arXiv subjects

Andrew Gillespie

Publications and source records attributed to Andrew Gillespie.

6 recordsLinked to original sources

arXiv2026

Determination of Tritium Content in D2 Gas and Heavy Water

A simple experimental method for the determination of tritium concentration in natural hydrogen and deuterium gas down to the femtomole level is described. Palladium and platinum catalysts were used to react hydrogen and oxygen, creating water that could be analyzed in a Revvity Quantulus GCT 6220. This analysis produced sub-femtomole detection limits of tritium present in hydrogen gas or heavy water. A contamination level of $\sim 1\text{ femtomole/SL}$ was found in the $\text{D}_2$ gas sample that was analyzed. A contamination level of $\sim 0.025\text{ femtomole/SL}$, which is below the noise level of the Quantulus, was found in the standard hydrogen gas sample that was analyzed. The choice of palladium or platinum catalyst did not significantly affect the resulting tritium measurement. By showing that common $\text{D}_2$ samples can be contaminated with trace amounts of tritium orders of magnitude above natural abundance, this test demonstrates that a baseline tritium measurement for deuterium samples is highly important for determining the validity of results in nuclear fusion yield experiments.

nucl-ex↗

arXiv2026

Alpha Particle Induced Collision Cascade Fusion

We report experimental and computational investigations of a collision-cascade mechanism to induce deuterium-deuterium (D-D) fusion. Evidence of neutron production was observed from a pressurized deuterium target exposed to energetic alpha particles emitted by a $^{210}\text{Po}$ source. A 5-mCi $^{210}\text{Po}$ alpha source was placed within a chamber containing pressurized deuterium gas, and neutron emission was monitored for 18 h using two Mirion SN-S $^{3}\text{He}$ neutron detectors. Alpha particles incident on pressurized deuterium gas produced an average excess of $\sim$74 neutrons after background subtraction, corresponding to a fusion neutron rate of $\sim$2.24 n/s. With LiD in the pressurized deuterium, the average excess increased to 268 neutrons, corresponding to 8.1 n/s. Since D-D fusion branches into two equally likely pathways, these correspond to a fusion rate near 4.5 and 16.2 fusions per second, respectively. MCNP simulations incorporating experimental geometry, source activity, and detector configuration predicted neutron yields within 5.4% of the measured values and reproduced the detector response within experimental uncertainty. The tight agreement between measured and simulated neutron counts suggests that energetic alpha-particle interactions within the deuterium may contribute to measurable D-D fusion reactions through the D(d,n)$^{3}\text{He}$ channel.

nucl-ex↗

arXiv2026

Production of Low-Density Aerogel Nuclear Fuels for Use in Fission Fragment Rockets and Novel Reactor Design

Graphene hydrogels were created and loaded with uranyl nitrate or thorium nitrate and freeze-dried to produce graphene aerogel nuclear fuels. These aerogels had densities between 0.018-0.035 g/cm3 and consisted of ~7.3 +- 0.5% uranium/thorium by mass. The ultra-low density of the aerogels allows for high energy ions to escape the fuel particles without depositing all their energy as heat, as is typical in nuclear fuels. Their measured alpha activity was ~16 pCi/mg, which could be enhanced up to ~49 pCi/mg by decreasing the thickness of aerogel samples to allow all alpha particles to escape. Additionally, high energy neutrons were used to induce fission to provide a source of fission fragments from the aerogel fuels. This novel form of nuclear fuel has potential applications in space propulsion such as fission fragment rocket engines, as well as in terrestrial applications for modular reactors, direct conversion methods, and in medical radiotherapeutics.

cond-mat.mtrl-sci↗

arXiv2025

Boron Nitride Coatings for the Enhanced Detection of Neutrons in CR-39

The neutron detection efficiency of Columbia Resin 39 (CR-39) nuclear track detectors was assessed for AmBe, 252Cf, and D-T (14 MeV) neutron source spectra. A boron nitride (BN) coating for CR-39 was developed to enhance the neutron detection efficiency by converting neutrons into energetic alpha particles through the well-known 10B(n,a)7Li reaction. Separate partially coated CR-39 pieces were exposed to each neutron source and subsequently analyzed under optical microscope and through large-area Scanning Electron Microscopy (SEM) imaging over the irradiated area. The detection efficiency (tracks per neutron) was evaluated for each source spectra under optical and scanning electron microscopes and with or without BN coating. This resulted in a comprehensive guide to neutron detection with various sources using CR-39.

physics.ins-det↗

arXiv2024

Progress in Fission Fragment Rocket Engine Development and Alpha Particle Detection in High Magnetic Fields

In this article, we present our recent experiments on fission fragment rocket propulsion, and on an innovative new design for an alpha particle detection system that has been inspired by these rocketry results. Our test platform, which operates within high magnetic fields 3 T over a large cross$\unicode{x2013}$section (approximately 40 cm in diameter), has been used as a test platform to evaluate the containment and thrust within a future fission$\unicode{x2013}$fragment rocket engine (FFRE). This much more efficient nuclear rocket propulsion FFRE design was first proposed in the 1980s with the intent of greatly reducing transit times in long$\unicode{x2013}$duration space travel. Our objective is to enhance the operational efficiency of this nuclear rocket while gaining deeper insights into the behavior of fuel particles and of the fission$\unicode{x2013}$fragment ejecta within strong magnetic fields experimentally. Through a combination of simulations and experimental work, we established a method for the production and detection of alpha particles as a surrogate for fission fragments. To achieve this, we employed Americium$\unicode{x2013}$241 ($^{ 241}$Am) sources, which were situated within a cylindrical vacuum chamber positioned in a 3$\unicode{x2013}$T Siemens MRI superconducting magnet. By simulating, measuring, and analyzing the emitted alpha particle flux, we gained valuable information about the distribution and likelihood of escape of fission fragments in a future FFRE design. This approach could potentially achieve both high specific impulse and power density in advanced nuclear propulsion systems, such as the FFRE. More generally, this work provides a powerful new approach for analyzing ion flux and nuclear particle or nuclear reaction fragments from a wide variety of experimental designs.

physics.ins-det↗

arXiv2024

Simulation and Experimental Analysis of Aerogel Attenuation for High Energy Alpha Particles in Fission Fusion Fragment Rocket Applications

Emerging studies are geared toward exploring new methods of nuclear rocket propulsion to provide more efficient space transit beyond Earth's orbit. One method is to employ a Fission Fragment Rocket Engine utilizing fissionable layers embedded in a low-density aerogel. A quantitative understanding of particle attenuation is essential for developing a functional prototype that permits fission fragments to escape the layers and contribute to specific impulse rather than being attenuated and generating waste heat. In this investigation, the MCNP code was used to theoretically analyze the attenuation of alpha particles from Am-241 sources within aerogel materials. Simulations were conducted on aerogels with various densities and compositions. These simulations aimed to predict the expected intensity of alpha particles reaching a detector. CR-39 was employed as a Plastic Nuclear Track Detector to assess particle attenuation by the aerogels. The threshold areal density of atoms was found to be around $10^{ 20}$ atoms/$cm^{ 2}$ for the three materials studied in this project. Using a 0.22 mm thick SiO$_2$ aerogel with a density of 90 mg/$cm^{ 3}$, which exceeds the threshold, nearly all alpha particles were attenuated. Conversely, employing a 1.6 mm thick graphene aerogel with a density of 12.5 mg/$cm^{ 3}$ resulted in an average attenuation of 32.3%.

physics.ins-det↗