26 January 1995 Physics Letters B 344 (1995) 72-78 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH PHYSICS LETTERS B The research of 2p decay of ’ %Zd with enriched “%ZdWO4 crystal scintillators EA. Danevich, A.Sh. Georgadze, V.V. Kobychev, B.N. Kropivyansky, V.N. Kuts, A.S. Nikolaiko, V.I. Tretyak, Yu. Zdesenko ’ zyxwvutsrqponmlkjihgfedcbaZYX Institute for Nuclear Research of the Ukrainian National Academy of Sciences, 252028 Kiev, Ukraine Received 7 July 1994; revised manuscript received 16 November 1994 Editor: R.H. Siemssen zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLK Abstract The experiment was performed at the Solotvina Underground Laboratory with CdW04 crystal scintillators enriched in “(?Jd to 83%. The total data collection time was about 30000 hours. Limits of 7$ _>2.9.10” y (90% CL) and T$ >1.8.10’9 y (99% CL) were obtained for Ou2p and 2v2p decay of ‘16Cd. After subtraction of the spectrum obtained with a natural CdW04 scintillator a remaining yield was seen consistent with 2v2p decay of ‘16Cd with T$= {2.7+_odi( stat.)?\%( syst.)}. lOI y. However, the imitation of the effect by impurities of 90Sr (at the level of 2.10e3 Bq/kg) cannot be excluded. 1. Introduction During the last decade remarkable advances have been made in the investigation of double beta decay and the theoretical interpretation. We name here: - a half-life limit of greater then 1O24 y for the Ov2p decay of 76Ge [ I-41 ; - the large scale experiments on 76Ge using enriched HP Ge detectors [ 3,4] ; - half-life limits of greater than 1O23y for the Ov2p decayof’36Xe[5]and1022yfor82Se[6],’00Mo[7] and ‘16Cd [ 81; - a low temperature high energy resolution bolome- ter with a TeOz crystal created for the study of the 2p decay of 13’Te [9]; - observation in direct counting experiments of the 2v2p decay of 76Ge [2-41, 82Se [ 61, ‘O”Mo [ 10-121, ’ E-mail: intemet::kinr@sovam.com; fax: 7(044)265 22 10 ‘16Cd [ 131 and ‘*‘Nd [ 11,141; - progress in the theoretical interpretation of double beta decay [ 15-171. The interest in double beta decay originates from the possibility to study the neutrino properties. It rep- resents the only way to measure an effective Majorana mass of the electron neutrino and it yields presently the most stringent limits on this mass as well as on lep- ton charge nonconservation, right-handed admixtures in the weak interaction, the neutrino-Majoron coupling constant and other parameters of theories beyond the Standard Model. The progress made during the last decade would be impossible without advances in ex- perimental techniques: the success of 2/3 decay exper- iments depends on many factors, the most important of which are the right choice of nuclides for the inves- tigations, the development of adequate detectors with the required properties (a maximal content of nuclei to be examined, a low level of impurities, high effi- 0370-2693/95/$09.50 @ 1995 Elsevier Science B.V. All rights reserved SSD10370-2693(94)01528-7