 2568.0(1/2,3/2) 2606.2(3/2 − ) 3079.3(1/2,3/2) 3393.9(3/2 − ) 3590.4(1/2,3/2) 4136.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . Sn Figure 7. The level scheme of
Sn, populated through the β -decay of the (1/2 − ) 459-keV isomer of In. The colour (red)represents new transitions and levels found in this work. The half-life of the
Sn ground state is 2.23(4) min, as given byTimar, Elekes and Singh [31]. Information about γ -ray intensity and their uncertainties can be found in Table I. cludes a systematic uncertainty associated with the chopanalysis, has an error of a factor of five times smaller thanthe established value, quoted by Timar, Elekes and Singh[31], as t / = 0 . s. The weighted average betweenthe half-life in the evalution and the half-life observed inthis work is 0.65(2) s, with the uncertainty increased by (cid:112) χ .
16 17 18 19 20 21 In m2 t = 0.65(2) s Time (s) C o un t s ( m s / b i n ) Figure 8. A spectrum of total counts as a function of cycletime, representing four transitions associated with In m decay into states in Sn. The fit, seen in red, returned avalue of t / = 0 . s. The reduced χ for this fit is 2.2. β -feeding and logft values The level scheme associated with the β -decay of the In m is shown in Figure 9. Table VI shows the β feeding intensities and log ft values obtained in this work,along with a comparison to those observed by Gausemelet al.[17]. One new transition was observed in the present work. The branching ratios measured for the decay ofthe 3993-keV (21/2 − ) level to the 1762-, 1803- and 2277-keV levels and for the decay of the 2277-keV level to the1762- and 1803-keV levels are in reasonable agreementwith previous data [17], as seen in Table I. However, the β feeding intensity of the 2277-keV level is nearly a factorof ten smaller than the value previously observed.Direct β -feeding to the 1803-keV level was estimatedbased on the intensities of the γ -rays populating thisstate and the γ -ray intensities depopulating states be-low, connected through two transitions, a 41.0(2)-keVtransition from the 1803-keV state to the 1762-keV state,and a 19.7(10)-keV transition from the 1762-keV state tothe 1742-keV state. A direct β -feeding of 10(4) % to the1803-keV state was observed, consistent with the previ-ously reported value of 14(4) % β -feeding intensity ob-served previously [17]. Table VI also summarizes the β -feeding intensities and the log ft values for the 2277-keVand 3993-keV states. E. Decay of (29/2 + ) In m Above the 1630-keV isomer in
In, there is anotherisomer at 1911 keV with spin (29/2 + ). This state hasbeen shown to decay through a 281-keV internal transi-tion to the 1630-keV In m isomer. This transition liesvery close in energy to two known transitions in the Snnucleus, at 278.0(2)-keV and 280.4(2)-keV, which depop-ulate the 1047-keV and 1044-keV states, respectively, asseen in Figure 5.1 In /2 (( - 163023 − − ) 1171.5(13/2 − ) 1359.5(15/2 + ) 1741.9(19/2 + + − ) 2406(21/2 − ) 39933/2 + . . . . . . . . . . . Sn )) β Figure 9. The level scheme of
Sn, populated through the β -decay of the (23/2 − ) In. The colour (red) represents newtransitions and levels found in this work. The half-life of the
Sn ground state is 2.23(4) min, as given by Timar, Elekes andSingh [31]. Information about γ -ray intensity and their uncertainties can be found in Table I. The dashed lines presented twoknown states, at 1762 keV and 1803 keV, whose energies can only be inferred in this work from to feeding from above.Table VI. The β -feeding intensities and log ft values, calcu-lated for states in Sn, observed through the β -decay of the(23/2 − ) In m isomer and calculated with the weighted av-erage half-life of 0.65(2) s. The values are calculated in thiswork are compared to those calculated by Gausemel et al. [17]. E x (keV) I β (%) log ft This work Ref. [17] This work Ref. [17]1803(1) 10(4) 14(4) 5.92(18) 5.8(2)2277(1) 0.5(3) 8.0(12) 7.1(3) 5.9(1)3993(1) 89(4) 75(4) 4.31(2) 4.4(1)
The total relative intensity obtained in the addbacksingles γ -ray spectrum was 0.0805(4) for the triplet cen-tered around 280-keV. This was inconsistent with themeasured intensity of either the 278-keV and 280-keVtransitions, observed in previous studies [17], and there-fore the intensities of the transitions were measured bygating from below, on the 769-keV transition depopu-lating the 769-keV state for the transition at 278-keV,and the 728-keV transition that depopulates the 764-keVstate for the 280-keV transition.The relative intensity of the 278-keV transition wasfound to be 0.0080(10), consistent with previous mea-surements of both γ -ray intensity and the β -feeding ofthe 1047-keV state. Similarly, the relative intensity of the280-keV transition in Sn was measured to be 0.0068(8),in agreement with the previously measured γ -ray inten-sity and β -feeding to the 1044-keV state. The remainingintensity at 281-keV, amounting to 0.0657(11), must thenbe due to the internal transition of the In m . Time (s)
16 17 18 19 20 21 In m3 = 0.085(15) s C o un t s ( m s / b i n ) Figure 10. A spectrum of total counts as a function of cycletime for the 281-keV transition. The fit, in red, returned avalue of t / = 0.085(15) s, which is in good agreement withthe half-life of the 1911-keV In m , quoted at 0.110(15) s[31]. The fit returned a reduced χ of 1.1. The fit includeda component associated with the β -decay of the In gs sincethe energy of the 281-keV internal transition in In is unre-solved from two transitions in
Sn at 278 and 280-keV (seethe text for details).
