SPIDER IC (MS Thesis)

At the University of New Mexico (UNM) I worked as a graduate research assistant for Dr. Adam Hecht in the nuclear engineering department. With the help of two undergraduate students, I redesigned an existing ion chamber (IC) in order to optimize the energy measurement resolution and to allow for a secondary measurement to be taken. By redesigning the electrical signal outputs, I was able to pull off two timing signals and measure a time-of-flight (TOF) of alpha particles and fission fragments.

Our project was done in collaboration with Los Alamos National Laboratory (LANL), this gave me experience working at the LUJAN center with engineers and researchers. This detector project has also allowed me to exercise my skills in Solidworks CAD design and draft drawing in order to design a thin Mylar window frame to hold chamber pressure differentials. I have been able to communicate my various mechanical designs to machinists in another department. My Master’s project has given me further experience with in-lab equipment, design, analysis, testing, technical writing, public speaking, and electronics debugging.

Thesis Available Here

The 2.5 micron Mylar window attached to my newly designed aluminum “mesh” backing plate. Using SolidWorks, I designed this window piece, as well as the Teflon isolation pieces for the IC.

The electrically isolated window that I designed using SolidWorks. This window uses a piece of 2.5 micron thick Mylar stretched over a 3 cm diameter hole, to hold a pressure differential of up to 350 Torr between the IC and TOF chambers. Electrical isolation is achieved through the large Teflon seal.

Undergraduate poster by Paul Gilbreath and Corey Vowell on the ionization chamber. Presented at the ANS student conference, April 2014.

Inner electrodes, cathode, anode, and Frisch grid of the ionization chamber.

ANS Student conference presentation paper on fission fragment spectroscopy. Presentation given at Penn State, April 2014.

Plot generated from IC timing and energy data showing two distinguishable groups of light and heavy fission fragments from a Cf-252 source.

An image of our oscilloscope reading in comparison to previous research done by T. Sanami. You can see a time difference between the peaks for the cathode signal (blue, ‘start’ signal) and the anode signal (yellow, ‘stop’ signal).

The internal pressure of the IC, external pressure, and external temperature were recorded to determine if the pulse heights read out from the IC were being affected by the building HVAC system. This data was recorded using an Arduino Uno microcontroller that utilized a voltage divider circuit to record the internal pressure from the piezo gauge, as well as a Bosch BMP180 pressure and temperature sensor. The data was saved to a .txt file every 5 seconds from the Arduino using a python script that I wrote.

Correlated time-of-flight and IC analyzed mass data for Pu-239 and Cf-252 alpha particles.

Preliminary Results of a 2v-2E Fission Fragment Spectrometer. Poster presented at UNM Shared Knowledge Conference, April 2014.

Our lab recently received a DOE research grant to continue working on this project with Los Alamos National Labs. Here is a recent image of our ionization chamber data, taken using a thermal energy neutron beam at Los Alamos’ LANSCE facility.

Publications:

K. Meierbachtol, F. Tovesson, D. Shields, C. Arnold, R. Blakeley, T. Bredeweg, M. Devlin, A.A. Hecht, L.E. Heffern, J. Jorgenson, A. Laptev, D. Mader, J.M. O׳Donnell, A. Sierk, M. White, “The SPIDER fission fragment spectrometer for fission product yield measurements,” Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Volume 788, 11 July 2015. (https://www.sciencedirect.com/science/article/pii/S0168900215002314)

Abstract:
We developed the SPectrometer for Ion DEtermination in fission Research (SPIDER) for measuring mass yield distributions of fission products from spontaneous and neutron-induced fission. The 2E–2v method of measuring the kinetic energy (E) and velocity (v) of both outgoing fission products has been utilized, with the goal of measuring the mass of the fission products with an average resolution of 1 atomic mass unit (amu). Moreover, the SPIDER instrument, consisting of detector components for time-of-flight, trajectory, and energy measurements, has been assembled and tested using 229-Th and 252-Cf radioactive decay sources. For commissioning, the fully assembled system measured fission products from spontaneous fission of 252-Cf. Individual measurement resolutions were met for time-of-flight (250 ps FWHM), spacial resolution (2 mm FHWM), and energy (92 keV FWHM for 8.376 MeV). Finally, these mass yield results measured from 252Cf spontaneous fission products are reported from an E–v measurement.