The Effect Of The Shape Driving In The γ-soft Nucleus Of Fast Rotation

This thesis introduces some basic theories about high spin state physics firstly. They include mainly the independent particle model which is based on the mean field of Nilsson potential, the pair theory which is performed using the superconduct thought or Bogoliubov transformation, the cranking shell model which can deal with single particle movement and collective movement simultaneously and the Hatree-Fock-Bogoliubov-Cranking theory which is based on these basic theories. Whereafter we make mention of the basic theory model which we apply in the thesis later, viz. the calculating model of potential surface, and discuss the source and solution of every term..Especially we discuss the solution of the term of liquid drop energy in detail.According to the in-beam experiment of ¹²⁹Cs which was completed on the HI-13 tandem accelerator of CIAE, the method of experiment of high spin state and the process of experiment are introduced. According to the out-beam data analysis, we have expanded the energy scheme of ¹²⁹Cs. We have pushed the states of partial rotating bands to higher spin. Then we introduce the universal phenomenon of backbanding in the high spin state physics and discuss the reason of it.The TRS program which we apply in the theoretical analysis is based on the Nilsson—Strutinsky—Cranking model . This program is written by Y.S.Chen and Frauendorf, and we have mended it partially. Using the program firstly we calculate separately the liquid drop potential,shell correction potential,pair potential and the potential surface of the core of ¹²⁹Cs. Meanwhile we have discussed the effect of them in driving the shape of the nucleus, and acquire the deformation value of the core, and identify theγ-soft of ¹²⁹Cs. Then we have discussed the effect of the different single quasi-particle driving potential to the nuclear shape in detail, we have found that the quasi-particle of high j orbit influences the shape of nucleus abundantly. Whileω= 0.02ω₀ , according to the calculation we have acquired the deformation value of 1/2[550]( 1h_11/2),3/2[422](1g_7/2 ),1/2[420](2d_5/2 ) state of ¹²⁹Cs. Going with the increase of the rotating frequency, whileω= 0.05ω₀ , we have calculated the deformation value of 1/2[550](1h_11/2),3/2[422](1g_7/2)state after the backbanding, namely the three quasi-particle band after a pair of neutrons having aligned. According to the comparison we have found a distinct change of deformation value before and after the band crossing, which changes fromγ～0°toγ= -60°. This can display theγ-soft character of the ¹²⁹Cs and we can conclude that this change ought to reduce the signature split through the band crossing, and the conclusion accords with the experiment, so we can explain the correctness of the state which we suppose. In order to acquiring more systemic conclusions, we execute calculation versus ¹²⁵Cs,¹²⁷Cs as we do previously, and acquire the deformation value of the two nuclear cores and 1/2[550]( ),3/2[422]( )state bands. We can see the common character of ¹²⁹Cs,¹²⁷ Cs,¹²⁵Cs :γ-soft. And after the alignment of quasi-particle theγdeformation value will move towardsγ=-60°. We have found that for the ¹²⁵Cs > ¹²⁷ Cs >¹²⁹CsAssociated with the up-tilted and down-tilted shape of Nilsson orbit we can explain the reason of the absence of the state in ¹²⁹Cs and the absence of the d_5/2 [420]1/2 state in¹²⁵Cs. Likewise we have executed the CSM calculation versus ¹²⁷Cs,¹²⁵Cs and have acquired the crossing frequency, which we compared with the experiment value.