Hi! I wish to estimate with FLUKA the range R and the range straggling S of 4 MeV protons in LiF. Assuming a Gaussian distribution of the final particle positions along the penetration depth z, I score the proton fluence with a USRBIN and plot its 1D Projection along z. To my understanding, at this energy the 1D-projected fluence per primary should approximately follow this law:
1/2 - (1/2) * erf [(z-R) / (sqrt(2)*S)]
By best fitting the obtained FLUKA simulation with the above function, I get R = 118.0 um and S = 1.801 um. I compare these values with values found with SRIM: while the ranges agree within a small error (118.0 um vs. 118.8 um), the range stragglings differ much more, as from SRIM I get S = 2.081 um, 16% larger than 1.801 um of FLUKA.
It must be said that the value of S found from SRIM seems to be correct at least when using an analytical model for LET curve calculation: the SRIM S value works well to replicate the LET curve calculated by FLUKA, besides that calculatd by SRIM itself. However, analytical formulas such the one I used (derived from Bortfeld’s) could give uncorrect results below say 10-12 MeV.
Nonetheless, I would like to check if there is something wrong in my way to estimate S from the FLUKA simulation of fluence. Do you spot any bug in it? Alternatively, is there a more direct way to score range and range straggling in FLUKA?
Thank you a lot in advance for your help and kind regards,