High-spin states in 123I were populated in the reaction 80Se(48Ca,p4n)123I at a beam energy of 207 MeV and γ-ray coincidence events were measured using the Gammasphere spectrometer. Three weakly populated, high-spin rotational bands have been discovere

Burger, A.

Carpenter, M P

Chmel, S.

Fallon, P

Ha, Hoa

Hagemann, G B

Herskind, B.

Hubel, H

Korichi, Amel

Ragnarsson, I

Rogers, Jeffrey

Singh, A.K.

Singh, Purnima

Timar, J.

Wilson, Anna

Physical Review C

English

The Australian National University

PHYSICAL REVIEW C 86, 067305 (2012)High-spin rotational bands in 123IPurnima Singh,1 A. K. Singh,1 A. N. Wilson,2 I. Ragnarsson,3 H. Hübel,4 A. Bürger,4 M. P. Carpenter,5 S. Chmel,4 P. Fallon,6G. B. Hagemann,7 B. Herskind,7 Hoa Ha,8 R. V. F. Janssens,5 K. Juhász,9 A. Kardan,10 T. L. Khoo,5 G. Kondev,5 A. Korichi,8T. Lauritsen,5 B. M. Nyakó,11 J. Rogers,2 G. Sletten,7 J. Timár,11 and S. Zhu51Department of Physics & Meteorology, Indian Institute of Technology, Kharagpur, IN-721302, India2Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200, Australia3Division of Mathematical Physics, LTH, Lund University, Box 118, S-22100 Lund, Sweden4Helmholtz-Institut für Strahlen-und Kernphysik, Universität Bonn, Nussallee 14-16, D-53115 Bonn, Germany5Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA6Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA7Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen, Denmark8CSNSM-IN2P3, Orsay Campus, F-91405 Orsay, France9Department of Information Technology, University of Debrecen, H-4032 Debrecen, Hungary10School of Physics, Damghan University, P.O. Box 36715-364, Damghan, Iran11Institute of Nuclear Research of the Hungarian Academy of Sciences, H-4001 Debrecen, Hungary(Received 28 September 2012; revised manuscript received 28 November 2012; published 17 December 2012)High-spin states in 123I were populated in the reaction 80Se(48Ca,p4n)123I at a beam energy of 207 MeVand γ -ray coincidence events were measured using the Gammasphere spectrometer. Three weakly populated,high-spin rotational bands have been discovered with characteristics similar to those of the long collectivebands recently observed in other nuclei of this mass region. Configuration assignments are proposed based oncalculations within the framework of the cranked Nilsson-Strutinsky approach.DOI: 10.1103/PhysRevC.86.067305 PACS number(s): 21.10.−k, 23.20.Lv, 23.20.En, 27.60.+jThe nuclei in the A = 125 mass region, with a limitednumber of valence nucleons outside the 114Sn core, undergoa transition from weakly prolate deformation at low spin toan oblate shape at medium spin. The shape change is inducedby the successive alignment of nucleons along the rotationaxis and, finally, the level sequences terminate in maximallyaligned oblate states [1–6]. In addition, several high-spinrotational bands have recently been observed in 120Te [7],124Ba [6], 125I [8], 125Xe [9], and 126Xe [10], which extendfar beyond the noncollective oblate states. Only some of thesesequences are firmly connected to lower-lying levels; theyfeed normal-deformed states in the spin range of I  25 atexcitation energies around 10 MeV.In the present work, the results of a further analysis ofthe data from the experiment to investigate the high-spinstructure of 123I [2] are reported. This investigation revealedthree highly deformed bands in this nucleus. Their propertiesare similar to those of the long bands observed in neighboringnuclei. Cranked Nilsson-Strutinsky (CNS) calculations havebeen employed to propose configurations for the new bands.High-spin states in 123I were populated using the reaction80Se(48Ca,p4n)123I. The beam with an energy of 207 MeVwas provided by the ATLAS accelerator at ANL. The targetconsisted of a 80Se layer with a thickness of 0.6 mg/cm2.Gamma-ray coincidence events were recorded with the Gam-masphere spectrometer [11]. Further details on the experimentand the data analysis are given in previous publications by thepresent collaboration [2,7].The three rotational sequences with large moments ofinertia discovered in 123I are displayed in Fig. 1. Theirintensities are <1% of the channel strength. Bands a and b areabout equal in intensity, while band c is weaker. Such smallintensities preclude a measurement of directional correlations.However, the regularity