Development of the STEFF detector for the neutron Time Of Flight facility (n TOF), CERN.

Abstract

Significant work has been performed on the development of STEFF (SpecTrometerfor Exotic Fission Fragments), a 2E2V (2-Energy 2-Velocity) spectrometer built bythe University of Manchester Fission Group. The majority of this work was in thedevelopment of the time-of-ight systems, in particular the stop detector; withthe main goals of improving the timing resolution and the detection effciencyof the fission fragments. Further development of the STEFF spectrometer wasdone to enable 2E2V measurements of the 235U(n,f) reaction with coincident measurements using a white neutron spectra of energies ranging from 10 meV to200 MeV provided by the n TOF (neutron Time Of Flight) facility, CERN.The STEFF spectrometer was successfully operated twice on the ExperimentalArea-2 high ux pulsed neutron beam line resulting in 2E2V measurements forfission events with neutron energies ranging from 20 meV to 10 MeV. The firstexperiment received 1.36x10^18 POT (Protons On Target) with stable conditionsand the second received 1.53x10^18 POT with stable conditions.The development of the stop detector resulted in a replacement MWPC (Multi-Wire Proportional Counter) detector for the second of the two experiments. Thisallowed direct comparison for the timing coincidence resolution, sigma_c, between thestart and stop detectors and gave sigma_c = 0.81+/-0.08 ns for the prior PPAC (ParallelPlate Avalanche Counter) detector and sigma_c = 0.40 +/- 0.04 ns for the MWPC. TheMWPC gave improved the detection eficiency per fission fragment of Eff = 0.67compared to Eff = 0.43 for the PPAC.The methods and research described in this work also provided alternate stopdetector designs with greater performance. This work produced two large data setsfrom the two successful deployments of the STEFF spectrometer on the n TOFbeam line that will be the future work of many nuclear structure scientists tocome.

Date of Award	1 Aug 2017
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Alastair Smith (Supervisor)