Nuclear Reactions - Definition, Types, Examples and Properties

Nuclear reactions are a key process in atomic physics, where a stable element changes into a different element when it interacts with energetic particles. These reactions involve the collision of atomic nuclei, leading to the creation of new subatomic particles and nuclides. The main feature of a nuclear reaction is that at least one nucleus is changed, creating a new nuclide with different properties from its original nucleus.

What is a Nuclear Reaction?

A nuclear reaction is a process in which two atomic nuclei, or a nucleus and a subatomic particle, collide, resulting in the formation of new nuclei that are different from the original ones. These reactions can be initiated by bombarding a nucleus with a particle or can occur spontaneously without external influence.

Nuclear reactions involve changes in the identity or properties of the participating nuclei, including alterations in their structure, composition, or energy state. As a result, new elements or isotopes can be formed, often accompanied by the release or absorption of energy.

Types of Nuclear Reaction

There are four main types of nuclear reactions:

1. Nuclear fission
2. Nuclear fusion
3. Alpha decay
4. Beta decay

Let's explore each of these in detail:

1. Nuclear Fission: Nuclear fission occurs when a heavy atomic nucleus, such as uranium-235 or plutonium-239, splits into two smaller nuclei, accompanied by the release of a significant amount of energy. This reaction is triggered when the nucleus absorbs a neutron, becoming unstable and breaking apart.

Along with the formation of new smaller nuclei, additional neutrons are released, which can trigger a chain reaction if these neutrons strike other fissile nuclei. Fission is the process used in nuclear reactors and atomic bombs to produce energy.

Example : In a nuclear power plant, uranium-235 undergoes fission to produce energy, which is then used to generate electricity.

2. Nuclear Fusion: Nuclear fusion is the opposite of fission. In fusion, two light atomic nuclei, typically isotopes of hydrogen like deuterium and tritium, collide and fuse to form a heavier nucleus, such as helium. This reaction releases an immense amount of energy, much more than fission.

Fusion is the process that powers stars, including the sun, and is the basis for hydrogen bombs. Fusion on Earth is difficult to achieve because it requires extremely high temperatures and pressures to overcome the electrostatic repulsion between the positively charged nuclei.

Example: The energy produced by the sun comes from the fusion of hydrogen nuclei into helium, releasing vast amounts of energy.

3. Alpha Decay: Alpha decay occurs when an unstable atomic nucleus emits an alpha particle, which consists of two protons and two neutrons. This emission causes the original nucleus to lose two protons and two neutrons, thereby transforming it into a new element.

Alpha decay typically happens in heavy elements like uranium, radium, and thorium. The emitted alpha particles have low penetration power and can be stopped by a sheet of paper or human skin.

Example: Uranium-238 undergoes alpha decay to form thorium-234, releasing an alpha particle in the process;

²³⁸U₉₂ → ²³⁴Th₉₀ + ⁴He₂

4. Beta Decay: Beta decay is a type of radioactive decay in which a neutron in an atomic nucleus turns into a proton, releasing an electron (beta particle) and an antineutrino. This process increases the atomic number of the nucleus, changing the element into a different one.

Beta decay can occur in two forms: beta-minus decay, where a neutron decays into a proton, and beta-plus decay (positron emission), where a proton decays into a neutron, emitting a positron (the antimatter counterpart of an electron).

Example: In beta-minus decay, a neutron in a carbon-14 nucleus decays into a proton, turning the carbon into nitrogen-14 and emitting a beta particle (electron);

¹⁴⁶C → ¹⁴⁷N + ⁰β_-1

Properties of a Nuclear Reaction

• Nuclear reactions always conserve mass and energy, with any mass loss being converted into energy.
• These reactions can release or absorb significant amounts of energy depending on the type, such as fission and fusion releasing energy, and neutron capture absorbing it.
• Nuclear reactions involve the transformation of atomic nuclei, resulting in new elements or isotopes.
• Particles like neutrons, protons, alpha, or beta particles are often emitted in nuclear reactions and are essential for sustaining chain reactions.
• Some nuclear reactions occur spontaneously, like alpha and beta decay, while others, such as fission and fusion, require external conditions like particle bombardment or extreme temperatures.
• The strong nuclear force governs nuclear reactions, which holds protons and neutrons together within the nucleus.
• Nuclear reactions can change one element into another, which is important for creating new elements or isotopes in laboratories.

