Study of the Chemical Effect Accompanyling Nuclear Transformation by Coincidence M ssbauer Spectroscopy

As the first part of this study，我们建立一个Mossbauer-spectroscopic assembly with the coincidence circuit system. This assemblywas tested with a ^<57>Co source. It was found that the distinction of a real coincidence fromrandom coincidences was very difficult and that high technique was essential both for electronicsradiochemistry. Although coincidence-spectra from a TAC clearly showed a real coincidence peakon the plateau of random coincidencesthe background of the random coincidece is ill very high even under the best presentconditions.From the several preliminarily tested substanceswe chose yba_2 cu_3o_ <7-x> (<equal or less than>x <equal or less than>0.5) with super conductivitybelow 80 - K for the investigation. This substance has the anomality that its one Cu has （2+x）valence. Special yba_2 cu_3o_ <7-x> cotaining 1 % of ^<57>Fe-enriched Fe was prepared and its spectrumwas measured by a sual absorption method at room temperature. Another doped sample was also madein the following way that a slightly acidic solution of carrier-free <57>Co^<2+> was doped and that这是heated at 850 C in air for 3小时。After removing the surface layer，this sample subjected to emission M ssbauer spectroscopy at room temp. both in a usual way andtime-differential ways under the time conditions of 0[20 and 0[40 ns after the deexcite to the Mssbauer level. In all the cases，the peak was symmetrical doublet doublet which has very large QS（1[2mm/sec）corresponding to Fe(III). In the emission case，FWHM of the component peaks wch larger than in the absorption case. It suggests that<57>Co introduced might be located at the unstable site with low symmetric oxygen coordination andtha disturbance due to EC-decay might be added to that in the emission case. the moreenlargement of the width in time-differential cases interpreated to be due to the uncertainityfrom counting period。

As the first part of this study, we constructed a Mossbauer-spectroscopic assembly with the coincidence circuit system. This assembly was tested with a ^<57>Co source. It was found that the distinction of a real coincidence from random coincidences was very difficult and that high technique was essential both for electronics and radiochemistry. Although coincidence-spectra from a TAC clearly showed a real coincidence peak on the plateau of random coincidences, the background of the random coincidece is still very high even under the best present conditions.From the several preliminarily tested substances, we chose YBa_2Cu_3O_<7-x> (<equal or less than>x <equal or less than>0.5) with super conductivity below 80゜K for the investigation. This substance has the anomality that its one Cu has (2+x) valence. Special YBa_2Cu_3O_<7-x> cotaining 1 % of ^<57>Fe-enriched Fe was prepared and its spectrum was measured by a usual absorption method at room temperature. Another doped sample was also made in the following way that a slightly acidic solution of carrier-free ^<57>Co^<2+> was doped and that it was heated at 850゜C in air for 3 hours. After removing the surface layer, this sample was subjected to emission M ssbauer spectroscopy at room temp. both in a usual way and time-differential ways under the time conditions of 0[20 and 0[40 ns after the deexcite to the M ssbauer level. In all the cases, the main component of the peak was symmetrical doublet doublet which has very large QS(1[2mm/sec) corresponding to Fe(III). In the emission case, FWHM of the component peaks was much larger than that in the absorption case. It suggests that ^<57>Co introduced might be located at the unstable site with low symmetric oxygen coordination and that tha disturbance due to EC-decay might be added to that in the emission case. The more enlargement of the width in time-differential cases was interpreated to be due to the uncertainity from counting period.