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. 

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) 

To calculate the exposure rate, multiply the exposure rate constant by the source activity, then divide by the distance squared.

How to Calculate Exposure Rate?

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

Example Problem #1

  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.
  2. Next, determine the source activity (Ci).
    • The source activity (Ci) is measured to be: 5.
  3. Next, determine the distance (cm).
    • The distance (cm) is found to be: 2.
  4. 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)