普适费米气体型能级密度公式及其参数

A Universal Nuclear Level Density Formula and Its Parameters

在费米气体模型基础上,考虑了低能修正,建立起了普适费米气体型能级密度公式。使用27.8个核素的平均中子共振间隔D数据及268个核素的能级累计数sN(E)数据,用最小二乘法,在高速计算机上拟合得到了一组普适参数。使用这组参数,D计算值的平均相对误差为36.51％,比实验值平均相对误差(26.69％)高38.6％。能级累计数N(E)的计算结果也有较大改进,其平均相对误差为40.56％,仅比在D计算值的平均相对误差高 14.3％。我们用若干组不同参数分别计算诸核素的D值和N(E)值,相对误差控制在20％以内。然后按核素列出它们的实验值和计算值,连同其相应参数,均在附录中给出,以便查阅。

In this paper a universal nuclear level density formula is proposed. At higher excitation the recommended level density is adopted and at low excitation energies we in- troduced a low-energy correction to modify the Fermi gas one. From the experimental data of the mean neutron resonance spacing D-exp for 278 nuciel and cumulative num- bers of levels N (E) at low energies for 268 nuclei, a set of optimum parameters is deter- mined. with these parameters the calculated average relative error of mean neutron reso- nances spacing D is no more than 36. 51% for 278 nucei, higher than the experimental av- erage relative error (26. 69%) by about 38. 6%. For the cumulative numbers of levels N (E), the calculated average relative error is no more than 40. 56% for 268 nuclei, higher than the average relative error of D-cal by about 14. 3%. If we use a few groups of these parameters, the calculated values of are in good agreement with observed values for all of the 278 nuclei, 50 do the calculated values of-cumulative number of D levels N (E). We tabulate the results in appendix.