Question

When exposed to a radioactive source which emits 1.2-MeV gamma-rays, a particular material is found to have a half-value thickness X of 10 cm How thick would a shield made of this material need to be in order to block 75% of the radiation? A. 5 cm B. 20 cm C. 15 cm D. 25 cm E. 10 cm

Answer 1

Answer:E

Explanation:

It is given that Energy of gamma ray is E=1.2 Mev

Shielding effect can be measured by measuring the fraction of gamma rays blocked by shield. If certain thickness will able to block half the radiation then to block 75% radiation we need to add same amount of thickness in order to block the remaining radiation.

i.e. $\frac{E}{2}$ fraction is blocked by 10 cm thickness

then remaining radiation is $\frac{E}{2}$

another 10 cm thickness will block the remaining half radiation i.e. $\frac{1}{2}\times \frac{E}{2}=\frac{E}{4}$

so total 75 % radiation will be blocked