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AWARENESS
results from electron-nucleus Coulomb interactions.
4. Annihilation rays, which result from positron-electron annihilation.
X-rays and gamma rays are forms of EM radiation that do not differ in their nature and properties; rather they differ in their origin; i.e., the way in which they are produced. The production of X-rays is an extra-nuclear process, which means that they are generated in an electric device that accelerates electrons to very high energy and then stops them abruptly in a target (usually gold nuclei). Part of the kinetic energy of motion of electrons is converted into photons of X-rays. The production of gamma rays is an intra- nuclear process, which means that they are produced when unstable nuclei, e.g., Cobalt-60 or Caesium-137, break up and decay into stable nuclei. X-rays and gamma rays themselves do not produce any damage chemically or biologically to matter. But when these radiations pass through a medium, they get absorbed and give up their energy to produce fast moving electrons by photoelectric, Compton and pair production processes, which cause the damage.
Measurement of radiations
In medical field, radiations serve a very crucial part. Radiation quantity is generally measured in terms of
‘Exposure’ and ‘Dose’. Exposure is the concentration of radiations at a specific part of the body. As air is exposed to large number of radiations, the amount of air ionization is measured in terms of most widely used radiation quantity known as “exposure”.
The conventional units of exposure are “Roentgen” while SI units are Coulombs/ kg. The total radiation delivery to a body is called Surface Integral Exposure (SIE) and is measured in R-cm2. For example, if the two persons are exposed to the same radiation concentration, the SIE will be greater in the person with a large surface area exposure. Exposure alone is of no use as dose plays the lead role to determine the amount and effect of radiations. Dose, here specifically, does not mean the amount of medication taken in absolute measureable quantity. It is the combination of exposure due to radiation, intensity of radiation and the type of matter with which radiation is interacting-which in medical terms refers to the sensitivity of skin. Dose is further divided into four categories: Absorbed dose, Integral dose, Equivalent dose and Effective dose.
1. Absorbed dose - Absorbed dose is the average amount of energy deposited on human tissue per unit mass through ionizing radiations. Radiations affect the organs less which are covered by bones
(e.g., lungs covered by ribs), but have more impact on the directly exposed organs (e.g., stomach).
2. Integral dose - Integral dose is the product of absorbed dose and the mass of tissue irradiated. In other words, it is the product of volume of matter and mean dose.
3. Equivalent dose - Equivalent dose calculates the impact or effectiveness of radiations on a specific tissue/organ. It addresses the damage caused by radiation on the tissues.
4. Effective dose - Effective dose is the quantity of total effect of radiations on the whole body. In medical field, it is a general quantity which is determined by the type of medical procedure (e.g., X-ray, CT scan, etc.).
To estimate the radiation quantity/ exposure/dose received by an individual through exposure to radiations present in the environment, one must have a thorough knowledge of benefits and risks of these radiations. So, it is very important to quantify the radiation quantity. For example, the CT scan of a head should have an absorbed dose of the range 42-71 mGy (milli-Gray) and an effective dose of 2.1 mSv (milli-sievert). During an examination, the doctor is concerned about the effective dose i.e., the long-term effects of the radiations on body. Usually, the absorbed dose and equivalent dose are not considered much because a perfectly performed procedure will have negligible short-term risks. But an average person is also exposed to the naturally-occurring background radiations. Hence the ultimate effect is much more than anticipated.
Effects of Radiations
Although there is a plethora of radiations used in the field of medicine, agriculture, research, industry and energy production, beyond a certain point, these “effective” radiations become “destructive”. So, radiations are like a “double-edged sword”. On the brighter side, they have the potential to cure cancer, but on the other side, they can lead to cancer itself.
Effect of naturally-occurring and man- made radiations
If you look at your surroundings,
Shows conventional units and SI units of Exposure, Absorbed dose, Integral dose, Equivalent dose, and Effective dose.
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