power-to-weight ratio is said to be comparable to an air-breathing engine with fuel tanks. The advantage of this design is that precision electrode assemblies are not needed, and most beta particles escape the finely-divided bulk material to contribute to the battery's net power. Disadvantages High price of the radionuclides. High-pressure (up to 10 MPa or 100 bar) heavy containment vessel. A failure of containment would release high-pressure jets of finely-divided radioisotopes, forming an effective dirty bomb. The inherent risk of failure is likely to limit this device to space-based applications, where the finely-divided radioisotope source is only removed from a safe transport medium and placed in the high-pressure gas after the device has left Earth orbit. As a DIY project A simple betaphotovoltaic nuclear battery can be constructed from readily-available tritium vials (tritium-filled glass tubes coated with a radioluminescent phosphor) and solar cells. One design featuring 14 22.5x3mm tritium vials produced 1.23 microwatts at a maximum powerpoint of 1.6 volts. Another design combined the battery with a capacitor to power a pocket calculator for up to one minute at a time. See also Nuclear battery Betavoltaic device Radioisotopic thermoelectric generator Radioisotope piezoelectric generator List of battery types References Polymers, Phosphors, and Voltaics for Radioisotope Microbatteries, by Kenneth E. Bower (Editor), et al. US Patent 7,482,533 Nuclear-cored battery Nuclear technology Battery types