Instant capture of recoil51Cr(III) from neutron activated K2CrO4

We have recently developed a new method of measuring the initial⁵¹Cr(III) produced from nuclear recoil of K₂CrO₄. In our method, K₂CrO₄ was mixed with MgO in the presence of a small amount of water, and the mixture was irradiated in a nuclear reactor. After irradiation, the mixture was dissolved in water, and MgO precipitate was separated from the solution. The yield of recoil⁵¹Cr(III) could be calculated from the⁵¹Cr activity in the precipitate measured. On the other hand, the yield of retention of⁵¹Cr as chromate could be calcualted from the activity found in the supernatant. The⁵¹Cr(III) yield thus obtained is almost a factor of 2 higher than observed in pure K₂CrO₄ without mixing with MgO, irradiated under the same condition. Another important observation is that the⁵¹Cr(III) yield is independent of irradiation time in the presence of MgO. Without MgO, the observed⁵¹Cr(III) yield decreases with increasing irradiation time, suggesting possible oxidation of Cr(III) to chromate during irradiation. This variation is not observed in the system of K₂CrO₄ containing MgO, indicating that the initial Cr(III) is adsorbed immediately after nuclear recoil by MgO and is protected from oxidation by gamma radiation.