Energy and energy spread definition in flair and source.f

Dear FLUKA experts,

I use BEAM card in flair with beam energy and beam momentum spread (Guass,FWHM) to calculate dose distribution for heavy ions. But there is no definition of beam momentum spread in source.f. I tried to use formula (energy *(1+FWHM *RGAUSS)in source.f to calculate the Kinetic energy of the Particle (GeV). The result of DDD distribution is quite different from the calculation with flair.
How to count this beam energy and beam momentum spread in flair to calculate dose distribution? In which way I can achieve the same result with source.f?

Thanks in advance for your help.

Best regards,

Jingfang (2.7 KB) (4.8 KB)

Dear FLUKA experts,

Thanks for the reminder of @horvathd in another discussion. I find the problem by myself. The formula seems right. I can repeat the same results as flair beam card by using source.f.