New search for correlated e+e- pairs in the $ \alpha$ decay of 241Am

Abstract

A new search for production of correlated e + e − pairs in the α decay of 241 Am has been carried out deep underground at the Gran Sasso National Laboratory of the I.N.F.N. by using pairs of NaI(Tl) detectors of the DAMA/LIBRA setup. The experimental data show an excess of double coincidences of events with energy around 511 keV in faced pairs of detectors, which are not explained by known side reactions. This measured excess gives a relative activity λ = (4.70 ± 0.63)×10 −9 for the Internal Pair Production (IPP) with respect to alpha decay of 241 Am; this value is of the same order of magnitude as previous determinations. In a conservative approach the upper limit λ < 5.5 × 10 −9 (90% C.L.) can be derived. It is worth noting that this is the first result on IPP obtained in an underground experiment, and that the λ value obtained in the present work is independent on the live-time estimate.

First model independent results from DAMA/LIBRA-phase2

“…throughout the year). Thus, this period cannot be used for the annual modulation studies; however, it has been used for other purposes [6,13]. Therefore, as shown in Table 1 the considered annual cycles of DAMA/LIBRA-phase2 are six (exposure of 1.13 ton×yr).…”

“…: χ 2 /d.o.f. = 2.5/6 and 40.8/38 for the energy intervals (1)(2)(3)(4) and (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) keV, respectively (∆E = 0.5 keV). This shows that the effect is also well shared between inner and outer detectors.…”

“…The DAMA/LIBRA [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20] experiment, as the pioneer DAMA/NaI [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48], has the main aim to investigate the presence of DM particles in the galactic halo by exploiting the DM annual modulation signature (originally suggested in Ref. [49,50]).…”

Experimental searches for rare alpha and beta decays

“…29 together with the estimated systematic uncertainties. The main sources of the system- CdO sample in proportional counter [237] (1962) = (9.3 ± 1.9) × 10 15 Enriched 113 CdO sample in proportional counter [238] (1970) = (4 − 12) × 10 15 CdTe detector [239] (1988) = [9.3 ± 0.5(stat) ± 1(syst)] × 10 15 CdWO4 LT bolometer [240,241] (1994) = (7.7 ± 0.3) × 10 15…”

“…The IPP in the α decay has been measured for 210 Po, 239 Pu, and 241 Am (see Ref. [15] for a recent measurement and references therein).…”