Titanium Tritide Research Articles

Preparation and Electrical Performance Analysis of a GaAs‐Based Tritium Battery

A nuclear battery is a promising candidate for small power supply sources in the military and commercial fields, but its output power and energy conversion efficiency need to be improved. This paper mainly describes a design, preparation, and electrical performance analysis of a GaAs-based tritium battery. The design of the tritium battery uses a multistage process with Monte Carlo and Matlab simulations. A titanium tritide source was prepared by a high-temperature tritium absorption device, and a GaAs semiconductor transducer was developed using a metal-organic chemical vapor deposition method. The D/Ti ratio and T/Ti ratio of the deuterium/tritium titanium films were 1.9 and 1.7, respectively. Two kinds of GaAs-based PIN junction semiconductor transducers were proposed and irradiated with the prepared tritium source. Their electrical properties were measured in situ and analyzed qualitatively. Under the irradiation of a 0.61-Ci tritium source, the short-circuit current of the device was 0.3 to 0.38 μA, the open-circuit voltage was 35 to 63 mV, the peak power was 2.8 to 6.4 nW, and the energy conversion efficiency of the GaAs semiconductor transducer was about 1.86%. It was found that an air gap between the GaAs semiconductor transducer and the radioactive source caused serious loss of beta particle energy, resulting in low output power and low energy conversion efficiency of the nuclear battery. The open-circuit voltage of the devices with a SiO2 passivation layer on the surface decreased both in a dark environment and in light illumination, but SiO2 passivation did not reduce surface recombination as expected. The research work in this paper will provide some valuable reference for the preparation and performance optimization of nuclear batteries.

Neutron emission characterization of IPR 14 MeV neutron generator

Accelerator-based neutron sources are being developed worldwide due to their wide applications. Institute for Plasma Research in India has developed an accelerator-based high-yield 14 MeV neutron generator based on deuterium-tritium (D-T) reaction to perform fusion-related benchmark experiments. This neutron generator is designed to produce 1012 neutrons per second in both mode continuous and pulse. The emission of neutrons from an accelerator-based neutron generator is not isotropic due to target geometry and angular dependency of reaction cross-section. A detailed and accurate description of neutron source emission and distribution is required to use such a neutron generator for various experiments. The neutron generator is characterized using experiments and simulations to accomplish the request. Energy and angular distributions of emitted neutrons are measured using a calibrated single crystal diamond (SCD) detector. Experimental data of neutron distributions are used to validate source neutron definition for Monte Carlo N Particle (MCNP) simulation. An accurate model of the Titanium Tritide (TiT) target and its holder geometry is prepared for the simulation. Finally, to validate the simulation model, simulated neutron fluxes are compared with measured ones by the SCD detector. This paper discusses the methodology adopted to characterize emitted neutrons and its results.

Tritium Content Determination in Titanium Tritide Targets from Romanian Decommissioned Nuclear Facilities

The decommissioning or refurbishing processes of nuclear facilities result in significant amounts of radioactive wastes. Radiological characterization is essential to ensure safe handling, transportation, and disposal of these wastes and includes the assessment of the radioactivity levels and types of radioactive materials present in the wastes. The present paper presents the tritium activity determination in used titanium tritide targets from different decommissioned nuclear facilities from Măgurele Area – Romania. The determination of tritium content in tritiated targets involves the use of the Total Combustion technique coupled with Liquid Scintillation Counting analysis of the resulting tritiated water. The tritiated testosterone controlled contaminated titanium powder was used to determine the overall yield of the Total Combustion facility. The determined yields were then used to correct the experimental values obtained during the process.

