Radioactivity
In 1896, Henry Becquerel observed that the uranium salt was
emitting a penetrating type of radiation spontaneously. A little later, Curie
suggested that these radiations were from a uranium compound. He termed this an
atomic phenomenon and named this Radioactivity.
The phenomenon of spontaneously emitting active radiations from an unstable
atomic nucleus is called radioactivity. The substances emitting such
radiations are called Radioactive. Such elements in the periodic table
can be distinguished by their atomic weights given in parentheses.
In 1905, Rutherford analyzed the radiations emitted by naturally
occurring radioactive elements as three types depending on the effect of a
magnetic or electric field on them. These radiations are named alpha (
a?), beta ( b?)
and gama ( g?). They are schematically
shown in figure 4.
For chemical purposes, the most important types of radiation are alpha and
beta particles
Every emission of an a - particle leaves a new
element with atomic mass 4 units less and atomic number 2 units less than the
parent; but the emission of a b - particle leaves the
atomic mass unchanged and increases the atomic number by one unit.
An a - particle is a
2He4
nucleus with 2 protons and 2 neutrons
Transmutation :
The phenomenon of the conversion of a radioactive element like Ra, Pa, Ac
etc. into a new element by the emission of radiations is called Transmutation
(meaning conversion).
The process of conversion of one element into another by bombarding with fast
moving particles such as protons, neutrons, deuterons etc is known as
artificial transmutation.
The new element formed in the transmutation may be radioactive or
non-radioactive.
The other way to induce transmutation is by negative beta particles which are
electrons emitted from within atomic nuclei.
92U239 emits
b-particle and forms an element with atomic
number 93. This element is called neptunium.
|
