Radioactivity - Introduction | Causes and Types | Chemistry Grade XI


Radioactivity - Introduction | Causes and Types | Chemistry Grade XI

Radioactivity - Introduction | Causes and Types

The branch of chemistry which deals with the study of nuclear phenomenon like radioactivity, nuclear transmutation is called Nuclear Chemistry.

Radioactivity was first observed by Henry Bacquerel while performing an experiment to establish relationship between fluorescence of glass wall of x-rays tube and phosphorescence. He observed that uranium salt accidentally placed above photographic plate, darkened the photographic plate wrapped in thick and black paper. He concluded that this is due to the spontaneous emission of some rays from the uranium compound. Subsequently, Marie and Piere Curie studied the phenomenon in uranium, polonium and radium.

The spontaneous emission of radiation or particle from the atom of same element having unstable nuclei (radioactive substance) is called radioactivity. It is spontaneous self-disintegration activity in which one nucleus is changed into another.

The units of radioactivity are dps( disintegration per second), Bacquerel, Curie and Rutherford. The SI unit is Bacquerel.

1 Bacquerel = 1 dps
1 Curie = 3.7 * 1010 dps
1 Rutherford= 106 dps
1 Curie is the quantity of radioactive substance decaying at the same rate of 1 gm of radium (3.7 * 1010 dps).
The stability of nucleus of an atom is determined by the value of n/p ratio. The range of value of n/p ratio between 1 to 1.6 is called zone of stability. The nucleus of atom whose value of n/p ratio lies between 1 to 1.6 are stable. The nucleus whose value of n/p ratio lies below or above the zone of stability are unstable and emits rays or particles from the nucleus to be stable which is the cause of radioactivity.

If the value of n/p ratio is greater than the value of zone of stability, a neutron transforms into proton with emission of beta particles and increase the atomic number by 1.

0H ----------------> 1H + -1­0e
614C -------------> 714N + -10e
3687Kr -----------> 3787Rb + -10e
If the value of n/p ratio is lower than the value of zone of stability, nucleus emits alpha particles. Loss of one alpha particle decreases atomic number by 2 and atomic mass decreases by 4 units.
92238U ------------> 90234Th + 24He


Natural Radioactivity: The spontaneous disintegration of natural unstable nuclei which have the value of n/p ratio greater than 1.6, with emission of radiation is called natural radioactivity. For example;
92238U -------------------> 90234Th + 24He
614C ----------------------> 714N + -10e
Artificial Radioactivity: The radioactivity due to the transformation of stable nucleus into unstable nucleus by bombarding it with particles like alpha particles, beta particles, protons having high energy is called artificial radioactivity.
1327Al + 24He ----------------> 1530P + 01n

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