Reinvestigation of the irregularities in the 3H decay
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].
Section snippets
Experiment
The tritium source count rate was measured by the liquid scintillation spectrometer, powered by stabilized voltage supply in order to avoid influence of possible voltage variation on registered count rate. Quantulus 1220 is a low-level background liquid scintillation counter (LSC) manufactured by Perkin Elmer, Finland [14]. This instrument has its own background reduction system around the vial chamber, which consists of both an active and passive shield. The passive shield is made of lead,
Results and discussion
In order to reinvestigate the results of Veprev and Muromtsev [13] in our first experiment we did an effort to follow their experimental conditions in detail. We measured the 3H decay in the 14C mode of Quantulus. The lower level cut-off of the spectrum was placed to the same level as in [13] taking into account the source activity in both experiments. More precisely, the cut-off of the spectrum was moved till the integrated count rate reached the value 0.6 relative to the integrated count rate
Conclusion
In the experiments presented, we have reinvestigated the liquid scintillation measurements of the count rate of a 3H source measured by three different set-ups: (1) High-energy tail of 3H spectrum recorded in 14C mode, (2) 3H spectrum recorded in 14C mode and (3) 3H spectrum recorded in 3H mode. Only in the case when high-energy tail of 3H spectrum is measured in 14C mode, we have registered 22-day periodicity in the acquired data, with small amplitude (below 0.5%) that exceeds spectral
Acknowledgment
The authors acknowledge the financial support of the Ministry of Education and Science of Serbia, within the projects No. 171002 and No. 43002.
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