237Np Mössbauer spectroscopic study on heptavalent neptunium compound

237Np Mössbauer spectrum of the heptavalent neptunium compound [Co(NH3)6][NpO4(OH)2]·2H2O was remeasured for certification of the previous investigations. The isomer shift value of the Mössbauer spectrum showed a characteristic value for the heptavalent neptunium at 4.7K. Although the spectrum seemed to consist of two quadrupole-split peaks as previously reported byStone et al., the fitting with using two quadrupole-split peaks did not give a good agreement withStone's data.