Enter the exposure rate constant (R-cm^2/hr*Ci), the source activity (Ci), and the distance (cm) into the Exposure Rate Calculator. The calculator will evaluate the Exposure Rate.

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## Exposure Rate Formula

The following formula is used to calculate the Exposure Rate.

**EX = R * a / r^2**

- Where EX is the Exposure Rate (roentgen per hour)
- R is the exposure rate constant (R-cm^2/hr*Ci)
- a is the source activity (Ci)
- r is the distance (cm)

## How to Calculate Exposure Rate?

The following two example problems outline the steps and information needed to calculate the Exposure Rate.

**Example Problem #1**

- First, determine the exposure rate constant (R-cm^2/hr*Ci).
- The exposure rate constant (R-cm^2/hr*Ci) is calculated to be : 12.838.

- Next, determine the source activity (Ci).
- The source activity (Ci) is measured to be: 5.

- Next, determine the distance (cm).
- The distance (cm) is found to be: 2.

- Finally, calculate the Exposure Rate using the formula above:

EX = R * a / r^2

The values provided above are inserted into the equation below and computed.

EX = 12.838 * 5 / 2^2 = 16.0475 (roentgen per hour)

**Example Problem #2**

The variables required for this problem are provided below:

exposure rate constant (R-cm^2/hr*Ci) = 6

source activity (Ci) = 7

distance (cm) = 8

Test your knowledge using the equation and check your answer with the calculator.

EX = R * a / r^2 =** **(roentgen per hour)