Algorithms for nuclear data analysis applied to safety and materials

Fang, Ming

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https://hdl.handle.net/2142/106263 Copy

Description

Title

Algorithms for nuclear data analysis applied to safety and materials

Author(s)

Fang, Ming

Issue Date

2019-12-09

Director of Research (if dissertation) or Advisor (if thesis)

Di Fulvio, Angela

Committee Member(s)

Singer, Clifford E.

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Digital
• Post processing
• Nuclear measurements
• Safeguards
• Materials
• Organic scintillator

Abstract

Digital electronics are gradually replacing analog signal conditioning modules in many radiation detection applications. Direct analog-to-digital conversion of radiation-induced signals yields performances comparable to or better than analog electronics, in terms of time and energy resolution. The availability of large amounts of digitized data gives rise to the necessity of processing digital signals efficiently. We have developed a general-purpose pulse post- processing program based on the ROOT framework to process the digital signals acquired with fast digitizers. We have considered the major difficulties in general pulse post-processing, such as anomalous pulse rejection. We have optimized the software to maximize detectors’ time and energy resolution. The program is based on the data processing framework ROOT, which is developed by the European Organization for Nuclear Research (CERN) and is widely used in high energy physics and nuclear physics community. The program is written in C++ and achieves higher processing speed compared with other proprietary software. The program is distributed under a Creative Commons License and is available at GitLab. We used the software to process raw data acquired in two experiments: a Positron Annihilation Lifetime Spectroscopy (PALS) experiment and an active interrogation experiment for the non-destructive assay (NDA) of uranium samples. PALS is a widely-used non-destructive technique used to study defects and vacancies in a variety of different materials. The positron trapping at vacancies in the material results in an increased positron life- time. PALS typically relies on a complex analog coincidence measurement setup. We have developed and optimized a PALS experimental setup using organic scintillators and digital electronics. We have designed a digital filter to accurately recover the pulse shape and implemented a constant-fraction discrimination (CFD) timing algorithm to calculate the pulse arrival time. We achieved an excellent time resolution of 198.3 ± 0.8 ps using plastic scintillators. The experimental setup, coupled with optimized data processing algorithms, was used to analyze the Positron Annihilation Lifetime in two single-crystal quartz samples. We found that the positron lifetimes in quartz are 161 ± 4 ps, 343 ± 12 ps and 1.34 ± 0.05 ns, in good agreement with lifetime values found in the literature for this material. The system will be used to investigate the nature and density of defects in scintillation crystals. We performed the NDA of five different assemblies of natural uranium samples available at NPRE, using a DD fast-neutron generator, operated in pulsed mode. The generator provides higher neutron yield and higher penetrability compared to an 241AmLi source, which is typically used in this application. We used the program to perform pile-up rejection and pulse shape discrimination (PSD) to discriminate and select neutron from gamma- ray pulses. We implemented a shift-register algorithm to calculate the time- correlated neutron count rate. We also measured the rate at which the time- dependent neutron count rate decays after a generator pulse and compared it for the different assemblies. The time-dependent neutron count rate is of potential interest for nuclear treaty verification applications. In future work, we will characterize this signature as a function of differing sample mass and enrichment. The program we have developed is capable of executing complex algorithms at high speed (1E5 pulses/s). It also allows for incorporating other advanced algorithms, making it practical to quickly evaluate the performance of increasingly complex radiation detection systems and their integration into real-time applications.

Graduation Semester

2019-12

Type of Resource

text

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http://hdl.handle.net/2142/106263

Copyright and License Information

2019 by Ming Fang. All rights reserved.

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