Purdue University Graduate School
Cheu_Dissertation_Final.pdf (13.87 MB)

Optimization and Evaluation of Tritium Storage Mediums for Betavoltaic Devices

Download (13.87 MB)
posted on 2023-04-25, 01:21 authored by Darrell Shien-Lee CheuDarrell Shien-Lee Cheu


Betavoltaics are self-contained  radioisotope power sources where radioisotopes irradiate a semiconductor and  generate electricity similar to a photovoltaic cell. Betavoltaics differ from  other power sources as it is ideal for long-lasting (>20 years), low,  continuous power applications where battery replacement is not feasible. Ideal  functions for betavoltaics include sensors in hard to reach places such as  underwater and deep space applications, as well as cardiac pacemakers where  power source replacement is undesirable or impossible. However, betavoltaics  are limited in application by its power output since it only produces power in  the nanowatt range. Betavoltaic performance can be improved by two methods:  Increasing the amount of activity of the radioisotope or increasing the  performance of the semiconductor. Currently, commercial betavoltaics utilize a  titanium tritide film to irradiate a gallium arsenide semiconductor. The  objective of this dissertation is to identify a tritium storage medium that  can produce more power in the betavoltaic than the currently used titanium  tritide. This was done in three steps: First, metal film options were  simulated in MCNP to evaluate tritium substrate self-shielding, semiconductor  beta irradiation and determine ideal thicknesses. Second, metal film options  at ideal thicknesses were manufactured and evaluated during the hydrogen  loading process to determine the viability of materials fully absorbing  hydrogen. Lastly, the loading kinetics would be evaluated to further investigate  hydride/tritide formation in the storage medium if full loading is not  realized to determine the ideal thickness required, or if other factors during  the loading process need to be considered.

Metallic films were evaluated to  maximize tritium packing and optimized for minimizing self-shielding to  improve performance for betavoltaic cells beyond the titanium tritide films  currently used. Ideal, fully loaded tritium metallic films, such as lithium,  aluminum, titanium, magnesium and palladium tritides, were simulated in MCNP6  (Monte Carlo N-Particle 6) to evaluate power deposition into a gallium  arsenide semiconductor by varying the thickness of the films. Lithium was  identified as the best storage option with an optimal thickness of 4 μm and a  theoretical betavoltaic current output of 644 nA for a gallium arsenide  semiconductor, tripling the current output emitted by an ideal titanium-loaded  film. 

The viability of lithium and  aluminum film loading were evaluated in the hydrogen loading system while comparing  to titanium as a benchmark. Unlike titanium and aluminum films where films  were in a solid state through the loading process, lithium has to be melted  into a liquid state to be loaded. The uptake of hydrogen by the films was  determined by Sievert's method, where the pressure drop recorded by the  Hydrogen Loading System was the measured pressure of hydrogen absorbed by the  film. All film loadings showed a pressure drop that corresponded to the  expected pressure drop from loading. The films were characterized after  loading to confirm hydrogen absorption and formation of hydride. Both lithium  and titanium demonstrated hydride formation while the aluminum did not.

The pressure drops during loading  were compared to the Mintz-Bloch model. For some loadings in all materials,  there was good correlation between experimental loadings and Mintz-Bloch  models, primarily due to the hydride formation happening quickly. Differences  can be explained from the speed of the hydride reaction and thermal  decomposition of the hydride during loading. The Mintz-Bloch model further  confirmed that the aluminum did not form a hydride during loading.

Lithium was demonstrated to be a  viable hydrogen loading substrate. The film was characterized to be lithium  hydride after hydrogen loading and its loading kinetics matched very well with  the Mintz-Bloch model. Aluminum was demonstrated to not be viable as a  hydrogen loading substrate as it requires significantly higher pressures,  beyond the allowed limits for tritium handling, to form a hydride and  permanently hold when exposed to atmosphere.


Degree Type

  • Doctor of Philosophy


  • Nuclear Engineering

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Shripad Revankar

Advisor/Supervisor/Committee co-chair

Thomas Adams

Additional Committee Member 2

Stylianos Chatzidakis

Additional Committee Member 3

Yunlin Xu

Usage metrics



    Ref. manager