Search Pabitras

Radioactive Decay

Radioactive Decay

Introduction

Radioactive Decay is the process of emission of radioactive radiations from a nucleus of an atom. The unstable nuclei ( generally the nuclei of atomic mass greater than 83 ) and having more number of protons than that of neutrons are unstable nuclei. These nuclei get disintegrated themselves, forming nuclei of more stable atom ( especially isotopes of lead ). The process of radioactive decay continues until the unstable nuclei is converted into stable nuclei.

Radioactive Decay
Radioactive Decay

Types of Radioactive Decay

Depending upon the types of particles emitted, radioactive decay can be classified into three types:

  • Alpha decay (α-decay):

    Alpha decay is the process of radioactive decay in which alpha particle is released from the nucleus of an unstable atom. During alpha decay, the atomic number of parent atom decreases by two units and mass number decreases by four units. Alpha decay is represented in the equation as:
    ZXAZ-2XA-4 + 2He4
    Here, X is the parent nucleus, Y is the daughter nucleus and He is alpha particle representing Helium atom.
    Thus in alpha decay, atomic number of nucleus shifts two steps backwards.
    Eg. If an atom of uranium (92U238) decays, it changes into Thorium atom (90Th234). Along with Thorium atom, an alpha particle(2He4) is also formed.
    92U23890Th234 + 2He4
  • Beta decay (β-decay):

    Beta decay is the process of radioactive decay in which beta particle is released from the nucleus of an unstable atom. During beta decay, the atomic number of parent atom remains unchanged. Beta decay is represented in the equation as:
    ZXAZ+1YA + -1e0
    Here, X is the parent nucleus, Y is the daughter nucleus and e is alpha particle representing an electron.
    Thus in beta decay, atomic number of nucleus shifts one steps forward.
    Eg. If an atom of radium (88Ra228) decays, it changes into Actinium atom (89Ac228). Along with Actinium atom, an beta particle(-1e0) is also formed.
    88Ra22889Ac228 + -1e0
    During beta decay from nucleus of an atom, an electron is released. But it doesn’t mean that nucleus of atom contains electron. In fact, the neutron disintegrates to form a proton, electron and an anti-neutrino. So, elements having high neutron-proton (n/p) ratio show beta decay.
  • Gamma Particle (γ-decay):

    Gamma decay is the process of radioactive decay in which gamma ray is produced from the nucleus of an atom. During gamma decay, atomic mass and atomic number of an atom remains unchanged. So, no new element is formed. In gamma decay, the nucleus achieves the state of stability by emitting photons of suitable frequency.

Generally, during alpha and beta decay, the daughter nuclei are in the excited state. These excited nuclei return to their respective ground state by emitting gamma ray. So alpha and beta decay is followed by gamma decay.

Laws of Radioactive Decay

1. Radioactive decay is a spontaneous phenomena and is unaffected by external conditions like temperature, pressure, magnetic filed, etc.
2. In all known radioactive transformations, either alpha particle or beta particle is formed. i.e. Never both or more than one of each kind is emitted by an atom.
3. The rate of disintegration of radioactive substance is directly proportional to the number of radioactive atoms present at that time.
If dN/dT be the number of disintegrations per second then,
Rate of decay ∝ Number of atoms
or, dN/dT ∝ N
or, dN/dT = -λN,
where λ is a proportionality constant called decay constant and negative sign indicates that the rate of disintegration decreases with increase in time.

Mathematical Treatment

From law of radioactive decay,
dN/dT = -λN
On solving this, we get
N = N0eλt
where, N0 is the initial number of radioactive atoms at t = 0.

Applications of Radioactive Decay

Following are the applications of radioactive decay

  1. Radiocarbon Dating:

    It is the process of estimation of age of archeological organic materials by radioactive process. By measuring the number of N-12 and N-14 atoms present in given specimen, we can calculate the age of given specimen.
  2. Agricultural application:

    Radioactive radiations are used to produce the diseases resistance seeds. It is also used in making radio-phosphorous which is used as fertilizer.
  3. Industrial application:

    Radioisotopes are used in quality checking of some industrial products like machinery parts, lubricants, etc
  4. Medical application:

    Radioactive radiations are used to detect different diseases like brain tumor, hemorrhage (internal bleeding), etc. It is also used in the treatment of many diseases like blood cancer, bone fracture, etc.

Radiation Hazard

Radiation hazard refers to the harmful effects which is caused due to over exposure of living body to radioactive radiations like alpha-particle, beta-particle, etc. When a living cell comes in contact with radiations, its normal functioning is disturbed. Similarly, whole tissue gets damaged and organ is destroyed. Radiation hazards are so intense that they even change the genetic information and produce mutation. These radiations cannot be prevented completely. However, we can control radiation hazards by minimizing the use of radioactive materials and using them far away form human inhabitation.

Leave a Reply

Your email address will not be published. Required fields are marked *