Promethium

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Promethium

Promethium is a chemical element in the periodic table that has the symbol Pm and atomic number 61.

Notable characteristics

Promethium has no stable isotopes. It is a man-made soft beta emitter; it does not emit gamma rays, but beta particles impinging on elements of high atomic numbers can generate X-rays. Pure promethium exists in two allotropic forms, but little else is known about the metal. Promethium salts luminesce in the dark with a pale blue or greenish glow due to their high radioactivity.

Applications

Uses for promethium include:

Beta radiation source for thickness gauges.
Light source for signals that require reliable, independent operation (using phosphor to absorb the beta radiation and produce light).
In a nuclear battery in which photocells convert the light into electric current, yielding a useful life of about five years using 147-Pm.
Possibly in the future as a portable X-ray source, as an auxiliary heat or power source for space probes and satellites.

History

The existence of promethium was first predicted by Bohuslav Brauner in 1902; this prediction was supported by Henry Moseley in 1914, who found a gap for a missing element which would have atomic number 61, but was unknown (however, Moseley of course had no sample of the element to verify this). Several groups claimed to have produced the element, but they could not confirm their discoveries because of the difficulty of separating promethium from other elements. Proof of the existence of promethium was obtained in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell during the analysis of byproducts of uranium fission; however, being too busy with defense-related research during World War II, they did not announce their discovery until 1947. ^* The name promethium is derived from Prometheus in Greek mythology, who stole the fire of the sky and gave it to mankind.

In 1963, ion-exchange methods were used to prepare about 10 grams of promethium from atomic reactor fuel processing wastes.

Today, promethium is still recovered from the byproducts of uranium fission; it can also be produced by bombarding ¹⁴⁶Nd with neutrons, turning it into ¹⁴⁷Nd which decays into ¹⁴⁷Pm through beta decay with a half-life of 11 days.

Occurrence

Promethium does not naturally occur on Earth, but has been identified in the spectrum of the star HR 465 in Andromeda, and possibly HD 101065 (Przybylski's star) and HD 965 ^*.

Compounds

Promethium compounds include:

Chlorides
- PmCl₃
Bromides
- PmBr₃
Oxides
- Pm₂O₃

Isotopes

36 radioisotopes of promethium have been characterized, with the most stable being ¹⁴⁵Pm with a half-life of 17.7 years, ¹⁴⁶Pm with a half-life of 5.53 years, and ¹⁴⁷Pm with a half-life of 2.6234 years. All of the remaining radioactive isotopes have half-lives that are less than 364 days, and the majority of these have half lives that are less than 27 seconds. This element also has 11 meta states with the most stable being ¹⁴⁸Pm^m (T_½ 41.29 days), ¹⁵²Pm^m2 (T_½ 13.8 minutes) and ¹⁵²Pm^m (T_½ 7.52 minutes).

The isotopes of promethium range in atomic weight from 127.9482600 u (¹²⁸Pm) to 162.9535200 u (¹⁶³Pm). The primary decay mode before the longest-lived isotope, ^{145^{Pm, is electron capture, and the primary mode after is beta minus decay. The primary decay products before ¹⁴⁵Pm are neodymium (Nd) isotopes and the primary products after are samarium (Sm) isotopes.}}

Precautions

Promethium must be handled with great care because of its high radioactivity. In particular, promethium can emit X-rays during its beta decay. Note that its half-life is less than that of plutonium-239 by a factor of multiple thousands to tens of thousands. Promethium has no biological role.

References

Los Alamos National Laboratory – Promethium

External links

Chemical elements | Lanthanides

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