SBA — Single Best Answer · Review
Question 592
Biophysics → General
Classification
Question
SSBAQuestion Header
Two gamma-ray beams are passed through the same shielding material. Beam X requires a greater thickness than beam Y to reduce ionisation to 50% of its initial value. Which conclusion is most appropriate?
Question Stem
Select the single best answer.
Options
A
Beam X has a shorter radioactive half-life
B
Beam X has greater penetrating power
C
Beam Y necessarily has greater radioactive activity
D
Beam X necessarily undergoes more transformations per second
E
Beam Y has a longer radioactive half-life
Explanation
The half-value layer is the thickness of material required to reduce ionisation to half its initial value and provides a measure of the penetrating power of X-rays and gamma rays. A greater half-value layer therefore indicates greater penetrating power.
Option Validity
A) Half-value layer does not determine radioactive half-life.
C) Penetrating power does not establish radioactive activity.
D) Transformations per second measure activity and cannot be inferred from half-value layer.
E) Radioactive half-life cannot be inferred from the shielding thickness required.
Further Reading
Saxena R. Textbook for MRCOG-1. Chapter 9: Biophysics, pp.278–279.