To confirm this assignment, a spectrum of total countsas a function of time, gated on the 281-keV transitionwas produced in the same manner as described in Sec-tions III B 1, III C 1 and III D 1. The fit, shown in Fig-ure 10, returned a half-life value of 0.085(15) s, in goodagreement with the 0.110(15) s half-life of the 1911-keV In m state [31] and much shorter than the half-lives ofthe other β -decaying states in In. This confirms thatthe presence of the excess intensity at 280 keV was dueto the internal transition from In m to In m .If this 1911-keV In m isomer were to populate statesin Sn through β -decay, these would have to be veryhigh spin states. One such candidate is the 2552-keVstate, with a proposed spin of (27/2 − ). Lozeva et al. − ) 2406-keV state, having populated states in Snthrough
U fission and
Xe fragmentation experi-ments. The present work observed the 146-keV transitionin coincidence with the 604-keV transition from the 2406-keV state to the (23/2 + ) 1803-keV state, also observed byLozeva et al. and shown in Figure 12. Figure 11 showsthe coincidence spectrum, produced by gating on the 604-keV transition. This gate clearly shows the presence ofthe coincidence with the 146-keV γ -ray.An intensity balance calculation of the 2552-keV stateimplies β -feeding, since there is no known higher-lyingstate in In that could potentially populate this state.This feeding would amount to the portion representedby the intensity of the 146-keV transition, with respectto the sum of the intensities of the 146-keV and the 281-keV transitions, corrected for internal conversion.Comparing the β -feeding of the 2552-keV state andthe 281-keV internal transition yielded a β -branching ra-tio of 2.0(5) % . The log ft value for the β -decay of the(29/2 + ) 1911-keV isomer in In to the (27/2 − ) 2552-keV state in Sn is then 5.68(12), consistent with afirst-forbidden transition from the (29/2 + ) In m stateto the (27/2 − ) state in Sn. This log ft value is calcu-lated with a half-life of 0.10(1) s, the weighted averageof the present result with the literature value. The log ft value in this transition is comparable to the 5.8 observedby Gausemel et al. between the (23/2 − ) 1630-keV iso-mer in In to the (23/2 + ) 1803-keV state Sn, whichis expected given the nearly pure π ( g − / ) → ν ( h − / ) β transition [17]. This is the first time the 1911-keV isomerin In has been observed to β -decay to excited states of Sn. Figure 12 shows the partial level schemes of thestates in both
In and
Sn involved in this decay.
