Hydrogen Loading System Development and Evaluation of Tritiated Substrates to Optimize Performance in Tritium Based Betavoltaics
Adams, Thomas E. Ph.D., Purdue University, December 2014. Hydrogen
Loading System Development and Evaluation of Tritiated Substrates to
Optimize Performance in Tritium Based Betavoltaics. Major Professor:
State-of-the-art hydrogen loading system for thin metallic films has been
developed for maximum operational pressures and temperatures up to 69 bar
and 500°C, respectively. Hydrogen loading experiments on aged palladium
films of thickness 50 and 250 nm were conducted at pressure ranging from 0.2
bar to 10 bar. An optimal loading temperature of 310°C was found to be
adequate for hydrogen loading on these aged films. For first time hydrogen
loading on fresh titanium films was carried out at 1 bar and at room
temperature. Emission from metal tritide films has been modeled with MCSET
(Monte Carlo Simulation of Electron Trajectories in solids) to
investigating surface beta flux. Improvements were made in the model to
include film density changes due to tritium loading and effects of beta decay.
Simulation results indicated that a 300 nm slab of MgT2 has surface flux three
times higher than that for ScT2, and six times higher than that for TiT2.
Commercial betavoltaic cells were tested at different temperature conditions
to characterize and assess their performance.
CHAPTER 1. INTRODUCTION
1.1 Significance of Research Problem
Radiation interaction with materials can have beneficial uses, such as in
betavoltaic cells, a type of radioisotope power source that utilize energy of beta
radiation converted into electricity (Adams 2011). The specific development of
betavoltaic devices has arisen out of the need for reliable, long-lived, high
energy density power sources for operating electrical systems in hostile and
inaccessible environments. It is well established that conventional
electrochemical batteries, despite their widespread use in electronic devices,
have limited longevity and a strong tendency to degrade under extreme
environmental conditions (Manasse, Pinajian et al. 1976). For situations
where battery replacement is inconvenient or impossible, such as in remote
sensing applications in space or aquatic environments, and where low-power
generation can be utilized, the diminutive energy generated from a betavoltaic
is suitable as an alternative to electrochemical battery technologies.
Betavoltaic power sources can potentially replace conventional chemical
batteries in many low-power applications, since they can also operate well in
extreme environmental conditions.
Betavoltaics find application in present-day micro-electromechanical and
electronic devices, implantable biomedical prosthetic devices, and in the
military intelligence applications (Guo and Lal 2003; Bao, Brand et al. 2012;
Olsen, Cabauy et al. 2012). Though not new, research and development of
these low-power sources was minimal for many years due to limited low
power applications, rapid semi-conductor degradation, limited availability,
and high cost of suitable radioisotopes (Adams 2011). Current developmental
progress is encouraging, and these sources potentially can provide power to
military and commercial devices for 20 years and beyond.
The ragone plot of power density (W/kg) versus energy density (W-hr/kg) in
Figure 1-1 illustrates where betavoltaic power fits in with other energy storage
devices. Diagonal lines represent duration of operation. In the upper left part
of the plot, super capacitors dominate by delivering large amounts of power
quickly. The bottom right represents devices that deliver low power for long
periods, such as betavoltaics. Radioisotope thermoelectric generators (RTG)
exhibit moderate power and operate for long periods as evident by the Voyager
space probe, which is powered by several kilograms of plutonium-238. Lithium
batteries provide high power, but typically operate for less than 5 years.
Figure 1-1 Ragone plot of energy storing devices