Radionuclide batteries

M Radionuclide batteries provide high-performance satellites with electricity when solar energy is not enough. 

Plutonium is the most important transuranium element. Its two isotopes Pu-238 and Pu-239 have the widest applications among all plutonium isotopes. Plutonium-239 is the fuel for nuclear weapons. The detonation power of 1 kg of plutonium-239 is about 20,000 tons of chemical explosive. The critical mass for its fission is only a few pounds for a solid block depending on the shape of the mass and its proximity to neutron absorbing or reflecting substances. This critical mass is much lower for plutonium in aqueous solution. Also, it is used in nuclear power reactors to generate electricity. The energy output of 1 kg of plutonium is about 22 million kilowatt hours. Plutonium-238 has been used to generate power to run seismic and other lunar surface equipment. It also is used in radionuclide batteries for pacemakers and in various thermoelectric devices. 

The latter is used as energy source in radionuclide batteries, for instance in satellites. Ehi is the most important radioclement produced in nuclear reactors. About 9 kg Pu is generated per ton of spent fuel after a burn-up of 35 000 MW d per ton. The main part is - Pu (about 5.3 kg) produced via... 

Energy production by nuclear fission and by thermonuclear reactions has been discussed in chapter 11. In this section, energy production in radionuclide batteries by the radiation emitted by radionuclides will be considered. 

Radiophotovoltaic (photoelectric) radionuclide batteries operate in two stages. First the radiation energy is converted to light by means of luminescent substances and then to electric energy by means of photoelements. Because of radiative decomposition of luminescent substances, the number of radionuclides applicable is limited. Alpha emitters are unsuitable, and the most suitable f emitter is " Pm. The construction of this kind of radionuclide batteries is relatively simple radionuclide and luminophore are mixed in a ratio of about 1 1 and brought between two photoelements (e.g. Cu-Se or Ag-Si) in form of a thin layer. Efficiencies of the order of 0.1 to 0.5% and powers of the order of lOpW per cm are obtained. Because of the low efficiency, this type of radionuclide battery has no technical significance. 

The isotope Cm is the largest contributor to the alpha activity of irradiated uranium fuel from power reactors. It is an important source of the 2n + 2 decay chain in the high4evel wastes from fuel reprocessing. The alpha activity of Cm results in an internal heat-generation rate of 120 W/g of pure Cm. Separated Cm, prepared by the neutron irradiation of Am, provides a useful alternative for a thermoelectric source and for radionuclide batteries when relatively high outputs are desired over short periods of the order of its half-Ufe of 163 days. For example, a space power generator denoted as SNAP-11 contained 7.5 g of Cm and produced 20 W of thermoelectric power. Cm is also the decay source of Pu, which is used as a longer-lived radioisotope heat source. 

Cm. The isotope Cm, an alpha emitter with a half-life of 17.6 years, is useful as a longer-lived decay-heat source and as a source for radionuclide batteries. Its specific heat-generation... 

USE 238Pu as heat source as radioisotope thermoelectric generator in radionuclide batteries for pacemakers with Be as neutron source. in atomic weapons in power reactors. Caution Radiation hazard concentrates in bone. 

Both Cm and have been used in radionuclide batteries as power... 

Including 590 TBq from a SNAP 9A radionuclide battery in a satellite that vaporized upon re-entering the... 

In thermophotovoltaic batteries the heat emitted by the radionuclides is converted to electric energy by means of infrared-sensitive photoelements (e.g. Ge diodes), which must be cooled effectively because the efficiency decreases drastically as the temperature rises. With respect to high emitter temperatures, thermophotovoltaic conversion is of interest for power levels between about 10 W and 1 kW, but the efficiency is relatively low (up to about 5%). 

Today there are hundreds, possibly thousands, of uses for synthetic radionuclides. The best known of these are in medicine. People are not usually aware of others, although at times they may be close at hand. For example, do you have a smoke detector in your home Battery-powered smoke detectors use a chip of americium-241, 2 Am. The americium ionizes the air in the detector, which causes a small current to flow through the air. When smoke enters, it breaks the circuit and sets off the alarm, which is powered by a battery (Fig. 20.13). With a half-life of 458 years, the americium doesn t need changing every year as the battery does. 

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