Spectroscopy of 193Bi

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Spectroscopy of 193Bi Herzan, Andrej; Juutinen, Sakari; Grahn, Tuomas; Greenlees, Paul; Hauschild, Karl; Jakobsson, Ulrika; Jones, Peter; Julin, Rauno; Ketelhut, Steffen; Leino, Matti; LopezMartens, Araceli; Nieminen, Päivi; Nyman, M.; Peura, Pauli; Rahkila, Panu; RintaAntila, Sami; Ruotsalainen, Panu; Sandzelius, Mikael; Sarén, Jan; Scholey, Catherine; Sorri, Juha; Uusitalo, Juha Herzan, A., Juutinen, S., Grahn, T., Greenlees, P., Hauschild, K., Jakobsson, U., Jones, P., Julin, R., Ketelhut, S., Leino, M., Lopez-Martens, A., Nieminen, P., Nyman, M., Peura, P., Rahkila, P., Rinta-Antila, S., Ruotsalainen, P., Sandzelius, M., Sarén, J., . . . Uusitalo, J. (2014). Spectroscopy of 193Bi. In S. Lunardi, P. Bizzeti, S. Kabana, C. Bucci, M. Chiari, A. Dainese, P. D. Nezza, R. Menegazzo, A. Nannini, C. Signorini, & J. Valiente-Dobon (Eds.), INPC 2013 – International Nuclear Physics Conference Firenze, Italy, June 2-7, 2013 (Article 02047). EDP Sciences. EPJ Web of Conferences, 66. https://doi.org/10.1051/epjconf/20146602047 2014 Spectroscopy of 193Bi A. Herzᡠn1,a, S. Juutinen1, T. Grahn1, P.T. Greenlees1, K. Hauschild1,2, U. Jakobsson1, P. Jones1,3, R. Julin1, S. Ketelhut1,4, M. Leino1, A. Lopez-Martens1,2, P. Nieminen1, M. Nyman5, P. Peura1, P. Rahkila1, S. Rinta-Antila1, P. Ruotsalainen1, M. Sandzelius1, J. Sarén1, C. Scholey1, J. Sorri1, and J. Uusitalo1 1Department of Physics, University of Jyväskylä, P.O. Box 35, Jyväskylä FI-40014, Finland 2CSNSM , IN2P3-CNRS, F-91405 Orsay Campus, France 3iThemba Laboratory for Accelerator Based Sciences, P.O. Box 722, 7129 Somerset West, South Africa 4TRIUMF, Westbrook Mall, Vancouver, BC, V6T 2A3, Canada 5European Commission, Joint Research Centre, IRMM, Retieseweg 111, B-2440 Geel, Belgium Abstract. An experiment aiming to study the shape coexistence in 193Bi has been performed at the Accelerator laboratory of the University of Jyväskylä, Finland (JYFL). Many new states have been found, hugely extending the previously known level scheme of 193Bi. The Iπ=29 2 +member of the πi13/2band de-excites also to the previously, only tentatively placed long-lived isomeric state. This link determines the energy of the isomeric state to be 2260(1) keV and suggests a spin and parity of 27 2 +. The half-life of the isomeric state was measured to be 84.4(6) µs. A level structure on top of this isomeric state was constructed. However, transition directly depopulating this state could not be identified. A superdeformed band almost identical to that present in the neighboring isotope 191Bi has been identified. 1 Introduction In certain nuclear mass regions, low-lying excited states can be associated with a variety of nuclear shapes. One such region with the large selection of nuclei in which coexistent deformed configurations at relatively low excitation energies have so far been observed, has a proton number close to the magic Z=82 and lie in the neutron mid-shell region. There have been two main approaches on how to explain these structures, namely either the intruder picture, associated with shell-model intruder states formed by exciting protons across the magic shell gap [1] or an alternative approach provided by the Nilsson model [2]. As the bismuth nuclei have only one extra proton coupled to Z=82 proton magic lead core, 193Bi is a unique nucleus for the investigation of the shape coexistence and studies of the isomeric states built on the multiquasiparticle configurations. 193Bi has shown itself to be just on the edge between very neutron deficient odd-A prolate bismuth nuclei on the left [3] and heavier odd-A bismuth isotopes with the absence of any regular bandlike structures for the low-lying states on the right in the chart of nuclei [4]. Moreover, searching for highly excited superdeformed bands for better understanding of nuclear properties under extreme deformation has proven itself to be very efficient in this region of the nuclear chart [5]. a. e-mail: [email protected] DOI: 10.1051/ C Owned by the authors, published by EDP Sciences, 2014 , / 02047 (2014) 201 66 epjconf EPJ Web of Conferences 46602047 This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article available at http://www.epj-conferences.org or http://dx.doi.org/10.1051/epjconf/20146602047 2 Experimental setup The 193Bi nuclei were produced in the total fusion-evaporation reaction 165Ho(32S,4n)193Bi at the bombarding energy of 152 MeV. The reaction products were studied using in-beam γ-ray spectroscopy combined with decay spectroscopy. The fully digitized JUROGAM2 array was used to detect prompt γrays at the target position. The array consisted of 24 Clover and 10 Phase1 or GASP Comptonsuppressed HPGe-detectors. The JUROGAM2 array was coupled to the gas-filled high-transmission recoil separator RITU [6] to separate