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Test of fast neutron detectors for spectroscopy with (3He,n) two proton stripping reactionsElbasher, Mohamed Elbasher Ahmed 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Nine 100x100x600 mm3 plastic scintillators, formerly built for the neutron time
of ight measurements at iThemba LABS, were refurbished. The position resolution
of these detectors was determined using muon cosmic rays and coincident
measurement techniques. Average position resolution of 4.28 cm (FWHM)
was found. In order to predict the time spectrum of the large-volume detector
Monte Carlo simulations have been performed. These simulations aimed at
anticipating the separation of statistical neutrons, prompt gamma rays and
uncorrelated gamma rays from the fast neutrons emitted in the reaction of
interest. One of the neutron detectors was tested using fast neutrons from
the 232Th( ,xn) reaction at 42 MeV. Statistical neutrons from fusion evaporation
reactions were produced in 152Sm(12C,xn) fusion evaporation reaction.
Coincidences between neutrons and gamma rays were successfully identi ed.
Prompt gamma rays and uncorrelated gamma rays were also identi ed. / AFRIKAANSE OPSOMMING: Nege 100x100x600 mm3 plastiese scintillators, wat aanvanklik gebou was vir
neutron vlugtyds meetings by iThemba LABS, was hernu. Die posisie resolusie
van die detektore was bepaal deurmiddel van muon kosmiese straling en koïnsidensie
meet tegnieke. Posisie resolusie van 4.28 cm (FWHM) was verkry.
Monte Carlo simulasies is gebruik om die posisie resolusie van'n groot volume
detektor te voorspel. Hierdie simulasies is daarop gemik om onderskeid te
maak tussen statistiese neutrone, gelyktydige gamma strale en ongekorreleerde
gamma strale vanaf vinnige neutrone in die reaksie van belang uitgestraal word.
Een neutron detektor was getoets deur gebruik te maak van vinnige neutrone
wat uit die reaksie 232Th( ,xn) by 42 MeV ontstaan. Statistiese neutrone vanaf
splitsings verdampingsreaksies, gelyktydige gamma strale en ongekorreleerde
gamma strale was geidenti seer. Statistiese neutrone van samesmelting verdamping
reaksies was geproduseer in die reaksie 152Sm(12C,xn). Toeval tussen
neutrone en gamma strale was suksesvol geïdenti seer, gevra gamma strale en
ongekorreleerd gamma strale was ook geïdenti seer.
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A MEASUREMENT OF THE PROMPT FISSION NEUTRON ENERGY SPECTRUM FOR <sup>235</sup>U(n,f) AND THE NEUTRON-INDUCED FISSION CROSS SECTION FOR <sup>238</sup>U(n,f)Miller, Zachariah W. 01 January 2015 (has links)
Two measurements have been made, addressing gaps in knowledge for 235U(n,f) and 238U(n,f). The energy distribution for prompt fission neutrons is not well-understood below 1 MeV in 235U(n,f). To measure the 235U(n,f) prompt fission neutron distribution, a pulsed neutron beam at the WNR facility in Los Alamos National Laboratory was directed onto a 235U target with neutron detectors placed 1 m from the target. These neutron detectors were designed specifically for this experiment and employed a unique geometry of scintillating plastic material that was designed to reject backgrounds. Fission fragments were detected using an avalanche counter. Coincidences between fission fragment production and neutron detector events were analyzed, using a double time-of-flight technique to determine the energy of the prompt fission neutrons. A separate measurement was made, investigating the neutron-induced fission cross section for 238U(n,f). This measurement also used the pulsed neutron beam at the WNR facility. The neutron flux was normalized to the well-known hydrogen standard and the fission rate was observed for beam neutrons in the energy range of 130-300 MeV. Using an extrapolation technique, the energy dependence of the cross section was determined. These new data filled a sparsely populated energy region that was not well-studied and were measured relative to the hydrogen standard, unlike the majority of available data. These data can be used to constrain the fission cross section, which is considered a nuclear reaction standard.
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