Problem in scoring fluence spectrum of primary particle

Dear Experts,
I have made a spherical geometry filled with Vacuum. A isotropic point beta source (see attached spectrum in .dat file and source.f) is placed at the centre of the sphere. Using USRTRACK scoring card, I am scoring fluence spectrum.

I am supposed to get the input primary spectrum as the media is vacuum. However, I am getting spectrum up to 0.27 MeV whereas the end-point energy of the input spectrum is 0.49 MeV.

Why this kind of mismatch is coming. Am I doing anything wrong ?

Kindly suggest me some way out.

Thanking you in advance.
Lu177_498keV_beta.dat (624 Bytes)
Lu177_spectra_rebin.flair (7.6 KB)
Lu177_spectra_rebin.inp (1.4 KB)
source_newgen.f (18.9 KB)

Dear ArghyaC,

you need to uncomment the line

energy_logical_flag = .true.

to interpret the spectrum as energy, otherwise, it is taken as momentum.

Furthermore, there is an error with the parameters you use in annular sampling. The [ and ] must be removed to set the radii correctly.