57Fe Mossbauer spectroscopy of radiation damaged allanites

Abstract

Metamict minerals contain radioactive elements that degrade the crystal structure of the minerals. The degradation occurs primarily through progressive overlapping recoil nuclei collision cascades from ®-decays of 238U, 232Th, 235U and their daughter products. We report the results of 57Fe Mossbauer spectroscopy, gamma-ray spectrometry and microprobe analysis of three partially metamict allanites, (Ca,Ce,REE)2(Fe2+; Fe3+)(Al; Fe3+)2O[Si2O7][SiO4](OH) where REE stands for rare earth elements. The samples were collected in pegmatites from Reno, Nevada (USA), Franklin, New Jersey (USA) and Nya Bast- nas Field (Sweden). The absorbed ®-dose for these minerals was found to range from 5:8 £ 1014 ®-decay/mg for the allanite from Reno to 1:9 £ 1015 ®-decay/mg for the allanite from Franklin. The Mossbauer spectra show a decrease in the Fe2+ doublet intensity with increasing absorber ®-dose. We also observe an increase in the line widths of the Fe2+ and Fe3+ doublets with increasing absorbed ®-dose.