[en] In order to carry out a full range of testing and experimental work in the MUTR experimental facilities, it is highly desirable to have a standardized measurement of the neutron flux spectrum. A series of experiments were conducted on the MUTR to characterize the neutron flux spectrum in the experimental facilities. Measurements and analysis were carried out in accordance with American Society for Testing Materials (ASTM) standard methods. Various ASTM recommended foils were activated in the experimental facilities, activities measured on a NBS traceable calibrated GeLi detector, and neutron energy fluxes computed from the activities using the SAND II computer code. In addition, the 1 MeV equivalent Silicon fluence rate was calculated from knowledge of the neutron flux spectra and tabulated neutron displacement kerma factor. (author)