8 Why is a material with a low Moderating Ratio not consider

8. Why is a material with a low Moderating Ratio not considered to be a good moderator? How does the Moderating Ratio of the moderator used in our cores compare to other possible moderators? Explain.

Solution

the modertation ration is the most complete and the most effective measure of a moderator. Moderation ratio is the ratio of macroscopic slowing down power to the macroscopic cross section for absorption. the Macroscopic slowing down power indicates how rapidly a neutron can slow down in a material and the macroscopic cross section for absorption accounts for the absorption of neutron by materiuals. so a material should have high macvroscopic slowing down powert and low macroscopic cross section for absorption which will make high modertation ratio. in other words material with highj moderation ratio is considered as better moderator because it slows down the high speed of neutrons very rapidly with out absorbing neutrons.

moderation ratio of few materials are....

1. H₂O = 62

2. D₂O =4830

3. Helium =51

4. Berellium = 126

5. Boron = 0.00086

6. Carbon =216

these are the few example of the moderation ratios of the materials. here material like D2O is the best moderator used in most cores where as Boron is the worst moderator.