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| Nucleus
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Nuclear Fussion:-
the process of combining two light nuclei to form a heavy nucleus is known as nuclear fusion
when two light nuclei (having low binding energy the nucleon)are combined to form a heavy nucleus there
occurs a small mass defect which gets converted in to energy
eg: 
process requires very high temperature for occurnce.
Dumb question:
why such a high temperature necessary?
Ans: This is because when possitively changed nuclei come close to each other for Fusion they required very high energy to counter replusive
force between them.
[illustration] Two determine nuclei fuse to form a tritium nucleus and a proton as by product . compute the energy released.
given: Mass of deterium=2.01414
Mass of tritium nucleus=3.01605u
and mass of proton=1.00782u
[solution]
mass of reactants = 2.0141 x 2 = 4.028204
mass of products=3.01602 + 1.00782=4.02387u
mass defect = 4.0282 - 4.02387 = 0.00433u
Energy released = 000433 X 931 = 4.03 Mev
Dumb Question:
how has the factor 931 come in computation?
Ans:  E = mc2, if mass is 1amu
and it is converted in to energy by this relation then
E = 931 Mev
1u mass defect is equivalent to931Mev of energy produced
Radioactivity: the phenomenon of sportaneous emission of radiation from radioactive substance is known as Radioactivity.
This is exhibited naturally by certain heavy elements like uranium,Radium, thorium etc. Few radioactivity decay are:
 - decay: in this case an particle(helium nuclus) is ejected and parent nucle looses two protons and two neutrons
 - decay: in this process change Ze of nucleus changes but the number of nucleons remin unchanged. This happens if
nucleus emits an electron(- decay) or positron.
In this process either protons is converted in to neutron or vice-versa (+ decay) is also accompained by release of a changeless
and massless particle called neutrino
 decay: a gamma ray emmision does not affect either the change or number
Radioactive Law
In a typical decay process, unstable nucleus (parent0 decays and results in the formation of daughter. Thus effectively no. of parent nucleus decress in the process.
If initially there were N0 unstable nucleus, then after time t, the no. of parent nucleus N remaining is given by
N = N0 where  decay constant.
This law is followed by all radioactive decays
• The time Required to get the number of parents nuclei halved is given by
• Another quantity that measure the rapidity of decay is the average or mean life time of a nucleus,
tav is given by
Average life=1.44 times the half life
why??
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