The yrast structure of 207Pb above the 13=2+ isomeric state has been investigated in deep-inelastic collisions of 208Pb and 208Pb at ATLAS, Argonne National Laboratory. New and previously observed transitions were measured using the Gammasphere detector array. The level scheme of 207Pb is presented up to ∼ 6 MeV, built using coincidence and γ-ray intensity analyses. Spin and parity assignments of states were made, based on angular distributions and comparisons to shell model calculations

Bowry, M.

Brown, B.A.

Bunce, M.

Carpenter, M.P.

Carroll, R.J.

Chiara, C.J.

Cieplicka-Oryńczak, N.

Deo, A.Y.

Dracoulis, G.D.

Fornal, B.

Grawe, H.

Hoffman, C.R.

Janssens, R.V.F.

Kempley, R.S.

Kondev, F.G.

Lane, G.J.

Lauritsen, T.

Lotay, G.

Podolyák, Zs.

Reed, M.W.

Regan, P.H.

Rodriguez-Triguero, C.

Seweryniak, D.

Shand, C.M.

Szpak, B.

Walker, P.M.

Wilson, E.

Zhu, S.

Carolina Digital Repository

Vol. 46 (2015) ACTA PHYSICA POLONICA B No 3STRUCTURE OF 207Pb POPULATED IN 208Pb + 208PbDEEP-INELASTIC COLLISIONS∗C.M. Shanda, E. Wilsona, Zs. Podolyáka, H. GrawebB.A. Brownc, B. Fornald, R.V.F. Janssense, M. BowryaM. Buncea, M.P. Carpentere, R.J. Carrolla, C.J. Chiarae,fN. Cieplicka-Oryńczakd, A.Y. Deog, G.D. DracoulishC.R. Hoffmane, R.S. Kempleya, F.G. Kondevi, G.J. LanehT. Lauritsene, G. Lotaya,j, M.W. Reeda, P.H. Regana,jC. Rodriguez-Triguerok, D. Seweryniake, B. SzpakdP.M. Walkera, S. ZhueaDepartment of Physics, University of Surrey, Guildford, GU2 7XH, UKbGSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, GermanycNational Superconducting Cyclotron Laboratory and Dept. of Physics andAstronomy, Michigan State University, East Lansing, MI 48824, USAdThe Henryk Niewodniczański Institute of Nuclear Physics, Kraków, PolandePhysics Division, Argonne National Laboratory, Argonne, IL 60439, USAfDepartment of Chemistry and Biochemistry, University of MarylandCollege Park, MD 20742, USAgDept. of Physics, University of Massachusetts Lowell, Lowell, MA 01854, USAhResearch School of Physics and Engineering, Australian National UniversityCanberra, ACT 0200, AustraliaiNuclear Eng. Division, Argonne National Laboratory, Argonne, IL 60439, USAjNational Physics Laboratory, Teddington, TW11 0LW, UKkSchool of Computing, Engineering and Mathematics, University of BrightonBrighton, BN2 4GL, UK(Received January 29, 2015)The yrast structure of 207Pb above the 13/2+ isomeric state has beeninvestigated in deep-inelastic collisions of 208Pb and 208Pb at ATLAS, Ar-gonne National Laboratory. New and previously observed transitions weremeasured using the Gammasphere detector array. The level scheme of207Pb is presented up to ∼ 6 MeV, built using coincidence and γ-ray inten-sity analyses. Spin and parity assignments of states were made, based onangular distributions and comparisons to shell model calculations.DOI:10.5506/APhysPolB.46.619PACS numbers: 29.30.Kv, 23.20.Lv, 23.20.En, 21.60.Cs∗ Presented at the Zakopane Conference on Nuclear Physics “Extremes of the NuclearLandscape”, Zakopane, Poland, August 31–September 7, 2014.(619)620 C.M. Shand et al.1. Introduction207Pb is a one-neutron-hole nucleus with respect to the doubly-magic208Pb core. The low-lying single-particle states of 207Pb are described bythe νp−11/2, νf−15/2, νp−13/2, and νi−113/2 orbitals. The 13/2+ single-particle stateis isomeric with a half-life of t1/2 = 0.806(5) s [1]. Little is known concerningthe structure of the yrast states above 13/2+, which require the core to bebroken. It is expected that the νi−113/2 state will couple to states within the208Pb core to produce core-breaking states.Schramm et al. were the first to suggest that a 2485 keV transition liesabove the 13/2+ state in 207Pb [2]. The 2485 keV transition was placedconnecting a (19/2−) state to the 13/2+ isomer, with the expectation thatit is a collective E3 transition. Also placed at the time were six new tran-sitions in coincidence with the 2485 keV γ ray, with the spin and parityassignments of the corresponding depopulated states based purely on shellmodel calculations. The level scheme up to Iπ = (29/2+) was suggested.2. Experiment and resultsThe experiment was conducted at the ATLAS facility at Argonne Na-tional Laboratory, USA. A 75 mg/cm2 thick target of 208Pb was bombardedwith a 1446 MeV beam of 208Pb. γ rays following deep-inelastic collisionswere detected by the Gammasphere detector array. Experimental details ofthis reaction are elaborated in [3].The γ-ray spectrum gated on the known 2485 keV 207Pb transition isshown in Fig. 1. All previously identified γ-ray transitions are present in thegated spectrum. In addition, several new γ rays are visible, including two at412 and 569 keV. The focus of the work presented here is the level schemeup to ∼ 6 MeV; thus, a number of the new transitions observed are notdiscussed. Angular distribution spectra were produced with a single gate on 0 5000 10000 15000 20000 0  200  400  600  800  1000CountsEγ [keV]$ 231# 323$ 329 $ 366# 383$ 412$ 569# 592# 626$ 696# 749$ 788# 793$ 939$ 987#  previously seen$  newFig. 