Question

Discuss the mechanisms that drive nuclear reactions which result in the emission of alpha, beta (plus and minus) and gamma rays.

Answer 1

Alpha decay- It is a phenomenon of emission of an alpha particle (helium nucleus) from a radioactive nucleus.

Basically, when a nucleus emits an alpha particle, its mass number decreases by 4 and atomic no decreases by 2. For example, when uranium - 238 (atomic no 92) undergoes alpha decay, the resulting element has mass no 234 and atmoic no 90. This new element corresponds to Thorium. Thus new elements are formed in alpha decay.

Gamow explained alpha decay in terms of penetration of the nuclear potential barrier on the basis of quantum theory. Accordingly, an alpha particle exists as an entity within a heavy nucleus and it is in constant motion. Quantum mechanically there is a finite probability that it may pass through the nucleus even if it's energy is lower than the barrier potential.

Beta decay: In case of beta decay a radioactive nucleus emits beta particles (positive and negative) which are nothing but electrons (or positrons). This emission accours from inside the nucleus when a neutron decays into a proton and electron (as well as an anti neutrino). The electron is emitted out as a negative beta particle. On the other hand if a proton decays into a neutron and positron (and a neutrino) then the emitted particle is positive beta particle (positron). In this decay there is no new particle created

Gamma decay: In this decay a radioactive nucleus emitts photons as it decays. This happens because a nucleus has a many number of different energy levels. And it can transit between higher levels to lower leaves by emitting the difference of their energies. When am excited nucleus makes a transition to a state of lower energy it emits a photon. On the other hand it can go up the energy ladder to become excited by absorbing a photon. This process also doesn't create any new elements.

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