Nuclear Chemistry pdf

Nuclear Chemistry is the branch of Chemistry deals with the nuclear processes, radioactivity and transformations in the nuclei of atoms such as nuclear properties and nuclear transmutation. It involves the study of the production and use of radioactive sources for a range of processes. In this branch of Chemistry we study about the structure of nucleus, relationship between structures of nucleus and stability of nucleus. Elements does not change in chemical reaction but changed in nuclear reactions. Transformation of nucleus takes place and new products are form. Amount of heat evolve during chemical reaction is in small quantity but radioactive rays evolve in nuclear reactions contain huge amount of energy.

Radiochemistry discuss about the radioactive species and their applications in various fields. Radiation Chemistry deals with chemical effects produced when radioactive radiations interact with matter.

Structure of Atom:

Atom is neutral in nature because of presence of equal numbers of electrons and protons. It is complicated structure having central core. In 1898, J.J.Thomson discovered that atoms consists of numbers of negative charges revolve around the central positive charge spot called nucleus. In 1913, proved that there is a dense center in an atom called nucleus. He proved that by bombarding alpha particles on gold layer. Nucleus consists of about 32 fundamental particles.

Properties of Nucleus:

• Nucleus is a fundament particle.

• Columbic forces binds electron to the nucleus.

• Size of Nucleus is 10^-13 cm.

• Volume of nucleus is 10^-36 cm^-3.

• Density of nucleus is 10^14 g per cm^3.

• Density of nucleus can contrast for any nucleid.

Atomic Number of an element is the number of protons found in the nucleus of an atom. For example atomic number of sodium is 11 and chlorine is 17. Mass Number or Atomic Mass is the sum of numbers of protons and neutron present in the center of an atom. Neutron Number is the number of neutrons present in the center of an atom or in the nucleus. The difference between the mass number and atomic number gives the value of neutron number. Isotopes are the atoms of elements having same atomic number but different mass number. The phenomenon of isotopy discovered by soddy. Relative abundance of isotopes measure by mass spectroscopy. Isobars are the atoms of different  elements having same mass number but different atomic number. For example Ar and Ca have 40 mass number but have different atomic number.

 Isotones are the atoms of an element that contains same numbers of neutrons but different mass numbers and atomic numbers. For example sulfur and phosphorous have 16 numbers of neutrons but have different masses 32,31 and different atomic number. Nuclear Isomers are atoms with same mass number and atomic number but different stages of excitation in atomic nucleus. The higher or excited is called metastable state but the stable and unexcited state is called ground state.

Mass Defect and Nuclear Binding Energy:

Energy is released during attraction due to which mass before attraction and after attraction becomes changed and it is termed as mass defect. In other words difference between the mass of an atom and sum of electron, proton, neutron is called mass defect. Mass defect impacts the stability of nucleus and it is a binding energy released from its constituents when nucleus is formed. The binding energy functions is in nuclear reaction as ∆H for chemical reaction. Heavier nucleid show fission and lighter nucleid show fusion. Einstein helps to find out the binding energy or mass defect. We can calculate it by using equation (E= mc^2). And final result after solving this equation, the value of binding energy is 28.30 MeV / atin.

Nuclear stability; Some nucleids are neutral and some are man made. Overall we divide all these into two types. One is Stable nucleid that contains 274 and other is unstable nucleid that contains 2000 neutral and artificial.

Rules of Stability:

• Odd Even Rule; Most of the naturally occurring nucleid have even number of protons and neutrons. About 165 follow this rule. 

• Magic Number ; Nucleons are arranged into shells within atomic nucleus. The most widely seven digits are named magic numbers includes atomic number 2,8,20,28,50,82, and 126. These are helium, oxygen, calcium, nickel, tin, lead and unbihexium. These nucleons have high average binding energy per nucleons. 

