HALF
LIFE


"Halflife
of radioactive element in the time interval during
which one half (50%) of the atom are disintegrated". OR "Half life of a radioactive element in the time interval during which (50%) of parents atoms are converted into daughter atoms or daughter element. 

FORMULA



l
x T_{1/2}
=0.693


where
l = Decay constant and T_{1/2} = Halflife. 

Different
substances have different halflives. FOR EXAMPLE: 1. Halflife of Krypton is 3.16 minutes. 2. Halflife of Radon 1s 3.82 days. 3. Halflife of Radium is 1600 years. 4. Halflife of Uranium is 4.47 x 10^{9} years. 

Write four precautions to minimize radiation dangers (hazard)?  
Radioactive
radiation are very harmful for life i.e. for human being. Therefore, we
must have precautions against them: (i) One should keep a safe distance away from the 'radiation emitting source'. the source emits radiation in all directions [it falls according to the relation 1/r^{2}]. Where r is the distance of the source from the body. (ii)The doctor, while giving the treatment to a patient by radiation should take the minimum possible time for radiation exposure. (iii) The radiation from a nuclear reactor are shielded by thick concentrate wall. (iv) In a laboratory, where radioactive materials are handled, the radioactive substance must be covered in a lead box with a lid made of lead. 

Write any four uses of radioactive isotopes?  
Radioactive
isotopes are widely used in the field of industry, agriculture and medicine. 

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