In turn, 99Mo is usually created commercially by fission of highly enriched uranium in a small number of research and material testing nuclear reactors in several countries.

In 1938, Emilio Segrè and Glenn T. Seaborg isolated for the first time the metastable isotope technetium-99m, after bombarding natural molybdenum with 8 MeV deuterons in the 37-inch (940 mm) cyclotron of Ernest Orlando Lawrence's Radiation laboratory.

This chain of decay was later shown to have the mass number 99, and (...) the 6.6-h activity acquired the designation ‘technetium-99m.Later in 1940, Emilio Segrè and Chien-Shiung Wu published experimental results of an analysis of fission products of uranium-235, including molybdenum-99, and detected the presence of an isomer of element 43 with a 6-hour half life, later labelled as technetium-99m.

While Richards was in charge of the radioisotope production at the Hot Lab Division of the Brookhaven National Laboratory, Walter Tucker and Margaret Greene were working on how to improve the separation process purity of the short-lived eluted daughter product iodine-132 from its parent, tellurium-132 (with a half life of 3.2 days), produced in the Brookhaven Graphite Research Reactor.

[13][14] Sorensen and Archambault demonstrated that intravenously injected carrier-free 99Mo selectively and efficiently concentrated in the liver, becoming an internal generator of 99mTc.

Union Carbide actively developed a process to produce and separate useful isotopes like 99Mo from mixed fission products that resulted from the irradiation of highly enriched uranium (HEU) targets in nuclear reactors developed from 1968 to 1972 at the Cintichem facility (formerly the Union Carbide Research Center built in the Sterling forest in Tuxedo, New York (41°14′6.88″N 74°12′50.78″W / 41.2352444°N 74.2141056°W / 41.2352444; -74.2141056)).

[22][23] At the end of the 1970s, 200,000 Ci (7.4×1015 Bq) of total fission product radiation were extracted weekly from 20 to 30 reactor bombarded HEU capsules, using the so-called "Cintichem [chemical isolation] process.

Initially, two identical MAPLE reactors were to be built at Chalk River Laboratories, each capable of supplying 100% of the world's medical isotope demand.

[32] 99Mo was initially supplied by Amersham, UK, then by the Australian Nuclear Science and Technology Organisation (ANSTO) in Lucas Heights, Australia.

Global shortages of technetium-99m emerged in the late 2000s because two aging nuclear reactors (NRU and HFR) that provided about two-thirds of the world's supply of molybdenum-99, which itself has a half-life of only 66 hours, were shut down repeatedly for extended maintenance periods.

[35][36][37] In May 2009, the Atomic Energy of Canada Limited announced the detection of a small leak of heavy water in the NRU reactor that remained out of service until completion of the repairs in August 2010.

After the observation of gas bubble jets released from one of the deformations of primary cooling water circuits in August 2008, the HFR reactor was stopped for a thorough safety investigation.

The nucleus will eventually relax (i.e., de-excite) to its ground state through the emission of gamma rays or internal conversion electrons.

Pure gamma emission is the desirable decay mode for medical imaging because other particles deposit more energy in the patient body (radiation dose) than in the camera.

This is still a short half-life relative to many other known modes of radioactive decay and it is in the middle of the range of half lives for radiopharmaceuticals used for medical imaging.

[48] The recent shortages of 99mTc reignited the interest in the production of "instant" 99mTc by proton bombardment of isotopically enriched 100Mo targets (>99.5%) following the reaction 100Mo(p,2n)99mTc.

Depending on the time required to process the target material and recovery of 99mTc, the amount of 99mTc relative to 99gTc will continue to decrease, in turn reducing the specific activity of 99mTc available.

It has been reported that ingrowth of 99gTc as well as the presence of other Tc isotopes can negatively affect subsequent labelling and/or imaging;[53] however, the use of high purity 100Mo targets, specified proton beam energies, and appropriate time of use have shown to be sufficient for yielding 99mTc from a cyclotron comparable to that from a commercial generator.

Instead, its parent nuclide 99Mo is supplied to hospitals after its extraction from the neutron-irradiated uranium targets and its purification in dedicated processing facilities.

[notes 1][69] It is shipped by specialised radiopharmaceutical companies in the form of technetium-99m generators worldwide or directly distributed to the local market.

The generators, colloquially known as moly cows, are devices designed to provide radiation shielding for transport and to minimize the extraction work done at the medical facility.

Other ligands include sestamibi for myocardial perfusion imaging and mercapto acetyl triglycine for MAG3 scan to measure renal function.

[71] In 1970, Eckelman and Richards presented the first "kit" containing all the ingredients required to release the 99mTc, "milked" from the generator, in the chemical form to be administered to the patient.

Klaus Schwochau's book Technetium lists 31 radiopharmaceuticals based on 99mTc for imaging and functional studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton, blood, and tumors.

For example, when 99mTc is chemically bound to exametazime (HMPAO), the drug is able to cross the blood–brain barrier and flow through the vessels in the brain for cerebral blood-flow imaging.

[80] This level of radiation exposure is estimated by the linear no-threshold model to carry a 1 in 1000 lifetime risk of developing a solid cancer or leukemia in the patient.

And because technetium-99m has a short half-life, its quick decay into the far less radioactive technetium-99 results in relatively low total radiation dose to the patient per unit of initial activity after administration, as compared with other radioisotopes.

[citation needed] Single-photon emission computed tomography (SPECT) is a nuclear medicine imaging technique using gamma rays.

Following this, myocardial stress is induced, either by exercise or pharmacologically with adenosine, dobutamine or dipyridamole(Persantine), which increase the heart rate or by regadenoson(Lexiscan), a vasodilator.

The general location of the sentinel node is determined with the use of a handheld scanner with a gamma-sensor probe that detects the technetium-99m–labeled tracer that was previously injected around the biopsy site.