 # Nuclear Physics

## Atomic and Nuclear Physics

The nucleus is an integral part of the atom. So why do we use the terms nuclear physics and atomic physics separately? So, let’s begin our discussion with atomic and nuclear physics notes. The branch of Atomic Physics involves the study of the atom's properties, which are primarily influenced by the atom’s electron configuration. In Atomic Physics, the nucleus is treated as a single large particle with a specific charge, mass, and spin, while its internal workings are irrelevant to the scope.

So, what is nuclear physics? Nuclear Physics involves the study of the nuclei of atoms, its structure, interactions, and reactions.

The following discussion on nuclear physics class 12 will help you understand the meaning of nuclear physics, problems on nuclear science math, different nuclear science topics, and their application to any project on nuclear physics for class 12.

### Properties of Nuclear Force

• The overall effect of nuclear forces is attractive.

• Nuclear forces are non-electrical.

• There is no gravitational force between the nuclear particles.

• Nuclear forces are powerful.

• Nuclear forces act within a very short-range (multiples of 10-15 m).

• Nuclear forces are charge- independent.

• Nuclear forces are spin-dependent.

The spontaneous emission of rays from a substance is called radioactivity, and such materials are called radioactive substances. According to Rutherford and Soddy, the rate of instantaneous decay of radioactive atoms is proportional to the number of atoms present.

If N is the number of atoms present in a radioactive substance at any instant t, the disintegration rate -dN/dt is proportional to N, given as:

• dN/dt = λN, where λ is the decay constant for the given substance.

After integration, we get:

logeN0 = -λt + C

Applying N = N0 at t=0,

logeN = -λt + logeN0

or, N = N0e-λt

The rate of disintegration of radioactive material is called the activity of that substance.

• The traditional unit of activity is Curie, where one Curie is defined as 3.7 x 1010 disintegrations taking place per second in a radioactive substance.

• Another unit of radioactivity is Rutherford, where 1 Rutherford = 106 disintegrations per second.

• The SI unit of radioactivity is Becquerel, where 1 Becquerel is equivalent to one disintegration per second.

### Alpha, Beta, and Gamma Decay from Radioactive Nuclei

Atoms of a radioactive element emit alpha particles or beta particles and also gamma rays. As a result, both the atomic number and atomic weight are changed.

• Alpha-Decay: The release of an alpha (α) particle from a radioactive nucleus is called alpha decay. Alpha particle is a helium nucleus whose atomic number is two, and the mass number is four. Thus, during the emission of alpha particles from the nucleus of a radioactive atom, the atomic number decreases by two, and the mass number decreases by four.

Example: U92238  → Th90234 + He24 + energy

• Beta-Decay: The generation of a beta (β) particle from a radioactive nucleus is termed as beta decay. At the time of emission of a beta particle (electron), a neutron in the nucleus is transformed into a proton. A new particle called anti-neutrino (⊽) originates, which has zero mass and charge. Thus, during beta emission, the atomic number increases by one, and the mass number remains unchanged.

Example: Th23490  →  Pa23491 + β-10 + ⊽

• Gamma Decay: The emission of gamma rays (Ɣ), along with the emission of alpha or beta particles from a radioactive nucleus is called gamma decay.

### Mass Defect

Mass defect is the difference between the sum of masses of the nucleons (neutrons + protons) constituting a nucleus and the rest mass of the nucleus and is given as:

Δm = Zmp + (A - Z) mn - M

Where Z = atomic number, A = mass number, mp = mass of 1 proton, mn = mass of 1 neutron and M = mass of nucleus.

The lost mass appears as energy during the formation of the nucleus.

### Uses of Nuclear Physics

The utility of nuclear physics can be understood from the following two examples of nuclear physics application:

• In radiation therapy, ionizing radiations are used to treat medical conditions such as thyroid cancer and blood disorders.

• Nuclear fission reactions release thermal energy, which is converted to electricity in nuclear power plants.

1. What Does The Term Half-life Of A Radioactive Substance Mean?

The atoms of a radioactive substance decay continuously so that their number goes on diminishing. The time in which the number of its atoms or the mass of a radioactive substance is reduced to half its initial value is called the half-life of that substance. For a particular radioactive material, the half-life remains constant.

If N0 is the number of atoms present in a radioactive substance at time t=0, and N the amount at a later time t, then, by Rutherford-Soddy law, we have:

N = N0e-λt , where λ is the decay constant for the substance.

If the half-life is denoted by T, then at time t=T, the number of remaining atoms will be N0/2. Putting  t=T  and N= N0/2 in the above equation,

N0/2 = N0e-λT

or, 1/2 = e-λT

or, eλT = 2

or, λT = loge 2

or, T = loge 2 / λ

2. What Are The Downsides To Nuclear Energy Applications?

• The radioactive wastes generated from nuclear power plants are hazardous and toxic for living organisms and the environment. The persisting aftermath of the Chernobyl disaster and the use of atomic bombs on Hiroshima and Nagasaki bear testimony to the disastrous consequences.

• Radioactive waste management is a crucial factor in determining the extent of damage caused by radioactive effluents. The waste could be in solid, liquid, or gaseous form, and unless judiciously disposed of, the waste gets discharged into the environment.

• The use of nuclear energy in any sector involves massive capital costs - the construction and maintenance of nuclear power plants demand enormous capital investments.

• Scientists state that radioactive waste takes about 10,000 years to neutralise. In the meantime, contaminated waste run-off from land can cause eutrophication of water bodies, destroying aquatic life.

• Uranium, once depleted, cannot be replenished.