IV. CONCLUSION
The present work reports new information observedthrough the β -decay of In to
Sn. The half-lives ofthe ground state and isomeric states in
In have been
Energy (keV)
135 140 145 150 155 160 C oun t s / k e V − Energy (keV)
598 602 606 610 C oun t s / k e V × k e V Figure 11. A spectrum showing the 146-keV transition inthe 604-keV gate. Note the red lines in the inset denote theplacement of the gate. (23/2 − + . In IT β (23/2 + − − . . Sn ))))) Figure 12. Partial level scheme showing the decay of the(29/2 + ) 1911-keV In m isomer into the (27/2 − ) 2552-keVstate in Sn. The intensity of the 146-keV transition wasobtained in coincidence with the 604-keV transition. confirmed, with the uncertainty in the half-life value ofthe In m isomer improved. The level scheme of Snhas been greatly expanded, with nine new excited statesand thirty-one new γ -ray transitions. Furthermore, thiswork observed, for the first time, the β -decay of the(29/2 + ) 1911-keV In m state. More work is needed, inparticular in the determination of the spins and paritiesof the states above the ground state, the 35-keV isomerand the 315-keV first excited state of Sn. This workprovides more rigid constraints on the spins of a numberof the excited states, but further studies are needed inorder to properly assign these values. This new infor-mation on these two nuclei, lying close to doubly magic Sn , provides important constraints and will guidefuture theoretical models in this region. ACKNOWLEDGEMENTS
The authors would like to thank the GRSI collabora-tion at TRIUMF for their aid during the course of thiswork. This work was supported, in part, by the Natu-ral Sciences and Engineering Research Council of Canada(NSERC). C.E.S. acknowledges support from the CanadaResearch Chairs program. Phase I of the GRIFFIN spec-trometer was funded by the Canadian Foundation of In-novation (CFI), TRIUMF and the University of Guelph.TRIUMF receives funding from the Canadian FederalGovernment via a contribution agreement with NRC.3 [1] P. Cottle, Nature , 430 (2010).[2] D. Bazin, Nature , 330 (2012).[3] F. Andreozzi et al. , Phys. Rev. C , R16(R) (1997).[4] T. Otsuka et al. , Phys. Rev. Lett. , 082502 (2001).[5] T. Otsuka et al. , Phys. Rev. Lett. , 232502 (2005).[6] J. Beun et al. , J. Phys. G , 025201 (2009).[7] R. Surman, J. Beun, G. C. McLaughlin, and W. R. Hix,Phys. Rev. C , 045809 (2009).[8] E. M. Burbidge, G. R. Burbidge, W. A. Fowler, andF. Hoyle, Rev. Mod. Phys. , 547 (1957).[9] A. G. W. Cameron, Publ. Astron. Soc. Pac. , 201(1957).[10] A. G. W. Cameron, J. J. Cowan, and J. W. Truran,Astrphys. Space Sci. , 235 (1983).[11] M. R. Mumpower et al. , Prog. Part. Nucl. Phys. , 86(2016).[12] J. Pinston et al. , Phys. Rev. C , 024312 (2000).[13] K. Aleklett, E. Lund, and G. Rudstam, Phys. Rev. C , 462 (1978).[14] L.-E. De Geer and G. B. Holm, Phys. Rev. C , 2163(1980).[15] L. Spanier, K. Aleklett, B. Ekström, and B. Fogelberg,Nuc. Phys. A , 359 (1987).[16] H. Huck, M. L. Pérez, and J. J. Rossi, Phys. Rev. C ,621 (1982).[17] H. Gausemel et al. , Phys. Rev. C , 054307 (2004).[18] R. Warner and P. Reeder, Radiat. Eff. , 27 (1986). [19] G. Rudstam, K. Aleklett, and L. Sihver, Atomic Dataand Nuclear Data Tables , 1 (1993).[20] J. Genevey et al. , Phys. Rev. C , 034322 (2002).[21] R. L. Lozeva et al. , Phys. Rev. C , 064313 (2008).[22] J. Dilling, R. Krücken, and G. Ball, Hyperfine Interact. , 1 (2014).[23] P. Van Duppen, in The Euroschool Lectures on Physicswith Exotic Beams Vol II (Springer, 2006).[24] I. Bylinskii and M. K. Craddock, in
ISAC and ARIEL:The TRIUMF Radioactive Beam Facilities and the Sci-entific Program , edited by J. Dilling, R. Krücken, andL. Merminga (Springer, 2013).[25] S. Raeder et al. , Rev. Sci. Instrum. , 033309 (2014).[26] P. Bricault et al. , in ISAC and ARIEL: The TRIUMFRadioactive Beam Facilities and the Scientific Program ,edited by J. Dilling, R. Krücken, and L. Merminga(Springer, 2013).[27] C. E. Svensson and A. B. Garnsworthy, Hyperfine Inter-act , 127 (2014).[28] A. B. Garnsworthy et al. , Nucl. Instrum. Meth. Phys.Res. A , 85 (2017).[29] A. B. Garnsworthy et al. , Nucl. Instrum. Meth. Phys.Res. A (2019).[30] U. Rizwan et al. , Nucl. Instrum. Meth. Phys. Res. A ,126 (2016).[31] J. Timar, Z. Elekes, and B. Singh, Nuc. Data Sheets , 143 (2014).[32] T. Kibédi et al. , Nucl. Instrum. Meth. Phys. A589