Types of radiation

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Ionizing radiation is the radiation which can penetrate tissues and deposit its energy within them. They are of three types of electromagnetic radiation: alpha particles, beta particles (electron) and protons.

Alpha particles are 10 times more harmful than X-rays, beta particles or gamma rays but they have very little penetrating force. But they are dangerous it enters the body by inhalation or wound. X-rays & gamma rays are of short wave length and can penetrate deep.

Alpha particles can penetrate 4cm in air, 0.05mm in tissue and no penetration in lead. Beta particles can penetrate 6 to 300cm in air, 0.06-4mm in tissue and 0.005 to0.3 mm in lead. Gamma rays can penetrate 400 meters in air, 50cm in tissue and 40mm in lead. X-rays can penetrate 120-240 meters in air 15 to 30cm in tissue and 0.3 mm in lead.

“Non ionizing radiation” in compare to ionizing radiation have longer electro magnetic wave length. As the wave length becomes longer the energy of the electro magnetic wave decreases. So all the non-ionizing radiation have lesser energy than ionizing radiation. In order of increasing wave length that means lesser energy, non ionizing radiation include ultraviolet rays (UV), visible light, infrared rays, microwave radiation and radio frequency radiation.

Units of Radiation

The activity of radioactive material is the number of nuclear disintegration per unit of time. The unit of radioactive activity is Becquerel(Bq). 1 Bq is equal to one disintegration per second. Formerly unit of radiation was curie (Ci).

The potency of radiation is measured in three ways. Roentgen: It is the unit of exposure. . It is the amount of radiation absorbed in air at a given point, that is the number of ions produced in one ml of air . Rad: It is the unit of absorbed dose of radiation, that is the amount of radioactive energy absorbed per gram of tissue in humans or in any material. 1mrad (milliard ) is equal to 0.001rad of radiation. Rem: This is the product of absorbed dose and modifying factors, that means the effects of modifying factors are deducted from absorbed dose and we get the rem. Due to high speed and high penetrating power of x-rays and gamma rays the rem and rad of these are equal. This means the entire dose which is absorbed and modifying factors have no effect.

The above radiation units (roentgen, rad & rem) have been replaced by the new SI units (International System of Units). They are of three types

(1) Coulomb per kilogram(c/kg)has replaced Roentgen unit. 1 roentgen unit is equal to 2.58×104 C/kg. This is the unit for exposure.

(2) Gray(GY): It has replaced rad. It is the unit of dose of ionizing radiation that imparts 1 joule of energy to one kilogram of absorbed material. 1rad is equal to 0.01Grey (GY).

(3) Sievert (sv) has replaced rem. It is the unit of dose equivalent. 1 seivert (Sv) is equal to 100rem.

Dose equivalent(H): The concept of dose equivalent has been introduced due to the fact that all types of radiation do not produce same biological effect per unit of energy absorbed. The dose equivalent (H) of seivert, which is equal to the absorbed dose (D) of grays, multiplied by a quality factor Q, which depends upon the density of ionizing radiation produced in the tissue by the radiation.

H = DQ

The quality factor (Q) of X-ray, gamma ray and electron is equal to 1 (one), whereas for a particle it is 20. From this fact it is clear that particles like ? rays are 20 times more harmful than X-ray or gamma ray.

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1 Comment

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