Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.........5f&link_type=abstract
Thesis (PhD). QUEEN'S UNIVERSITY AT KINGSTON (CANADA), Source DAI-B 60/02, p. 696, Aug 1999, 195 pages.
Astronomy and Astrophysics
Astrophysics
5
Sudbury Neutrino Observatory, Laserball System
Scientific paper
The Sudbury Neutrino Observatory (SNO) is a second generation water Čerenkov detector using 1000 tonnes of heavy water to study neutrino astrophysics. Using deuterium neutrino reactions, SNO will measure the flux and energy spectrum of solar electron neutrinos, and will measure the flavour-blind flux of neutrinos. A nitrogen/multi-dye laser diffuser ball has been designed and installed in SNO for calibration of the electronics, photomultiplier tubes (PMTs) and optical parameters. The laser provides pulsed radiation at 337.1 nm with a 600 psec width and pulse rate up to 50 Hz. The laser can be used directly or as a pump for one of four dye laser resonators, which provides five wavelength selections from 337-500 nm. The light is delivered to a pseudo-isotropic diffuser ball (the laserball) by a 100 μm UV-VIS fibre bundle with less than 1 nsec dispersion at 337 nm. The laserball can be deployed throughout the detector with the rope manipulator system. The laserball output is adjustable from 0.01 to 1000 photo-electrons (PE) and has a pulsewidth of 0.90 nsec at 386 nm and 1.18 nsec at 337.1 nm. A method has been developed for measuring the optical attenuation and scattering in SNO using the laserball and single photo-electron (SPE) PMT time histograms. At SPE intensity the nanosecond PMT timing can be used to separate direct and scattered light, and the extinction coefficients determined using varying path lengths from the source. A calibration function has been developed that accounts for the position and direction dependence of the response for electrons and gamma rays. The calibration function uses simplified or parameterized distributions for the Čerenkov output and detector geometry. The function is fast enough to be built in to neutrino spectrum analysis and can be used to evaluate the uncertainties in the position response. The laserball system has been tested and used to provide a PMT and electronics calibration of the detector for analysis of the airfill commissioning runs. The electronics channels were calibrated for charge pedestals and slopes, time offsets and slopes and discriminator walk (slewing). The PMT occupancies were measured and a method was developed for measuring the mean SPE gain. Finally, event reconstruction was studied for the airfill data, and a time biased reconstruction algorithm was created for cutting flashing PMT events.
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