If the tenth value layer of lead for cobalt-60 gamma rays is 1.5 inches and the dose rate is 2 R/h, what thickness of lead shielding is needed to reduce the dose rate to 20 mR/h?

If the tenth value layer of lead for cobalt-60 gamma rays is 1.5 inches and the dose rate is 2 R/h, what thickness of lead shielding is needed to reduce the dose rate to 20 mR/h?

• A. 2 inches
• B. 3 inches
• C. 4 inches
• D. 5 inches

Answer: (C)

To determine the thickness of lead shielding required to reduce the dose rate from 2 R/h to 20 mR/h using the tenth value layer (TVL) concept, it’s important to understand how the TVL interacts with dose rate reductions. The tenth value layer of a material is the thickness needed to reduce the intensity of radiation to one-tenth of its original value. For cobalt-60 gamma rays, the TVL is given as 1.5 inches. Starting with the original dose rate of 2 R/h, the goal is to reduce this to 20 mR/h, which is equivalent to 0.02 R/h. To find the number of TVLs needed for this reduction, we can first calculate how many times we need to reduce the dose rate by a factor of ten: 1. From 2 R/h to 0.2 R/h takes one TVL (first reduction to 0.2). 2. From 0.2 R/h to 0.02 R/h takes another TVL (second reduction to 0.02). This means that two TVLs are required for the reduction from 2 R/h to 20 mR/h. Knowing that each TVL for cobalt

To determine the thickness of lead shielding required to reduce the dose rate from 2 R/h to 20 mR/h using the tenth value layer (TVL) concept, it’s important to understand how the TVL interacts with dose rate reductions.

The tenth value layer of a material is the thickness needed to reduce the intensity of radiation to one-tenth of its original value. For cobalt-60 gamma rays, the TVL is given as 1.5 inches.

Starting with the original dose rate of 2 R/h, the goal is to reduce this to 20 mR/h, which is equivalent to 0.02 R/h. To find the number of TVLs needed for this reduction, we can first calculate how many times we need to reduce the dose rate by a factor of ten:

1. From 2 R/h to 0.2 R/h takes one TVL (first reduction to 0.2).

2. From 0.2 R/h to 0.02 R/h takes another TVL (second reduction to 0.02).

This means that two TVLs are required for the reduction from 2 R/h to 20 mR/h.

Knowing that each TVL for cobalt