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Application of probability generating function to the essentials of nondestructive nuclear materials assay system using neutron correlation

中性子相関を利用する核物質非破壊測定システムの基礎への確率母関数の適用

細馬 隆 

Hosoma, Takashi

核物質非破壊測定システムの基礎への確率母関数の適用について研究を行った。最初に、高次の中性子相関を七重相関まで代数的に導出し、その基本的な性格を調べた。高次の中性子相関は、漏れ増倍率の増大に応じて急速に増大し、検出器の効率や設定によるが漏れ増倍率が1.3を超えると、より低次の中性子相関と交わり追い越してゆくことを見出した。続いて、高速中性子と熱中性子が共存する系において、高速中性子による核分裂数と二重相関計数率及び熱中性子による核分裂数と二重相関計数率を、代数的に導出した。従来の測定法と、differential die-away self-interrogation法によって得られるRossi-alpha結合分布と各エリアの面積比を用いれば、高速中性子と熱中性子それぞれの単位時間あたりの誘導核分裂数、ソース中性子1個あたりそれぞれの誘導核分裂数(1未満)及びそれぞれの二重相関計数率を、推定可能であることを見出した。

Application of probability generating function for nondestructive nuclear materials assay system was studied. First, high-order neutron correlations were derived algebraically up to septuplet and basic characteristics of the correlations were investigated. It was found that higher-order correlation increases rapidly in response to the increase of leakage multiplication, crosses and leaves lower-order correlations behind, when leakage multiplication is $$>$$ 1.3 that depends on detector efficiency and counter setting. Next, fission rates and doubles count rates by fast neutron and by thermal neutron in their coexisting system were derived algebraically. It was found that the number of induced fissions per unit time by fast neutron and by thermal neutron, the number of induced fissions ($$<$$ 1) by one source neutron, and individual doubles count rates were possible to be estimated from Rossi-alpha combined distribution and measured ratio of each area obtained by differential die-away self-interrogation and conventional assay data.

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