A Double Time of Flight Method For Measuring Proton Light Yield

Organic scintillators have been used in conjunction with photomultiplier tubes to detect fast/nneutrons since the early 1950s. The utility of these detectors is dependent on an understanding/nof the characteristics of their response to incident neutrons. Since the detected light in/norganic scintillators in a fast neutron radiation field comes primarily from neutron-proton/nelastic scattering, the relationship between the light generated in an organic scintillator and/nthe energy of a recoiling proton is of paramount importance for spectroscopy and kinematic/nimaging. This relationship between proton energy deposited and light production is known/nas proton light yield./nSeveral categories of measurement methods for proton light yield exist. These include/ndirect methods, indirect methods, and edge characterization techniques. In general, measurements/nfor similar or identical materials in the literature show a large degree of variance/namong the results. This thesis outlines the development of a new type of indirect method/nthat exploits a double neutron time of flight technique. This new method is demonstrated/nusing a pulsed broad spectrum neutron source at the 88-Inch Cyclotron at Lawrence Berkeley/nNational Laboratory./nThe double time of flight method for proton light yield measurements was established/nusing two commercially available materials from Eljen Technology. The first is EJ-301, a/nliquid scintillator with a long history of use. Equivalent materials offered by other manufacturers/ninclude NE-213 from Nuclear Enterprise and BC-501A from Saint-Gobain Crystals./nThe second material tested in this work is EJ-309, a liquid scintillator with a proprietary/nformulation recently introduced by Eljen Technology with no commercial equivalents. The/nproton light yield measurements were conducted in concert with several system characterization/nmeasurements to provide a result to the community that is representative of the material/nitself. Additionally, the errors on the measurement were characterized with respect to systematic/nuncertainties, including an evaluation of the covariance of data points produced and/nthe covariance of fit parameters associated with a semi-empirical model./nThis work demonstrates the viability of the double time of flight technique for continuous/nmeasurement of proton light yield over a broad range of energies without changes to the/nsystem configuration. The results of the light yield measurements on EJ-301 and EJ-309/nsuggest answers to two open questions in the literature. The first is that the size of the/nscintillation detector used to measure the proton light yield should not effect the result if/nthe spatial distributions of Compton electrons and proton recoils are equivalent. Second, the/nshape of the scintillation detector should not effect the light yield with the same constraint/non the spatial distributions./nA characterized hardware and software framework has been developed, capable of producing/nproton light yield measurements on additional materials of interest. The acquisition,/npost processing, error analysis, and simulation software were developed to permit characterization/nof double time of flight measurements for a generic system, allowing it to be utilized to/nacquire and analyze data for an array of scintillation detectors regardless of detector size or/ngeometric configuration. This framework establishes an extensible capability for performing/nproton light yield measurements to support basic and applied scientific inquiry and advanced/nneutron detection using organic scintillators.

Advisor: Vujic, Jasmina