Sample Problems

Question 1: Complete the following nuclear reactions:

1. ¹n₀ + ⁴⁰Ar₁₈ ⇢ … +α
2. ¹n₀ + ²³⁵U₉₂ ⇢ ⁹⁸Zr₄₀ + …+ 3¹n

Answer:

1. By equating mass number's:
A = 40 + 1 - 4 = 37,
By equating atomic number's,
Z = 18 + 0 - 2 = 16,
So the nucleus formed is ³⁷S₁₆

2. By equating mass number's:
A = 235 + 1 - 98 - 3 = 135
By equating atomic number's,
Z = 92 + 0 - 40 = 52,
So the nucleus formed is ¹³⁵Te₅₂

Question 2: Consider the reaction  

¹³C₆+¹H₁ ⇢ ⁴He₂+¹⁰B₅

1. Use the masses of the nuclides involved to determine where it is endogenic or exoergic.
2. If it is exoergic, find the amount of energy released, if it is exoergic find the threshold energy.

Answer:

Now,
So, according to the Equation for 
Reaction energy:  E react = (M₁ + M₂ - Sum) × c²,
Where,
Variable Sum is the sum of all "Outgoing Particles" masses;
⇒Variable M₁ is the "Target Nucleus" mass,
⇒Variable M₂ is the "Incident Particle" mass.
Which comes negative. So reaction is endogenic.
Now threshold energy =  E_th = [(Sum + M₁ + M₂) × (Sum - M₁ - M₂) / (2 × M₁) ] × c²,
The total mass of outgoing particles is:
So,
Sum of Outgoing Masses=4.00260325415+10.01293699=14.01554024415 u
Now, calculate the reaction energy:
Ereact=(13.0033548377+1.00782503207−14.01554024415)×c2
Energy Threshold: 4.37714 MeV

Question 3: Calculate the energy released in the fission reaction:

¹n₀ + ²³⁵U₉₂ ⇢  ⁸⁸Sr₃₈ + ¹³⁶Xe₅₄ + 12n

Answer:

Now,
So, according to the Equation,
Reaction energy: E react = (M₁ + M₂ - SUM) × c₂
Where variable SUM is the sum of all "Outgoing Particles" masses;
Variable M₁ is the "Target Nucleus" mass,
⇒M1​=235.0439299u
M₂ is the "Incident Particle" mass.
⇒M2​=1.008664923u
Mass of Fission Fragments
⁸⁸Sr_{38 :} 87.9056121 u
¹³⁶Xe_{54​ :} 135.9072187u
Mass of 12 neutrons:
12×1.008664923 u=12.10397898888 u.
The sum of the outgoing particles' masses is:
Sum of Outgoing Masses=87.9056121+135.9072187+12.10397898888=235.91680978888 u.
Now, calculate the reaction energy:
Ereact=(235.0439299+1.008664923−235.91680978888)×c2
Energy release of 126.4828 MeV,

Question 4: Find the threshold energy for the following reaction:

¹⁶O₈ + ¹n₀  ⇢  ¹³C₆ + ⁴He₂ 

Answer:

Now,
So, according to the equation for 
Reaction Energy :  Ereact = ( M1 + M2 - SUM ) * c2,
where variable SUM is the sum of all "Outgoing Particles" masses;
⇒Variable M1 is the "Target Nucleus" mass,
⇒Variable M2 is the "Incident Particle" mass
Now threshold energy =  Eth = [ ( SUM + M1 + M2 ) * ( SUM - M1 - M2 ) / ( 2 * M1 ) ] * c2,
The sum of the outgoing masses is:
Sum of Outgoing Masses=4.00260325415+13.0033548377=17.00595809185 u
So, Threshold energy of 2 MeV

Question 5: Find the threshold energy for the following reaction:

³He₂ + ¹n₀  ⇢ 2²H₁ 

Answer:

Now,
So, according to the equation for 
Reaction:
3He₂+1n_0→²H₁
⇒M1​=3.0160293191u
Variable M₂ is the "Incident Particle" mass
⇒M2​=1.008664923u
Mass of Outgoing Particle (H-2):
2.01410177785 u

Conclusion

In conclusion, nuclear reactions are fundamental processes that involve changes to atomic nuclei, leading to the creation of new elements or isotopes. Unlike chemical reactions, which deal with electron interactions, nuclear reactions focus on the nucleus, where the release or absorption of energy can have significant effects. Whether through fission, fusion, or radioactive decay, these reactions play important roles in various fields.

You may also Read,

• What is Nuclear Energy?
• Alpha Decay
• Atomic and Nuclear Physics
• Applications of Alpha decay in Everyday life