NEUTRON MODERATIONDOE-HDBK-1019/1-93Reactor Theory (Neutron Characteristics)NP-02Page 26Rev. 0(2-9)where:E= initial neutron energyoE= neutron energy after N collisions Nx= average fractional energy loss per collision N= number of collisionsExample:If the average fractional energy loss per collision in hydrogen is 0.63, what will be theenergy of a 2 MeV neutron after (a) 5 collisions? (b) 10 collisions?Solution:a)b)MacroscopicSlowingDownPowerAlthough the logarithmic energy decrement is a convenient measure of the ability of a materialto slow neutrons, it does not measure all necessary properties of a moderator. A better measureof the capabilities of a material is the macroscopic slowing down power. The macroscopicslowing down power(MSDP) is the product of the logarithmic energy decrement and themacroscopic cross section for scattering in the material. Equation (2-10) illustrates how tocalculate the macroscopic slowing down power.(2-10)

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