1. Spectrum gated on the 2485 keV 207Pb transition, showing transitionsabove the 13/2+ isomeric state. Indicated are, transitions previously seen [2] anda number of new transitions identified in this work.Structure of 207Pb Populated in 208Pb + 208Pb Deep-inelastic Collisions 6212485 keV, except for the 2485 keV angular distribution spectra which wereungated. Subsequent angular distributions were fitted with the function ofthe standard form W (θ) = A0{1 +A2P2(cos θ)}, where θ is the angle of theγ ray relative to the beam, Ai are the angular distribution coefficients, andPi are the Legendre polynomials. From measurements of intense transitionsin 208Pb with known multipolarities, we expect stretched transitions to have:A2 ∼ 0.36 for an octupole, A2 ∼ 0.22 for a quadrupole, and A2 < 0 for adipole [4].Angular distributions are shown in Fig. 2, along with the fitted A2 co-efficient values and deduced multipolarities. Spins and parities of the stateswere assigned based on the γ-ray multipolarities. Parities of the 23/2(−)2and 29/2(+) states were ascertained from the shell model calculations. Thededuced level scheme up to ∼ 6 MeV, shown in Fig. 3, is in agreement withthe previous work of Schramm et al. [2]. A 57 keV γ ray is inferred fromcoincidence relationships.0.30.81.31.8323 keV (D)A2 = -0.03(5)383 keV (D)A2 = -0.13(3)412 keV (D, ∆Ι=0)A2 =  0.48(13)0.30.81.3W(θ)/A0568 keV (D)A2 = -0.04(8)592 keV (M1+E2)A2 = -0.64(4)626 keV (E2)A2 =  0.22(5)0.30.81.30.0 0.3 0.6 0.9749 keV (E2)A2 =  0.15(2)0.0 0.3 0.6 0.9cos2θ793 keV (E2)A2 =  0.10(7)0.0 0.3 0.6 0.92485 keV (E3)A2 =  0.34(2)Fig. 2. Angular distributions of transitions in 207Pb above the 13/2+ isomeric state.Deduced multipolarities are indicated, D denotes dipoles.Two shell model calculations were performed using the KHH7B andKHM3Y interactions, descriptions of which can be found in [4]. The KHH7Bcalculation used in this work differs from the prescription in [4], in that t = 1proton and neutron mixing is considered. Figure 3 compares the calcula-tions to the experiment, displaying a good agreement. The differences be-tween the calculations become apparent when looking to the octupole state,19/2−. Variations in the octupole state can be explained by the number of∆j = ∆l = 3 pairs in each calculation, as discussed in [4].622 C.M. Shand et al.2485.5592.5 749.1412.4 569.057.4626.4383.4365.9323.4793.213/2 163319/2 411921/2 471123/2 486823/2( ) 528025/2 533827/2 566129/2( ) 60457727809313/2 163319/2 399621/2 483523/2 489825/2 544827/2 564829/2 631429/2 632431/2 628635/2 752937/2 806523/2 537135/2 796435/2 842319/2 467521/2 468623/2 484025/2 525827/2 548831/2 603229/2 609829/2 611335/2 732635/2 767337/2 787639/2 825513/2 163331/2 690231/2 700131/2 726031/2 733231/2 748231/2 757733/2 711133/2 719023/2 5196 i13/2-1 i13/2-1  3- i13/2-1 g9/2 p1/2-1 i13/2-1 g9/2 f5/2-1 i13/2-1 j15/2 p1/2-1207PbExpKHM3Y KHH7BFig. 3. Experimental level scheme of 207Pb above the 13/2+ isomer, compared totwo shell model calculations described in [4].3. ConclusionThe level scheme of 207Pb up to ∼ 6 MeV is presented, and is in agree-ment with the previous work by Schramm et al. [2]. An additional excitedstate and three γ rays were identified. Our spin and parity assignments arebased on angular distribution measurements. Future work will detail theextension of the 207Pb level scheme to ∼ 10 MeV.This work is supported by the U.S. Department of Energy, Office ofNuclear Physics, under Contract No. DE-AC02-06CH11357 and the Scienceand Technology Facilities Council (STFC), UK. The contributions of theArgonne National Laboratory technical staff are gratefully acknowledged.REFERENCES[1] F. Kondev, S. Lalkovski, Nucl. Data Sheets 112, 707 (2011).[2] M. Schramm et al., Z. Phys. A344, 121 (1992).[3] E. Wilson et al., Acta Phys. Pol. B 44, 381 (2013).[4] Zs. Podolyák et al., J. Phys.: Conf. Ser. 580, 012010 (2015).

Structure of 207Pb populated in 208Pb + 208Pb deep-inelastic collisions

https://cdr.lib.unc.edu/downloads/05742293c

Structure of 207Pb populated in 208Pb + 208Pb deep-inelastic collisions

Abstract

Similar works

Full text

Available Versions

Carolina Digital Repository