of the bands and their similarity withhigh-spin bands in neighboring nuclei suggests that the in-bandtransitions are of E2 multipolarity. It was not possible toestablish linking transitions into known 123I levels. Excitationenergies and spins of the new bands were estimated on thebasis of the observed coincidences. These values were variedwithin reasonable limits to give agreement with theoreticalpredictions for the suggested configurations. The adoptedvalues are similar to those of the connected bands in theneighboring nuclei 125I [8], 125Xe [9], and 126Xe [10].Triple-gated γ -ray coincidence spectra for the three newbands are presented in Fig. 2. Although no linking transitionsbetween the bands and the lower-spin states could be estab-lished, transitions between the positive- and negative-paritystates of 123I [2] up to I  30 are visible in the three spectra.The spins assigned to the three new bands are plotted as afunction of transition energies in Fig. 3. A comparison with thehigh-spin bands in the neighboring nuclei 120Te [7], 125I [8],and 125Xe [9] demonstrates the similarity of their behavior.At high frequencies, above h̄ω = 0.95 MeV, the slopes of thecurves for the 123I bands change, however, not as drasticallyas for band L4 in 125Xe. These irregularities are indicative ofband crossings, probably caused by neutron alignments.Since firm spin assignments are missing, a comparisonwith theoretical predictions to assign configurations can onlybe viewed as tentative. In the following, suggestions forthe configurations are made. Calculations were performedwithin the framework of the CNS formalism [12–14]. Fordetails of the parameters used in these calculations seeRef. [2]. The configurations are labeled relative to the 100Sncore as [p1p2,n1(n2n3)], which is a shorthand notation for067305-10556-2813/2012/86(6)/067305(4) ©2012 American Physical SocietyBRIEF REPORTS PHYSICAL REVIEW C 86, 067305 (2012)12551363146215711682180519172010209112331321142215291644175618571916199612401345146315891715184919512060(61/2 )(13300)(65/2 )(69/2 )(73/2 )(77/2 )(81/2 )(85/2 )(89/2 )(93/2 )(97/2 )(55/2 )(11250)(59/2 )(13000)(59/2 )(63/2 )(67/2 )(71/2 )(75/2 )(79/2 )(83/2 )(87/2 )(91/2 )(63/2 )(67/2 )(71/2 )(75/2 )(79/2 )(83/2 )(87/2 )(91/2 )(a)(b)(c)FIG. 1. The three new rotational bands in 123I.π [(g9/2)−p1 (h11/2)p2 ]⊗ν[(h11/2)n1 (h9/2f7/2)n2 (i13/2)n3 ]. Theremaining particles outside the core are located in the mixedd5/2, g7/2, s1/2, and d3/2 orbitals.Studies of neighboring nuclei [6–10] as well as the presentcalculations for 123I, see below, indicate that the high-spinbands in the A  125 region are built on configurations withtwo proton holes in the g9/2 subshell. Representative potentialenergy surfaces (PES) for such configurations with parity andsignature (π, α) = (+, 1/2) are displayed in Fig. 4. The PESfor the other (π, α) combinations show a similar behavior.At low spin, the lowest-energy minimum corresponds to awell-developed prolate shape at ε2  0.28. With increasingspin, at I  30, it splits into two minima. The one that de-velops towards smaller deformation (ε2  0.2) corresponds toconfigurations with proton excitations from the g9/2 subshell,but without neutron excitations across the N = 82 shell gap.The recently observed highly deformed bands in 120Te were01000020000Counts400 800Energy [keV]01000020000010000200001200 1600 2000(a)(b)(c)x40x40x4012331321 14221529164417561857191619961240 13451463 158917151849195120601255 13631462157116821805 191720102091272353510574591 671814898272272353353510510574574591591671671814814898898898#758#758#7581469692148 748148148692692 748748FIG. 2. Triple-gated background-subtracted γ -ray coincidencespectra showing transitions of (a) band a, (b) band b, and (c) bandc. The spectra are separated into the two energy ranges: 100 keV– 1 MeV and 1.2–2.2 MeV, respectively. The labeled photopeaksbelow 1 MeV correspond to low-lying states in 123I. The peak at 758keV is an unresolved doublet. The spectra were produced from thehypercube by requiring two γ rays from a list of all transitions of thenegative-parity sequence 6 in 123I from 272 to 801 keV, see Ref. [2],and one γ ray from the list of all transitions of bands a, b, and c,respectively.associated with this minimum [7]. The minimum at ε2  0.3results from neutrons excited across