关於中子在两种介质中的慢化问题

本文根据年龄理论,考虑下列问题:二介质由球面r=a分开,球面外的介质一直延伸到无限,球面内的介质中在r=R处放有壳形单能快中子源;要求二介质中由此引起的中子慢化密度的空间分布。求解时应用了拉氏变换的方法。求出了适用於(τ₁)^1/2≤α情形的展开式,这里τ₁是中子在球面内介质中的年龄、物理上出现的实际情形多半满足(τ₁)^1/2?α的条件,这时展开式收敛很快。对於二介质是重水和石墨的一个实例;我们算出了热能处中子慢化密度的数值结果(假定快中子源的能量为2兆电子伏),并和用通常二群近似方法求得的结果进行了比较。

ON THE SLOWING-DOWN OF NEUTRONS IN TWO ADJACENT MEDIA

We have calculated the slowing-down densities of neutrons in two adjacent media of different slowing-down properties according to the age theory. The outer medium is extended to infinity. The inner medium consists of a sphere of radius a, and contains a monoenergetic fast neutron-source in the form of a concentric spherical shell of radius R.The method of Laplace transformation is used in solving the problem. The results are given by the expansions (25), (25′), (28) & (28′), which converge rapidly for those cases we usually meet with.For a concrete case where the two media are heavy water and graphite, and the fast neutron-source is of energy 2 Mev, numerical results for the slowing-down densities at thermal energy are obtained and compared with those obtained by the usual two-group approximation (Fig. 1, 2 & 3).