Nuclear Emissions from Metal Bodies (PhD Research)

My secondary project work is with Dr. Lindy Elkins-Tanton on characterizing the radiation environment of iron meteorites that may be related to 16-Psyche. This project came about when my sister-in-law gifted me an iron meteorite for Christmas, and I said, “I want to irradiate this.” Our experiments use DT & DD neutron generators, spontaneous fission sources, GRNS, and metallic samples. These experiments were done through continued collaboration with Dr. Burks at LLNL and planetary scientists at JHU APL.

Gamma-ray spectroscopy is a well-known technique used in measuring planetary elemental compositions and provides key information for understanding planet formation and evolution. Metal dominated asteroids, such as (16) Psyche and (216) Kleopatra, are hypothesized to be the remnants of exposed cores of protoplanets; future spacecraft missions to these metal bodies may include neutron and gamma-ray spectrometers (GRNS). In this study, we used neutron generators and spontaneous fission sources to irradiate a variety of iron-nickel meteorites, as well as other materials, based on hypothesized formation histories and inferred rock geochemistries related to Psyche-specific scenarios. Below are some of the preliminary results of our active neutron experimental studies of prompt gamma-rays resulting from inelastic neutron scatter on metal dominated objects and other Psyche-related compositions.

Neutron activation analysis of iron IV meteorite samples with the GeMini, a high-resolution gamma-ray spectrometer designed for extraterrestrial missions, podium presentation given at LunGradCon, the seventh annual Lunar and Small Bodies Graduate Conference at NASA Ames, CA, July 2016. Image from APL.

Gamma-ray spectra from multiple test samples using a DD (2.45 MeV) neutron generator. Key elemental lines are labelled.

Gamma-ray spectra for five target sample materials with incident DD (2.45 MeV) neutron source. Present in the spectra are 27-Al (2211 keV), 1-H (2224 keV), and 32-S (2230 keV).

Example python curve fitting and peak deconvolution for various datasets resulting from NAA. (A) Fitting the 1236 keV iron peak for DT activation of an Odessa iron IAB-Mg meteorite. (B) Fitting the magnesium (1348 keV), iron (1236 keV), and nickel (1332 keV) peaks for DD activation of a Sericho pallasite. (C) Fitting the iron (1408 keV) and nickel (1454 keV) peaks for DT activation of am Odessa meteorite. (D) Fitting the sulfur (2230 keV) peak for DD activation of a terrestrial iron pyrite sample.

MCNP 6.1 output grid for the neutron energy spectrum of pallasite material with a wt % change in sulfur. Note that this is very similar to the neutron energy spectrum expected at (16) Psyche. The addition of sulfur to the neutron spectrum has very little overall effect, though there is some the suppression of thermal neutrons (low energy). The source used is the result of a GCR photon spectrum.

MCNP 6.1 output grid of gamma-ray spectra of pallasite material with a wt % change in sulfur. Note that the inset plot is on a logarithmic scale. This output has not yet gone through an instrument response function and was done as a photon surface tally (20% HPGe will be the instrument used). The source used is the result of a GCR photon spectrum.

Public Abstracts/Presentations:

AGU Abstract Fall Meeting 2018 Download

AGU Poster Fall Meeting 2018 Download

Publications in prep:

Working Title: Neutron activation and bulk geologic sample gamma-ray measurements: Experimental methods and application to nuclear spectroscopy of asteroid (16) Psyche (First Author, in-prep)

Abstract:
Gamma-ray spectroscopy is a well-known technique used in measuring planetary elemental compositions and provides key information for understanding planet formation and evolution. Metal dominated, M-class, asteroids, such as (16) Psyche and (216) Kleopatra, are hypothesized to be the remnants of exposed cores of protoplanets; future spacecraft missions to these metal bodies may include neutron and gamma-ray spectrometers (GRNS). In this study, we used neutron generators and spontaneous fission sources to irradiate two iron-nickel meteorites (a Sericho pallasite and an Odessa IAB-MG iron meteorite), as well as other materials, based on hypothesized formation histories and inferred rock geochemistries related to Psyche-specific scenarios. Here we describe and present the details of our systematic active neutron experimental study of prompt gamma-rays resulting from inelastic neutron scatter on metal dominated objects and other Psyche-related compositions. We introduce a new method of active interrogation on bulk meteorite samples (2-15 kgs) and compare the method to known values from the literature. We report on experimental sensitivity limits for various samples interrogated based on input neutron energies and discuss possible limitations for detection on asteroid (16) Psyche using passive GRNS instrumentation.

Working Title: Alternative iron and nickel emission lines for determining planetary elemental abundances in high-energy neutron environments (Co-Author, in-prep)