New Glasses for Low Background Countings

Abstract

The following characteristics of glass materials suitable for liquid scintillator container vials and shell tubes of external cathode G-M counters are discussed: (1) natural radioactivities in glass materials, (2) optical transmittance and index, (3) phosphorescence emitted from glass materials excited by visible light, (4) chemical resistance of glass materials to scintillator solvents e.g. toluene, (5) suitability for shell tubes of G-M counters. Particularly, correlations between counting rates in ¹⁴C energy region and potassium contents in various glasses are experimentally determined. Phosphorescence emitted from Superrex Glass (Vycor equivalent) is observed, whose decay constant is ea. 30 sec. Higher counting rate is obtained for a uranium glass than a quartz, but no decaying component of them is observed. The alkaline component of a glass solved into hot toluene is not detected within errors of the measurement. As the results of the mentioned above a new glass (LB-47) for container vials of liquid scintillators is produced, whose contents of potassium oxide is 0.0116 (1±0.07) weight %. In the case of 200 ee vials made of LB-17 the background counting rate caused from ⁴⁰K in the glass is estimated to be ca. 0.4 epm in the quarter of ¹⁴C energy region. While, , for shell tubes of external cathode G-M counters a glass, named LB-96, is newly developed. It contains potassium oxide of 0.014-0.020 weight % and has specific resistance of 7.5-15×10¹¹ (ohmcm) at 10°C.