LARGE-VOLUME CSI(TL) SCINTILLATORS FOR EXOTIC PARTICLE SEARCH IN ZR-90

The E0 transition of first excited Zr-90 nucleus has been studied with an octagonal configuration of 30 cm length CsI(Tl) scintillators and a strong Sr-90 beta source. To study a contribution of yet unknown neu tral particles or phenomena in this transition, the precision measurem ent of even conventional transition processes with electron- and photo n pairs is necessary. The rates for these transition modes are substan tially small, and the background reduction from the data is of primary importance. Based on the present observation, we introduce somewhat n obel attempt to the efficient rare decay experiment as well as a metho d for position measurement of low energy gamma rays.