Transmutation

The radioactive elements which tend to decay under natural conditions are readily involved in chemical reactions to form new elements (radioactive or non-radioactive) with the emission of some radiations.

The reactions which involve the radioactive materials to form new nuclei are called nuclear reactions. The nuclear reactions must accelerate to achieve the extreme energies needed for their reactions.

What is Transmutation?

Transmutation is a process in which the nucleus changes in the number of protons to produce an atom with a different atomic number. The process of transmutation can be represented in terms of a chemical reaction as it is also a conversion of one element into another. It can be done in an artificial manner and also occurs naturally.

First artificial transmutation was done by Lord Rutherford in 1911. He bombarded alpha particles on Nitrogen-14 to produce Oxygen-17 with protons. The process can be written as;

\(^{14}_{7}N + ^{4}_{2}He \rightarrow ^{17}_{8}O + ^{1}_{1}H\)

See the reaction given for the above process. It is a balance reaction in which both sides, the total number of protons is 9 and the total mass is 18.

Fission and Fusion Reactions

There are mainly two types of nuclear reactions; fission and fusion reactions.

  • The fission reaction is a nuclear reaction which involves the splitting of heavy nuclei to two approximately equal fragments.
  • Neutrons are present in these reactions as reactants as well as products.
  • Fission reactions release a large amount of energy that can be used for various applications.
  • Another type of nuclear reaction is a fusion reaction in which small nuclei fuse together into one larger nucleus with the release of large amounts of energy.

Chemical Transmutation Definition

Chemical transmutation is the process of changing a substance from one form or state into another. It represents the transformation of one element into another by a series of reactions.

These reactions can be nuclear decays and involve some energy change. We know that each element has a certain atomic number so transmutation involves the change in atomic number leads to the formation of new elements. For example decay of 232Th starts with the spontaneous emission of α–particle that is a He nucleus with 2 protons and 2 neutrons.

The reaction is a chain reaction which finally results in the formation of 228Ra. Further 228Ra nucleus spontaneously emits a beta-particle and forms 228Ac. The beta particle is an electron that converts a neutron to a proton and raises the atomic number of the daughter nucleus by one but there will be no change in the atomic mass. Successive emission of alpha and beta particles from 228Ac forms stable 208Pb.

Transmutation Reactions

So we can say that transmutation of elements results in the formation of new elements from some radioactive elements with the emission of radiation like alpha, beta or gamma rays.

Natural transmutations are spontaneous process and usually occur with unstable radioactive elements. The series of chain reaction results in the formation of stable elements like uranium 238 spontaneously transmute to lead 206 that is a stable element.

Unlike natural transmutations, artificial transmutation occurs in nuclear reactors with the bombardment of particles like neutrons. Transuranium elements are synthesized through induced transmutation. Some common examples of transmutation reactions as given below.

  1. \(^{131}_{53}I \rightarrow ^{131}_{54}Xe + ^{0}_{-1}e\)
  2. \(^{131}_{53}I \rightarrow ^{131}_{54}Xe + ^{0}_{-1}e\)
  3. \(^{14}_{7}N + ^{4}_{2}He \rightarrow ^{17}_{0} + ^{1}_{1}H\)
  4. \(^{222}_{88}Ra \rightarrow ^{4}_{2}He + ^{218}_{86}Rn\)
  5. \(^{234}_{90}Th \rightarrow ^{234}_{91} + ^{o}_{-1}e\)
  6. \(^{22}_{11}Na \rightarrow ^{22}_{10}Ne + ^{o}_{1}e\)

Transmutation Chemistry Equations

The transmutation chemistry equations can be balanced by using simple rules. The mass number of reactants and products must be conserved in a nuclear change. If there are more than one reactants or products, the sum of the mass numbers must remain the same before and after the chemical reaction. Similarly the electric charge must conserve in any transmutation process.

Transmutation results in the emission of some particles which may have more or less energy. These particles can continue the process of that is the reason the transmutations are also called as chain reactions. In some of the transmutation equation, element captures its own electron and undergoes transmuted to the new element. This is called K-capture like Ruthenium converts to Tc by K-capture.

\(^{100}_{44}Ru + ^{0}_{-1}e \rightarrow ^{100}_{43}Tc\)

Remember unstable radioactive nuclei involved in transmutation to convert into stable nuclei so stable isotope will not spontaneously decay. High binding energy per nucleon makes the nucleus more stable and nuclei of low atomic numbers with a 1:1 neutron to proton ratio are also very stable. Such nuclei are usually not involved in natural transmutation.