# Exponential Attenuation and Beta Particle Range

1. Oct 9, 2008

### Ishy

Exponential Attenuation and Beta Particle Range (solved)

1. The problem statement, all variables and given/known data
I am given a beta emitter and its atomic mass, as well as the atomic mass of its daughter, which have a difference of 0.0034 amu. I am to determine the range of the particles in air.

2. Relevant equations
I am given the law of exponential attenuation:
I=I0e^(-ux)
And substituted for mass attenuation coefficient:
I=I0e^(-um*px)
um and p(rho) are readily available, and can be considered given

3. The attempt at a solution
So I am looking for x, but I do not know I0 (is there some relation between mass or energy and intensity?), and if I'm looking for the range, I assume I to be 0 (if intensity is energy flux x velocity, at the end of the range it must approach 0) which opens up all sorts of nasty when we try to find ln0 (which, essentially approaches infinity).

Last edited: Oct 10, 2008
2. Oct 10, 2008

### Gokul43201

Staff Emeritus
1. What is the relevance of the mass defect?

2. You can not set I=0, because that will only happen at x=infty, which is useless.

3. You want to find a characteristic length scale, typically the distance over which the intensity drops by a factor of e.