Penetration Power Of Radiation Energies

The penetration power of the radiation energy is related to the type of radiation. The radioactive chemicals emit radiation in the form of particles or rays and the penetration power of these particles or rays in the tissues of our body varies due to variation in the energy of these particles or rays. The alpha (α) particles can not penetrate more than a few micrometers in our body tissue, and are of little practical importance in medicine. The beta negative (β^-) and beta positive (β⁺) particles have penetrating power varying from 100 to 500 micrometers (mm) as in case of radiations of Carbon-14 (¹⁴C) and Sulphur-35 (³⁵S) to over a centimeter (cm) as in case of Yttrium-90 (⁹⁰Y) radioisotope. The beta negative (β^-) particles from Gold-198 (¹⁹⁸Au), Gold-199 (¹⁹⁹Au) and Iodine (Iodine-125, 130, 131, 132 etc) have a penetration power in tissues ranging from 1 to 3 millimeters (mm). The gamma rays (g-rays) are like x-rays and are usually very penetrating. The energy range of gamma rays (g-rays) is almost equal to that from 40 kilovolt (KV) to 3 megavolt (MV) x-ray machines. Negative beta (b^-) particles may or may not have accompanying gamma rays (g-rays). The gamma rays (g-rays) emitted by a particular radioisotope would always have the same penetrating power or energy. The positrons or positive beta (b⁺) particles in addition to possible gamma rays (g-rays) are always accompanied by 50 KV x-rays.

Quantity of radioactive material is always expressed in terms of radioactive disintegrations per second. The major unit of expression of radioactivity represents 37 billion (37 x10⁹) disintegrations per second and is called Curie (Ci). One thousandth (¹/₁₀₀₀) part of a Curie is called milliCurie (mCi) and one thousandth (¹/₁₀₀₀) part of a milliCurie is called microCurie (mCi). Brief description of these units is as below:

1. Curie (Ci): 37x10⁹ disintegrations per second


2. milliCurie (mCi): 37x10⁶ disintegrations per second


3. microCurie (mCi): 37x10³ disintegrations per second

There are quite many radioisotopes used in medical practice as a therapy and also in medical diagnostic procedures. The quantities of radioactive materials used in therapy are in milliCuries (mCi) and those used in diagnostic procedures is in microCuries (mCi).

What Is Radioactive Decay Or Half Life Of A Radioisotope

Radioactive isotopes or radioisotopes of an element are always in the process of nuclear disintegration in order to acquire the stable form. The major unit of radioactivity is Curie (Ci) which means 37x10⁹ disintegrations per second. One thousandth (¹/₁₀₀₀) part of a Curie is called milliCurie (mCi) and one thousandth (¹/₁₀₀₀) part of a milliCurie is called microCurie (mCi). Other units of the radioactivity will be discussed in some other article. The radioactive chemical is being expressed in terms of radioactivity it possessed at the time (0 hour) of evaluation and labeling. Every radioisotope undergoes decay or nuclear disintegration at a uniform rate and the time after which it loses the half of its activity is called its Half Life.

Radioactivity is linked to per unit mass or volume of radioactive chemical. The radioactive Half Life could be a few hours, days or many years. For example ²⁴Na has a Half Life of 15 hours, ¹²⁵I has a Half Live of 60 days, ⁶⁰Co has a Half Live of 5.2 years and ¹⁴C has a Half Live of 5730 years. If 1gram of a radioactive chemical has 2Ci radioactivity at 0-hour, it would be reduced to 50% (1Ci) after the completion of 1st Half Life, 25% after completion of 2nd Half Life, 12.5% after the completion of 3rd Half Life and 6.25% after the completion of 4th Half Life and goes on reducing to 50% on the completion of successive Half Lives as depicted below, through the Radioactivity Decay Graph.

However the mass or volume of the radioisotope would not under go any change with the reduction in radioactivity due to passage of time and completion of successive Half Lives one after the other. Preparation of Radioactivity Decay Graph is must for the radioisotope users to workout the radioactivity at a particular time or date with respect to the Half Life of a radioisotope.