Co-60 Unit Activity: Treatment Time Calculation

[sciencegeek101]

Homework Statement

A patient is treated for cancer using radiation from a cobalt-60 unit. Exactly 1.5 years later another patient is treated for the same cancer using the same co-60unit previously used. How much longer would treatment be for the second patient?

Homework Equations

Decay Constant (λ)
A(t)= Activity after 1.5 years
A0= original activity

A(t)=A0(e^-λt)
=A0(0.165)
Therefore the activity after 1.5 years is 16% of the original activity, so the treatment time would be 83.5% longer than the original treatment time

The Attempt at a Solution

Decay Constant (λ)= 0.1 months^-1

A(t)=A0(0.165)
Therefore the activity after 1.5 years is 16.5% of the original activity, so the treatment time would be 83.5% longer than the original treatment time

 

[TSny]

What quantity should be the same for each treatment?