In a Technetium generator, there are 100 µg of 99Mo initially. The half lives of
ID: 1544583 • Letter: I
Question
In a Technetium generator, there are 100 µg of 99Mo initially. The half lives of 99Mo and 99mTc are 66 h and 6 h, respectively. What is the mass of 99mTc in 12 h, 24 h and 36 h? What are the radioactivities of 99Mo and 99mTc at these time points?
99mTc is generated from a long-lived parent, 99Mo, obtained from a nuclear reactor.
99mTc has a half-life of 6.02 hr, an emission of 140-keV -ray, and an HVL of 4.6 cm.
Production of Technetium The number of 99Mo atoms, denoted by N1, decrease with time from an initial maximum value No at time t 0 99 (NI) (N2) (N3) The value of M1 2.92x10-6 s 1 and -5 s dN. dNExplanation / Answer
Technetium-99m's short half-life of 6 hours makes storage impossible and would make transport very expensive. It is instead its parent nuclide 99Mo that is supplied to hospitals after its extraction from the neutron-irradiated uranium targets and its purification in dedicated processing facilities.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 a moly cows, are devices designed to provide radiation shielding for transport and to minimize the extraction work done at the medical facility. A typical dose rate at 1 metre from Tc-99m generator is 20-50 Sv/h during transport.These generators' output declines with time and must be replaced weekly, since the half-life of 99Mo is still only 66 hours.
Molybdenum-99 spontaneously decays to excited states of 99Tc through beta decay. Over 87% of the decays lead to the 142 keV excited state of Tc-99m. A
electron and a
eelectron antineutrino are emitted in the process (99Mo 99mTc +
+
e). The
electrons are easily shielded for transport, and 99mTc generators are only minor radiation hazards, mostly due to secondary X-rays produced by the electrons (also known as Bremsstrahlung).
At the hospital, the 99mTc that forms through 99Mo decay is chemically extracted from the technetium-99m generator. Most commercial 99Mo/99mTc generators use column chromatography, in which 99Mo in the form of water-soluble molybdate, MoO42 is adsorbed onto acid alumina (Al2O3). When the 99Mo decays, it forms pertechnetate TcO4, which, because of its single charge, is less tightly bound to the alumina. Pulling normal saline solution through the column of immobilized 99MoO42 elutes the soluble 99mTcO4, resulting in a saline solution containing the 99mTc as the dissolved sodium salt of the pertechnetate. One technetium-99m generator, holding only a few micrograms of 99Mo, can potentially diagnose 10,000 patients because it will be producing 99mTc strongly for over a week.