FIZIKA B 14 (2005)  2, 139 - 164

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Instituto de Física, Universidade de Sao Paulo, 05315-970 Sao Paulo-SP, Brazil,
Instituto de Física La Plata, CONICET, 1900 La Plata, Argentina, and
Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, 1900 La Plata, Argentina

Paper devoted to honour the memory of Professor Dubravko Tadiæ

Received 6 May 2005;  revised manuscript received 2 August 2005
Accepted 12 September 2005        Online 2 December 2005

The possibility of applying the quasiparticle Tamm-Dancoff approximation (QTDA) to describe the nuclear double beta decay is explored. Several serious inconveniences found in the quasiparticle random phase approximation (QRPA), such as: i) the extreme sensitivity of the 2nbb decay amplitudes M2n on the residual interaction in the particle-particle channel, ii) the ambiguity in treating the intermediate states and iii) the need for performing a second charge-conserving QRPA to describe the bb-decays to the excited final states, are not present in the QTDA. Also, the QTDA allows for explicit evaluation of energy distributions of the double-charge-exchange transition strengths and of their sum rules, and can be straightforwardly applied to single- and double-closed shell nuclei. As an example, the 48Ca®48Ti decay is discussed within the 1fp-shell in the particle-hole limit of the QTDA. The general [(1,1)-Padé-approximant-like] behavior of the 2nbb-decay amplitude in the plain QRPA as well as within its different variations is briefly reviewed.

PACS numbers: 21.80.+a,21.60.-n,13.75.Ev,25.80.Pw
UDC 539.165

Keywords: 2nbb-decay, quasiparticle Tamm-Dancoff approximation, single- and double-closed shell nuclei

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