Shape coexistence of neutron-rich $^{69,71,73}$Co isotopes

4 Jun 2018, 11:03
Kunibiki Messe (Matsue)

Kunibiki Messe


Oral contribution Session 2


Mr Taras Lokotko (The University of Hong Kong)


Observation of high 2$^{+}$ excitation energy in $^{68}$Ni (Z = 28, N = 40) had drawn a clear signature of double magic character in this nucleus [1]. And while $^{68}$Ni can be described as spherical isotope, 2$^{+}$ excitation energy of $^{66}$Fe drops significantly [2], indicating deformed shape of $^{66}$Fe. $^{67}$Co isotope is in between $^{68}$Ni and $^{66}$Fe nuclei and found to share coexistence of both spherical and deformed structures in low-lying excited states [3]. This effect can be described as superposition of a proton f$_{7/2}$ hole coupled to neighbouring spherical even-even nickel isotope and a prolate proton-intruder state coupled to the $^{66}$Fe isotope [4]. Discovery of shape coexistence in $^{67}$Co rose an interesting question about further shape evolution in Co nuclei, namely $^{69,71,73}$Co and shell transformation from N = 40 to N = 50.
In-beam gamma experiment was performed at Radioactive Isotope Beam Factory, RIKEN Nishina centre, Japan. Secondary beam of $^{70,72,74}$Ni and $^{72}$Co isotopes at energy of 260 MeV/µ bombarded liquid hydrogen target (MINOS) to produce $^{69,71,73}$Co nuclei via (p, 2p) and (p, pn) reactions. DALI2 NaI(Tl) detector array was used to measure $\gamma$-rays. Energy levels were studied using $\gamma$-$\gamma$ coincidence technique. Systematics of excited states of cobalt isotopes was compared with Lenzi-Nowacki-Poves-Sieja (LNPS) model [5] of nuclear interaction using fpgd model space. Experimental results of $^{69,71}$Co spectrums show that isotopes share shape coexistence, as spherical structure coexists with deformed band. In case of $^{73}$Co nucleus, due to the lack of statistics only spherical band is confirmed.
In this talk the evolution of shell structure in $^{69,71,73}$Co isotopes will be discussed together with physics behind the shape coexistence in neutron-rich Co nuclei.

1. R. Broda, B. Fornal, W. Krolas, and T. Pawkat, Phys. Rev. Lett. 74, 868 (1995);
2. S. Lunardi, S. M. Lenzi, F. Della Vedova, Phys. Rev. C, 76, 034303 (2007);
3. F. Recchia et al., Phys. Rev. C 85, 064305 (2012);
4. D. Pauwels et al., Phys. Rev. C 78, 041307(R) 2008;
5. S. M. Lenzi, et. al., Phys. Rev. C 82, 054301 (2010).

Primary authors

Dr Jenny Lee (The University of Hong Kong) Mr Taras Lokotko (The University of Hong Kong)


Dr Alexandre Obertelli (TU Darmstadt) Dr Alfredo Poves (Departmento de Fiica Teorica and IFT-UAM/CSIC, Universidad Aut ́onoma de Madrid) Dr Frédéric Nowacki (Institut de Recherches Subatomiques (IN2P3-ULP) F 67037 Strasbourg Cedex 2, France) Dr Pieter Doornenbal (RIKEN) Dr Sylvain LEBLOND (Laboratoire de Physique Corpusculaire de Caen (LPC Caen))

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