"Half-life of radioactive element in the time interval during
which one half (50%) of the atom are disintegrated".

"Half life of a radioactive element in the time interval during which
(50%) of parents atoms are converted into daughter atoms or daughter element.
l x T1/2 =0.693
where   l = Decay constant
and T1/2 = Half-life.
  Different substances have different half-lives.
Half-life of Krypton is 3.16 minutes.

Half-life of Radon 1s 3.82 days.
3. Half-life of Radium is 1600 years.
4. Half-life of Uranium is 4.47 x 109 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/r2]. 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.
Radio isotopes are used to check cracks,wear and tear in machine parts. For example a radioactive      substance is inserted into bearing , fine bearing filling, obtained as result of wear and tear are washed      away by lubricating oil. An examination of the radioactivity of the bearing's filling containing oil will      indicate the wear of the bearing.
) Cobalt (Co-60) emits high-energy g-rays. Therefore it can be used the detect cracks in welded joint.
Radio isotopes to also be used detect leakage in pipes. This is done by introducing small quantities of     radio isotopes into the fluid of pipe. A radiation detector is used to check whether the isotope is leaking     any where in the pipe and thus indicating fault in the pipe.
The seeds which resist attack of pest and give higher production is achieve by radiation. These of      seeds are produced after mutation through radiation.
Radiation is also used to kill bacteria.
) Radio isotopes are used to determine the optimum amount of fertilizers and other nutrients for the     proper growth of plants
) Radio phosphorous-32 and radio iodine-131 are used as tracer to trace out the path of an element in     the human body, animal and plant.
) Phosphorous-32 is used to locate precisely the location of brain tumor.
) Radio phosphorous-32 has been found effective for treating leukemia.
) iodine-131 is used for the study of thyroid gland disorder.
) Radio cobalt-60 is widely used to treat cancerous tumors in human body.
) Radiation in low dosages can also be used for sterilizing bandages and surgical instruments.

      For latest information , free computer courses and high impact notes visit : www.citycollegiate.com