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# Nuclear Physics

The branch of science that deals with the fundamental particle namely nucleus is called Nuclear Physics. Nuclear physics basically deals with the structure and components of nucleus. The properties like radius, mass etc are dealt with and studied. Various models related to the nucleus and their development by various scientists, their experiments, theories etc. are the part of Nuclear Physics.

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## What is Nuclear physics?

Nuclear physics basically deals with the structure and components of nucleus. The properties like radius, mass etc are dealt with and studied. Various models related to the nucleus and their development by various scientists, their experiments, theories etc. are the part of nuclear physics.

The interaction and constituents of nuclei are studied in nuclear physics. There are various applications of nuclear physics such as:
Nuclear power generation, Nuclear weapons technology, Nuclear medicine, Magnetic resonance imaging, Ion implantation in materials engineering, radiocarbon dating in geology and archaeology.

## Father of Nuclear Physics

Ernest Rutherford is a very famous chemists. He is also known as Father of Nuclear physics as he was the first to propose the Nuclear model with a charged nucleus in the center. He found the nucleus by his very famous gold scattering experiment.
According to this model,
1. All the mass of atom is concentrated within a small positively charged region at the center called the NUCLEUS.
2. The nucleus is surrounded by the electrons which are negatively charged that move around it in circular paths. These circular paths are called the ORBITS.
3. The Rutherford model resembles our solar system. Here electrons and the nucleus are held together by Electrostatic forces of attraction.

The Radius of nucleus denoted by R is given by,
R = Ro $A^{\frac{1}{3}}$
Here,
A is the mass number of the element,
(Mass number = Total no of protons + Total no of neutrons)
R0 = Proportionality Constant,
R is directly proportional to $A^{\frac{1}{3}}$,
Volume of nucleus = $\frac{4}{3}$ $\pi$ R3,
Thus V $\alpha$ A
His model developed a new idea for the scientists which made Bohr to give his Bohr’s model for an atom. Thus he was awarded the Nobel Prize in Chemistry in 1908.

## Nuclear Physics Equations

The Mass number (A), also called atomic mass number or nucleon number, is the total number of protons and neutrons in a nucleus.
A = Z + N
where A = Mass number,
Z = Proton number,
N = Neutron number.

When Proton and Neutron combines together in order to form nucleus then in this process some mass gets lost and this lost mass is known as Mass defect. More is the mass defect more is presumed to be stability of product nuclei.

Mathematically,
$\Delta$ m = Mass of Nucleons – Mass of Nucleus.
= A – M
= (Z mp + N mn) – M.
$\Delta$ m = Z mp + (A – Z) mn – M
Here M = Mass of the nucleus
$\Delta$ m = Mass of the nucleons - Mass of the nucleus.
mp = Mass of the Proton and
mn = Mass of the Neutron.

Packing fraction
is defined as Mass defect per nucleon.

Packing fraction (f) = Mass defect per nucleons
= $\frac{\Delta m}{A}$
= $\frac{M – A}{A}$
Packing Fraction (f) = $\frac{[Z m_{p} + (A – Z) m_{n} – A]}{A}$
Greater the negative value of packing fraction higher is the stability of product nuclei.

## Nuclear Binding Energy

In Nucleus, Proton and Neutron are contained in small sphere. Due to such small small distance between two protons, they exert a very large force of repulsion on each other.
Therefore to prevent nucleus from bursting, certain amount of energy needed to bind the nucleus. This energy needed is known as Binding Energy. When nucleus is formed, the mass of nucleons forming it decreases. This mass defect provides the required binding energy. The energy equivalent to mass defect is called Binding Energy.
Binding energy of a nucleus may also be defined as the amount of work required to separate the nucleons at infinite distance. It is the measure of stability of nucleus.

Greater the binding energy per nucleons greater will be nucleus stability.

## Rutherford Gold Foil Scattering

In 1910, a physicist from New Zealand, Ernest Rutherford performed an experiment known as Rutherford’s Gold Foil Experiment. This experiment was determined to find out the structure of an atom.
Rutherford gave this atomic theory on the basis of following observations during the gold foil experiment:
1. Since most of the alpha particles passed through the foil without any deflection, thus it was concluded that most of the atom is empty.
2. As some particles deflected by small angles, it indicated that positively charged alpha particles were attracted by negatively charged particles means electrons.
3. Large angles of deflection experienced by the alpha particles indicated that there is a massive positively charged region present in the atom and due to repulsion alpha particles were deflected at large angles.

## Compton Scattering

Compton effect was first observed by Arthur Compton in 1923. It occurs when the incident x-ray photon interacts with the electron which makes the incident photon to deflect away from its original path.

