THE PROTON-RICH N = 82 AND N = 83 NUCLEI THULIUM-151, HOLMIUM-150, ERBIUM-151, AND THULIUM-152

The yrast level structures of the proton-rich N = 82 and N = 83 nuclei ('151)Tm, ('150)Ho, ('151)Er, and ('152)Tm have been investigated by in-beam (gamma)-ray spectroscopy following reactions induced by 240-255 MeV ('58)Ni and ('60)Ni beams. The five valence proton N = 82 nucleus ('151)Tm was studied using the ('96)Ru(('58)Ni,3p) reaction. Of particular interest are the 31/2('-) and 35/2('-) yrast levels in ('151)Tm at 3988 and 4613 keV, which are interpreted as seniority-five members of the (pi)h(,11/2)('5) spectrum. The experimental ph(,11/2)('5) level spacings are found to agree fairingly well with calculations based on empirical proton-proton interactions taken from ('148)Dy, but much better with the results of a fractional parentage reduction procedure which also takes account of experimental (pi)h(,11/2)('3) energies in ('149)Ho. Similar experimental methods were used to investigate the odd-odd N = 83 isotones ('150)Ho and ('152)Tm, produced by the reactions ('92)Zr(('60)Ni,pn), ('93)Nb(('60)Ni,2pn), and ('94)Mo(('60)Ni,pn). The ('150)Ho level scheme was constructed up to a 751 nsec isomer at (TURN)7.9 MeV, and the ('152)Tm level scheme up to a 42 nsec isomer at 6280 keV. In both nuclei, states with the configuration (pi)h(,11/2)('n)(nu)f(,7/2) form the main yrast sequences up to 17('+) isomers at 2625 keV in ('150)Ho (T(,1/2) = 84 nsec) and at 2555 keV in ('152)Tm (T(,1/2) = 294 nsec). Other levels located in both nuclei are described as 9('+) x 3('-) octupole, (pi)h(,11/2)('n)(nu)i(,13/2) v = 2, (pi)h(,11/2)('n-1)s(,1/2)(nu)f(,7/2) v = 4, and (pi)h(,11/2)('n-1)d(,3/2)(nu)f(,7/2) v = 4 states, which extend the systematics of such excitations in the N = 82 and N = 83 isotones. Two strongly populated levels in ('152)Tm, which have no observed counterparts in ('150)Ho, are interpreted as (pi)h(,11/2)('n)(nu)h(,9/2) 9('+) and 10('+) states. The even-odd N = 83 nucleus ('151)Er was studied using the ('94)Mo(('60)Ni,2pn) and ('93)Nb(('60)Ni,pn) reactions. The yrast level scheme was constructed up to a 625 nsec isomer at (TURN)10.2 MeV, but there are many uncertainties in transition ordering, and only a few spin-parity assignments are made. The decay of a previously reported 0.62 sec isomer at (TURN)2.5 MeV was confirmed, and it is interpreted by analogy with the decay of the known 0.50 sec ((pi)h(,11/2)('2)(nu)f(,7/2))27/2('-) isomer in the ('149)Dy isotone. The energy of the missing 27/2('-) (--->) 21/2('+) E3 transition in ('151)Er was shown to be less than 80 keV. (Abstract shortened with permission of author.)