Helium atom diffusion in titanium tritides (TiT2-x, −0.02 ≤ x ≤ 0.25): A first-principles and kinetic Monte Carlo study

The tritium (T, or 3H) and helium (3He) diffusion properties are critical to the helium bubble nucleation and growth behaviors in tritium storage materials such as titanium tritide (TiT2-x). Hereby, the possible atom migration paths of T and He in TiT2-x as well as their barriers and prefactors are calculated by density functional theory calculations, and are further applied in kinetic Monte Carlo simulations to determine the overall diffusion rates. The correlations of diffusion coefficients of the He atom with temperature in different TiT2-x (0 ≤ x ≤ 0.25) are shown as Arrhenius plots. The results show that two diffusional regimes, migration more via tetrahedral vacancies or octahedral interstitials, are presented depending on temperature and composition for both stoichiometric and non-stoichiometric tritides. Comparing with T, He exhibits similar diffusion mechanisms but faster diffusion rates. Our results suggest that the tritium (or vacancy) concentration, temperature, and axial strain are effective for tuning the diffusion mechanism and rate of a helium atom in titanium tritides.

Prediction of Betavoltaic Battery Parameters

The approaches for predicting output parameters of betavoltaic batteries are reviewed. The need to develop a strategy for predicting these parameters with sufficient accuracy for the optimization of betavoltaic cell design without using the simple trial and error approach is discussed. The strengths and weaknesses of previously proposed approaches for the prediction are considered. Possible reasons for the difference between the calculated and measured parameters are analyzed. The depth dependencies of beta particles deposited energy for Si, SiC, GaN, and Ga2O3 and 20% purity 63Ni and titanium tritide as radioisotope sources are simulated using the Monte Carlo algorithm taking into account the full beta energy spectrum, the isotropic angular distribution of emitted electrons and the self-absorption inside the radioisotope source for homogeneously distributed emitting points. The maximum short circuit current densities for the same semiconductors and radioisotope sources are calculated. The methodology allowing the prediction of betavoltaic cell output parameters with accuracy no worse than 30% is described. The results of experimental and theoretical investigations of the temperature dependence of betavoltaic cell output parameters are briefly discussed. The radiation damage by electrons with the subthreshold energy and the need to develop models for its prediction is considered.

Optimization design of 4H–SiC-based betavoltaic battery using 3H source

This paper describes the theoretical calculation and optimization design of the PN junction betavoltaic batteries with 4H–SiC-based energy converter and titanium tritide source. The self-absorption of radioactive isotope sources and the energy deposition distribution in the semiconductor converter are simulated using the Monte Carlo method. The relationship between doping concentrations and basic factors such as minority carrier diffusion lengths and the width of the depletion region are analyzed via the calculation formulas. Then the maximum output power density and energy conversion efficiency are calculated. The optimal thickness of the titanium tritide film is about 0.7 μm, the doping concentrations are 2.5 × 1016 cm−3, and the junction depth of PN junction is 0.1 μm. The surface recombination velocities of electron and hole are 1 × 106 cm/s, respectively. The maximum output power density and energy conversion efficiency are 0.22 μW/cm2 and 2.37%, respectively.

Regulating the helium bubble nucleation in the titanium tritides by environment temperature during the early aging period

The nucleation of helium bubbles in the early aging stage of tritium storage materials will have an important influence on the bubble growth behavior in the whole of aging. Herein, the nucleation of helium bubbles was adjusted by environment temperature at the first 15 days immediately after preparation of polycrystalline titanium tritide films. The influence of the environment temperature on the nucleation of helium bubbles were studied by X-ray diffraction (XRD), positron annihilation spectroscopy (PAS), thermal helium desorption spectroscopy (THDS) and scanning transmission electron microscopy (STEM). Results demonstrate that the helium bubble nucleation is significantly affected by the environment temperature of −60 °C, 20 °C and 120 °C. The higher the environment temperature, the lower number density of helium bubble in the titanium tritide films. The helium bubble nucleation mechanism is strongly correlated to the helium atom diffusion coefficient that is controlled by the environment temperature. During the following aging, the rate of helium atoms captured by a single helium bubble increases in titanium tritides with low number density bubbles, which accelerates the growth of helium bubbles in the matrix. However, the low number density bubbles also decrease the capture probability of free helium atoms by helium bubbles, resulting in the increase of helium atoms diffusing to infinite size defects such as grain boundaries macroscopically, and accelerating the evolution of helium in titanium tritides.

