If a tenth-value layer is placed on a 100 mrem/hr source, the dose rate should be reduced to:

If a tenth-value layer is placed on a 100 mrem/hr source, the dose rate should be reduced to:

• A. 1 mrem/hr
• B. 10 mrem/hr
• C. 100 mrem/hr
• D. 1000 mrem/hr

Answer: (B)

A tenth-value layer reduces the dose rate by a factor of ten. So you divide the original dose rate by 10. With 100 mrem/hr at the source, one TVL brings it down to 100 ÷ 10 = 10 mrem/hr. The other numbers would require different degrees of shielding: 1 mrem/hr would need a hundredfold reduction, 100 mrem/hr would mean no shielding, and 1000 mrem/hr would imply an increase, which shielding doesn’t do.

A tenth-value layer reduces the dose rate by a factor of ten. So you divide the original dose rate by 10. With 100 mrem/hr at the source, one TVL brings it down to 100 ÷ 10 = 10 mrem/hr. The other numbers would require different degrees of shielding: 1 mrem/hr would need a hundredfold reduction, 100 mrem/hr would mean no shielding, and 1000 mrem/hr would imply an increase, which shielding doesn’t do.