Differences between proposed and calculated Am/Be point source spectrum

Validation and Verification
1

I have a question about shielding estimation for a Am/Be source with OpenMC. I’m using a point source located at the origin, to which I’ve given the relative intensities of the Am/Be spectrum. I generated a Tally sphere in the center with the same medium composition (air). When I compare the proposed spectrum with the spectrum on the sphere, they don’t match. Did I make a mistake?

energies = np.array([1.5, 2, 2.5,

                 3, 3.4, 4.2,

                 5.4, 6, 6.7,

                 7.2, 7.6, 8.1,

                 8.7, 9.4, 10.2,

                 10.8, 11.7\])       #----- MeV

pond = np.array([1.5, 1.85, 2.20,

             2.55, 2.76, 2.5,

             2.65, 2.20, 1.5,

             1.6, 1.4, 1.6,

             1.25, 0.6, 0.65,

             0.26, 0.001\])          #----- ponderación

pond = pond / pond.sum()
energies_eV = energies * 1e6

source_energy_dist = openmc.stats.Tabular(energies_eV.tolist(), pond.tolist(), interpolation=‘histogram’)

src = openmc.Source()
src.space = openmc.stats.Point((0.0, 0.0, 0.0))
src.angle = openmc.stats.Isotropic()
src.energy = source_energy_dist

And this is my detector:

region_fuente = openmc.Sphere(r = 1)
celda_fuente = openmc.Cell(fill = puntual_mat, region = -region_fuente)

tallies_file = openmc.Tallies()
energy_filter = openmc.EnergyFilter(energies_eV)
cell_filter = openmc.CellFilter(celda_fuente)

tally = openmc.Tally(name=‘flux’)
tally.filters = [cell_filter]
tally.filters.append(energy_filter)
tally.scores = [‘flux’]
tallies_file.append(tally)
tallies_file.export_to_xml()