Reinvestigation of the irregularities in the 3 H decay K. Bikit, J. Nikolov, I. Bikit ⇑ , D. Mrda, N. Todorovic, S. Forkapic, J. Slivka, M. Veskovic University of Novi Sad, Faculty of Sciences, Department of Physics, Trg Dositeja Obradovica 4, 21000 Novi Sad, Serbia article info Article history: Received 13 August 2012 Received in revised form 9 February 2013 Accepted 28 May 2013 Available online 10 June 2013 Keywords: 3 H radioactive decay Liquid scintillation counting Cosmic rays 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 3 H. Making use of the sophisticated Quantulus liquid scintillation spectrometer, we found that the measurement of the high-energy tail of 3 H spectrum may be significantly influenced by instru- mental 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 spec- trum, although weak variations of different origin could be masked by such cut-off drifts. In our exper- iment we have also registered the oscillatory behavior of measured high-energy tail of 3 H spectrum, but with very small amplitude (less than 0.5%), which cannot be easily explained only by instrumental insta- bility. When the total 3 H spectrum was measured, no significant variations in the count rate were found. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The exponential decay law of radioactive decay is one of the oldest well established laws of nuclear physics. According to thou- sands of measurements, the probability of the decay - the decay constant k of isolated nuclei is constant. Several authors challenged [1–3] 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/k 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 187 Re atom, the half-life can be changed 8 orders of magnitude via bound state b 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 180m Ta 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 nu- clear 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 neu- trinos [9–12]. The most striking report of this type is the paper of Veprev and Muromtsev [13] dealing with the 3 H decay. About 60% daily changes and 20% 27 day periodical variations are attributed to neu- trino induced reactions or to some much more exotic interactions. Making use of our highly stabilized Quantulus [14], low back- ground liquid scintillation spectrometer, and the standard 3 H source, we started a series of measurements in order to reinvesti- gate results of this paper [13]. 2. Experiment The tritium source count rate was measured by the liquid scin- tillation 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 scin- tillation 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 pas- sive shield. The passive shield is made of lead, copper and cad- mium and the active shield is based on a mineral oil scintillator. Low-activity materials were used in the construction of Quantulus, so it is useful for measuring low-level radiation activity. The sys- tem is provided with two pulse analysis circuits that are accessible for the users: a pulse shape analysis (PSA) and pulse amplitude comparator (PAC) circuit. There is also a delayed coincidence cir- cuit (DCOS) inside the Quantulus, which is useful for the correction of chemiluminescence. 0927-6505/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.astropartphys.2013.05.013 ⇑ Corresponding author. Tel.: +381 63 517 875; fax: +381 21 459 367. E-mail address: bikit@df.uns.ac.rs (I. Bikit). Astroparticle Physics 47 (2013) 38–44 Contents lists available at SciVerse ScienceDirect Astroparticle Physics journal homepage: www.elsevier.com/locate/astropart