2. What is Nuclear Force?
Nuclear forces (also known as nuclear interactions) are the forces that act between
two or more nucleons. They bind protons and neutrons (nucleons) in atomic nuclei.
The nuclear force is about 10 million times stronger than the chemical binding that
holds atoms together in molecules.
There are two fundamental forces in the nucleus that aren't observed outside of
nuclei. These forces are creatively named the strong force and the weak force.
Binding Energy
Nuclear binding energy is the energy required to split a nucleus of an atom into its
component parts: protons and neutrons, or, collectively, the nucleons. The binding
energy of nuclei is always a positive number, since all nuclei require net energy to
separate them into individual protons and neutrons.
3. What is Mass Defect?
Mass defect is the difference between the actual atomic mass and the predicted mass
calculated by adding the mass of protons and neutrons present in the nucleus. The actual
atomic mass is less than the predicted mass calculated by adding the masses of
nucleons. This additional mass is accounted for by binding energy that is released when a
nucleus is formed. When a nucleus is formed, some of the mass is converted to energy
and this results in the mass defect. Due to this reason, the actual mass of an atomic
nucleus is less than the mass of particles it is made up of.
Mass defect (Md) can be calculated as the difference between observed atomic mass (mo)
and that expected from the combined masses of its protons (mp, each proton having a
mass of 1.00728 amu) and neutrons (mn, 1.00867 amu):
Md=(mn+mp)−mo
Definition of packing fraction
Where M is atomic mass and A is the mass number of the atom.
4. Radioactive decay and the exponential law
Radionuclides are said to decay when they change from one nuclear configuration to
another. This decay takes several forms, including the ejection of alpha-particles, beta-
particles (both positive and negative) and gamma-rays from the nucleus.
The law of radioactive decay states that the rate of decay of a particular nuclide (i.e. the
number of nuclei decaying per second) is proportional to the number of such nuclei left
in the sample (i.e. it is a fixed fraction of the number of nuclei left in the sample).
Radioactive decay law: N = Noe-λt
Derivation of Exponential Decay Law
6. Half -Life
Half-life, in radioactivity, is defined as the time interval required for one-half of the
atomic nuclei of a radioactive sample to decay (change spontaneously into other
nuclear species by emitting particles and energy).
Mean or Average Life
Mean life, in radioactivity is defined as the average lifetime of all the nuclei of a
particular unstable atomic species. This time interval may be thought of as the sum of
the lifetimes of all the individual unstable nuclei in a sample, divided by the total
number of unstable nuclei present.
