Nuclear Transmutations by alpha particle, deuteron, proton, neutron and electron

Nuclear transmutation is a process that involves a change of one atomic nucleus into another. It can be either natural or artificial. Transmutation can be achieved by elementary particles react with a nucleus or by radioactive decay.

Natural transmutation:

It occurs normally in unstable radioactive elements. These unstable radioactive elements will be transformed into stable one over a series of decays. For Example Uranium-238 is converted into Pb-206 (Isotope of Lead) through a series of steps. Lead-206 is used as target material in biomedical field. It is used to measure lead level in blood.

Artificial or induced transmutation:

This type of transmutation is achieved by the radioactive decay of a nucleus, or the bombardment of atomic nuclei with elementary particle. The bombardment of nitrogen nuclei with helium nuclei (alpha particle) was the first induced transmutation done in Ernest Rutherford's Laboratory in the year of 1919. And also it leads to Rutherford receiving the Nobel Prize in chemistry. 

₇N¹⁴ + ₂He⁴ →₈O¹⁷ + ₁H¹

These two product elements (Oxygen 17 and proton nuclei)  are stable and not possible for further nuclear changes.

Since Positive charged particles like alpha particles, protons and deuterons are repelled by nucleus and hence these are not good projectiles. The particle like neutrons have no charge. These are not repelled by nucleus. So they are the best projectiles. Product element released from the reaction that depends upon the velocity of neutrons. Slow neutrons is also called thermal neutrons. They can easily penetrate the nucleus. And also these are more effective in producing nuclear reactions. But High speed neutrons are easily passes through the nucleus and not involved in the reaction. 

a) Transmutation by α-particles:

(i)           (α,p) reaction

The elements are bombarded by alpha particles. Protons are ejected.

₅B¹⁰ + ₂He⁴ → ₆C¹³ + ₁H¹

In these reactions, the atomic number of the product nucleus increases by one and mass number by three.

(ii)          (α,n) reaction

₅B¹¹ + ₂He⁴ → ₇N¹⁵ → ₇N¹⁴ + ₀n¹

In this case, the atomic number increases by two and mass number by three. It leads to the discovery of neutrons.

The three “conservation laws” apply to nuclear reactions:

1. The charge is conserved.
2. The number of nucleons is conserved.
3. The mass-energy relation is conserved.

b) Transmutation by protons:

(i)           (p,α) reaction

Lithium was bombarded with protons. It broke up into two alpha particles.

₃Li⁷ + ₁H¹ → 2  ₂He⁴  

(ii)          (p,d) reaction

In some cases, possibility to emit deuteron.

₄Be⁹ + ₁H¹ → ₅B¹⁰ → ₄Be⁸ + ₁H²

(iii)        (p,n) reaction

₅B¹¹ + ₁H¹ → ₆C¹¹ + ₀n¹

(iv)         (p,γ) reaction

₃Li⁷ + ₁H¹ → ₄Be⁸  + γ

c) Transmutation by deuterons:

          In most cases, high energy deuterons are used for the bombardment. To achieve this high speed, we need accelerate the particle. So Particle accelerators are necessary for transmutation reaction. Generally accelerators use magnetic and electric fields to increase the speeds of deuteron particles. The particles always move in a vacuum because to avoid collisions with gas molecules. Cyclotron (uses a spiral path) is used to accelerated the deuterons to achieve the very high energy.

(i)           (d,α) reaction

₃Li⁶ + ₁H² → ₂He⁴ + ₂He⁴

(ii)          (d,p) reaction

₆C¹² + ₁H² → ₆C¹³ + ₁H¹

(iii)        (d,n) reaction

₆C¹² + ₁H² → ₇N¹³ + ₀n¹

d) Transmutation by neutrons:

(i)           (n,α) reaction

₅B¹⁰ + ₀n¹ → ₅B¹¹ → ₃Li⁷ + ₂He⁴

(ii)          (n,p) reaction

₇N¹⁴ + ₀n¹ → ₇N¹⁵ → ₆C¹⁴ + ₁H¹

(iii)        (n,2n) reaction

₁₃Al²⁷ + ₀n¹ → ₁₃Al²⁸ → ₁₃Al²⁶ + 2 ₀n¹

(iv)         (n,γ) reaction

₁₃Al²⁷ + ₀n¹ → ₁₃Al²⁸ → ₁₃Al²⁸ + γ

e) Disintegration by electrons (Beta particle):

Betatrons (uses a circular path) is a compact accelerator for electron. It produces very high speed electrons. 

₄Be⁹ + _-1e⁰ → ₃Li⁹ → ₃Li⁸ + ₀n¹

Photo disintegration (or) Photo transmutation

          In this process, an atomic nucleus absorbs a high energy gamma ray and jump to the excited state, and immediately decays by emitting a subatomic particle.

i) Photodisintegration of deuterium:

A photon carrying 2.22 MeV or more energy can photo disintegrate an atom of deuterium.

₁H² + γ → ₁H¹ + ₀n¹

ii) Photodisintegration of beryllium:

A photon carrying 1.67 MeV or more energy can photodisintegrate an atom of beryllium – 9.

₄Be⁹ + γ → 2  ₂He⁴ + ₀n¹ 

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