(178) Of Os Nuclear Excited State Lifetime Measurements,

In 1988, J.Burde and his colleagues in Lawrence Berkeley Laboratory studied the high spin states in ¹⁷⁸Os populated via heavy ion fusion evaporation reaction ¹⁵⁴Sm(²⁹Si,5n)¹⁷⁸Os. In their research, an unusual rotational band was found, it consists of seven regularly spaced transitions about 36 keV apart, which correspond closely to that of the super deformation band in ¹⁵²Dy. But, the moment of inertia J⁽¹⁾ is found to be much smaller than the J⁽²⁾. Therefore, it is necessary to determine the deformation of these states through lifetime measurement.The experiment was carried out in September of 2004, the fusion evaporation reaction ¹⁵⁴Sm(²⁹Si,5n) ¹⁷⁸Os with beam energy 155MeV was used to populate the high spin states of ¹⁷⁸Os, the target consists of a 1.4mg/cm² Sm foil, which was evaporated onto a 20mg/cm² Pb foil. Theγrays emitted by the reaction products were observed by 14 Compton-suppressed HPGe detectors, 115 million two fold and higher-fold events in total were recorded.Through comparison of the quadrupole deformationβ₂ of the first 2⁺ states in the Os isotopes, the magnitude increases when moving toward the middle shell between the neutron magic number 82 and 126 except ¹⁷⁴Os. In this work Doppler shift attenuation method was used to measure the states of 8⁺ to 16⁺ in the ground states band in ¹⁷⁸Os, through comparison with transition quadrupole moments Qt of 8⁺ and 10⁺ states, our data agree well with those A.D ewald and his colleagues derived through RDDS method, the quadrupole deformationβ₂ is also derived, its average magnitude is 0.28, in large spin range, theβ₂ is almost not change, it indicates that in the spin range from 8 to 14 h in the ground states band ¹⁷⁸Os is a good rigid rotor.