RADIOACTIVITY
 |
| RADIOACTIVITY | NUCLEAR FISSION,NUCLEAR FUSION |
Radioactivity was
discovered by a French physicist Henry Bacquerel in 1896.The term radioactivity
was given by Marie Curie, the scientist who got Nobel twice for physics and
chemistry. The spontaneous emission of invisible radiation by some elements due
to the splitting of their nucleus is called radioactivity.
The invisible rays
emitted by radioactive elements consist of
(a) Alpha (ɑ)
particles i.e., 2He4(+2 unit charge and
mass four units).They are deflected towards negative plate in electric field.
(b) Beta (β)
particles i.e., electrons (-1 charge and mass zero).They are deflected
towards positive plate in electric field.
(c) Gamma (𝜸) rays (no charge and no mass).They are not deflected from their path in
electric or magnetic field. They are electromagnetic radiations. Emission
of 𝜸-rays is the secondary effect of radioactive
change.
Stable nuclei are those
for which of neutrons and protons are equal.
Isotopes of all the
known elements with Z>83 are radioactive.
Soddy and Fajan's group
displacement law is used to determine group of the daughter element.
The time taken by half
of the atoms of a radioactive element to disintegrate is called its half-life.
The unit of half life
period is time -1.
NUCLEAR FISSION
The splitting of a heavy
nucleus into two smaller almost equal nuclei along with the production of two
or three neutrons and about 200 MeV of energy is called "nuclear
fission".Nuclear fission was discovered by "Hahn"and
"Strassmann" in 1939.
Atom bomb is the result of uncontrolled nuclear
fission.
The device in which
controlled nuclear fission is carried out is called nuclear reactor.The fission
is controlled by absorbing neutrons by using cadmium or boron rods.Heavy water
(D2O,mol wt. 20) and graphite is used for slowing down the fast
moving neutrons. U235 is used as a nuclear fuel.
NUCLEAR FUSION
The union of lighter
nuclei to form a big nucleus is called the nuclear fusion.Nuclear
fusion is also accompanied by release of energy because the total mass of
products is lesser than total mass of reactants.
Nuclear fusion occurs
only at extremely high temperature (>106K), so it is also
called thermo-nuclear reaction.
Hydrogen bomb is the
result of nuclear fusion.It contains a mixture of deuterium oxide (D2O)
and tritium oxide (T2O) in a space surrounding an ordinary atom
bomb.
Source of solar and
steller energy is nuclear fusion.
APPLICATIONS OF RADIOISOTOPES
Radio carbon dating is
used to determine age of dead specimen with C14 content by
comparing it with C-12, content.
N = N0 (1/2)n
Where, n = total time/t1/2.
Rock dating or uranium
dating is used to determine the age of rocks or earth.It is based on Pb and U
ratio.
USES OF RADIOISOTOPES
|
RADIOISOTOPE
|
USES
|
|
I131(Iodine-131)
|
(i)To study the structure and
activity of thyroid gland.
(ii)For the treatment of thyroid
disease.
|
|
I123(Iodine-123)
|
Brain imaging.
|
|
Co60(Cobalt-60)
|
Treatment of cancer.
|
|
Na24(Sodium-24)
|
To trace flow of blood.
|
|
P33 (Phosphorus-32)
|
For leukemia therapy.
|
|
C-14 (Carbon-14)
|
To study the kinetics of
photosynthesis.
|
ConversionConversion EmoticonEmoticon