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Natural Transmutation

If we see the Modern Periodic Table in we could see which elements are arranged in increasing order of their atomic number. Observe the elements which are placed just below the main table. There are two series of elements (14 elements in each series) at the bottom of main table. These are called as f-block elements.

Observe the atomic number of these elements. These elements have high atomic numbers. Similarly last series of d-block elements also have very high atomic numbers.

Such elements are not stable and tend to convert in to stable ones by losing their energy and mass in the form of small particles and radiations. These elements are commonly called as radioactive elements. They emit radiations like alpha and beta particles, gamma and X-rays etc. This phenomenon is called as radioactivity. In these radiations, alpha particles have 2 protons and 2 neutrons like Helium nuclei. On the contrary, beta particles are negatively charged particles or we can say that they are stream of electrons. Unlike alpha and beta particles, gamma rays are highly energetic forms of electromagnetic radiation like visible light.

They can be described as oscillating perpendicular electric and magnetic fields. Nuclear reactions in which nuclei fuse or break into other nuclei with the emission of large amount of heat and some small particles like neutrons. The conversion of some radioactive nuclei to other nuclei is called as transmutation.

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Natural Transmutation Definition

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The transmutation that occurs in nature without any external induction is called as natural transmutation. We know that heavier elements have more number of neutrons compare to protons whereas lighter elements with low atomic numbers have almost same number of neutrons and protons in their nucleus. That is the reason; heavier elements are not stable and tend to convert into small elements. After Pb-82, all elements are radioactive in nature and decay to form more stable nuclei.

The decay depends on whether the proton/neutron ratio in the nucleus is too high or too low. It can be done by beta emission, alpha emission, positron emission and electron capture. The emission of beta particles changes the nucleus into another nucleus which has same mass number but one unit greater atomic number.

Natural Transmutation Equation

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Natural transmutation can be represented in terms of chemical equations which are same as other chemical equations. The nuclear equations can balance in which the sum of the mass numbers as well as the sum of the atomic numbers must be the same on both sides of the equation.

In case of alpha emission during transmutation, the daughter nuclei has a mass number four units lower while atomic number will be two units lower. In case of positron emission, the mass of daughter remains same while the atomic number will be one unit less.

Gamma radiations are mass less radiation so they always emit along with some other particles. Emission of gamma radiations causes the relaxation of an excited nucleus to a lower energy state.

Natural Transmutation Example

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One of the most common examples of natural transmutation is decay of Uranium-238 to lead-206. 

Natural Transmutation

Another example of natural transmutation is decay of Iodine-131 to Xe-131 with the emission of one beta particle in each step.

$l^{131} \rightarrow Xe^{131} + \beta$

The alpha decay from Radium-222 results the formation of Radon-218.

$Ra^{222} \rightarrow Rn^{218} + \alpha$

Similarly beta emission from Thorium-234 forms Pa-234. 

$_{90}Th^{234} \rightarrow _{89}Pa^{234} + \alpha$

Positron decay produces a particle with same mass with one unit less atomic number. Positron decay from Sodium-22 produces neon-22.

$_{11}Na^{22} \rightarrow _{10}Na^{22} + e$

Natural Transmutation Reaction

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The natural transmutation does not require any acceleration from energetic particles like alpha, beta, positron or neutrons. These reactions occur due to instability of heavy nuclei which tend to convert into small nuclei along some energetic particles.  Some other examples of natural transmutation are as given below.

$_{92}U^{238} \rightarrow  _{2}He^{4} + _{90}Th^{234}$

$_{6}C^{14} \rightarrow  _{7}N^{14} + _{-1}e^{0}$

$_{88}Ra^{226} \rightarrow  _{2}He^{4} + _{86}Rn^{222}$

Natural vs Artificial Transmutation

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Natural transmutation occurs spontaneously whereas artificial transmutation cannot occur spontaneously. For example; nuclear fusion in which small nuclei like hydrogen or helium combines under high temperature and pressure and produces nuclei with higher atomic and mass numbers. This transmutation is used in hydrogen bomb as large amount of energy produces during reaction.

Nuclear fission is also an artificial transmutation in heavy elements fragment into less massive elements in the presence of neutrons. For example, nuclear fission of Uranium-235 produces large amount of energy with small nuclei. Some of the common differences between natural and artificial transmutations are listed below.

 NATURAL TRANSMUTATION   ARTIFICIAL TRANSMUTATION 
  • The element undergoes spontaneous decay because it is unstable.
  • These reactions occur spontaneously.
  •  For this change to happen, high‐energy particles are fired at the element.
  •  In this reaction, two reactants interact with each other to form new nuclei. 

The reaction of Al-27 with alpha particle forms P-30 with emission of neutrons. Similarly reaction of U-238 with neutrons results the formation of Pu-239 with beta particles. Another example of artificial transmutation is reaction of Pu-239 with neutrons produces Ba-147, Sr-90 with three neutrons.

So we can say that artificial transmutation is an induced transmutation that occurs with the bombardment of small particles in a nuclear reactor. These particles accelerate the transmutation of radioactive nuclei.

The trans uranium elements or man-made elements usually produce through artificial transmutation. Irradiation, nuclear fission, fusion, and radioisotope production are good examples of artificial transmutation.
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