RADIOACTIVITY

Henri Becquerel 1852-1908

strong nuclear force weak nuclear force

What happens when an element undergoes radioactive decay? During radioactive decay an unstable nuclei of an isotope emits particles and releases energy, to become a stable isotope Energy "NUCLEAR" Radiation To radiate means "to give off" Radioactive Atom Particle

alpha beta gamma

Decay Type Generic Equation Model A 4 Alpha decay 4 2 Alpha Particle Parent Daughter 0 Beta decay Daughter Beta Particle Parent Gammaa emmission 7 Relaxation 0 0 Gamma ray Parent (excited nuclear state) Daughter

(Number of Neutrons) 126 82 Type of Decay 50 Fission Proton Neutron Stable Nuclide Unknown 28 14 6 14 28 50 82 (Number of Protons)

LAW OF RADIOACTIVE DECAY

The no. of atoms present in the radioactive substance depends upon the rate of disintegration. Accordin to the following relation. dN dt It states that "rate of disintegration is directly proportional to the number of atoms present". This is known as law of Radioactive decay as well.

Ll if t 0 and N- N. logeNoc now eqn ii becomes logeNAt +log,N log N log,NoAt log 0 At N Ne-it

2 Ne 2 -A ti 2 0.693 A t 0.693 1 This expression gives the half size of the radioactive substance in terms of decay constant. Here, half life is reciprocal of decay constant.

MEANLIFE

Derivation of mean life: Let us consider, No be the total number of radioactive atoms present initially After time t, total no. of atoms present (undecayed) be N. IN further dt time dN be the no. of atoms disintegrated. So, the life of dN atoms ranges lies betweent + dt and dt. Since, dt is very small time, the most appropriate life of dN atom is t. So the total life of N atom t. dN No sum of ages of all atoms- 0

Now substituting the value of dN and changing the limit in equation i from i we get 0 0 0 - sum of life of all atoms

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Shivam PARASHAR

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