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Nuclear Reactions

Problem 6.282

Determine how many times the intensity of a narrow beam of thermal neutrons will decrease after passing through the heavy water layer of thickness d=5.0 cm.d=5.0 \mathrm{~cm} . The effective cross-sections of interaction of deuterium and oxygen nuclei with thermal neutrons are equal to σ1=7.0 b\sigma_{1}=7.0 \mathrm{~b} and σ2=4.2 b\sigma_{2}=4.2 \mathrm{~b} respectively.

Reveal Answer
I0/I=exp⁡[(2σ1+σ2)nd]=20, where n is the concentration of heavy water molecules I_{0} / I=\exp \left[\left(2 \sigma_{1}+\sigma_{2}\right) n d\right]=20, \text { where } n \text { is the concentration of heavy water molecules }
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