Gamma rays are emitted during radioactive decay as nuclei transition to lower energy states. They are produced through three main processes: 1. Alpha and beta decay leave nuclei in excited states, which then emit gamma rays as they fall to lower energy levels. 2. Gamma decay directly involves gamma ray emission as excited nuclei transition to the ground state. 3. Induced gamma emission occurs when absorption of photons or neutrons excites a nucleus, which then emits gamma rays as it decays to lower energy states.

1. 1. The emission of gamma rays is secondary effects of atomic disintegration.
2. The emission of alpha and beta particles leaves the nucleus at higher energy level which
makes the nucleus unstable and this extra amount of energy released in form of radiation
called as gamma rays.
3. Gamma rays have very small wave length of the order of 10-10 to 10-12 m and extremely
high penetration power so can penetrate 0.15 m of steel sheet. These rays are charge less
and not deflected in either electric field or magnetic field.
4. Hence because of gamma decay the excited nucleus falls down to a lower energy state
with the emission of a high energy photon known as a gamma particle, hence there is no
change in atomic number and mass number in daughter nuclei compare to parent nuclei.
For example the gamma decays with helium-3.
Another example of gamma decay is from Dysprosium.
http://chemistry.tutorvista.com/nuclear-chemistry/decay-rate.html
http://chemistry.tutorvista.com/nuclear-chemistry/gamma-decay.html
Atoms consist of three subatomic particles, electrons, protons, neutrons.
Some elements are not stable and easily disintegrated to small nucleus with the emission of
ionizing radiations like alpha, beta or gamma rays. These ionized radiations are termed as

2. radioactive rays, elements called as radioactive element and the property of emission
of radiations is known as radioactivity.
Radioactive elements have high neutron to proton ratio which makes them unstable. Since there is a
repulsionforce between positively charged protons located in a small region called as nucleus. Hence
there must be some strong force greater than the repulsion force between protons which can make
nucleus stable.
If there are a large number of protons in an atom, the repulsion force becomes very high and nucleus
disintegratedinsmall nucleuswiththe emissionof energy.The energy emitted in the form of radiation
that is known as radioactive radiations.
Hence nuclear decay or radioactive decay is the process in which a nucleus of an unstable atom
lose convertsina stable bythe emissionof ionizingparticlesorionizing radiation. This unstable nucleus
calledasparentnuclide andthe newelement formedin nuclear decay is known as daughter nuclei and
the nuclear decay also called as nuclear transmutation.
Apart from these charged particles, there is a possibility of emission of gamma rays also. Emission of
gamma rays during any radioactive decay is termed as gamma emission. Gamma rays are high
energy and high frequency electromagnetic radiations.
When the energy of gamma rays transfer to one of the most tightly bound electrons, that electron
ejected from the atom and results photoelectric effect. The best example of gamma emission is beta
decay of cobalt-60 forms Nickel-60 with the emission of gamma rays involve two nuclear reactions.
In this gamma emission which follows beta decay, first Cobalt-60 show beta decays and converts into
excited Nickel-60 nuclei with the emission of an electron and anti neutrino particle. The energy of
released electron is 0.31 MeV.

3. In secondstepsthisexcitedNickel-60dropsdownto the groundstate with the emission of two gamma
rays of 1.17 MeV then 1.33 MeV.
When a photon is absorbed by target nucleus in its initial state, the nucleus will be moved to at high
energy level and becomes excited. The excited nucleus emitted energy in the form of a cascade of
transitions which is also called as "gateway state" or "trigger level" or "intermediate state". In this
processfluorescentphotonsare emittedbutafter some delaysof the initial absorption and this process
is an example of induced gamma emission.
Anotherexampleof inducedgammaemissionisneutronabsorptionanalysis(NAA).Neutron absorption
analysis is a sequence of events starting from the neutron capture by a target nucleus through a non-
elastic collision and forms a compound nucleus in an excited state. The energy of excited state is
because of binding energy of the neutron with the target nucleus and due to high energy,
it disintegrated instantaneously into a more stable nucleus by the emission of gamma rays.
http://oregonstate.edu/instruct/ch374/ch418518/Lesson10-rev.pdf