Perusing the Radioactive Thermoelectric Generator or rtg tag in Space SE will show how important these items are for Space exploration both as a source of heat to keep spacecraft instrumentation warm, and to power the thermoelectric generators for electricity. The Curiosity rover on Mars uses it's RTG for both and includes a fluid circulation system to heat (or cool) various sections.

RTG's most often use an alpha decay source like Plutonium-238 or perhaps in the future Americium-241) rather than a fission source, to minimize longer range radiation that can damage the spacecraft.

Question: I'm not sure if the self-heating of a radioactive sample was first noticed then explained, or predicted and then demonstrated. But in either case, when was a measured or even noticed temperature rise first documented or reported?

  • $\begingroup$ THere's a fine line between "gives off energy in the form of photons and particles" and "gets warm" , as both of those indicate energy release. $\endgroup$ Commented Jun 25, 2018 at 12:03
  • $\begingroup$ @CarlWitthoft Luckily language provides us with good clear words to make various distinctions clear. I think "warm" and "temperature" will do the trick in this case. $\endgroup$
    – uhoh
    Commented Jun 25, 2018 at 14:34

1 Answer 1


I found the following at an AIP site on Marie Curie, apparently a copy of an article of hers in Century Magazine, pp 461-466 (January 1904). It appears to be a non-technical journal:

Radium possesses the remarkable property of liberating heat spontaneously and continuously. A solid salt of radium develops a quantity of heat such that for each gram of radium contained in the salt there is an emission of one hundred calories per hour. Expressed differently, radium can melt in an hour its weight in ice. When we reflect that radium acts in this manner continuously, we are amazed at the amount of heat produced, for it can be explained by no known chemical reaction.The radium remains apparently unchanged. If, then, we assume that it undergoes a transformation, we must therefore conclude that the change is extremely slow; in an hour it is impossible to detect a change by any known methods.

One possible technical article as the first report, although I can't access it on-line to check, is: 'On heat spontaneously extricated by salts of radium', P. Curie and A. Laborde, Comptes Rendus 136, 673-675 (1903). Note that the author is Pierre Curie, not Marie Curie.

Previous articles, similarly hard to get, may have a comment on the warmth of the various entities that the Curies were isolating, but that would take finding a library with Comptes Rendus from the early 1900's.

  • $\begingroup$ This is a great source and a great find, thank you! For a split second I thought about trying to compare the rate of heat production to the radioactivity, until I read that Radium has 33 known isotopes, with mass numbers from 202 to 234: all of them are radioactive. Combining that with the possibility that the sample is not elementally pure, it sounds like quite a challenge. $\endgroup$
    – uhoh
    Commented Jun 29, 2018 at 16:44
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    $\begingroup$ Even worse, even if the sample were 'pure' Radium with a specific isotope ratio, you would quickly go down a rabbit hole of decay chains... $\endgroup$
    – Jon Custer
    Commented Jun 29, 2018 at 16:56

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