Re: Energy deposition too low

Dear Joel,

> I've made FLUKA runs using the suggested changes for 30 g/cm2
> polyethylene, aluminum, and copper. The good part is that FLUKA
> outputs the expected dose-depth behavior; the bad part is that the
> energy deposition per unit ion is roughly two orders of magnitude
> lower than experiment. Why do you think the energy deposition is
> down?

I guess that the point still lies in the crucial BEAM card.
You are considering a beam with a uniform square spot (10cm side), i.e. a
primary fluence of 0.01 cm-2. The energy deposition density (GeV cm-3)
scored by USRBIN of course incorporates this factor (roughly speaking -
assuming just ionization - it is equal to stopping power [-dE/dx] times
primary fluence). This means that broad beams induce (obviously) low
energy deposition density (i.e. - through the density factor - dose).
If now what is measured, is the energy deposited over a transverse slice
(GeV/cm as a function of z, longitudinal position i.e. depth), you should
multiply the average energy deposition density over the slice by the slice
area (this way in your case you get back two orders of magnitude)

Hope this helps

Francesco

**************************************************
Francesco Cerutti
CERN-AB
CH-1211 Geneva 23
Switzerland
tel. ++41 22 7678962
fax ++41 22 7668854
Received on Thu Mar 27 15:02:28 2008