Engineering Chemistry S Datta

64 ENGINEERING CHEMISTRY
Q. 8. What do you mean by natural radioactivity and artificial radioactivity?
Ans. Natural radioactivity is exhibited by heavier elements found in nature. Whereas
modern techniques of artificial transmutation of elements have made it possible to produce
radioactivity in many other lighter elements. Such type of radioactivity is known as “artificial
or induced radioactivity”.
Q. 9. What do you mean by radioactive series?
Ans. If, during radioactive disintegration, the daughter element is also radioactive then
it decays further and the process continues till a stable isotope is reached. This chain of successive
disintegrations is termed ‘radioactive series’.
Q. 10. What do you mean by radioactive decay constant?
Ans. The radioactive decay equation is,
d N
− = λ N
dt
or λ= − dN/
dt
N
So, the radioactive decay constant (λ) may be defined as the ratio of the amount of the
substance, which disintegrates in a unit time to the amount of the substance present.
Alternatively, it may be defined as the rate of disintegration when the number of
radioactive nucleus present is one.
Q. 11. Compare radioactive change and chemical change.
Ans.
Radioactive change
(i) Radioactive change does not depend upon
external conditions like temperature,
pressure, etc.
(ii) Radioactive change is irreversible.
(iii) Radioactive change is always exothermic.
(iv) Radioactive change is a nuclear phenomenon.
Chemical change
(i) Chemical change depends upon external
conditions like pressure, temperature, etc.
(ii) Chemical change is mostly reversible.
(iii) Chemical change may be exothermic or
endothermic.
(iv) Chemical change involves only outermost
electrons of the atoms. No change takes place
of the nucleus of the atom.
Q. 12. What do you mean by nuclear fission?
Ans. The division of a nucleus into two approximately equal parts is termed ‘nuclear
fission’. As for example:
140 93 1
Ba + Kr + 3 n
56 36 0
235 1 236
U + n U
92 0 92
144 90 1
54Xe +
38Sr + 2
0n
144 90 1
Cs + Rb + 2 n
55 37 0
A huge amount of energy is released during nuclear fission according to famous Einstein’s
equation E = mc 2 , and this reaction is the principle for atom bomb.