L. Periale

THE EFFECT OF WAVELENGTH SHIFTERS ON WATER CHERENKOV DETECTORS

Abstract We report the results of a test showing that concentrations of ≈2 mg/l of wavelength shifter in water give almost the maximum efficiency of detection without losing the directionality of Cherenkov light.

Search for low energyνe,μ,τ andve,μ,τ in coincidence with BATSE gamma ray bursts

A search for low energy neutrinos of all flavours in correlation with 553 γ ray bursts detected by BATSE aboard the Compton Observatory has been performed by the LSD (Liquid Scintillator Detector) neutrino telescope. No excess ofνe,μ,τ orve,μ,τ candidate has been detected by LSD during the time interval in which BATSE detected the 90% of the photon flux for any of the GRBs analyzed. Upper limits on the neutrino fluxes are given in the paper.

Study of the low energy background radiation and the effects of the 222Rn in the LSD underground experiment

Abstract A systematic study of the low energy background radiation has been performed under several conditions in the underground experiment at Mt. Blanc laboratory. The information gathered using three different types of detectors: LSD (90 tons of liquid scintillator) with energy threshold E th > 800 KeV , Nal (5” × 5”) with E th > 220 KeV and a Radon-meter (alpha spectrometer) running at the same time, has been analyzed during long and continuous time periods. It was found that the variations in counting rate of the low energy background is due to the presence of 222Rn in the laboratory room. Three types of variations were found: 1) a correlation with the tunnel ventilation system, 2) a daily modulation and 3) a sporadic increase in the counting rate not correlated to any man-made intervention. We emphasize the importance of knowing the background and its variations in underground laboratories dedicated to low energy neutrinos and dark matter searches.

U.H.E. γ‐ray observations with the EAS‐TOP array

The EAS‐TOP array at Gran Sasso (Italy) has been fully operating as a gamma‐ray astronomy observatory since the beginning of 1989 (energy range 1014‐1017 eV). We present the results on search for gamma ray emission from candidate point sources in northern hemisphere obtained by data collected through 1989‐1990. The UHE energy event observed from Crab Nebula on February 23rd, 1989, is also discussed.