• Neutro Proton Ratio; Ratio N/P ≈ 1 , for stable. If it will exceeds 1, then it will be unstable. Those Nucleid which have atomic numbers more than 83 are usually unstable.

Radioactivity:

The production of particles and ionizing radiations caused by the spontaneous disintegration of atomic nuclei is called radioactivity. A substance which have unstable atomic nuclei is considered to be radioactive. Natural Radioactivity involves the spontaneous emission of radiations from an unstable nuclei. Artificial Radioactivity involves the process of emission of radiations from naturally occurring isotopes when they are bombarded with gamma rays and sub-atomic particles or high levels of X-rays.

Types of Radioactivity:

• Alpha:

 These are fast moving helium atoms that have high energy mainly in MeV but have high mass so that these can be stopped by piece of paper or ife inches of air.

• Beta:

 These are fast moving electrons that have few hundred KeV to several MeV energies range. That’s why electrons are lighter than that of helium atoms. They can penetrate through several millimeters of plastic, several feet of air and less of very light metals.

• Gamma:

 These are photons having from several keV to several MeV energies range and is just like light. Gamma rays and X-rays are very similar to each other. It can be stopped by a piece of aluminium foil and it can penetrate through several inches of lead because of their energies.

Radioactive Decay:

Radioactive decay involves loses energy by radiation by an unstable atomic nucleus. A material containing unstable nuclei is considered radioactive. The spontaneous break down of nucleus results in the emission of energies and matter from the nucleus. Radioisotope is unstable because it has not enough binding energy to hold the nucleus. Rate of disintegration helps to determines daughter nuclei. Rate of disintegration can not be controlled by changing environment. There is no effect of temperature, pressure and chemical or physical environment. Radioactive isotopes usually produced alpha and gamma rays, beta and gamma rays but some nuclides emit beta particles that’s why these are called pure beta emittors.

Types of Radioactive Decay:

• Alpha Decay

• Beta Decay

• Gamma Decay

• Internal conversion

• Isomeric transition

Nuclear Reactor:

Nuclear reactor is used to carry fissionable and non-fissionable materials in such a way that produces fruitful products. In other ways, finite numbers of protons are produced. Only that neutron can be controlled which has high speed otherwise it is not good. Neutron machine is used to fulfil our desires to produce neutrons and for the production of electricity power generator is used. Nuclear Reactor or Nuclear Machine is a system in which fissionable and non-fissionable materials are assembled in such a way that it makes fission chain reaction and proceed in a controlled manner. 

Uses of Nuclear Reactor/Nuclear Machine/Power Generator:

• It provides heat.

• It gives mechanical energy.

• It supplies radioisotopes.

• We get weapon materials from it.

• It gives neutrons for nuclear research.

Working:

Energy is transfer from controlled fission chain reaction to coolant. High pressure steam is produced. Electrical energy is produced when we turn turbine attach with the generator. This is named power generator.

Components:

Fuel Elements:

Uranium is a fuel element. Natural uranium have 99.27% fertility. Fertile uranium converted into platinum. Nuclear fuel may be in solid or liquid form. If it is a solid phase then it is incorporated by a material as a protective covering named cladding. There is coating of zirconium. The fuel used are uranium 233, 235 and Pu 239.

Moderator:

Moderator is a device used to slow down the speed of fast moving neutron. For example ordinary water, graphite and helium used as a moderator.

Coolant:

The heat energy is released in nuclear reactor. Coolant capture this heat and remove heat from the core and send to the electrical generator. Coolant also maintains the pressure. For example CO2, H2, He, CH4 and air etc.

Properties of Coolant:

• It has high thermal capacity.

• It has low viscosity.

• It is chemically inert.

• It can not cause corrosion.

 Control road: 

These are inserted into the core and used to absorb neutron. For example B, Cd etc.

Shielding

For protection inner walls must coated with steel. Outside wall coating is done with concrete. Workers should wear protective dresses. Coating from inner and outer side is done because gamma radiations and neutrons are produced.