Energy dense power sources are critical to the development of compact, remote sensors for terrestrial and space applications. Nuclear batteries using β-emitting radioisotopes possess energy densities 1000 times greater than chemical batteries. Their power generation is a function of β flux saturation point relative to the planar (2D) configuration, β range, and semiconductor converter. An approach to increase power density in a beta-photovoltaic (β-PV) nuclear battery is described. By using volumetric (3D) configuration, the radioisotope, nickel-63 (Ni) in a chloride solution was integrated in a phosphor film (ZnS:Cu,Al) where the β energy is converted into optical energy. The optical energy was converted to electrical energy via an indium gallium phosphate (InGaP) photovoltaic (PV) cell, which was optimized for low light illumination and closely matched to radioluminescence (RL) spectrum. With 15mCi of Ni activity, the 3D configuration energy values surpassed 2D configuration results. The highest total power conversion efficiency (η) of 3D configuration was 0.289% at 200µm compared 0.0638% for 2D configuration at 50µm. The highest electrical power and η for the 3D configuration were 3.35 nW/cm at an activity of 30mCi and 0.289% at an activity of 15mCi, respectively. By using 3D configuration, the interaction space between the radioisotope source and scintillation material increased, allowing for significant electrical energy output, relative to the 2D configuration. These initial results represent a first step to increase nuclear battery power density from microwatts to milliwatts per 1000cm with the implementation of higher energy β sources.
Summary 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 ()Pβ−, 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.
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