Alpha, Beta and Gamma Rays

Alpha, Beta, and Gamma Rays are types of rays that are radiated when particles or nuclei disintegrate. The nature of these three rays is different based on their composition. Alpha rays consist of two protons and two neutrons and have two positive charges. Beta Rays consist of electrons and have a negative charge while Gamma Rays consist of photons and are neutral.

In this article, we will learn what are alpha, beta, and gamma rays along with their properties, and comparison between them in tabular form.

Alpha (α) Rays

An alpha particle is a helium nucleus (₂He⁴) having two protons and two neutrons. The spontaneous emission of an alpha particle from a radioactive nucleus is called Alpha decay. α decay occurs when the nucleus emits α particles.

This process involves the spontaneous emission of nucleons since α particles (₂He⁴) contain two protons and two neutrons therefore the emission of α particles causes the nucleus to get transmuted into a daughter nucleus having atomic number (Z) two less and atomic mass (A) four less.

Disintegration of a radioactive nucleus by emitting an α-particle as follows:

_zX^A → _z-2Y ^A-4 + ₂He⁴

(Parent nucleus) (Daughter nucleus) (α-particle)

Properties of Alpha Rays

• Alpha particles have charge +2e and mass 4u.
• Alpha particles have a kinetic energy of 5MeV.
• Nearly 90% of the 2500 known nuclides are radioactive. They are not stable but decay into other nuclides.
• When unstable nuclides decay into different nuclides, they usually emit alpha or beta particles.
• Alpha emission occurs principally with nuclei that are too large to be stable.
• Alpha decay is mainly governed by strong nuclear force and electromagnetic force.

α -particle	Values
Mass	6.64 x 10-27 kg
Charge	3.2 x 10-19 C
Speed	1/10th -1/100th speed of light
Penetrating power	Minimum

Beta (β) Rays

A β-particle is a fast moving electron (e⁰⁾. The spontaneous process of emission of beta particles from a radioactive nucleus is called Beta-decay.

The nucleus achieves greater stability in beta decay. In beta decay, either a neutron is converted into a proton or a proton is converted into a neutron.

The decay of a radioactive nucleus by emitting β-particle is represented as follows:

_zX^A → _z+1Y^A + _-1e⁰ + Ƴ

(Parent nucleus) (Daughter nucleus) (β-particle) (Antineutrins)

Beta-decay is mainly of three types: Beta-minus (β–), Beta-plus (β+), and electron capture.

Beta-Minus (β–)

• In beta-minus, the neutron inside the nucleus is converted into a proton and an electron like a particle.
• Those nuclei having more neutrons (N) than protons (Z) become unstable and tend to be beta-minus decay (β–).
• A β– particle is like an electron. The emission of β– involves the transformation of a neutron into a proton, an electron, and a third particle called Antineutrino.

For Example:

₁₅P³² ⇢ ₁₆S³²+ _-1e⁰

Beta-plus (β+)

• In a β+ decay, a proton is converted into a neutron and a positron (-1e0 ) is emitted if a nucleus has more protons than neutrons.
• Nuclides for which N/Z is too small for stability can emit a positron, the electron’s antiparticle, which is identical to the electron but with a positive charge. The basic process is called beta-plus (β+) decay.

The process is represented as:

p ⇢ n + β+ + v (v=neutrino)

Electron Capture

• Electron capture, nucleus absorbs one of the inner electrons revolving around it and hence a nuclear proton becomes a neutron and a neutrino (v) is emitted.
• Electron capture is compatible with a positron emission as both processes lead to the same nuclear transformation.

The process is represented as:

₁H¹ + _-1e⁰ ⇢ ₀n¹ + v (v=neutrino)

Properties β Rays:

• β -particle has a negitive charge equal to the charge on an electron.
• They are deflected by electric and magnetic feilds.
• In a β decay, the neutron inside the nucleus changes into protons, as a result, the charge number remains the same, and the atomic number increases by one.
• In emission of β particle is accompanied by a companion particle having variable energy.
• The companion particle is massless and chargeless and is called Antineutrino.
• The emission of Antineutrino along with β particle conserves the angular momentum during β decay.
• The mass of neutrino and antineutrino is zero. The spin of both is 1/2 in units of h/2π. The charge on both is zero.
• The spin of neutrino is antiparallel to its momentum while that of antineutrino is parallel to its momentum.
• β particle can travel in air upto few metre.

