Radioactivity and radioisotopes Gamma rays range in air

Radioactivity and radioisotopes • Gamma rays range in air • Inverse Square Law

Inverse Square Law for g-rays Using the same equipment investigate how the distance from the g-source affects the Activity I detected. The limit of activity in the environment where medical staff operate g-rays machinery from is 0. 3 Bq. In your investigation you are required to find the minimum distance away from the source to ensure the appropriate protection for medical staff, i. e. no more than 0. 3 Bq in the operating room. Use the apparatus drawn underneath and think of a way to account for background radiation. g-source embedded in lead casing Distance from source GM-tube Counter

Inverse Square Law for g-rays Here are some hints: • Plot a graph of 1/√C against the distance from the source. • Your graph should be a straight line if the count rate follows the Inverse Square Law: • • Use your graph to find the value of C and the distance from the source required for the limit of activity of 0. 3 Bq. Suggest why the graph doesn’t intercept the x-axis at the origin (hint: a diagram of the g-source and the G-M tube might help you to understand the problem)

Inverse Square Law for g-rays The intensity of radiation is obviously proportional to the count rate C, so a similar equation applies for it: • This equation can be solved to give: • Where I is the intensity at distance x from the source and I 0 the intensity for x = 0

Inverse Square Law for g-rays But why does the Intensity follows that pattern?