Mass Attenuation coefficient greater than 1

[superduke1200]

Hello everyone,

I don't seem to understand why mass Attenuation coefficient is greater than 1 at low energies where photoelectric effect is dominant.

5.2 cm^2 /g at water for 10 kev incident photons.

Since it is the probability to interact per g of water how can it be greater than 1?

I woukd really appreciate your help

 

[mfb]

5.2 cm^2/g = 5200 cm^2/kg = 0.052 cm^2/mg = 0.0052 m^2/g

There is nothing special about 1, and the numerical value depends on the units you choose. A larger value just means it is absorbed more.

 

[PSRB191921]

What is the problem ?
Mu/rho=5.2 so mu=5.2 /cm for water
So 1 cm of water it comes an attenuation of exp (-5.2) not illogical for 10 kev in waer
PSR

 

[superduke1200]

What is the problem ?
Mu/rho=5.2 so mu=5.2 /cm for water
So 1 cm of water it comes an attenuation of exp (-5.2) not illogical for 10 kev in waer
PSR

I think I am getting it.

Exp(-5.2)=0,0055 which means that out of 10.000 incident photons only 55 of them would make it through 1 cm of water without interacting at all.

All the others will remain in the water and produce mainly electrons since the photoelectric effect is dominant?

 

[superduke1200]

Or to be correct: all the remaining 9945 photons will produce photoelctrons.

Since the average Etr=9,25 Kev we will 9945 photoelctrons with a mean kinetic energy of 9,25 kev

 

[mfb]

Or to be correct: all the remaining 9945 photons will produce photoelctrons.

Technically some of them can interact with nuclei and some can do Compton scattering but these processes are very unlikely at 10 keV.

Where does the 9.25 keV come from?

 

[superduke1200]

9.25 comes from this appendix