SIJU PRAKASH ASST. PROFESSOR VIP-KUTCH Radiopharmaceuticals

Contents Radiopharmaceuticals Radio activity Units of Radioactivity Properties of α, β, γ radiations Radio isotopes Half life Radioactive Decay Measurement of radioactivity Sodium iodide I 131 Storage conditions and precautions Pharmaceutical application of radioactive substances.

Radiopharmaceuticals A radiopharmaceutical is a radioactive compound used for the diagnosis and therapeutic treatment of human diseases In nuclear medicine nearly 95% of the radiopharmaceuticals are used for diagnostic purposes, while the rest are used for therapeutic treatment.

Radioactivity The phenomenon of spontaneous emission of certain kind of invisible radiation by certain substance is called Radioactivity. OR Transformation or disintegration of the radionuclide is known as ‘Radioactivity’. The substances which emit such radiation is called Radioactive substance. The radioactivity of a preparation is the number of nuclear disintegrations or transformations per unit time.

Radionuclide Radionuclide: Nuclides containing an unstable arrangement of protons and neutrons that transform spontaneously to either a stable or another unstable combination of protons and neutrons with a constant statistical probability by emission of radiation. These are said to be radioactive and are called radionuclides.

Units of Radioactivity In the International System (SI), the unit of radioactivity is one nuclear transmutation per second and is expressed in Becquerel (Bq), named after the scientist Henri Becquerel. The old unit of radioactivity was Curie (Ci), named after the scientists Madam Marie Curie and Pierre Curie, the pioneers who studied the phenomenon of radioactivity. One Ci is the number of disintegrations emanating from 1 g of Radium-226, and is equal to 3.7 x Bq. Roentgen (R): it is the unit of exposure; 1 R = 2.58 x C Kg -1 (C=coulomb). RAD: it is the unit of absorbed dose; 1 Rad = 10-2 J Kg -1.

Units of Radioactivity  REM: it refers to the unit of the dose equivalent. The dose in REM has been equal to the dose in RADS multiplied by quality factor and the distribution factor.  Exposure rate constant: it refers to the dose rate in roentgens per hour at 1 m distance from 1 curie. It is about one tenth of the dose at a distance of 1 foot from 1 curie.  RBE: since the effect of given radiation on biological system depends upon the type of radiation a unit known as relative biological effectiveness or RBE has been introduced. This expresses the relative effects of radiation alpha, beta and gamma on the biological system.  Annual Limit of Intake (ALI): ALI ensures that the maximum annual equivalent dose from that radionuclide will always be less than the equivalent dose even if intake occurred every year for 50 years.

Radioisotopes Atoms of an element which have the same atomic number but have different mass number are called Isotopes. When the radioactive isotopes undergo nuclear reactions they produce alpha, beta and gamma particles. The original nuclide is called the parent and product of that called daughter nuclide. The phenomenon of nuclear changes called disintegration of radioactive decay.

Radioactive Decay Rate of disintegration is directly proportional to the amount present Where is a decay or disintegration rate constant. Integrating the above equation (1) C is the constant of integration and log N stands for log e N.

Since the number of atoms of the radioactive substance present initially i.e t = 0 is N 0 Substituting the value of integration constant

Converting log to the base e to the base 10, we get: Where N=number of atoms that nucleid present after time t. N 0 = Initial number of atoms of the nucleid at time 0. = Decay constant This equation is similar to that of first order reaction, hence it is seen that radioactive disintegration are example of first order reactions.

The half life period is defined as the time required for a radioactive isotope to decay to one half of its initial value. It is denoted as t ½

Average half life :- the reciprocal of the radioactive constant or decay constant is called average half life period. It is denoted as.