SEARCH FOR THE ADMIXTURE OF HEAVY NEUTRINOS IN THE RECOIL SPECTRA OF AR-37 DECAY

Neutrino-induced recoil spectra of Cl-37 ions produced in the electron capture (EC) decay of Ar-37 were measured and searched for the presen ce of massive neutrinos admired to the dominant electron neutrino. Fra ctions of a monolayer of Ar-37 were physisorbed on Au and on several u nderlayers of Ar-40 adsorbed on both Au and graphite substrates cooled to less than or equal to 20 K under ultrahigh vacuum conditions. Time -of-flight spectra of the recoiling ions were recorded in coincidence with x rays and Auger electrons emitted following the EC decay. By sea rching these spectra for peaks with energies between 7.6 eV and 3.6 eV upper limits were placed on the mixing probability of the electron ne utrino with heavy neutrinos in the 370-640 keV mass range. These limit s vary from 1 to 4 %, at the 90% confidence level. [S0556-2813(98)0381 0-2].