Pacemakers are used to stimulate a regular heartbeat when the body's natural electrical pacing system stops working or is not working properly. For many years, the best "batteries" have been sought for pacemakers.
In the 1970s, before the use of lithium-ion batteries to power pacemakers in the United States, batteries were used that draw energy from the alpha decay of plutonium-238. Alpha decay is accompanied by the emission of a heavy helium nucleus, which quickly loses energy and is inhibited: therefore, the thin body of the battery is able to completely protect the human body from alpha particles. Alpha decay is usually accompanied by strong gamma radiation, which is precisely dangerous, but Plutonium-238 is a stunning exception, for which the emission of gamma quanta is rare. The additional dose of radiation from one such battery in a pacemaker is only 0.1 mSv per year, while an ordinary person receives about 2.4 mSv of background radiation per year of life.
How did these eternal batteries work? How dangerous is it for humans?
As you can see in the photo of the pacemaker (already without plutonium) above, the electronics of the device are enclosed in epoxy resin. The solid titanium case is engineered to withstand any likely damage event, including gunfire and cremation.
Radioactive batteries have a huge lifetime, as the half-life of plutonium-238 is 88 years, and lithium-ion batteries can only envy plutonium. So, this year in the Int. J. Cardiol. published a scientific article describing a patient who successfully used a plutonium pacemaker for 35 years before deciding to change the battery.
The radiation dose on the surface of the pacemaker is approximately 5-15 mrem (microrem, "biological equivalent of X-ray", a unit of measurement) per hour from the emitted gamma rays and neutrons. It is estimated that total body irradiation is approximately 0.1 rem per year for the patient and approximately 7.5 mrem per year for his spouse. For comparison, 100 mrem is the background radiation that a person receives on average per year.
Often times, plutonium pacemakers were worried about their owners. In 1973, Dr. Victor Parsonnett, a staff member at Newark Beth Israel Medical Center, fitted a 20-year-old woman with a Numec NU-5 pacemaker. At that time, the device cost the patient $ 23,000 in terms of a modern course. However, in the long term, a nuclear pacemaker has proven to be very economical - any other similar device would have to be replaced four to five times in such a period.
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According to Parsonnet, 139 patients were installed NU-5. Most of them are no longer alive.
The battery in such a pacemaker, as we have already said, is a radioisotope thermoelectric generator (RTG), which uses thermal energy released during the natural decay of radioactive isotopes and converts it into electricity using a thermoelectric generator. Compared to nuclear fission reactions that take place at conventional nuclear power plants, RTGs are much more compact. Their efficiency is low, as is the output power, but they do not require maintenance and have been working for decades. Many satellites that we launched into the cold depths of space, like the Voyagers, carried away RTGs with plutonium-238 - this is the secret of their long-term operation.