Experimental searches for rare alpha and beta decays

Abstract

The current status of the experimental searches for rare alpha and beta decays is reviewed. Several interesting observations of alpha and beta decays, previously unseen due to their large half-lives (10 15 − 10 20 yr), have been achieved during the last years thanks to the improvements in the experimental techniques and to the underground locations of experiments that allows to suppress backgrounds. In particular, the list includes first observations of alpha decays of 151 Eu, 180 W (both to the ground state of the daughter nuclei), 190 Pt (to excited state of the daughter nucleus), 209 Bi (to the ground and excited states of the daughter nucleus). The isotope 209 Bi has the longest known half-life of T 1/2 ≈ 10 19 yr relatively to alpha decay. The beta decay of 115 In to the first excited state of 115 Sn (Eexc = 497.334 keV), recently observed for the first time, has the Q β value of only (147 ± 10) eV, which is the lowest Q β value known to-date. Searches and investigations of other rare alpha and beta decays ( 48 Ca, 50 V, 96 Zr, 113 Cd, 123 Te, 178m2 Hf, 180m Ta and others) are also discussed.

Novel Cs2HfCl6 Crystal Scintillator: Recent Progress and Perspectives

“…Figure 3 represents the experimental values of QF obtained with an internal alpha peaks from daughters of 232 Th and 238 U decay chains and an external 241 Am alpha source and the global fit according to phenomenological model proposed in [37]. This Df dependence indicates that the alpha particles produce more than a third of the light amount produced by gamma quanta in CHC crystals in the energy range (1)(2)(3)(4)(5)(6)(7)(8) MeV. Important to notice a great agreement between QF values achieved with external and internal alpha particles, and that both measurements were confirmed with a phenomenological model.…”

“…Within this approach, the alpha decay of 180 W with 116 CdWO 4 [3] and 151 Eu with CaF 2 (Eu) [4] crystal scintillators was registered at an experimental sensitivity level of over 10 18 y. A recent and comprehensive review on rare decays and techniques of their detection is given in [5]. However, the main disadvantage of the "source = detector" approach is the limitation to certain target elements which are suitable for detector manufacturing.…”

First search for $$\alpha $$ decays of naturally occurring Hf nuclides with emission of $$\gamma $$ quanta

“…The process played a crucial role in the development of nuclear models, since it offers information about the nuclear structure, the nuclear levels and the properties of nuclei. In the last two decades many experimental and theoretical studies have been performed to investigate very rare α decays with long half-lives (10 15 − 10 20 a) or/and low branching ratios (10 −3 − 10 −8 ) (see review [1] and references therein). The progress has been become possible thanks to the substantial improvements in the experimental low-background techniques and underground location of the experimental set-ups.…”

Status and Perspectives of 2ϵ, ϵβ+ and 2β+ Decays

“…For example, the NaI(Tl) scintillator is being used to the search for solar axions, possible charge non-conservation processes, matter stability, rare nuclear decay modes, exotics in cosmic rays, DM, and others [67][68][69][70][71][72][73][74][75][76][77]. Moreover, low background crystal scintillators are being used for a long time in rare α and β decays (see e.g., [78]). Hoverer, a very wide choice of scintillators is available for DBD experiments, such as CdWO 4 (due to 106 Cd, 108 Cd, 114 Cd, 116 Cd, 180 W, 186 W), CaMoO 4 (due to 100 Mo), and their enrichments (such as 106 Cd, 116 Cd and 100 Mo) [31,[79][80][81][82][83][84] [51][52][53]58,[91][92][93][94][95][96][97][98][99][100][101][102][103][104].…”