Certified Hazardous Materials Manager (CHMM) Practice Exam 2025 - Free CHMM Practice Questions and Study Guide

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If the exposure rate at a distance of 1 foot from a radioactive source is 20 rnR/hr, what is the exposure rate at 10 feet in mR/hr?

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To determine the exposure rate at a distance of 10 feet from a radioactive source, it's crucial to understand the principles of radiation exposure and how it diminishes with distance. The exposure rate from a point source of radiation typically follows the inverse square law. This law states that the intensity of radiation (or exposure rate) decreases with the square of the distance from the source.

Starting with the exposure rate at 1 foot, which is 20 rnR/hr, when the distance increases to 10 feet, we can apply the inverse square relationship. The formula is:

Exposure rate at new distance = Original exposure rate x (Original distance / New distance)²

In this scenario:

- Original exposure rate = 20 rnR/hr

- Original distance = 1 foot

- New distance = 10 feet

Now, substituting the numbers into the formula:

Exposure rate at 10 feet = 20 rnR/hr x (1 ft / 10 ft)²

= 20 rnR/hr x (1/10)²

= 20 rnR/hr x (1/100)

= 20 rnR/hr x 0.01

= 0.2 rnR/hr

Since rnR/hr is equivalent

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