β-particle	Values
Mass	9.10 x 10-31 kg
Charge	-1.6 x 10-19 C
Speed	90% of speed of light
Penetrating Power	High

Gamma (γ) Rays

γ-rays are the high energy packets of electromagnetic radiation i.e high energy photons.When the nucleus is placed in an excited state, either by bombardment with high energy particles or by a radioactive transformation, it can decay to the ground state by emission of one or more photons called gamma rays.

It is the spontaneous process of emission of high energy photons from a radioactive nucleus. The emission of alpha and beta particles leave the daughter nucleus in the excited state which in turn emits one or more Gamma-ray photons in single or successive transitions.

Since the gamma rays are emitted by the daughter nucleus emission of gamma rays for the emission of alpha and beta particles. The energy of gamma-ray is equal to the difference between the energy of the excited state or higher energy state and the ground state of the nucleons.

The Disintegration of a radioactive nucleus by emitting an γ-ray is represented as follows:

_zX^A* → _zX^A + γ

(Exicted Nucleus) (ground state) (Gamma particle)

Properties Gamma (γ) Decay:

• They have no charge.
• They are not deflected by electric and magnetic feilds.
• They affect the photographic plates
• The order of energy of Gamma Photon is 100 KeV.
• The rest mass of the Gamma Photon is zero.
• They have very high penetration power.
• gamma rays follows the emission of alpha or beta particle.

γ-rays	Values
Mass	0
Charge	0
Speed	Equal to the speed of light
Penetrating power	Maximum

Properties of Alpha(α), Beta(β) and Gamma(γ) Rays

The difference between Alpha, Beta and Gamma Rays are tabulated below:

Difference Between Alpha, Beta and Gamma Rays
Properties	Alpha Rays	Beta Rays	Gamma Rays
Particle	2 Proton,2 Neutron	Electron	Proton
Types of Charged particle	+ve charge	-ve charge	Neutral
Charge	+2e	-e	0
Ionization power	Comparatively High	Comparatively Low	Very less
Penetrating Power	Low	higher than α rays	higher than β rays
Electric and Magnetic field	Deflected	Deflected	Not Deflected
Speed	1/100th of the speed of light	1/10th of the speed of light	Equal to the speed of light
Change in mass number and atomic number	When an alpha particle is emitted by a nucleus its atomic number decreases by 2 and the mass number decreases by 4.	When a beta particle is emitted by the nucleus its atomic number increases by 1 and mass number is unchanged.	Mass number and atomic number are not affected by the emission of gamma rays

FAQs On Alpha, Beta and Gamma Rays

1. How do we Depict the symbol for the alpha particle?

We depict the symbol for the alpha particle as α, &alpha²⁺, He²⁺.

2. Give some Examples of α Decay?

Some examples of α decay are:

• ₈₈Ra²²⁶ ⇢ ₈₆Rn²²²+ ₂He⁴
• ₉₂U²³⁸ ⇢ ₉₀Th²³⁴ + ₂He⁴
• ₉₄Pu²⁴² ⇢ ₉₂U²³⁸ + ₂He⁴

3. What is the difference between Alpha, Beta and Gamma Rays?

While alpha and beta particles have positive and negative charges, respectively, gamma rays are neutral. An alpha particle is made up of two protons and two neutrons. Beta particles are high energy electrons. Photons are electromagnetic energy waves, which are what gamma rays are.

4. Give some Examples of γ Decay?

Some examples of γ decay are:

• ₈₂Pb²¹⁰ ⇢ ₈₃Bi^210* + _-1e⁰ + Antineutrino
• ₈₃Bi^210* ⇢ ₈₃Bi²¹⁰ + γ-ray

5. What is meant by Antineutrino?

Antineutrino is a very little particle having almost no mass. It is emitted with beta-minus (β–) particles during radioactive decay.

6. What is meant by Positron?

Positron is the antiparticle of an electron. the properties of a positron are the same as that of an electron except a positron carries a positive charge while an electron carries a negative charge.

7. What is meant by Neutrino?

Neutrino is a very little neutral particle having almost no mass. It is emitted with β+ particles during radioactive decay. It interacts very weakly with materials and hence is not detected easily.

8. Are Alpha Particles made of Electrons?

An alpha particle has two protons and two neutrons, just like a helium atom without its two electrons.