Theoretical Nuclear Structure Physics

我们的目标是从第一性原理——即从自由核子-核子（强）相互作用和多体量子力学的角度来理解原子核的结构。为了达到这个目的，我们开发了一种新的“从头开始”的shell模型方法，我们在其中处理所有的问题。核子在一个非常大的基（模型）空间中作为活跃粒子。我们现在有了计算机代码，使我们能够对A=16以内的核（即16个活跃核子）进行这样的计算，并对迄今为止所研究的轻核得到了合理和令人鼓舞的结果。我们目前正在对A=6和7进行详细的计算，研究随着模型空间的增大，结合能、谱、半径等的收敛速度。现在正在测试一种新的计算机代码，用于计算12C到1000万个构型空间状态，这样我们就可以对A=12执行类似的计算，就像我们现在对A=6和7所做的那样。到目前为止，我们的主要成就之一是开发了一种精确计算有效的两体壳模型相互作用的技术，我们已经使用它来解决a =3和4核子系统。从A=3和4的精确解中，我们可以提取出有效的三体和四体相互作用。我们计划利用这些有效的三体和四体相互作用来构建有效的a -核子壳模型相互作用的扩展，这将大大提高我们计算的收敛速度。在不久的将来，我们还将在我们的壳模型研究中包括一个真正的三体相互作用。

0070858Barrett Our goal is to understand the structure of atomic nuclei from first principles---namely, in terms of the free nucleon-nucleon (strong) interaction and many-body quantum mechanics. Toward this end, we havedeveloped a new "ab initio" shell-model approach, in which we treat all. A nucleons as active particles in an extremely large basis (model) space. We now have computer codes, which allow us to perform such calculations for nuclei up to A=16, i.e., 16 active nucleons, and have obtained reasonable and encouraging results for the light nuclei studied so far. We are presently performing detailed calculations for A=6 and 7 to study the rate of convergence of the binding energies, spectra, radii, etc., as the size of the model space is increased. A new computer code is now being tested to do calculations for 12C up to 10 million configuration space states, so that we can perform similar calculations for A=12 as we are now doing for A=6 and 7. One of our major accomplishments, to date, is the development of a technique for computing exactly the effective two-body shell-model interaction, which we have employed to solve the A=3 and 4 nucleon systems. From these exact solutions for A=3 and 4, we can extract the effective three-body and four-body interactions. We plan to utilize these effective three- and four-body interactions to construct an expansion for the effective A-nucleon shell-model interaction, which will greatly improve the convergence rate for our calculations. In the near future we will also include a real three-body interaction in our shell-model investigations.