radioactive decay - Overview, Structure, Properties & Uses

Radioactive Decay - Meaning Types , FAQs

Edited By Team Careers360 | Updated on Jun 11, 2022 01:27 PM IST

In this article, we define radioactive decay is, radioactive decay law, concept of decay constant, disintegration constant, types of radioactive decay, radioactive equilibrium, and the difference between radioactive equilibrium and chemical equilibrium.

What is radioactive decay?

Radioactive decay is a process by which the nucleus of an unstable atom loses by emitting radiation. It is also called nuclear decay, radioactivity, or nuclear disintegration.

Explain the decay process.

The decay process or radioactive process is a property of the nuclei of an atom. A material is called a radioactive or radioactive element if it contains unstable nuclei. By this process, the nucleus becomes more stable by emitting its energy. The mass and charge are conserved in the decay process.

Theory of radioactivity:

Radioactivity or the radioactive decay process involves the continuous emission of radiation by unstable nuclei in the form of radiation. The nuclei of the atom emit ionizing particles by losing their energy spontaneously. Due to the loss of energy, two types of atoms called parent nuclide and daughter nuclide are formed. The parent nuclide is the decaying nucleus and the daughter nuclide is obtained from the parent nuclide. Radioactive decay is called a nuclear transformation that yields a daughter nuclide that has protons or neutrons. This condition is not applicable in gamma decay, a type of radioactive decay. A new element is obtained as the number of protons in the atom changes.

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Types of radioactive decay:

Radioactive decay is classified into three types:

Alpha decay: The nuclear decay process in which alpha particle is emitted is called alpha decay.

It is represented as, E=(m_i-m_f-m_p)c²

Here, E is the energy, c is the speed of light, mi is the mass of nucleus before decay, m_f is mass of nucleus after decay, and m_p is the mass of the particle emitted in the decay process. Consider an example for the alpha decay of Th-230.

90230Th→24He+88226Ra

In this equation, thorium-230 is converted to radium-226 with the emission of an alpha particle.

Beta-decay: In the decay process, if the beta particle is emitted then it is called beta decay. The nucleus emits a high-energy electron in the form of a beta particle. The beta particle is considered an electron as it is an electron ejected from the splitting of the neutron. An example for the beta decay of Th-234 is represented as:

90234Th→-10e+91234Pa

In the above equation, thorium-234 is converted to Pa-234 with the emission of a beta particle.

Gamma decay: A nuclear disintegration in which gamma rays are emitted is called gamma decay. Consider the example of U-238.

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92238U→24He+90234Th+200

In this equation, uranium-238 is converted to thorium-234 with the emission of gamma rays along with the alpha particle.

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State radioactive decay law.

Radioactive decay law states that “the rate of radioactive disintegration is directly proportional to the number of nuclei of the elements present at that time”.

If N is the number of nuclei and dN is the number of radioactive decay per unit time dt then, the law is represented as,

dN/dt=N

dN/dt=-λN

In the above equation, λ is the radioactive constant.

Derive the law of radioactive decay.

From the radioactive decay equation,

dN/dt=-λN ……………………………. (1)

Consider at time t=0, the number of nuclei is N0 and at time t, the number of nuclei is N.

On integrating equation (1),

$\int_{N_0}^{N}\frac{dN}{N}=-\int_{0}^{t}\lambda dt$

log_eN-log_eN₀=-λt

log_e(N/N0)=-λt

N/N₀=e^-λt

N=N₀e^-λt

The above equation is the formula for the radioactive decay law.

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Rate of disintegration or rate of radioactive decay:

The rate of disintegration or rate of radioactive decay is the number of radioactive nuclei reducing per unit time. The rate of disintegration is denoted by(-dN_t/dt).

What is the decay constant?

Decay constant lambda (λ) is the time taken by the nucleus of an atom to reduce half of its initial value. It is also defined as the reciprocal of the time in which the number of atoms in a radioactive element reduces to 36.8% of the initial value.

$\lambda=\frac{2.303}{t}log_{10}(N_0/N)$

SI unit of the decay constant is s^-1.

Radioactive disintegration series:

A radioactive nucleus undergoes a series of decay. In a radioactive disintegration series, the decay process is continued until the unstable nuclei become stable nuclei.

The half-life of a radioactive element:

The time taken by the radioactive element to reduce half of its initial value is called the half-life of a radioactive element. It is represented by T_1/2.

T_1/2=ln2/λ=0.693/λ

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Frequently Asked Question (FAQs)

1. Define decay meaning in physics.

Decay is the process in which an object gets decomposed.

2. What is the radioactive element definition?

The meaning of radioactive element is the element having unstable nuclei in its atom.

3. Define radioactive nuclei.

In the decay process, unstable nuclei that emit radiation are called radioactive nuclei.

4. What is radioactivity? Define decay constant class 12.

The process in which radiation is emitted in the form of particles or photons of high energy is called radioactivity.

The decay constant is the reciprocal of the time by which the left number of nuclei in the element decreases to 1/e times the number of nuclei before the decay.

5. What is the time required to decay from N to N0?

t=2.303log10(N0N)

Here λ is the decay constant.

6. What is the activity of radioactive samples?

The number of disintegration per second is the activity of the radioactive sample.

7. What is the decay of radioactive isotopes?

Decay of radioactive isotopes is the process of emitting radiation where the time period of the isotope is measured in half-life.

8. What is the use of the law of radioactive disintegration?

The law of radioactive disintegration is used in the calculation of decay rate.