Naturally occurring palladium (Pd) is composed of six stable isotopes, 102Pd, 104Pd, 105Pd, 106Pd, 108Pd, and 110Pd, although two of them are theoretically unstable. The most stable radioisotopes are 107Pd with a half-life of 6.5 million years, 103Pd with a half-life of 17 days, and 100Pd with a half-life of 3.63 days. Twenty-three other radioisotopes have been characterized with atomic weights ranging from 90.949 u (91Pd) to 123.937 u (124Pd). Most of these have half-lives that are less than a half an hour except 101Pd (half-life: 8.47 hours), 109Pd (half-life: 13.7 hours), and 112Pd (half-life: 21 hours).
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The primary decay mode before the most abundant stable isotope, 106Pd, is electron capture and the primary mode after is beta decay. The primary decay product before 106Pd is rhodium and the primary product after is silver.
Radiogenic 107Ag is a decay product of 107Pd and was first discovered in the Santa Clara meteorite of 1978. The discoverers suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a nucleosynthetic event. 107Pd versus Ag correlations observed in bodies, which have clearly been melted since accretion of the solar system, must reflect the presence of short-lived nuclides in the early solar system.
Relative atomic mass: 106.42(1)
Palladium-103
Palladium-103 is a radioisotope of the element palladium that has uses in radiation therapy for prostate cancer and uveal melanoma. Palladium-103 may be created from palladium-102 or from Rhodium-103 using a Cyclotron. Palladium-103 has a half-life of 16.99 days and decays by electron capture to rhodium-103, emitting gamma-rays with 21 keV of energy.
Palladium-107
Palladium-107 is the second longest lived (halflife of 6.5 million years) and least radioactive (decay energy only 33 keV, specific activity 5×10−5 Ci/g) of the 7 long-lived fission products. It undergoes pure beta decay (no gamma radiation) to Ag-107.
Its yield from thermal neutron fission of uranium-235 is 0.1629% per fission, only 1/4 that of iodine-129, and only 1/40 those of Tc-99, Zr-93, and Cs-135. Yield from U-233 is slightly lower, but yield from Pu-239 is much higher, 3.3%. Yields are higher in fast fission or in fission of heavier nuclei.
According to fission palladium contains the isotopes 104Pd (16.9%),105Pd (29.3%), 106Pd (21.3%), 107Pd (17%), 108Pd (11.7%) and 110Pd (3.8%). According to another source, the proportion of 107Pd is 9.2% for palladium from thermal neutron fission of U-235, 11.8% for U-233, and 20.4% for Pu-239. (and the Pu-239 yield of palladium is about 10 times that of U-235.)
Because of this dilution and because 105Pd has 11 times the neutron absorption cross section, 107Pd is not amenable to disposal by nuclear transmutation. However, as a noble metal, palladium is not as mobile in the environment as iodine or technetium.