2009: Smallest Known Q Value of Any Nuclear Decay: The Rare beta- Decay of 115In–>115Sn

Phys. Rev. Lett. 103, 122501 (2009)

J. S. E. Wieslander,1,2 J. Suhonen,2 T. Eronen,2 M. Hult,1 V.-V. Elomaa,2 A. Jokinen,2 G. Marissens, M. Misiaszek,3 M. T. Mustonen,2 S. Rahaman,2 C. Weber,2 and J. Äystö2

1)EC-JRC-IRMM, Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel, Belgium
2)Department of Physics, P.O. Box 35 (YFL), FIN-40014 University of Jyväskylä, Finland
3)Marian Smoluchowski Institute of Physics, Jagiellonian University, ul. Reymonta 4, 30-059 Krakow, Poland



The ground-state-to-ground-state Qbeta- value of 115In was determined to 497.68(17) keV using a high-precision Penning trap facility at the University of Jyväskylä, Finland. From this, a Qbeta- value of 0.35(17) keV was obtained for the rare beta- decay to the first excited state of 115Sn at 497.334(22) keV. The partial half-life was determined to 4.1(6)×1020 yr using ultra low-background gamma-ray spectrometry in an underground laboratory. Theoretical modeling of this 2nd-forbidden unique beta- transition was also undertaken and resulted in Qbeta-=57-12+19 eV using the measured half-life. The discrepancy between theory and experiment could be attributed to atomic effects enhanced by the low Q value. The present study implies that this transition has the lowest Q value of any known nuclear beta decay.