Type of Emission

When a radiochemist designs a radiopharmaceutical, there are many important factors to be considered. Optimal performance of a radiopharmaceutical requires that it possess certain characteristics. The first of these is that the radioisotope should be a pure gamma­ray emitter, decaying by either electron capture or isomeric transition. Other non-penetrating kinds of radiation, e.g., alpha and beta particles, are undesirable for two reasons: due to their high linear energy transfer (LET), the fraction of energy deposited per cm of travel is very high. This results in almost quantitative absorption in the body. The few particles that manage to escape the patient's body can't penetrate the crystal to interact. Consequently, alphas and betas are not imageable. In addition, because of their high LET, they confer a very significant radiation dose to the patient.