INVISIBLE AXION SEARCH IN LA-139 M1 TRANSITION

A search for invisible axions is Carried out by looking for invisible M1 transitions in La-139(5/2+ --> 7/2+) with a transition energy of 16 6 keV. A limit to the branching ratio of axion emission to that of gam ma emission is obtained to be GAMMA(alpha)/GAMMA(gamma) < 1.21 x 10(-6 ) at the 95% confidence level. Hadronic axions heavier than 26.7 keV a re excluded by this upper limit. It is also concluded that the branchi ng ratio of the second forbidden electron CaptUre decay of Ce-139 into the ground state of La-139(7/2+) is less than 9.7 x 10(-7) at the 95% confidence level.