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# Nuclear Chemistry

Top
 Sub Topics When Henri Becquerel discovered that uranium emitted radiation in 1896 he extended the field of chemistry to include nuclear variations. Soon after his discovery Marie Curie began studying radioactivity and found that radiation was a property of atoms.The first woman to win a Nobel Prize for discovering radioactivity was Marie Curie. Radioactive elements radium and polonium was also discovered by her.Nuclear chemistry is an important science that has undergone a major and rapid development in recent years. Three discoveries in the closing years of the nineteenth century not only had a profound effect on scientific progress and thought, but also created drastic change in the life pattern of a man. In nuclear reactions only components of the nuclei play a vital role. Besides this, the energy changes in nuclear reactions are numerous times higher than chemical reactions. The composition of the nucleus, its stability nuclear reactions and energy changes accompanied by them constitute nuclear chemistry.

## Definition

Whenever a charged particle approaches a nucleus, it experience a coulombic repulsive force and is deflected from its path. Thus charged particles such as protons, doubly charged helium ions, deuterons etc, can approach a nucleus sufficiently closely to bring about a nuclear reaction provided they have sufficient energy to overcome the coulombic repulsive force.

Neutron is the only uncharged particle that has a practical application in nuclear reaction and has the advantage that it does not require to overcome the coulombic repulsive force of the nucleus.
Nuclear Chemistry is a branch of Chemistry that deals with nuclear properties, radioactive elements and nuclear reactors designed to perform nuclear processes.

Nuclear Chemistry includes the study of chemical effects resulting from the absorption of radioactivity within living animals, plants, and other materials. Nuclear chemists work with various isotopic forms of elements to study fission and fusion processes.
Nuclear Chemistry is the branch of chemistry that is concerned with Nuclear reactions

## Components of the Nucleus

Atoms are composed of nothing more than protons, neutrons and electrons. Protons and neutrons each have a rest mass of approximately 1 atomic mass unit (amu). Electron are much smaller having a rest mass.

The total mass of an atom is determined largely by the number of protons and neutrons it contains. The electrical charge of an atom is determined by the relative number of protons and electrons. Each proton bears a positive charge of 1 electrostatic unit, each electron bears a negative charge of 1 esu. Neutrons bear no electrical charge.
Three subatomic particles make up all atoms; protons which are electrically positive, neutrons which are electrically neutral and electrons which are electrically negative. In the middle of the atom a small nucleus which contains two types of particles, called protons and neutrons. A third type of particle is found orbiting the nucleus - the electron.

Atomic nuclei that undergo spontaneous nuclear transformation is called radioactivity. Nuclear transformations are often accompanied by emission of nuclear radiation which is detectable and measurable by means of instruments and methods of nuclear technology. The history of radioactivity in the past century is linked to the progress of radiation and particle detectors, from photographic plates and electro meters, used by the pioneers of radioactivity studies in the 19th century, to modern semiconductors and scintillators, interfaced to computers by advanced microelectronic circuitry.

Radioactivity was discovered in 1896 by Henri Becquerel, it is the spontaneous emission of particles or high energy photons such as alpha, beta, neutron or radiation gamma, or both at the same time, from a nuclear reaction or decay of certain nuclides due to a change in the internal structure.
$A$ = $\frac{kN}{t_{\frac{1}{2}}}$

Where A is the number of radioactive disintegrations in a given time per second or a much larger unit, N is the number of radioactive atoms of a given kind often expressed in units of concentration, $\frac{t1}{2}$ is the time required for half of the initial number of radio nuclides to decay and k is a constant.

## Nuclear Power

To produce nuclear energy, certain types of atoms are needed. Usually they are atoms of the substances uranium or plutonium. Uranium and plutonium are both elements, which are basic substances that makes up all matter.

There are approximately 115 elements known to scientist today. Every element has a specific number of protons in the nuclei of its atoms. The number of neutrons may vary. The nuclei of uranium and plutonium have many protons and neutrons. Uranium has 92 protons, while plutonium has 94 protons. Some elements have much smaller nuclei. Oxygen for example, has only eight protons, carbon has six and hydrogen has just one proton.

## Fission and Fusion

Nuclear fission is a reaction in which an atom's nucleus splits into two or more elements that are lighter than the parent atom, releasing a large amount of energy, smaller nuclei or a number of neutrons and energy in the process.

For atoms of these radio isotopes fission takes place when they are hit by neutrons. Fission reactions of the neutral radioisotope uranium-235 and the artificial ones uranium-233 and plutonium-239 are useful as energy sources. The nuclear fission reaction is diagrammatically as

Nuclear fusion is a reaction in which two or more elements connect together to form one larger element, releasing energy. Fusion occurs when two light nuclei of hydrogen isotopes unite and undergo a fusion reaction from which neutrons of several MeV are emitted. Nuclear fusion gives out energy by turning two heavy isotopes of hydrogen into helium.

Three-quarters of the Sun's mass are hydrogen and most of the remaining quarter is helium. As time goes on, hydrogen in the core, where nuclear fusion takes place, will gradually be turned into helium. The nuclear fusion reaction is diagrammatically as

## Nuclear Reactions

Nuclear reactions are written as:

A + B $\rightarrow$ C + D

An example of a nuclear reaction is:

4He2 + 6Li3 $\rightarrow$ 9Be3 + 1H1

This equation does not tell us how likely the reaction is to take place, or whether it is exothermic or endothermic. Nuclear reactions for the most part take place in two stages. First a compound nucleus is formed from the two reactants, but that nucleus is unstable and so divided, most often into two components.

However only the mass and atomic numbers are of concern in nuclear reactions and the charges need not be included. Although fission can and does sometimes happen spontaneously on Earth, such events are not very common.

## Nuclear Magnetic Resonance

Chemists use nuclear magnetic resonance to establish atom-to-atom and through space connectivity that uniquely define the structures of the molecules. However the experimental techniques and especially the sensitivities of heteronuclear 2D NMR techniques have changed radically in those scant. Nuclear magnetic resonance study of a natural product is to begin to deduce structural fragments from genuine connectivity.

It has been demonstrated that solid state NMR spectroscopy provides useful information about the structure and dynamics of polymers in the bulk. Solid state NMR is recognized as one of the most powerful means for elucidating the structure and the dynamics of solid polymers in addition to X-ray diffraction. NMR has become a powerful tool for unraveling protein 3D structures.

NMR is unique for characterization of the dynamics of macromolecules in solutions under conditions close to those which are present.It also provides information on the stability of different regions of the protein.

## Nuclear Stability and Magic Numbers

It is found that the numbers of neutrons or protons lead to particular stability 2, 8, 20, 28, 50, 82, 126. These are called Magic numbers. A sharp reduction in the binding energy of the last nucleon added to the magic number nuclei, for example for a neutron added to N = 126 and a proton added to Z = 82 nuclides.

The plot of the binding energy per nucleon against a mass number shows special stability for the higher magic numbers. Especially significant are the changes in B/A at mass number 208 associated with the completion of the 82-neutron shell at or near mass number associated with the completion of the 50 - neutron shell. The known delayed neutron emitters are 87Kr36, 137Xe54 and 17O8, the emission occurring in all cases from one or in more excited states. These nuclei emit neutrons when excited by the $\beta$-decay of a parent radioactive fission product. The shell binding energy of the odd particle makes neutron emission possible at relatively low excitation energies.