Mössbauer Spectroscopic Studies of 237Np in frozen nitric acid solution

We applied Mossbauer spectroscopy to 237Np in nitric acid solutions to study chemical states. Sample solutions were adjusted to 50 mg/ml of Np(V) and Np(VI) concentration in 0.6 M nitric acid solutions. These solutions were put into original designed containers for samples and mounted to sample holders. The values of isomer shift (IS, relative to NpAl2) of Np(V) and Np(VI) in 0.6 M nitric acid were −17.4(1) and −37.2(3) mm/s at about 10 K, respectively. It was found that Np(V) had 7 coordination number and Np(VI) had 8 in nitric acid solutions from values of IS.