the N = 82 gap. Sucha deformation has been associated with high-spin bands in125Xe [9] and 126Xe [10] on the basis of measured transitionquadrupole moments.A systematic investigation has been performed to search forconfigurations, associated with these two minima, that may beassigned to the bands in 123I. It turns out that configurations1 1.5 2Eγ [MeV]304050Spin, I [h- ]band a 123I              band b 123I               band c 123I               band 6 125I                 band L4 125Xe        band b1 120Te        FIG. 3. (Color online) Spins as a function of γ -ray energydepopulating the states for the new bands in 123I and for the connectedbands in 120Te, 125I, and 125Xe.067305-2BRIEF REPORTS PHYSICAL REVIEW C 86, 067305 (2012)ε 2sin(γ+30°)60oγ =  0o I π=45/2 +0.10.20.360oγ =  0o I π=61/2 +ε2cos(γ+30°)ε 2sin(γ+30°)60oγ =  0o I π=77/2 +0 0.1 0.2 0.30.10.20.3ε2cos(γ+30°)60oγ =  0o I π=93/2 +0 0.1 0.2 0.323FIG. 4. (Color online) Potential energy surfaces for 123I withparity and signature (π , α) = (+, 1/2), with the additional constraintof two proton holes in g9/2 orbitals, in the spin range Iπ = 45/2+–93/2+. The contour line separation is 0.25 MeV.located in the minimum at ε2  0.2 give a better agreementwith experiment than those corresponding to the one at largerdeformation.In order to understand the single-particle occupancy of theorbitals for these configurations, calculated Routhians for theappropriate deformation are displayed in Fig. 5. For protons,in the frequency range of h̄ω  0.6–1.0 MeV, configurationswith two g9/2 holes and one or two h11/2 particles are favored;i.e., the π (g9/2)−2(g7/2d5/2)3(h11/2)2 configuration, or [22,..]in the shorthand notation, and the π (g9/2)−2(g7/2d5/2)4(h11/2)1configuration, or [21,..], respectively. Note that similar config-urations based on two-particle-two-hole (2p-2h) excitationsacross the Z = 50 shell gap have been suggested [8] forthe high-spin bands in neighboring 125I and 126Xe. Thefavored neutron configurations have five or six particles inthe h11/2 subshell. In addition, the number of neutrons excitedacross the spherical N = 64 shell gap from the orbitals ofg7/2d5/2 to orbitals of d3/2s1/2 character has to be considered.The neutron configuration ν(g7/2d5/2)−2(h11/2)6(d3/2s1/2)2, or[..,6(00)] in the shorthand notation, is favored in a largefrequency range. This configuration with (π , α) = (+,0),coupled to the (π , α) = (+,1/2) proton configuration [22,..]mentioned above, forms the [22,6(00)] band with (π , α) =(+,1/2). It is yrast in the spin range of I  30–40 witha maximum spin value of Imax = 105/2 and is the mostlikely candidate for band a. At this spin, the potential energyminimum lies close to γ = 60◦, corresponding to terminationin a noncollective state. However, if only the number ofh11/2 particles is fixed in the neutron configuration, the bandcan be followed up to Imax = 113/2 corresponding to theconfiguration (g7/2d5/2)−4(h11/2)6(d3/2s1/2)4.Another low-lying configuration can be obtained by chang-ing the signature of the Nosc = 4 protons in the configurationjust discussed; i.e., the [22,6(00)] configuration with (π , α) =41424344Single-proton energies, ei [MeV]52g9/2h11/2(a)53h11/2h11/24 5 4 6 4 7 4 8 4 9 4 105 1 5 2 0 0.5 1Rotational freqency, h- ω  [MeV]49505152Single-neutron energies, ei [MeV]70(b)i13/2i13/2h 11/2h 11/2f7/2 h9/2h11/24 105 2 5 3 [411] 1/2[402] 5/25 4 [404] 7/25 5 FIG. 5. (Color online) Single-particle (a) proton and (b) neutronenergies as a function of rotational frequency at a deformation of ε2 =0.20. The orbitals are labeled at h̄ω = 0 by the oscillator quantumnumber, Nosc, with the ordering within the Nosc shell as a subscriptor by their Nilsson quantum numbers. A few orbitals importantfor the present interpretation are labeled by their dominating jshell. Note that the [404]7/2 and [402]5/2 neutron orbitals are ofg7/2d5/2 character while [411]1/2 is of d3/2s1/2 character. The linetypes distinguish between different (π , α) combinations: solid linesrepresent (+, +1/2), dotted lines (+, −1/2), dashed lines (−, +1/2),and dash-dotted lines (−, −1/2).