Cyclotron production of radionuclides

The third means of radionuclide production involves target irradiation by ions accelerated in a cyclotron. One example of this approach is provided by the production of Ge, which decays with a 280 day half-life to the positron emitter Ga. Proton irradiation of Ga produces Ge in a (p,2n) reaction. After dissolution of the target material a solution of the Ge product in concentrated HCl is prepared and adsorbed on an alumina column which has been pre-equilibrated with 0.005 M EDTA (ethylenediaminetetraacetate) solution. The Ga daughter may then be eluted using an EDTA solution in a system which provides the basis of a Ga generator. Cyclotron production of radionuclides is expensive compared with reactor irradiations, but higher specific activities are possible than with the neutron capture process. Also, radionuclides with particularly useful properties, and which cannot be obtained from a reactor, may be prepared by cyclotron irradiation. In one example, cyclotron produced Fe, a positron emitter, may be used for bone marrow imaging while reactor produced Fe, a /3-emitter, is unsuitable. " ... 

As mentioned above, in cyclotron production of radionuclides, the reaction cross section data play a very important role (for detailed discussion c Qaim 1982, 2001a). One needs the fiiU excitation function of the nuclear process to be able to calculate the yield with reasonable accuracy. Another important point is the number of competing reaction channels. At an incident projectile energy of 20 MeV, for example, about six reaction channels with significant cross sections may occur. It is imperative to know the cross sections of aU those processes. The demands on the data may thus be extensive. At small-sized cyclotrons, low energy reactions Kke (p,n), (p,a), (d,n), (d,a), etc., are used. At higher energies, on the other hand, (p,xn) reactions are commonly utilized. In some special cases, the (p,spall) process is applied. 

Fora detailed discussion of various experimental and theoretical aspects of nuclear reaction cross section data relevant to cyclotron production of radionuclides, the reader is referred to two recent IAEA-coordinated efforts (cf. Gul et al. 2001 Qaim et al. 2008). 

Lagunas-Solar, M., Cyclotron Production of No-Carrier-Added Medical Radionuclides, 7th Conference on the Applications of Acceleration in Research and Industry, Denton, TX, 1982. 

In modem machines, protons, deuterons and a particles with energies of several 100 MeV up to about 1 GeV are available. Proton linacs serve frequently as injectors of 50 to 200 MeV protons into proton synchrotrons. For the production of radionuclides, relatively small cyclotrons are used by which particle energies of the order of 10 to 30 MeV and ion currents of the order of 100 pA are available. Radionuclides obtained by reactions with protons exhibit decay or electron capture (s). 

Figure 7.3. Production of radionuclides in a cyclotron. The amount of activity produced reaches a maximum (saturation) in five to six half-lives of the radionuclide.

Abstract Cyclotron products are gaining in significance in diagnostic investigations via PET and SPECT, as well as in some therapeutic studies. The scientific and technological background of radionuclide production using a cyclotron is briefly discussed. Production methods of the commonly used positron and photon emitters are described and developments in the production of some new positron emitters and therapeutic radionuclides outlined. Some perspectives of cyclotron production of medical radionuclides are considered. 

Radionuclides find applications in many fields. Their major use, however, is in medicine, in both diagnosis and therapy. The production of radionuclides is carried out using nuclear reactors as well as cyclotrons. The reactor produced radionuclides are generally neutron excess nuclides. They mostly decay by P emission. The cyclotron produced radionuclides, on the other hand, are often neutron deficient and decay mainly by EC or emission. They are especially suitable for diagnostic studies. The reactor production of radionuclides is described in Chap. 38 of this Volume this chapter treats radionuclide production with cyclotrons. It is worth pointing out that today more than 300 cyclotrons exist worldwide (cf. Directory of Cyclotrons, lAEA-DCRP/CD, 2004), many of them in hospitals they produce short-lived radionuclides for medical use. Thus, radionuclide production science and technology at cyclotrons has become a very important feature of modern nuclear medicine. 

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