High power direct energy conversion by nuclear batteries

The literature on direct conversion of radioisotope energy to electricity is reviewed. Considerations of the choice of radioisotope, converter, and device design are discussed. Recommendations for maximum specific power, energy, and lifetime based on available radioisotopes are made. It is found that nuclear batteries have the potential to achieve specific powers of 1–50 mW/g. Devices that utilize the beta emitter titanium tritide (TiT2) as the isotope are found to have the most potential in the short term to meet the combined performance objectives. TiT2 based devices have a specific power of 0.83 mW/g. Higher specific powers are achievable with the alpha emitter Am241 but with significantly reduced operational lifetime. In order to realize the full operational potential of Am241, radiation resistant converter materials will need to be developed.

Planar and textured surface optimization for a tritium‐based betavoltaic nuclear battery

Remote, terrestrial, and space sensors require sources that have high enough power and energy densities for continuous operation for multiple decades. Conventional chemical sources have lower energy densities and lifetimes of 10 to 15 years depending on environmental conditions. Betavoltaic (βV) nuclear batteries using β--emitting radioisotopes possess energy densities approximately 1000 times greater than conventional chemical sources. Their electrical power density (Pe,vol in W/cm3) in a given volume is a function of β--flux surface power density , surface interface type between radioisotope and transducer, β- range, and transducer thickness and conversion efficiency (ηs). Tritium is the most viable β--emitting radioisotope because of its commercial availability, low biotoxicity, half-life, and low energy, which minimizes the penetration depth and damage of transducer. To maximize Pe,vol, tritium in solid or liquid form must be used in the βV nuclear battery. A Monte Carlo source model using MCNP6 was developed to maximize the Pe,vol of a tritium-based βV nuclear battery. First, a planar coupling configuration with different tritiated compounds (ie, titanium tritide and tritiated nitroxide) and a semiconductor transducer (4H-SiC) with thicknesses of 1 and 100 μm were modeled. The results showed that β--source efficiency (ηβ), which is the percentage of energy deposited in the transducer, decreased as the tritiated compound's mass density increased. The highest Pe,vol was dependent on a combination of characteristics: specific activity (Am in Ci/g), mass density, and 4H-SiC layer thickness. The tritiated nitroxide with the highest Am at 2372 Ci/g produced the highest Pe,vol at 2.46 mW/cm3. Second, a 3-D coupling configuration was modelled to increase surface interfacing between the radioisotope source and textured transducer surface. 3-D coupling configuration increased the percentage of energy deposited into the transducer because of more surface interfacing between the transducer and source in the same volume. The tritiated nitroxide was selected as the radioisotope source coupled with five different textured surface feature types. The Pe,vol as a function of textured surface feature and gap, where the radioisotope is located, width was calculated for 1- and 100-μm 4H-SiC layer thicknesses. Results showed that ηβ increased compared with planar coupling configuration (ie, approximately 56.2% increase over planar with cylindrical hole array) except with the rectangular pillar array. Still, the rectangular pillar array produced the highest Pe,vol at 4.54 mW/cm3 with an increasing factor of 2.29 compared with the planar coupling configuration.

Design Principles of Narrow and Wide Bandgap-Based Betavoltaic Batteries

A Monte Carlo electron transport code PENELOPE was used to analyze beta particle energy deposition in semiconductors for titanium tritide and beryllium tritide. The source thickness was incorporated into the model in order to take into account the self-absorption of beta particles in the source material. Furthermore, an isotropic source was modeled with the full beta energy spectrum of tritium to make the beta particle transport method more realistic. The simulated results for a 0.4- $\mu \text{m}$ -thick titanium tritide source with silicon carbide agreed well with the experimental results. The simulated results obtained for an optimized 2.5- $\mu \text{m}$ -thick beryllium tritide source with silicon carbide was about two times higher than the power for a 0.4- $\mu \text{m}$ -thick titanium tritide source with silicon carbide. An approximately two times higher short-circuit current density was obtained for beryllium tritide with silicon compared to silicon carbide. However, the power output density was about $10\times $ higher for silicon carbide. The width of the depletion region for a p-type dopant concentration of $\textsf {1} \times \textsf {10}^{\textsf {19}}/\textsf {cm}^{\textsf {3}}$ and an n-type dopant concentration of $\textsf {5} \times \textsf {10}^{\textsf {14}}/\textsf {cm}^{\textsf {3}}$ is about 1.4 and $2.5~\mu \text{m}$ in silicon and silicon carbide, respectively. The estimated beta particle penetration depth is about 1.48 ± 0.015 and $\textsf {1.03} \pm \textsf {0.015}~\mu \text{m}$ in silicon and silicon carbide, respectively. This suggests that the proper choice of dopant concentrations will achieve greater energy deposition in the depletion region, which in turn will increase the power output.

