CALIBRATION OF THE ISOMER-SHIFT OF SB-121 AND SN-119 BY MEANS OF MOSSBAUER-SPECTROSCOPY AND MOLECULAR-ORBITAL CALCULATION

The relationship between the isomer shifts in Mossbauer spectroscopy and the electron contact densities has been investigated for several antimony and tin compounds. Mossbauer spectra for Sb-121 in rapidly frozen solutions of antimony compounds were measured. The isomer shifts are compared with the valence electron densities at the antimony nucleus calculated with the ab initio molecular orbital method. The relative difference of the nuclear charge radius DELTA-R/R could be obtained as DELTA-R/R = -(10.2 +/- 1.0) x 10(-4) for the 37.15 keV M1 transition of Sb-121. Further, some computations of the electron density at the tin nucleus for several tin compounds were performed. By comparing the valence electron contact densities with isomer shifts, which had been reported for several tin compounds in rare-gas matrix states, the value of DELTA-R/R for 23.87 keV M1 transition in Sn-119 was estimated to be (1.57 +/- 0.03) x 10(-4).