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Molybdenum and Technetium

Technetium-99m is a radioactive material which is frequently used in every hospital equipped for nuclear medical examination. Technetium is called the workhorse of nuclear medicine. In 1995 in Europe 6 million diagnoses were made by means of technetium and a further growth in technetium demand is to be expected.
Technetium is the favoured choice of the medical profession because it has the appropriate physical and chemical characteristics. The gamma radiation emitted has the appropriate energy to provide a good image whilst the radiation burden for the patient is very low. technetium can easily be bonded to many different chemical materials and can therefore be used for a variety of diagnoses.
Its half-life is 6 hours, long enough for a medical examination and short enough to allow the patient to leave the hospital directly afterwards.
Technetium seems to have only one drawback: artificial radioisotopes must be produced in centralised facilities like such at Petten. So how can a material - half of which has disappeared after 6 hours - be delivered to each hospital every day? Here nature comes to our aid. Technetium-99 is the decay product from molybdenum-99 which has a half-life of 66 hours. This longer half-life allows transportation, even over long distances. The only remaining question is now: how to produce molybdenum-99.

The shielded bottle contains molybdenum-99. The molybdenum (half-life 66 hours) decays into technetium-99 (half-life 6 hours). This technetium can easily be chemically separated. In hospitals it is frequently used for diagnostic purposes. If a hospital receives a fresh bottle - a so-called technetium 'cow' - every week, the doctors in the hospital can have technetium at their disposal any time of the day, seven days a week, by 'milking' the cow.

Neither molybdenum-99 nor technetium-99m exist in nature.
Molybdenum-99 can only be formed by means of nuclear reactions. It is formed during fission of uranium and consequently exists in 'used' fuel. Separation of molybdenum from used fuel is, chemically speaking, not very difficult. The only problem is the radiation level: fission products are highly radioactive.

In the 'Molybdenum-wing' in the Petten Laboratory for Highly Radioactive Objects, two lines of five hot-cells have been set up where molybdenum-99 is separated from irradiated uranium in five steps. The second line is basically a reserve line. Continuity must be guaranteed. It is of vital importance that sufficient molybdenum is available for distribution every week to the hospitals. With technetium-99m, the daughter of this molybdenum, 30,000 diagnoses are made daily in European hospitals.

The fresh molybdenum-99 in this tube (a few micrograms) is suficient for the diagnosis of some ten thousand patients. The highly radioactive molybdenum is divided over many hundreds of 'cows' which are shipped weekly to as many hospitals within and outside Europe. The molybdenum decays into technetium and with the technetium from one cow a large number of patients can be diagnosed.

  
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Update 18 June 2004