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The total neutron cross section of N¹⁴ was measured for neutron energies from 3.6 to 4 Mev. A 15-cm.-long liquid Nitrogen cell was irradiated with monochromatic neutrons from the D(d,n)He reaction, going in energy steps of approximately 15 kev. The transmission was measured at each energy, using a propane recoil counter for counting the transmitted neutrons. An identical counter was used at 90° for monitoring. The results appear to confirm Stetter and Bothe's measurements, which were made with a continuous neutron energy distribution. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Several simple and rugged neutron detecting scintillation counters have been built. The counters consisted of many layered lucite and zinc, sulfide powder sandwiches placed on the end of Dumont 6292 photomultipliers. One of these counters was used to measure the yield and angular distribution of neutrons produced by the bombardment of heavy ice with 1.5 Mev protons (below the D(pn)2p threshold). The angular distribution of the neutrons was found to be somewhat anisotropic and to depend on target thickness, the anisotropy increasing with target thickness. It is proposed that the neutron production is due to a double process; deuterons after being struck by incident protons collide with further deuterons in the target producing D(dn)He³ neutrons. This proposal has been confirmed by comparison of the experimental results with calculations for thin and thick targets of the yield and angular distribution of neutrons to be expected from the double process. A further confirmation has been obtained experimentally by observing that the yield of neutrons is proportional to the square of the D₂0 concentration in mixed D₂O and H₂O targets. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (Ph. D.)--Virginia Polytechnic Institute, 1963. / Vita. Abstract. Includes bibliographical references (leaves 63-66). Also available via the Internet.

Thesis--University of Michigan, 1967.

An in-core experiment is proposed to measure all delayed-neutron parameters (λᵢ and βᵢ for each delayed group) and the neutron generation time applicable for a given reactor system. The method uses a least-squares fitting technique to simultaneously fit a series of transient responses produced by step changes (or rapid ramps) in reactivity of arbitrary size. The function which is least-squares fit is the exact analytic solution describing a reactor response following a step change in reactivity as given by the standard multi-group point-reactor model. The method does not require any knowledge of the absolute reactivity of the system. The results are based solely upon the measurable quantities of relative power, time, and asymptotic inverse period. Unlike out-of-core delayed neutron experiments, the results are independent of the total number of fissions that have occurred in the fissioning isotope that produced the delayed neutrons, and are independent of the efficiency of the detector used to monitor the transients. Modal contamination is presumed not to be a serious problem in small or intermediate size cores as long as small reactivity changes are used (i.e. +$.10 to -$.25), which is consistent with the best method of performing this experiment. The method is equally applicable to both homogeneous and heterogeneous reactors and may be used in either thermal or fast systems. The number of delayed-neutron groups is not a constraint.

A Bonner Sphere neutron spectrometer for low background environment was developed. The spectrometer consists of a 3He neutron detector, eight high density polyethylene spheres with size ranging from 5-inch to 12-inch and two Lead shells with thickness 1cm and 2 cm, which is used to increase the detect efficiency at high energy range. The dead time of the spectrometer is about 3.7 microseconds, which is mainly contributed by the extended TTL signal from the DAQ. The background of 3He detector is measured in CJPL which is the deepest underground laboratory in the world. The detector background is 15.50 × 10-4 ± 8.1 × 10-5 counts per second. The responses of Bonner Spheres were obtained by Geant4 Monte Carlo simulation. The responses were verified by a 241AmBe neutron source in HKU. A genetic algorithm unfolding program(GA) was developed and tested by unfolding the 241AmBe neutron source. The background neutron in HKU Observatory was measured by the spectrometer and unfolded by GA s. The unfolded neutron flux is (56.84 ± 6.01) × 10-4 s-1 cm-1 by NSUGA version 3 and (56.43 ± 2.53) × 10-4 s-1 cm-1from NSUGA_FORTRAN. Another unfolding program "Equalizer" with different algorithm, by scaling a initial guess spectrum, was also used to unfold the background spectrum in HKU Observatory. The unfolded neutron flux from "Equalizer" is (51.69 ± 2.79) × 10-4 s-1 cm-1. The neutron flux from three unfolding programs agree with each other. The measurement was repeated in Daya Bay EH1 and the results were used to unfold the background neutron spectrum. The unfolded spectrum flux was (34.50 ± 3.13) × 10-5 s-1cm-1from NSUGA version 3, (35.13 ± 1.45) × 10-5 s-1cm-1 from NSUGA_FORTRAN. The unfolded neutron fluxes from GA s agree with each other. However the shape of spectra shows a chaotic pattern in low energy region. The unfolded neutron flux from "Equalizer" is (30.85 ± 1.95) × 10-5 s-1c m-1. The unfolding programs show a dominant thermal neutron peak, a tiny (α, n) peak and a small cosmic-ray neutron peak. The Bonner Spheres Spectrometer has flaws due to the geometry and the nature of unfolding process. Some ideas are suggested to minimize the effect from the error sources. / published_or_final_version / Physics / Master / Master of Philosophy

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