Most of you have probably learnt at school that radioactive isotopes are sources of radioactive emissions. Some radiate alpha, some beta, and some also generate X-ray and gamma rays, but no one ever told you that these isotopes are NOT the sources of such radiations but simply energy converters of the incoming planck frequency band radiation making up all matter, the same energy responsible for gravity. Most matter is not dense enough to create any noticable downshifting of the incoming radiation frequency (energy), hence we are not able to detect either incoming or outgoing radiation for most common substances. However, we notice that for mass numbers above that of lead, the high density of matter results in noticable frequency downshifting of this incoming energy, and we start to detect radiation in the highest bands of our presently known spectrum. The more dense is the substance, the more of incoming energy is trapped within its standing wave structure, and the less energetic is the outgoing/reflected energy. The less energetic the outgoing energy, the lower is its frequency, well, low enough for us to be able to detect them in the upper part of the known electromagnetic spectrum. In fact if one tries to slightly shield a gamma source with some aluminium foil, the aluminium foil will act as a downshifting device and generate X-rays. Yes, X-rays will be emitted from the other side of the aluminium foil, but no body ever says that aluminium generates X-rays. You can now finally understand why a radioactive isotope is simply tapping or downconverting this sea of energy of free space (ZPE) and not generating any radiation by itself.
Here I shall quote a very interesting and relevant statement written by Tesla, dated 10th July 1937. He says:
"There is no energy in matter other than that received from the environment. It applies rigorously to molecules and atoms as well as the largest heavenly bodies and to all matter in the universe in any pahse of its existence from its very formation to its ultimate disintegration."
RTGs It is a known fact that radioactive isotopes like Plutonium produce heat. This fact has already been exploited within RTG's. RTG's have proven their safety and capability in many space missions, including human missions. Radioactive material (plutonium 238) is used to produce heat, which is converted to electricity either by thermoelectric devices, such as peltiers and thermocouples, or by thermionic effect. When a material gets very hot (such as the hot filament in a television cathode ray tube), it can emit electrons from its surface. In a thermionic RTG, this electron emission is a direct source of electrical current. The Plutonium is not placed as a pure form in the RTG, but is installed as bricks of plutonium dioxide (PuO2), a ceramic which, if shattered, breaks into large pieces rather than smaller, more dangerous dust. The plutonium dioxide is encased in layers of materials, including graphite blocks and layers of iridium. Both materials are strong and heat resistant, which protect the plutonium bricks in the event of a launch explosion.
The RTG uses only decay heat, meaning there are no nuclear reactions involved, and also that the radioactive material can be encapsulated to prevent release into the atmosphere. As long as the capsule is not tampered with, an RTG is the nearest thing to a clean free energy device, directly converting free space energy to heat and electricity.
The above diagram shows the RTG used on board the Cassini, a NASA space probe still in operation. An RTG is fuelled with about 10.9 kilograms of plutonium dioxide (a ceramic form that is primarily composed of the plutonium-238 isotope) and can initially generate about 280 Watts of electrical power, and after ten years still be able to generate about 230 Watts of electrical power. Half-life time is 87 years. The outer shell is basically a heatsink, in contact with the cold side of the Si-Ge unicouple array. Two RTGs are needed to generate the 400 Watts of power that the Cassini orbiter needs.