the nuclei of interest from the unwanted beam and beam-like components. The ions transported through the separator were subsequently implanted in the GREAT focal plane spectrometer system [7] for the identification of fusion products of interest. The main instrument of the GREAT spectrometer - the double-sided silicon strip detector (DSSD) was used for the implantation of the fusion evaporation recoils and for the detection of their subsequent decays such as αdecay (DSSD-Y side) or internal conversion (DSSD-X side). To collect the αparticles and conversion electrons that have escaped from the DSSD, the PIN silicon detectors were mounted in a box arrangement upstream from the DSSD. A planar Ge-detector was mounted directly behind the DSSD to detect low energy γrays and X-rays. A set of three clover Ge-detectors was added to face the GREAT chamber from the sides and from above to detect higher energy γrays. All data channels were recorded synchronously using the triggerless total data readout (TDR) [8] data acquisition system. This allowed for using the very selective recoil-decay tagging, isomer-tagging and recoil gating techniques [9]. 3 Results 3.1 Long-lived isomer In the present work, the half-live and excitation energy of the long-lived isomer, only tentatively placed in the previous work [10], together with the transitions (see Fig. 1) feeding the isomeric state, have been unambiguously determined: T1/2=84.4(6) µs (see Fig. 2), Eex =2260(1) keV. This isomeric state is partially populated by the decay of the recently found higher lying states of the πi13/2band, indicating the spin and parity of this state to be 27 2 +. The spin and parity of the states shown in Fig. 1 have been determined and confirmed, respectively, by the angular distribution (DCO) and γ-ray linear polarization measurements. We suggest the configuration of this isomer to be πh9/2 coupled to the isomeric 9−state of the 192Pb core, which would be the maximum allowed spin for such configuration. Since no transition corresponding to the energy difference of ∼131 keV is seen in the focal plane γ-ray spectra or in the PIN diodes spectra, this isomeric state most likely decays via cascade of the low energy, highly converted transitions, overcoming the spin difference of ∆j=4~ (27 2 +→19 2 +, see Fig. 1). None of these transitions could be firmly identified in the planar Ge-detector intended for detecting low energy γrays or in the PIN diodes meant for detecting conversion electrons. EPJ Web of Conferences 02047-p.2 Figure 1. (Color online) Partial level scheme of 193Bi, showing the structure built on top of the long-lived isomer with only tentative spin assignment of the states, together with the feeding of the long-lived isomer from the upper part of the πi13/2band. Red-border arrow indicates a cascade of the low-energy transitions discussed above. Figure 2. Time difference spectrum of the recoil formation and observation of the 455 keV transition (as one of the many transitions below the long-lived isomer) in the focal plane clover detector. The exponential decay law was fitted to the data and is shown as the solid line through data points. INPC 2013INPC 2013 02047-p.3 3.2 Superdeformed band A superdeformed band has been identified in 193Bi. The spectrum gated on the transitions in band is shown in Fig. 3. In contrast with 193Bi, two superdeformed bands have been found in 191Bi [11]. They are interpreted as signature partner bands built on the proton i11/21 2 +[651] configuration. The newly found band in 193Bi is identical to the other of the bands in 191Bi. In both nuclei, superdeformed bands were found in the data obtained by tagging on alpha decays of the 1 2 +intruder states. However, no connecting links have been found yet. Figure 3. The γ-ray spectrum of the superdeformed band assigned to 193Bi as found in the 1 2 +proton intruder α-decay tagged spectrum. 4 Acknowledgments This work was supported by the Academy of Finland under the Finnish CoE Programme. The authors would like to thank the GAMMAPOOL European Spectroscopy Resource for the loan of germanium detectors for JUROGAM II. References [1] K. Heyde, P. Van Isacker, M. Waroquier, J.L. Wood and R.A. Meyer, Phys. Rep. 82, 291 (1983) [2] S.G. Nilsson, Kgl. Dan. Viden. Selsk. Mat. Fys. Medd. No. 16, 29 (1955) [3] A. Hürstel et al., Eur. Phys. J. A 15, 329 (2002) [4] T. Chapuran et al., Phys. Rev. C 33, 130 (1986) [5] R.M. Clark et al., Phys. Rev. C 53, 117-123 (1996) [6] J. Sarén et al., Nucl. Instr. and Meth. A 654, 508-521 (2011) [7] R.D Page et al., Nucl. Instr. and Meth. B 204, 634-637 (2003) [8] I.H. Lazarus at al., IEEE Trans. Nucl. Sci. 48, 567 (2001) [9] P. Rahkila, Nucl. Instr. and Meth. A 595, 637-642 (2008) [10] P. Nieminen et al., Phys. Rev. C 69, 064326 (2004) [11] M. Nyman, PhD Thesis, JYFL Research Report 12/2009 EPJ Web of Conferences 02047-p.4