Element of the week: Technetium
The most elusive element we’ve met so far, technetium’s existence was predicted long before its eventual, accidental, discovery
by GrrlScientist for The Guardian | @GrrlScientist
This week’s element is technetium, a naturally radioactive metal denoted by the chemical symbol, Tc, and the atomic number 43. Technetium, whose longest-lived isotope has a half-life of 4.2 million years, is vanishingly rare on earth. Interestingly, based on the spectral lines from light given off by stars, we can see a number of isotopes of technetium are common in stars. For this reason and because this element has a much shorter lifespan than do stars, we’ve concluded that the stars themselves are the birthplace of this element.
Technetium is created on earth from radioactive decay of molybdenum-99 (half-life; 67 hours) or by humans bombarding uranium-235 with neutrons. Because of its short half-life, technetium does not and never has played any biological role since it vanished (due to radioactive decay) long before life appeared on earth. However, technetium-99m (half-life; 6 hours), which results from molybdenum-99 decay, is important in medical imaging and diagnostics, particularly for detecting a number of rare and elusive cancers as well as damage to the heart muscle resulting from heart attack.
Perhaps the most interesting aspect of this element is its elusiveness: occupying the empty box beneath manganese on the periodic table, its existence had been predicted long before anyone found it. But despite numerous intensive efforts to isolate this element, its eventual discovery by Emilio Segrè in 1937 was accidental.
As the story goes, in 1937, Segrè visited Ernest Lawrence’s laboratory in Berkeley to see his 37-inch cyclotron. Later that year, the molybdenum foil from the cyclotron deflector, which had been exposed to a lot of deuterium bombardment, was sent to him after he’d returned home to Sicily. Segrè found that some of the radiation emitted by this foil was produced by a previously unknown element, which was later named technetium. Not only had Segrè discovered a new element, but because technetium does not occur in nature, it is the first element that had been artificially synthesised in a laboratory.
However, that said, there is a bit more to the story of the discovery of element number 43. It actually had been discovered in 1925 by a German group comprised of Ida Tacke, Walter Noddack and Otto Berg, who deduced the presence of element 43 after bombarding the mineral colombite with electrons and analysing the emitted x-rays. They named it masurium. However, no one believed that their instruments were sensitive enough to detect the small quantities of emitted x-rays — until their methods and results were replicated recently by several scientists around the world who used similar instruments. They concluded that the German group had discovered this element after all.
Oops.
Here’s our favourite Professor telling us a little more about technetium:
Meet next week’s element of the week: Ruthenium!
You’ve already met these elements:
Molybdenum: Mo, atomic number 42
Niobium: Nb, atomic number 41
Zirconium: Zr, atomic number 40
Yttrium: Y, atomic number 39
Strontium: Sr, atomic number 38
Rubidium: Rb, atomic number 37
Krypton: Kr, atomic number 36
Bromine: Br, atomic number 35
Selenium: Se, atomic number 34
Arsenic: As, atomic number 33
Germanium: Ge, atomic number 32
Gallium: Ga, atomic number 31
Zinc: Zn, atomic number 30
Copper: Cu, atomic number 29
Nickel: Ni, atomic number 28
Cobalt: Co, atomic number 27
Iron: Fe, atomic number 26
Manganese: Mn, atomic number 25
Chromium: Cr, atomic number 24
Vanadium: V, atomic number 23
Titanium: Ti, atomic number 22
Scandium: Sc, atomic number 21
Calcium: Ca, atomic number 20
Potassium: K, atomic number 19
Argon: Ar, atomic number 18
Chlorine: Cl, atomic number 17
Sulfur: S, atomic number 16
Phosphorus: P, atomic number 15
Silicon: Al, atomic number 14
Aluminium: Al, atomic number 13
Magnesium: Mg, atomic number 12
Sodium: Na, atomic number 11
Neon: Ne, atomic number 10
Fluorine: F, atomic number 9
Oxygen: O, atomic number 8
Nitrogen: N, atomic number 7
Carbon: C, atomic number 6
Boron: B, atomic number 5
Beryllium: Be atomic number 4
Lithium: Li atomic number 3
Helium: He atomic number 2
Hydrogen: H atomic number 1
Video journalist Brady Haran is the man with the camera and the University of Nottingham is the place with the chemists. You can follow Brady on twitter @periodicvideos and the University of Nottingham on twitter @UniNottingham
Originally published at The Guardian on 23 December 2011.