Optimization design of betavoltaic battery based on titanium tritide and silicon using Monte Carlo code

This article presents the optimization design and simulation of a betavoltaic battery composed of a silicon p-n junction converter and a titanium tritide film as an isotope source. The self-absorption of β particles emitted from the tritium radioisotope in the titanium tritide film and the energy deposition of β particles in the silicon converter are investigated by the Monte Carlo simulation with the Geant4 radiation transport toolkit. The relationships between doping concentrations and basic parameters such as depletion region width, minority carrier diffusion length and leakage current of the PN junction are discussed through the calculation formulas. By optimizing the doping concentrations in the P-type and N-type regions, the optimized betavoltaic battery can maximize the output power and the conversion efficiency based on the energy deposition in the silicon. The results show that the optimal thickness of the titanium tritide film is about 0.7 µm and the optimal doping concentrations of the battery with a PN junction depth of 50 nm are Na=5.75×1019cm−3,Nd=2.95×1018cm−3. Under these parameters, the size 1mm×1mm proposed battery with 2.9 mCi/mm2 3H can achieve the output power 0.902 nW and the conversion efficiency 0.91%. The open circuit voltage, short circuit current and fill factor of the battery are 0.389 V, 3.03 nA and 0.766, respectively.

Evolution of 3He bubble microstructure in TiT2 films during aging

TEM observation was performed on titanium tritide films at He:Ti ratios of 0.036–0.356. Most helium atoms remained in the TiT2 lattice until at a He/Ti ratio of 0.06, almost all helium atoms entered the bubbles. The density of helium bubbles in Ti tritide increased with the increase in helium content, while their size distribution remained almost unchanged until the bubbles in the samples begin to interconnect at a He/Ti ratio of 0.247. Helium bubbles preferred to distribute in Ti {111} planes for all the samples. The morphology of helium bubble distribution changes not only with the density of bubbles but also with the strain in the films. Helium tended to migrate to the grain boundaries, and plenty of cracks were developed along the grain boundaries. The extension of cracks to the film surface is the cause for the large bursts of 3He into the atmosphere. The observed microstructural evolution and its dependence on helium concentration, density of bubble, and stress distribution are discussed in terms of diffusion of interstitial He atoms and their clustering.

Development of tritiated nitroxide for nuclear battery

Beta radioisotope energy sources, such as tritium (3H), have shown significant potential in satisfying the needs of a sensor-driven world. The limitations of current beta sources include: (i) low beta-flux power, (ii) intrinsic isotope leakage and (iii) beta self-absorption. The figure of merit is the beta-flux power (dPβ/dS in μWn/cm2), where an optimal portion of incident beta particles penetrates the semiconductor depletion region. Thus, the goal of this research was to identify a compound to contain a beta emitter that can permit beta-flux power of at least 0.73 μWn/cm2 from one side, where it can be used for both planar and textured semiconductor structures. Nitroxides were chosen because of previous demonstrated deuteration, ease of synthesis, diversity of structure, and pliability. As a proof-of-principle, nitroxide [1] was prepared and tritiated with a specific activity of 103Ci/g. The corresponding tritiated nitroxide in toluene was found to have no measurable 3H2 outgassing after 27 days, thus it was considered stable. After 256 days in solution, analysis of the compound showed only 2% tritium loss, whereas in solid form, there was approximately 50% of tritium loss after 21 days. To compare with the performance of a typical metal tritide carrier, the standard MCNPX Monte Carlo code was used to calculate the beta-flux power of tritiated nitroxide and titanium tritide (0.2 μWn/cm2 and 0.70 μWn/cm2), respectively. The difference between numerical and empirical results of titanium tritide was 4%, showing the model validity. For the tritiated nitroxide to be comparable to titanium tritide in a planar configuration (2-D), the gravimetric density (3H weighted percentage) would need to be at least 9%.

