The radionuclide sensitivity of a plastic scintillator

Short-lived radionuclides are widely used in medical practice, these being made directly in the laboratory from generators. The activities of the solutions are about 109 Bq or more. Special radiometric instruments are used to determine the total activity and to dispense it for injection. Usually, one employs an ionization chamber or scintillation detector. A scintillation detector has high sensitivity and therefore has advantages over an ionization chamber, particularly in the measurement of small activities. We have devised a radiometer for measuring the activities of radiopharmaceuticals in the range 0.3 MBq-20 GBq. The radiometer employs a plastic scintillator (a solid solution of p-terphenyl in polystyrene with the addition of dibenzene) in the form of a cylinder with a hole through the center, which accomodates the vial containing the radioactive solution. This form of detector makes the reading almost independent of the solution volume. The wide measurement range (0.3 MBq to 30 GBq) means that the counting mode of operation commonly employed in radiometry cannot be used