# Homework Help: Linear attenuation coefficient

1. Apr 12, 2010

### timmo567

is the linear attenuation coefficient named like it is because it is linearly proportional (inversely) to the energy?

I have to read off the coefficient from a graph I have. I have the value for a 2MeV photon, if I want the value for a 1MeV photon is it simply twice the 2MeV value? Reading off the value for the 1MeV photon my value is close to twice the 2MeV value, so I'm wondering if it is meant to be off or is it an error? Thanks

2. Apr 18, 2010

### Rajini

No..you should not interpolate the graph. Linear attenuation coefficient should be determined from reliable sources..refer to NIST website.
Or you find from online using XCOM software.
$$A_{\rm mat}=A_0\exp\left(\frac{\mu}{\rho}t_{\rm mat}\rho\right)$$
where $$\frac{A_{\rm mat}}{A_0}$$ is the transmission through materials 'mat'
$$\mu, \rho$$ are linear att. coefficient and density of 'mat'.
$$t_{\rm mar}$$ thickness of 'mat'.
the value $$\frac{\mu}{\rho}$$ can obtained from NIST website for 1 MeV