Synthesis and characterization of helium-charged titanium hydride films deposited by direct current magnetron sputtering with mixed gas

Controllable helium-containing TiH2 phase films were prepared on Si (100) substances by magnetron sputtering with hydrogen-helium-argon mixed gas, in order to investigate the helium behavior in titanium tritide. The TiHxHe films were characterized by ion beam analysis (IBA) in which elastic recoil detection (ERD) and Rutherford backscattering spectrometry (RBS) methods are included, X-ray diffraction (XRD) and scanning electron microscope (SEM). It is found that with the increase in the relative hydrogen flow rate (QH: QAr) under the fixed helium flow and sputtering pressure, the hydrogen concentration in TiHxHe films increases at first, and then decreases. Though the hydrogen concentration in TiHxHe films can be greatly increased by increasing the total sputtering pressure, excessive sputtering pressure will deteriorate the crystallization quality. Although the helium concentration mainly relies on the relative helium flow rate of mixed gas during sputtering, the increase of the relative helium flow rate will reduce the concentration of hydrogen in films at fixed sputtering pressure dramatically. Fortunately, suitable relative hydrogen flow and sputtering pressure can maintain a high concentration of hydrogen in the films. Thus TiHxHe films with controllable hydrogen and helium content can be achieved.

High efficiency 4H-SiC betavoltaic power sources using tritium radioisotopes

Realization of an 18.6% efficient 4H-silicon carbide (4H-SiC) large area betavoltaic power source using the radioisotope tritium is reported. A 200 nm 4H-SiC P+N junction is used to collect high-energy electrons. The electron source is a titanium tritide (TiH3x) foil, or an integrated titanium tritide region formed by the diffusion of tritium into titanium. The specific activity of the source is directly measured. Dark current measured under short circuit conditions was less than 6.1 pA/cm2. Samples measured with an external tritium foil produced an open circuit voltage of 2.09 V, short circuit current of 75.47 nA/cm2, fill factor of 0.86, and power efficiency of 18.6%. Samples measured with an integrated source produced power efficiencies of 12%. Simulations were done to determine the beta spectrum (modified by self absorption) exiting the source and the electron hole pair generation function in the 4H-SiC. The electron-hole pair generation function in 4H-SiC was modeled as a Gaussian distribution, and a closed form solution of the continuity equation was used to analyze the cell performance. The effective surface recombination velocity in our samples was found to be 105–106 cm/s. Our analysis demonstrated that the surface recombination dominates the performance of a tritium betavoltaic device but that using a thin P+N junction structure can mitigate some of the negative effects.

Fluorine Assessment of Igneous Rocks by Neutron Activation Analysis

The main goal of the current study was to determine the fluorine in the rock samples coal (SARM-18, SARM-19, and SARM-20), opal glass NBS91 and phosphate rock NBS694 using neutron activation analysis. Neutrons energy of 14 MeV used for irradiation was produced by bombardment of a water-cooled titanium tri-tide target with a beam of deuterons accelerated to a potential of 350 KV to develop a neutron flux (108 n⋅cm-2⋅s-1) on the sample at the neutron generator in the ECN (Netherlands Energy Research Foundation) Petten. This new approach contributes to the existing knowledge of fluorine measurement by the coincidence channels investigation of the positron energy with respect to decay time for each radionuclide element. The present study was designed to determine the fluorine by fast neutron through the reaction of F19 (n, 2n) F18. Interference was treated by irradiating the standard of these elements and reasonable selection of the decay time between the end of irradiation and beginning of counting time. The results of this method indicate that the concentration of fluorine is agreed fairly with literatures.

