Production of a carrier-free standard ⁵⁶Mn source for the NRC manganese salt bath

The National Research Council (NRC) of Canada's primary method for emission rate for radionuclide neutron sources utilizes a manganese salt bath which was last calibrated in the 1960s. At that time, an NRC RaBe neutron source was used to irradiate a solution of calcium permanganate to take advantage of the Szilard-Chalmers effect in producing the bulk ⁵⁶Mn material for standardization and calibration of the bath. When attempting to repeat this exercise, a small amount (~100 kBq) was produced. This amount was sufficient for the standardization process but did not yield enough material to calibrate the bath to a sufficient level of precision. Improvements upon the previous separation scheme adopted at NRC for the separation of the ⁵⁶Mn from the bulk irradiated material included the rinsing of the ⁵⁶Mn dioxide precipitate using a mixture of sulfuric acid and hydrogen peroxide. While these improvements made in the separation chemistry improved the yield of ⁵⁶Mn extraction from 60% to above 95% the maximum amount of activity was still quite low. Hence in March of 2018, the SLOWPOKE-2 Facility at the Royal Military College in Kingston, ON, was used to irradiate three vials of KMnO₄ in solution. An estimated 2 GBq was produced and sent to NRC, from which the extraction procedure recovered essentially all of the available ⁵⁶Mn. The ⁵⁶Mn was standardized using the 4πβ-γ anti-coincidence counting system and confirmed using the CIEMAT/NIST primary method. The resulting bulk material was certified with an uncertainty of 0.8% (k = 2). Minor quantities of ⁶⁵Zn, ^69mZn and ⁴²K were unexpectedly observed but were in minute quantities so as not to affect the results of the standardization or calibration. The standardized ⁵⁶Mn artifact was used to calibrate the Secondary Standard Ionizing Radiation Chamber System (SSIRCS) for a more rapid deployment of the calibrant in the future.