TABLE OF CONTENTS Specific activity is an important parameter since in many cases the availability of very high specific activity or carrier-free radionuclides is required for biological applications. One example of the importance of high specific activity is the radiolabeling of tumor-specific antibodies or peptides for both diagnostic and therapeutic applications where only very small amounts of the radiolabeled antibodies are administered to ensure maximal uptake at the limited tumor cell surface antigen sites.
Another important need is the use of receptor-mediated radiopharmaceuticals that are potentially very important for the clinical evaluation of neurological diseases. Since the population of neurotransmitter sites is very limited, high specific activity agents are required to evaluate site-specific uptake and not saturate these binding sites with stable cold isotope.
Since the specific activity of a radionuclide produced by particle-induced reactions is a direct function of the incident particle flux, an increase in the incident particle flux results in an absolute increase in the specific activity of the product. This relationship is linear for simple reactions and non-linear for complex reactions. It is important to note that the half-lives, production and depletion cross sections, and irradiation time are equally important. Several important radionuclides have long physical half-lives and low production cross sections requiring long irradiation periods even in the highest neutron flux available. An example in this category is tungsten-188 (half-life 69 days; parent for rhenium-188).
In addition, the increased flux not only results in higher specific activity products, but can allow utilization...
