Nuclear energy power station & nuclear medicine imaging Nuclear energy is used to produce electricity and also in medicine imaging to identify the defects of a patient(NMR spectroscopy)

The atom is almost all empty space. If we had an atom and wished to see the nucleus, we would have to magnify it until the atom was the size of a large room, and then the nucleus would be a large speck which you could just make out with your eye. The radius of the nucleus is 1,00,000 times smaller than the atom and in terms of volume, atom is a thousand million million times bigger than nucleus.

But nearly all the weight of the atom is in the infinitesimal nucleus. As neutrons and protons in nucleus are very nearly of the same mass as each other and each is about 2000 times as massive as an electron, the total number of protons and neutrons in the nucleus determines all but a small fraction of the mass of an atom.

The energy of the nucleus reveals itself in many ways; nuclear warheads that can destroy cities, submarines driven by nuclear reactors, nuclear power plants and in destroying cancerous cells. Nuclear energy comes from the conversion of mass and can result from nuclear reactions like fission (the splitting of the nucleus) and fusion (the coming together of nuclei).

In case of nuclear fission, nucleus splits into two roughly equal fragments and two or three more neutrons. The sum of these masses is less than that of the original nucleus, and the difference in mass is converted into energy of the motion of fragments which can lead to a nuclear chain reaction in certain conditions. The energy released as a result of nuclear chain reaction is used to run commercial nuclear reactors and generate electricity.

Nuclear medicine is a branch of medicine that uses the nuclear properties of matter in diagnosis and therapy. Nuclear medicine is a safe, painless and cost–effective technique to image the body and treat disease. In diagnosis, radioactive substances are administered to patients and the radiation emitted is measured. In therapy, radio nuclides are administered to treat disease or provide palliative pain relief. Nuclear medicine imaging procedures often identify abnormalities very early in the progress of a disease ‐ long before many medical problems are apparent with other diagnostic tests.

Neutron diffraction spectrometer This is the spectrometer which was first used at Ryerson Laboratory, at the University of Chicago, USA, in the scattering of X‐rays by gases for free atom form factor determinations. In 1944 it was taken to Oak Ridge and set up at the face of the Graphite Reactor. There, it was used in 1945 by US physicist Ernest Omar Wollan (1902‐1984) to develop the techniques of neutron diffraction spectroscopy. This technique is used to determine the structure of materials in a similar way to X‐ray diffraction.

The central core of the Altatom which contains all of the atom’s positive charge and most of its mass is known as atomic nucleus. The size of the nucleus is 10,000 times smaller than the size of the atom, but more than 99.9% of the whole mass of the atom is concentrated in the nucleus. Therefore, a nucleus occupies a very small space in the atom consisting of protons and neutrons.

Since neutron is a neutral particle, it has high penetrating power and very low ionising power. Further, electric and magnetic fields have no effect on it. These two constituents of a nucleus (protons and neutrons) are called nucleons. Although the hydrogen nucleus consists of a single proton alone, the nuclei of other elements consist of both neutrons and protons. The different types of nuclei are often called nuclides

Proton is a positively charged particle and has a charge equal to that of an electron. However, the mass of a proton is about 1836 times that of the electron. Charge on proton, e = + 1.6 × 10⁻¹⁹ C and mass of proton, m_p = 1.6726 × 10⁻²⁷ kg = 1.007825 a.m.u.

Neutron is a neutral particle and has no charge. Its mass m_n = 1.6750 × 10⁻²⁷ kg = 1.008665 a.m.u. Atomic mass unit (a.m.u.) is a smaller unit of mass developed to make the study of nuclear masses for convenience. One atomic mass unit is defined as one–twelfth (1/12) of the mass of a atom. According to Avogadro′s hypothesis, there are 6.023 × 10²³ atoms in 12g of carbon.

The nucleus is believed to be spherical and hence its size is usually given in terms of radius. It has been found experimentally that the volume of a nucleus is directly proportional to its mass number A. If R is the radius of nucleus, its volume = (4/3) πR³, R = R₀A^1/3, where R₀ is a constant whose value is found to be 1.2 × 10⁻¹⁵ m. The radius of the nucleus depends upon the mass number A and therefore, atomic nuclei of different elements have different sizes.

As the radius of a nucleus is extremely small, is order of 10⁻¹⁵m. In a usual practice express the nuclear radius in a smaller unit of length called fermi, named after the famous physicist Enrico Fermi. (1 Fermi (1fm) = 10⁻¹⁵ m).

Example: Find the nuclear radius of (a) lead and (b) oxygen. R₀= 1.2 × 10⁻¹⁵ m

(a) Lead. Mass number, A = 208

∴ Nuclear radius, R = R₀ A^1/3= 1.2 × 10⁻¹⁵ × (208)^1/3 = 7.1 × 10⁻¹⁵ m =7.1 fm

(b) Oxygen. Mass number, A = 16

∴ Nuclear radius, R = R₀ A^1/3 = 1.2 × 10⁻¹⁵ × (16)^1/3 = 3.0 × 10⁻¹⁵ m = 3.0 fm