Moessbauer spectroscopic study of 57Fe species produced by 56Fe(n, γ)57Fe reaction in iron disulfide

Chemical and physical changes induced by nuclear reactions have been one of the research subjects of radiochemistry for several decades. Emission Moessbauer spectroscopy is a useful unique tool in investigating chemical and physical states of trace amounts of species formed by nuclear transformations in solids non-destructively. We have started a neutron in-beam emission Moessbauer spectroscopic study of 57Fe formed via the 56Fe(n, γ)57Fe reaction in solid materials using a parallel plate avalanche counter (PPAC). In this paper we report some results of the study on neutron induced changes of iron species in a binary semiconductor iron disulfide (FeS2). Both two polymok was oriented both to the beam and the PPAC detector at an angle of 45 degrees. The thermal neutron flux was about 1.0 x 108 cm-2S-l. Natural marcasite mineral obtained from Hori Mineralogy was also examined similarly. The in-beam emission Moessbauer spectrum of pyrite showed two Lorentzian doublets. One component corresponding to pyrite occupied 1/3 of the total peak area, and the other major component was tentatively assumed as Fe3+ at the interstitial site of pyrite. The emission spectrum of marcasite was also composed of two doublets: one corresponding to marcasite, and the other doublet. In both iron disulfides, it was revealed that recoil of the cascade γ-ray emission promptly after trphs of iron disulfide, pyrite having the rock salt type crystal structure, and marcasite with nickel arsenide structure, were investigated. Iron disulfide reagent (pyrite) was purchased from Kishida Kagaku Co., and used without purification. Finely ground powder was pressed to form a thin disk of 20 x 20 cm2 and about 100 mg cm-2 in thickness. Moessbauer measurements were carried out using the prompt γ-ray analysis setup at the neutron beam hall of the JRR-3M reactor of JAERI. The sample dishe neutron capture reaction produced one new species distinguishable from the original target compound by in-beam 57Fe Moessbauer spectroscopy.