38
3 Nuclear Reaction
Cyclotron is multistage particle accelerator. It operates under magnetic force on
a moving charge. The magnetic field is altered to maintain the acceleration optimized. The movement of a particle is in a semicircular path. An electron is accelerated by the applied electric field.
Synchrocyclotron is a modified version of a cyclotron. The frequency of the driving radio frequency electric field starts as a cyclotron, which gradually increases
till the desired energy is obtained. This helps to compensate for the relativistic
effect when the velocity of the particles approaches the speed of light. Heavier
particles like proton, deuteron, and α-particles can be accelerated by moving in
a circle of increasing radii. This instrument can accelerate Deuteron to 200 MeV
and even α-particles to 400 MeV.
3.5 Conservation of Mass and Energy
The energy released or absorbed in a nuclear reaction is calculated from the “concept
of
conservation
of
energy”.
As
an
example,
the
reaction
209 Bi(α, 2n)
211 At can be considered.
209 Bi 83 +
4 He 2
−→
211 At 85 +
2
1 n 0
+ Q
(208.980417 (4.00260361
(210.987496 (2.01733088
a.m.u.)
a.m.u.)
a.m.u.)
a.m.u.)
Thus, the value of Q is equal to the mass difference between the two sides of the
above equation, i.e., −0.021806 a.m.u., equivalent to −20.3 MeV. Since the value of
Q is negative, some kinetic energy of the incident particle has been used to create
products of greater mass than that of the target material. In other words, this reaction
needs the incident particle to have energy at least as great as the amount absorbed in
the reaction (i.e., 20.3 MeV). In such reaction, energy required for the bombarding
particle is much less. For example,
232 Th 90
+
1 n 0
−→
233 Th 90
+ γ + Q
(232.038211 a.m.u.) (1.008665 a.m.u.)
(233.041428 a.m.u.)
Here, the reactants are heavier than the product by an amount equivalent to 5.08 MeV.
Thus, it is concluded that, in an exoergic reaction, incident particles need not be energetic. Thermal neutrons having energy of about 0.025 eV are sufficient to enable the
neutron capture reaction to proceed.
3 Nuclear Reaction
Cyclotron is multistage particle accelerator. It operates under magnetic force on
a moving charge. The magnetic field is altered to maintain the acceleration optimized. The movement of a particle is in a semicircular path. An electron is accelerated by the applied electric field.
Synchrocyclotron is a modified version of a cyclotron. The frequency of the driving radio frequency electric field starts as a cyclotron, which gradually increases
till the desired energy is obtained. This helps to compensate for the relativistic
effect when the velocity of the particles approaches the speed of light. Heavier
particles like proton, deuteron, and α-particles can be accelerated by moving in
a circle of increasing radii. This instrument can accelerate Deuteron to 200 MeV
and even α-particles to 400 MeV.
3.5 Conservation of Mass and Energy
The energy released or absorbed in a nuclear reaction is calculated from the “concept
of
conservation
of
energy”.
As
an
example,
the
reaction
209 Bi(α, 2n)
211 At can be considered.
209 Bi 83 +
4 He 2
−→
211 At 85 +
2
1 n 0
+ Q
(208.980417 (4.00260361
(210.987496 (2.01733088
a.m.u.)
a.m.u.)
a.m.u.)
a.m.u.)
Thus, the value of Q is equal to the mass difference between the two sides of the
above equation, i.e., −0.021806 a.m.u., equivalent to −20.3 MeV. Since the value of
Q is negative, some kinetic energy of the incident particle has been used to create
products of greater mass than that of the target material. In other words, this reaction
needs the incident particle to have energy at least as great as the amount absorbed in
the reaction (i.e., 20.3 MeV). In such reaction, energy required for the bombarding
particle is much less. For example,
232 Th 90
+
1 n 0
−→
233 Th 90
+ γ + Q
(232.038211 a.m.u.) (1.008665 a.m.u.)
(233.041428 a.m.u.)
Here, the reactants are heavier than the product by an amount equivalent to 5.08 MeV.
Thus, it is concluded that, in an exoergic reaction, incident particles need not be energetic. Thermal neutrons having energy of about 0.025 eV are sufficient to enable the
neutron capture reaction to proceed.