OCA_D2O_ATTEN.FOR

This routine computes the D2O extinction coefficient and also attempts a crude estimate of the component which due to scattering. Data is selected for lightball positions within 50cm of the vertical (``Z'') detector axis inside the AV. PMTs are considered which lie within 200cm of the detector axis at the bottom of the PSUP. Photons arriving at these PMTS traverse approximately the same lengths of H2O and acrylic with similar incident angles so that effects related to the variation of these quantities can be ignored. For each PMT, at a given wavelength, the number of entries in the prompt peak is corrected for solid angle, laserball angular distribution and the Poisson probability for multiple hits within a single laser pulse. The resulting quantity as a function of the laserball position along the detector axis, yields an estimate of the D2O extinction coefficient. This procedure is repeated separately for each PMT, since each involves different tube/reflector efficiencies and different acrylic tile paths. However, the derived extinction coefficient should be the same in each case. The median of these values (which is more robust to occasional ``pathological'' fits than the average) is thus used to provide a good estimate for the extinction coefficient, and the spread of these values provides an estimate of the statistical uncertainty. These are assigned to the variables OCA_D2O_EXT(IW,1) and OCA_D2O_EXT(IW,2), respectively, where IW gives the wavelength index of the laserball (1-6). These variables are specified in OCA_OUTPUT.INC. This task requires data from at least 2 laserball positions along vertical detector axis.

Finally, a crude estimate of the amount of extinction due to scattering is attempted by fitting a $\lambda^{-4}$ component to the derived parameters. From this, one extracts an approximate isothermal compressibility, OCA_D2O_ISO(1), and its uncertainty, OCA_D2O_ISO(2). This is by no means meant as the definitive way to determine the scattering properties of D2O, but is simply meant as a rough guide and possible consistency check for better tests.