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An experimental study has been made of a number of factors that determine the pulse height resolution of Scintillation Counters. A statistical model is developed from which an analytic expression for the ideal line shape is obtained. Excellent agreement is found with observations using an artificial light pulser. An attempt to understand the noise spectra, exponential and non exponential under various conditions, has been made. A comparison is made between non crystalline organic scintillators and sodium iodide crystals of similar sizes. It is shown that for gamma-ray detection an important contribution to the line width originates with variations in the light collection efficiency from different regions of the scintillators. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Construction details of a 5" diameter 1.7 litre gas scintillation counter are given. The behaviour of the counter when containing He⁴ gas and a mixture of He⁴ and 10% Xe at various total pressures has been investigated. Two 5" photomultiplier tubes and a variety of different gas purifiers were tested in an attempt to obtain the best possible resolution. The pulse height was found to depend sensitively on the purification procedure adopted. A resolution of 10% for the Po²¹⁰ α-peak has been attained in two different chambers containing He⁴ plus 10% Xe. The voltage pulses rose in ≤300 nsec. Intense irradiation of a counter with 6 Mev x-rays caused only a slight increase in the maximum noise level already present from the photomultiplier tube. The behaviour of the counter as a fast neutron detector has been investigated using an uncollimated beam of 4.1 Mev neutrons. Pulses from recoiling protons and C¹² nuclei were observed as well as the He⁴ recoils. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

published_or_final_version / Physics / Master / Master of Science

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LD2668 .T4 1949 S73 / Master of Science

Scanning surveys of building surfaces and land areas are performed with radiation detection equipment to identify areas of elevated radioactivity. To quantify the extent and magnitude of the contamination, follow-up radiation surveys and soil sampling are usually required. The ability to accurately quantify discrete locations or "hot particles" of contamination requires a full understanding of the scanning detection efficiency of the instrument being used. A cylindrical sodium iodide detector's scanning detection efficiency was examined theoretically using the Monte Carlo N-Particle Code, version 4b, and examined experimentally using the Marianno Research Sled located in the Department of Nuclear Engineering, Oregon State University. A method is described for predicting instrument scanning detection efficiency for a 1 s observation interval over a range of scanning speeds using a series of static detection efficiency measurements. Testing of the prediction method and accuracy of predicted values was performed by comparison to experimentally determined values of scanning detection efficiency. Additionally, the validity of the predicted scanning detection efficiency values was tested by quantifying a radioactive source at a number of scanning speeds to quantitatively determine its activity. Activity values determined by scanning the source were compared against an activity value determined a by high purity germanium detection system. Results indicate that the method is both easy to perform and provides statistically accurate scanning detection efficiency values that can be utilized for the quantification of discrete locations or "hot particles" of radioactive contamination. / Graduation date: 2002

Thesis (M. Sc.)--University of Hong Kong, 1967. / Mimeographed.

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