(+,−1/2). This configuration with Imax = 103/2 (or 111/2with four Nosc = 4 neutrons excited across the N = 64 gap)may be associated with band c.A favored negative-parity configuration can be formed bycombining the neutron configuration [..,6(00)] with the protonconfiguration [21,..] to give the (π , α) = (−,−1/2) [21,6(00)]band with Imax = 99/2 (or 107/2 with more Nosc = 4 neutronsexcited). This configuration may be associated with band b,provided it has negative parity.It is worth noting that, at the deformation used in Fig. 5, theneutron orbitals emerging from the i13/2 and h9/2f7/2 subshellsabove the N = 82 gap become energetically competitive onlyaround h̄ω = 1.2 MeV. Therefore, they are not active in thecalculated high-spin bands of 123I.The tentatively assigned experimental energies of the bands,relative to the rotating liquid-drop energy, are displayed inpanel (a) of Fig. 6. The calculated energies of the configura-tions assigned to these bands are presented in panel (b). In067305-3BRIEF REPORTS PHYSICAL REVIEW C 86, 067305 (2012)0123(a) Exp123I  (Z=53, N=70)band aband bband c0123E−Erld(def) [MeV](b) CNS calc[22, 6(00)][21, 6(00)][22, 6(00)]51/2 71/2 91/2 111/2Spin, I [h-]-101Etheo.−Eexp.(c) Differenceband a - [22, 6(00)]band b - [21, 6(00)]band c - [22, 6(00)]FIG. 6. Comparison between the experimentally observed rota-tional bands in 123I (a) and the CNS predictions for the [22,6(00)] and[21,6(00)] configurations (b). Panel (c) shows the energy differencebetween theory and experiment.panel (c), the differences between calculated and experimentalenergies are plotted. With the present tentative spin and parityassignments, good agreement between theory and experimentis achieved. For these configuration assignments the observedbands in 123I reach spins close to the Imax value of therespective configurations. However, these configurations arecalculated to remain somewhat collective at the highestspins [15].Furthermore, it is interesting to note that, although almostall the highly deformed bands in the mass A ∼ 125 regionhave the same proton configuration; i.e., they involve twoholes in the g9/2 subshell, the neutron configurations appearto be different. Whereas the bands in 120Te (N = 68) and123I (N = 70) may be assigned to configurations withoutneutron excitations across the N = 82 shell gap, the bandsin 125Xe (N = 71), 125I (N = 72), and 126Xe (N = 72) havebeen suggested to be based on configurations involving suchexcitations. Note, however, the problems with the descriptionof several of the collective bands in the latter nuclei, as pointedout in Ref. [8]. These inconsistencies should be addressed infurther theoretical investigations.The authors thank A. O. Macchiavelli for his help duringthe experiment, and the ANL operations staff of ATLASand Gammasphere for their support. Purnima Singh acknowl-edges CSIR India for financial support, under Contract No.9/81(1108)/10-EMR-I. This work was supported by the DSTIndia, by the German BMBF under Contract No. 06 BN109, by the Swedish Natural Science Research Council, byOTKA, Hungary, under Contract No. K72566, by the NewHungary Development Plan under Contract No. TÁMOP4.2.1./B-09/1/KONV-2010-0007/IK/IT, by the Danish FNUCouncil for Natural Sciences, and by the US Demartmentof Energy, Office of Nuclear Physics, under Contracts No.DE-AC02-06CH11357 and No. DE-AC02-05CH11231.[1] E. S. Paul et al., J. Phys. G 19, 913 (1993).[2] P. Singh et al., Phys. Rev. C 85, 034319 (2012).[3] P. Singh et al., Phys. Rev. C 82, 034301 (2010).[4] A. Al-Khatib et al., Eur. Phys. J. A 36, 21 (2008).[5] A. K. Singh et al., Phys. Rev. C 70, 034315 (2004).[6] A. Al-Khatib et al., Phys. Rev. C 74, 014305 (2006).[7] S. Nag et al., Phys. Rev. C 85, 014310 (2012).[8] P. Singh et al., Phys. Rev. C 84, 024316 (2011).[9] A. Al-Khatib et al., Phys. Rev. C 83, 024306 (2011).[10] C. Ronn Hansen et al., Phys. Rev. C 76, 034311 (2007).[11] I. Y. Lee et al., Nucl. Phys. A 520, 641c (1990).[12] A. V. Afanasjev, D. B. Fossan, G. J. Lane, and I. Ragnarsson,Phys. Rep. 322, 1 (1999).[13] T. Bengtsson and I. Ragnarsson, Nucl. Phys. A 436, 14(1985).[14] B. G. Carlsson and I. Ragnarsson, Phys. Rev. C 74, 011302(R)(2006).[15] J. J. Valiente-Dobón et al., Phys. Rev. Lett. 95, 232501 (2005).067305-4

High-spin rotational bands in  123 I

https://openresearch-repository.anu.edu.au/bitstream/1885/69830/2/01_Singh_High-spin_rotational_bands_in__2012.pdf

High-spin rotational bands in 123 I

Abstract

Similar works

Full text

Available Versions

The Australian National University