Reinvestigation of the irregularities in the ³H decay

Highlights

• The variations of the ³H decay rate have been reinvestigated.

• The Quantulus LSC spectrometer was operated in the ¹⁴C and ³H mode.

• The ³H decay rate measurement in ¹⁴C mode introduces instrumental fluctuations.

• Low-amplitude variations of ³H count rate of high-energy tail were found.

• The ³H count rate variations of pronounced amplitude have not been registered.

Abstract

Having in mind the potential impact of the results presented by Veprev and Muromtsev (2012) [13] on our knowledge of the universe, we reinvestigated the liquid scintillation measurement of the count rate variations of ³H. Making use of the sophisticated Quantulus liquid scintillation spectrometer, we found that the measurement of the high-energy tail of ³H spectrum may be significantly influenced by instrumental instability. Thus, the possible explanation for the relatively high count rate variations of Veprev and Muromtsev (2012) [13] can be attributed mainly to the walk of the cut-off in the integrated spectrum, although weak variations of different origin could be masked by such cut-off drifts. In our experiment we have also registered the oscillatory behavior of measured high-energy tail of ³H spectrum, but with very small amplitude (less than 0.5%), which cannot be easily explained only by instrumental instability. When the total ³H spectrum was measured, no significant variations in the count rate were found.

Introduction

The exponential decay law of radioactive decay is one of the oldest well established laws of nuclear physics. According to thousands of measurements, the probability of the decay - the decay constant λ of isolated nuclei is constant. Several authors challenged [1], [2], [3] this generally accepted rule, seeking for deviations from the exponential decay law without sufficient experimental evidence. On the other hand, it is also well known that the half-life, T = ln2/λ of some nuclei embedded in matter can be influenced by temperature changes [4], pressure changes [5], irradiation [6], etc. These half-life changes are usually less than 1% and are explained by the influence of the atomic electron structure on the nucleus. By complete ionization of the ¹⁸⁷Re atom, the half-life can be changed 8 orders of magnitude via bound state β decay. Also, some significant accelerated decays of meta-stable states have been reported. It was shown that, by irradiation in strong gamma ray fields, the half-life of some meta-stable states can be changed by orders of magnitude. The accelerated decay of ^180mTa is explained by induced transition to the short-lived ground state via excitation to an excited state and its subsequent decay to the ground state [7]. Such type of research was also related to some astrophysical problems and to the possibility of stimulated gamma ray emission.

Besides such well explained and understood changes of the nuclear decay, the annual periodicity in decay data has been reported in open access journals [8]. Several authors relate the oscillations in the measured decay rate to solar influence, mostly to solar neutrinos [9], [10], [11], [12].

The most striking report of this type is the paper of Veprev and Muromtsev [13] dealing with the ³H decay. About 60% daily changes and 20% 27 day periodical variations are attributed to neutrino induced reactions or to some much more exotic interactions.

Making use of our highly stabilized Quantulus [14], low background liquid scintillation spectrometer, and the standard ³H source, we started a series of measurements in order to reinvestigate results of this paper [13].