Eur. Phys. J. A (2013) 49: 64
https://doi.org/10.1140/epja/i2013-13064-1

Regular Article - Experimental Physics

New search for correlated e⁺e^- pairs in the decay of ²⁴¹Am

¹⁹⁸⁹⁴ INFN, Sezione Roma “Tor Vergata”, I-00133, Rome, Italy
²⁹⁸⁹⁴ Dipartimento di Fisica, Università di Roma “Tor Vergata”, I-00133, Rome, Italy
³⁹⁸⁹⁴ INFN, Sezione Roma, I-00185, Rome, Italy
⁴⁹⁸⁹⁴ Dipartimento di Fisica, Università di Roma “La Sapienza”, I-00185, Rome, Italy
⁵⁹⁸⁹⁴ INFN, Laboratori Nazionali del Gran Sasso, I-67100, Assergi (AQ), Italy
⁶⁹⁸⁹⁴ IHEP, Chinese Academy, P.O. Box 918/3, 100039, Beijing, China
⁷⁹⁸⁹⁴ Dipartimento di Ingegneria Civile e Ingegneria Informatica, Università di Roma “Tor Vergata”, Rome, Italy
⁸⁹⁸⁹⁴ Institute for Nuclear Research, MSP 03680, Kyiv, Ukraine
⁹⁹⁸⁹⁴ University of Jing Gangshan, Jiangxi, China

^* e-mail: rita.bernabei@roma2.infn.it

Received: 15 February 2013
Accepted: 3 May 2013
Published online: 29 May 2013

Abstract

A new search for production of correlated pairs in the decay of ²⁴¹Am has been carried out deep underground at the Gran Sasso National Laboratory of the INFN by using pairs of NaI(Tl) detectors of the DAMA/LIBRA set-up. The experimental data show an excess of double coincidences of events with energy around 511keV in faced pairs of detectors, which are not explained by known side reactions. This measured excess gives a relative activity for the Internal Pair Production (IPP) with respect to the alpha decay of ²⁴¹Am; this value is of the same order of magnitude as previous determinations. In a conservative approach the upper limit (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 value obtained in the present work is independent of the live-time estimate.