The change in wavelength is given by:
$\lambda$' - $\lambda$ = $\frac{h}{m_{e} c}$ (1 - cos $\theta$)
Compton scattering is an inelastic scattering because the wavelength of the scattered light is different from that of the incident radiation. The change in the wavelength is called the Compton shift.

## Photoelectric Effect

When light of suitable wavelength is incident on the metal plate electrons are emitted. These emitted electrons are called as photo electrons and the phenomenon is Photoelectric Effect.

## Pair Production

When a photon is incident on the atomic nucleus, electron-positron pair is produced. This is called Pair-production. Pair production is a phenomenon of nature where energy is converted in to mass.

Cherenkov radiation is electromagnetic radiation emitted when a charged particle passes through a dielectric medium at a speed greater than the phase velocity of light in that medium.

## Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) is a technique used to determine the molecular structure of the substance by applying the external magnetic field to the atomic nuclei.
It has wide applications in medicine, tool analysis, analyzing quality and purity of the sample etc.

Radioactivity is a phenomenon which is discover by a French scientist Henri Becquerel in 1896. He verified that uranium is a powerful radiations that is capable of blackening a photographic plate. Here uranium was discovered about hundred years as these radiations are not observed.
Natural radioactivity is the phenomenon of spontaneous and uncontrollable emission of radiations. This process which is considered as the disintegration are not stopped or slowed down by the use of and instrument are not observed by Henri Becquerel in discover of radioactivity.

## Elementary Particles

Subatomic particles are small particles composed of nucleons or atoms. Elementary particles and composite particles are two type of sub atomicparticles. Elementary particles are those which are not measurable and are not made up of other particles and composite particles are made of some other particles also. Some of the Elementary particles are lepton, Hadron, Photon, graviton, quarks etc.

## Nuclear Spin

The Nuclear spin is different from the electron spin. The nuclear spin represents the total angular momentum of the nucleus. It is represented by symbol I. The nucleus is although, composed of neutrons and protons but it acts as if it is a single entity which has intrinsic angular momentum.
The Nuclear spin depends on the mass number, if the mass number is odd then the nucleus has half-integer spin like the electron while if the nucleus has even mass number then its spin will be integer spin.

## Nuclear Stability

Nuclear stability determines how stable the nucleus is? we know that the Nucleus is made of neutrons and protons. What causes them to stick together? Why do the protons not repel each other?

Surprisingly, the mass of the nucleus is less than the sum of the masses of the individual protons and neutrons which makeup the nucleus. The lost mass (mass defect) has been changed into the energy necessary to bind the nucleus together. Suppose the mass defect is $\Delta$ m. Then the energy binding the nucleus together $\Delta$ E is given by:
$\Delta$ E = $\Delta$ m $\times$ c2
where C is the speed of light.
If is divided by the number of nucleons in the nucleus, then the binding energy per nucleon is obtained. The higher this value is the more stable is the nucleus.

## Fermi Energy

The Fermi Energy is the energy of the highest level of quantum state which is occupied by the fermions (like electrons, protons or neutrons) at the absolute zero temperature.
The Fermi energy is useful in determining the thermal and electrical characteristics of the solids.

## Shell Model

The shell model of the atom was first proposed by Niels Bohr in 1923.
The Shell Model is the model which describes the distribution of the energy level into different shells in an atom or in the nucleus of the atom. A shell is the energy level where particles of same energy exist. The shell model describes the arrangement of the elementary particles in the different shells of the atoms.
For example, the electrons are distributed in different shells based on their energy level and their direction of their rotation.

## Millikan Oil Drop Model

The Millikan oil drop experiment is commonly known as Millikan experiment and was first performed by Robert Millikan and Harvey Fletcher in 1909. Robert Millikan was the professor of University of Chicago at that time. The experiment was performed by Professor Millikan with the useful inputs from Mr. Fletcher.

In this experiment a charged oil drop was suspended vertically between the two electrodes. Then the electric field is applied to such an extent that the free fall of the oil drop, under the influence of gravitational pull, was stopped. With the known electric field and other parameters Millikan was succeeded to calculate the charge on the drop. He published his findings in 1913 and was awarded Nobel prize for physics in 1923 for his work on finding the charge of the electron.

## Fission

Fission is the process whereby a some matter divides and becomes multiple states.
Here in Nuclear physics, Fission process is used to split up a single atomic nuclei into two or more fragments.

## Nuclear Fission

The Nuclear fission is defined as the process of splitting a heavy nucleus into two nuclei of smaller mass. Eg: Consider a Uranium Nuclei.

The process of fission is represented as follows:

92U235+0n1 --> 92U236 --> 56Ba141+36Kr92+30n1+ Energy