The Monte Carlo radiation transport code MCNP6 has been used to model dosimetry for biological pathogen samples placed within a MultiRad 225 irradiation chamber, in order to inform virus deactivation protocols. Full characterisations of the photon spectra generated by the chamber's x-ray tube were achieved for both 190 and 220 kV potentials, with and without aluminium and copper beam filters of different thicknesses. Dose rate maps to air and water within the chamber were then derived, along with corresponding conversion coefficient data. The maps were determined for samples located both on a shelf and on a dry ice refrigeration chamber, at different distances from the source. The potential depth-dose profiles through samples were also investigated. The optimum choice of filter for use in virus inactivation procedures will rely on a compromise between dose homogeneity and dose rate.