First observation of high spin states in90Tc

Abstract

Abstract. High spin states in 9~ have been studied via the ~8Ni (35C1, 2pn) 9~ reaction at beam energy of 124 MeV. Twenty-six new 7-rays were observed, a new level scheme was established and spins were assigned. Two band-like structures were established up to about 20 h with an excitation energy of 6-7 MeV. The band (B) shows collective characteristic at high spin. We suggest it to be of a quasi-particle configuration rCgg/2@vfs/2. 23.20.Lv; 27.60.+j The interest in the study of high spin states in 9~ originates from the systematics and observed deformation changes of the transitional nuclei with three neutron holes to the closure shell N= 50. So far, threre is no information about high spin states of 9~ but two isomers are known to have half-lives of 7.9 s and 50.0 s [1]. PACS: The nucleus 9~was populated through the ~SNi(~Cl, 2pn) 9~ reaction using the 124MeV 35C] beam provided by the HI-13 Tandem accelerator of CIAE in Beijing. The target was a 2 mg/cm 2 SSNi enriched to 99.8% and evaporated on a 30mg/cm 2 Pb backing. Gamma-gamma coincidences were measured by five BGO-HPGe spectrometers equipped with Compton suppression shields, neutron-gamma coincidence was selected by six NE213 neutron detectors, DCO ratios were deduced from a pair of detectors placed at 88 ~ and 32 ~ with respect to the beam, and excitation functions were recorded in the energy interval of 108-132 MeV.In order to confirm the population of 9~ the ),-ray decay was measured for 10 s after 5 s of irradiation at the beginning of the experiment. The y-rays of 1054 keV, 948 keV and 810 keV belonging to low-lying excited states of 9~ populated in the 9~ decay are very clearly seen. These ~-rays are also observed in prompt y-~ coincidences in the spectrum gated by 511 keV y-ray originating

TheN=47 shell model nucleus90Tc

“…The irregularity of the lifetimes of other levels and the small deduced B(E2) values do not support the interpretation by Zhang et al [21], who proposed rotational structures of both the positive and negative parity cascades built upon the 1939 keV 12 + and 1995 keV 11-states. Most of the lifetimes lie between 1 and 5 ps, only the yrast and yrare 11 -states have significantly longer lifetimes of 48(6) and 19(3) ps.…”