The3H(d,γ)5He Reaction forEc.m.≤ 300 keV

The 3 H(d , γ )5 He reaction has been measured using a 500-keV pulsed deuteron beam incident on a stopping titanium tritide target at Ohio University’s Edwards Accelerator Laboratory. The time-of-flight (TOF) technique has been used to distinguish the γ -rays from neutrons detected in the bismuth germinate (BGO) γ -ray detector. A stilbene scintillator and an NE-213 scintillator have been used to detect the neutrons from the 3 H(d , n )4 He reaction using both the pulse-shape discrimination and TOF techniques. A newly-designed target holder with a silicon surface barrier detector to simultaneously measure α -particles to normalize the neutron count was incorporated for subsequent measurements. The γ -rays have been measured at laboratory angles of 0°, 45°, 90°, and 135°. Information about the γ -ray energy distribution for the unbound ground state and first excited state of 5 He can be obtained experimentally by comparing the BGO data to Monte Carlo simulations. The 3 H(d , γ )/3 H(d , n ) branching ratio has also been determined.

Thermal desorption behavior of helium in aged titanium tritide films

The desorption behavior of helium in TiT(1.5∼1.8)−x3Hex film samples (x = 0.0022–0.22) was investigated by thermal desorption technique in vacuum condition in this paper. The thermal helium desorption spectrometry (THDS) of aging titanium tritide films prepared by electron beam evaporation revealed that, depending on the decayed 3He concentration in the samples, there are more than four states of helium existing in the films. The divided four zones in THDS based on helium states represent respectively: (1) the mobile single helium atoms with low activation energy in all aging samples resulted from the interstitial sites or dissociated from interstitial clusters, loops and dislocations, (2) helium bubbles inside the grain lattices, (3) helium bubbles in the grain boundaries and interconnected networks of dislocations in the helium concentration of 3Hegen/Ti > 0.0094, and (4) helium bubbles near or linked to the film surface by interconnected channel for later aging stage with 3Hegen/Ti > 0.18. The proportion of helium desorption in each zone was estimated, and dissociated energies of helium for different trapping states were given.

Effects of tritium content on lattice parameter, 3He retention, and structural evolution during aging of titanium tritide

Effects of tritium content on crystal lattice, 3He retention and structure evolution during aging of Ti tritides were investigated using X-ray diffraction, together with analysis of 3He release. Phase transformation and lattice parameters of the Ti tritides varied apparently depending on tritium stoichiometry. Initial tritium content in the Ti tritides showed significant effects on 3He retention due to the existence of α + δ phase boundaries and lattice symmetry in the Ti tritide. The critical contents of 3He release in the α + δ phase region and ε phase region were found to be smaller than that in the δ phase region. Variation of crystal lattice structures of α + δ, δ and ε phases in the Ti tritides has been investigated, and evolution of 3He during aging is mainly governed by the finite defects of self-interstitial atoms, dislocation loops, 3He bubbles, and dislocations created by formation and growth of 3He bubbles. In the α + δ two phase region, the phase boundaries played an important role to accumulate 3He bubbles and cause inter-bubble fracture. In the ε phase region, a preferred condensation of finite defects in basal plane of Ti tritide lattice and formation of a dislocation network were identified.

Thermal desorption of tritium and helium in aged titanium tritide films

Titanium films were deposited onto molybdenum substrates and then converted into titanium tritides (TiT1.5–1.8) films inside a tritiding apparatus loaded with pure tritium gas. Evolution of tritium and helium in the titanium tritide films over a period of four years was investigated using a thermal desorption technique, together with X-ray diffraction analysis. Results showed that desorption profiles of the tritium varied significantly with the evolution of He contents. Apart from the primary peak from tritium desorption located at a temperature between 610 and 840 K, another higher temperature tritium desorption peak (at ∼950 K) was observed, attributed to damages in the lattice structures induced by generation of 3He bubbles. Release of helium in the tritide film became significant after a long term aging process (i.e., after a few years). Depending on the amount of the 3He bubbles generated due to the decay of tritium, spectra of the thermal helium desorption showed five peaks in the range from room temperature to ∼1750 K, corresponding to different states of helium evolution during aging of the titanium tritide films. The amounts of helium desorption in different stages were estimated, and the dissociation energy of helium from different trap states as a function of the aging duration was obtained.