Nuclear Reactions

Nuclear Reactions

** In a chemical reaction there is merely a rearrangement of extranuclear electrons. The atomic nucleus remains intact.

** A nuclear reaction involves a change in the composition of the nucleus. The number of protons and neutrons in the nucleus is altered. The product is a new nucleus of another atom with a different atomic number and/or mass number. Thus:

Nuclear reaction: is one which proceeds with a change in the composition of the nucleus so as to produce an atom of a new element.

** The conversion of one element to another by a nuclear change is called Transmutation.

** We have already considered the nuclear reactions of radioactive nuclei, producing new isotopes.

** Here we will consider such reactions caused by artificial means.

Differences between Nuclear Reactions and Chemical Reactions

Nuclear Fission Reactions

** In these reactions an atomic nucleus is broken or fissioned into two or more fragments.

** This is accomplished by bombarding an atom by alpha particles (⁴He₂ ), neutrons (¹n₀), protons (¹H₁), deutrons (²H₁), etc.

** All the positively charged particles are accelerated to high kinetic energies by a device such as a cyclotron. This does not apply to neutrons which are electrically neutral.

** The projectile enters the nucleus and produces an unstable ‘compound nucleus’. It decomposes instantaneously to give the products.

** For example, ¹⁴N₇ when struck by an α-particle first forms an intermediate unstable compound nucleus, ¹⁸F₉ , which at once cleaves to form stables ¹⁷O₈

** Other examples are:

** Nuclear fission reactions are classified according to the projectile used and the particle that is emitted. In Figure above the type of the reaction has been stated.

** It is noteworthy that neutrons are particularly useful as projectile. Sir James Chadwick obtained these by bombarding beryllium-9 with α-particles. Being electrically neutral, neutrons pierce the positive nucleus easily.

Nuclear Fusion Reactions

** These reactions take place by combination or fusion of two small nuclei into a larger nucleus.

** At extremely high temperatures the kinetic energy of these nuclei overweighs the electrical repulsions between them. Thus they coalesce to give an unstable mass which decomposes to give a stable large nucleus and a small particle as proton, neutron, positron, etc.

** For example :

(1) Two hydrogen nuclei, ¹H₁ , fuse to produce a deuterium nucleus, ²H₁.

(2) Deuterium nucleus, ²H₁, and tritium nucleus, ³H₁ , combine to give helium nucleus, ⁴He₂ with the expulsion of a neutron.

Differences between Nuclear Fission and Nuclear Fusion

Reference: Essentials of Physical Chemistry /Arun Bahl, B.S Bahl and G.D. Tuli / multicolour edition.

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