Science Fair Project Encyclopedia
|Name, Symbol, Number||Promethium, Pm, 61|
|Group, Period, Block||_ , 6, f|
|Density, Hardness||7264 kg/m3, no data|
|Atomic weight||145 u|
|Atomic radius (calc.)||185 (205) pm|
|Covalent radius||no data|
|van der Waals radius||no data|
|e- 's per energy level||2, 8, 18, 23,8, 2|
|Oxidation states (Oxide)||3 (mildly basic)|
|State of matter||solid (__)|
|Melting point||1373 K (2012 °F)|
|Boiling point||3273 K (5432 °F)|
|Molar volume||20.23 ×10-6 m3/mol|
|Heat of vaporization||no data|
|Heat of fusion||86.7 kJ/mol|
|Vapor pressure||no data|
|Velocity of sound||no data|
|Electronegativity||1.13 (Pauling scale)|
|Specific heat capacity||180 J/(kg*K)|
|Electrical conductivity||no data|
|Thermal conductivity||17.9 W/(m*K)|
|1st ionization potential||540 kJ/mol|
|2nd ionization potential||1050 kJ/mol|
|3rd ionization potential||2150 kJ/mol|
|4th ionization potential||3970 kJ/mol|
|Most stable isotopes|
|SI units & STP are used except where noted.|
Promethium is a soft man-made beta emitter; it does not emit gamma rays, but beta particles impinging on elements of high atomic numbers can generate X-rays. Little is known as of today about the properties of metallic promethium; two allotropic modifications exist, and promethium salts luminesce in the dark with a pale blue or greenish glow due to their high radioactivity.
Uses for promethium include:
- Beta radiation source for thickness gauges.
- Light source for signals that require dependable 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 / power source for space probes and satellites, and to make lasers that can be used to communicate with submerged submarines.
The existence of promethium was first predicted by Bohuslav Brauner in 1902; this prediction was confirmed by Henry Moseley in 1914. 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 from 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 g 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.
Promethium is also the name of a fictional element in the DC Universe; writer Marv Wolfman has admitted having been unaware of the existence of a real substance by that name at the time he wrote the original script featuring the name.
Promethium compounds include:
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 148Pmm (T½ 41.29 days), 152Pmm2 (T½ 13.8 minutes) and 152Pmm (T½ 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 most abundant stable isotope, 145Pm, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 145Pm are element Nd (Neodymium) isotopes and the primary products after are element Sm (Samarium) isotopes.
Great care is required while handling promethium as a consequence 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.
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