MEASUREMENTS OF LIQUID SCINTILLATOR PROPERTIES FOR THE BOREXINO DETECTOR

The optical properties of various scintillators (both single component s and their mixtures) have been measured in order to choose the scinti llator composition offering the best compromise among the requirements of the large volume detector of the Borexino experiment on solar neut rinos. A pre-selection of the most interesting binary or ternary mixtu res has been carried out by using a relatively simple and fast optical method. This is based on the UV excitation of the solvent and the obs ervation of the emission properties in the spectral region of interest . Tile results obtained allowed the light output, response time and at tenuation lengths to be evaluated for a broad range of mixtures. The m ixtures offering the best properties for Borexino have been investigat ed in greater depth by using ionizing radiation as excitation source. The results were found to be in good agreement with those obtained by the optical method. In addition, the alpha quenching and the time resp onse of the scintillators to alpha and beta particles have been tested to evaluate the alpha/beta discrimination capability. The comparison of the results obtained in four laboratories using different technique s and methodologies, offered an exhaustive picture of the scintillator properties and provided the criteria for a good choice of the mixture for Borexino.