P.P. Sverzellati

New limits on double beta decay of 76Ge

Abstract New results are presented from an experiment on double beta decay of 76 Ge carried out with two Ge Li detectors in the Mont Blanc tunnel. No evidence has been found for neutrinoless double beta decay, and the obtained lower limit of the half lifetime (1.2 × 10 23 yr) is discussed in terms of the mass of Majorana neutrinos and of the possible presence of right-handed currents.

A search for two neutrino and neutrinoless double beta decay of 136Xe in the Gran Sasso underground laboratory

Abstract We have searched for two neutrino and neutrinoless double beta decay of 136 Xe with a multicell proportional counter in the Gran Sasso underground laboratory. The search for the two neutrino channel has been based on the comparison of spectra obtained in runs with natural and enriched xenon and with xenon which had been specifically cleaned with an ultracentrifuge. Special dedicated runs have been carried out with the various gases to evaluate the background from the rate of α-particles. No evidence has been found for two neutrino or neutrinoless double beta decay. The corresponding lower limits on the lifetime are evaluated with a new statistical procedure.

A new experimental limit on electron stability

Abstract Preliminary results are reported of an experiment on electron stability carried out with a Ge(Li) detector in the Mont Blanc laboratory at a depth of about 5000 mwe. No evidence was found either for the disappearance of K electrons in germanium atoms, or for the decay of electrons into a photon and a neutrino. Lower limits of 2 × 10 22 and 3 × 10 23 yr have been set for the corresponding half lifetimes.

A low activity gamma ray spectrometer

Abstract This paper reports on the features of a gamma ray spectrometer designed for very low activity measurement. Part of the measurements have been performed in an underground laboratory in the Mont Blanc tunnel. Comparative results obtained in different experiment conditions are reported.

Measurements of low radioactive contaminations in lead using bolometric detectors

Abstract Bolometric detectors made with samples of crystalline and polycrystalline lead have been operated to measure their internal radioactivity due to 210 Pb. It has been found that contaminations of hundreds of becquerels per kilogram are present in commercial low radioactivity lead and that these contaminations can be reduced by an order of magnitude by crystallisation. A low activity of a few hundreds of millibecquerels per kilogram still persists in specially prepared low radioactivity lead. No evidence for contamination is on the contrary found in a 2000 year old lead sample from a sunk Roman ship, at a level of less than 20 millibecquerel per kilogram.

Underground laboratory and milano double beta decay experiment

Abstract New half-life limits on the double beta decay of 76 Ge and 130 Te are presented. The design of a multielement proportional chamber for a double beta decay experiment on 136 Xe is described and test results obtained with one element counter filled with Ar and Xe are discussed. A comparison between background acitivities in the Mont Blanc and Grand Sasso underground laboratories is presented.

Separation of rare gases from radioactive contaminants by means of an ultracentrifuge

Abstract A sample of xenon enriched in 136Xe has been obtained with the ultracentrifuge system of the United States Department of Energy in Oak Ridge, Tennessee. The same system has also been used for cleanup only, namely to eliminate undesired gas impurities. Measurements of radioactivity carried out with a multicell proportional chamber show that ultracentrifugation is indeed very effective in the elimination of krypton.

A multi-element proportional chamber used in an experiment on ββ-decay of 136Xe

The lower limits on the neutrinoless and two neutrino ββ-decay of 136Xe, obtained with a multi-element proportional chamber, are reported. The sensitivity of the experiment was limited by the level of the background contamination. The experimental apparatus, its performance and the background analysis are discussed in detail.

GAMMA RAY ACTIVITY OF NEODYMIUM SAMPLES

Abstract The gamma ray activity of three samples of natural neodymium has been measured and the concentration of radioactive elements from uranium and thorium chains as well as that from radioactive isotopes of lantanium and lutetium has been quantitatively determined. All the samples show significant contaminations up to p.p.m.

Milano experiment on double beta decay of 136Xe and other nuclides: Status report

Abstract Current status of the Milano group experimental search for lepton number violating double beta decay of 136 Xe and other nuclides is reported. 136 Xe is being investigated using a Multielement Proportional Chamber. A 100 liter high pressure detector is presently running in Gran Sasso underground Laboratory and results from the first 150 hour live time run are presented. The use of calorimetric technique in double beta decay search was recently proposed; characterization of bolometric devices is now in progress and preliminary results are discussed.