Temperature effect on the decay periods of long-lived ^180mHf and ^87mSr isomers

Abstract

Experiments on measuring the decay periods of long-lived ^180mHf and ^87mSr isomers at room temperature and at 77 K in massive samples of HfO₂, Sr(NO₃)₂, and SrCO₃ are reported. The isomeric nuclear states were excited by irradiating the samples with neutrons from a Pu-Be source. According to the theory of V.I. Vysotski$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{l}$ et al., the T _1/2 value must increase if a γ-active nucleus is surrounded by many identical ground-state nuclei, because these distort the spectrum of electromagnetic vacuum oscillations near the nuclear energy level. As the temperature of the sample decreases, γ-ray lines narrow, especially for the low-energy Mössbauer transitions, thereby enhancing the resonance effect on the spectrum of vacuum oscillations. For the ^180mHf isomer, whose upper γ transition carries away 57.55 keV, the T _1/2 value was found to increase by 2.99±0.87% upon sample cooling. For ^87mSr, whose decay scheme has no Mössbauer lines, the relative change in T _1/2 was found to be 0.77±0.53%.