Question

A Cesium–137 (Cs-137) source is shipped to a company in a shield 2 cm thick. The exposure rate 12 cm from the source when unshielded is 24 mR/hr. What is the exposure rate at 12cm when the source is in the container? The tenth-value layer for a 0.6 MeV gamma radiation from the Cs –137 is 1.66 cm.

Answer 1

The tenth-value layer or TVL is the average thickness of shielding material needed to absorb 90% of all radiation, i.e., to reduce it to a tenth of the original intensity.

The solution to this question can be obtained by substituting the parameter values in the formula given below:

Where:

X = Shielded exposure rate

Xo = Unshielded exposure rate

h = Thickess of shield

TVL = tenth value layer

Given That:

Xo = 24 mR/hr

h = 2 cm

TVL = 1.66 cm

Substituting these values in the above equation:

X = 24*e-2.3X2/1.66

X = 24*e-4.6/1.66 = 24*0.062

X = 1.3 mR/hr

which is the required solution.