CHAPTER 5 - Radioassay

Abstract

Publisher Summary This chapter provides an overview of radioassay. Biological material that has been exposed in some way to a radioisotope requires a certain amount of preparation, sometimes quite a lot, before it is in a form suitable for satisfactory counting or radioassay. The chapter discusses primarily biological samples as soil is rarely counted for radioisotope content except when investigating ion or soil-water movement. In the same way, samples of radioactive fertilizers are easily brought into solution or extracted for counting. Basic preparation often follows classical methods. Preparation of adequate standards is a critical part of all radioassay. The standard must be as close as possible in all respects to the form in which the samples are prepared. In particular, the thickness, density, form, and mass should be the same, while the volume of liquid in liquid counters must always be the same, both for standards and samples. Sample holders must be identical. All standards should be prepared in duplicate or triplicate. There are a number of common methods of preparing plant material for counting, and their use depends on particular circumstances—the isotope being counted; the size of sample; the activity of the sample; and frequently the equipment available. A major advantage of liquid counting is the improved and uniform geometry.