Girish Kumar

Well its good question. As a person who is working in the same field, I do describe Radiation as a flux of energetic particles or rays which do have origin from atomic or nuclear transitions. And an interesting fact is that we are always in exposure of radiation. As I have told, the energetic particles emanating from outside universe would be reaching the surface of the earth but losing intensity by greater margin. The intensity of these radiations would be different in different regions due to magnetic belts of earth. Such radiation we usually call as cosmic or terrestrial radiation and commonly used word background radiation. The sunlight radiation contains UV, infrared also which are also called as solar radiation. The units of radiation are classified into 3 types. One is for estimating the exposure rate and the unit is R/hr (Roentgen/hour). It gives the amount of charge liberated in 1 cubic centimeter of air. Second is RAD(Radiation Absorbed Dose), which describes the amount of energy deposited in unit mass of a substance. Third is REM(Roentgen Equivalent Man) which is used for estimating biological effectiveness on living beings. I have answered you question briefly for your understanding. You can visit my blog http://physicsdatabank.blogspot.com for more answers on conceptual questions.

ALARA - Defined as As Low As Reasonably Achievable This is well known law in the field of radiation physics. It is evident that occupational workers in nuclear reactors, fuel reprocessing plants, accelerators etc... shall continue their work in radiation zones. Hence as they cannot avoid radiation exposure to zero level, they have to minimize it. The ALARA principle says the same. The measures required by law to minimize the risk is to practice the TDS principle. ' T ' stands for Time ; ' D ' stands for Distance ; ' S ' stands for Shielding Time ---- Radiation occupational workers shall minimize the exposure time by means of sharing the work between individuals. Hence many sites follow splitting of work in shifts which reduces the cumulative radiation dose. Distance ----- While handling radioactive sources, methods shall be adapted to maintain sufficient distance from the radioactive sources to minimize the exposure. For instance, the range of alpha, beta particles, and other massive particles in air is less and hence it is comfortable to reduce exposure to about zero level by keeping them at small distances away from the body. but when you handle sources emitting gamma, neutron good distance shall be maintained away from the sources to minimize the exposure though it is difficult to reduce the exposure to zero. For instance 1 meter / two meter tongs are normally used in laboratories to handle the low activity gamma / neutron sources as they obey inverse square law. Shielding -- Most important aspect in reducing the exposure. Suitable shielding methods shall be incorporated to handle the sources. For particles like alpha, beta a simple economical shielding is enough to restrict the escape of radiation through container. It should be kept in mind that three of the above parameters shall always be practiced simultaneously for achieving ALARA principle. Hope this clarifies your query. For other physics related answers you can visit my blog... Articles on Physical Sciences