2. THE Α,P REACTION
Bombardement of nitrogen gas with α particles from a radioactive source.
If Q is positive, energy has been released and the reaction is called exoergic.
If Q is negative, energy has been absorbed and the reaction is endoergic.
3. • Q is nuclear reaction energy or disintegration energy (as defined
earlier in decay reactions).
• Equal to the difference in the masses of the initial and final particles.
4. • The total mass of final particles is greater than that of the initial
particles. Difference in masses, Δm = 0.001281 u. 1 u = 931 MeV,
• Therefore the reaction is endoergic.
• A minimum threshold energy is required ;which is derived from the
kinetic energy of the bombarding particle.
5. • α particle interacts with a nucleus to eject of a proton, is called an
α,p reaction.
The first letter, α, stands for the bombarding particle
The second letter, p stands for the proton.
6. THE Α,N REACTION
• The bombardment of a nucleus by α particles with the subsequent
emission of neutrons is designated as an α,n reaction.
• A material containing a mixture of radium and beryllium has been
commonly used as a neutron source in research laboratories.
• In this case, the α particles emitted by radium bombard the beryllium
nuclei and eject neutrons.
7. PROTON BOMBARDMENT
• The most common proton reaction consists of a proton being
captured by the nucleus with the emission of a γ-ray.
• The reaction is known as p,γ.
• Examples are
• Other possible reactions produced by proton bombardment are of
the type p,n; p,d; and p,α.
• The symbol d stands for the deuteron
8. DEUTERON BOMBARDMENT
• Deuteron : combination of a proton and a neutron
• Deuteron bombardment results in a production of either neutron or
a proton
• Stripping: The bombardment of beryllium by deuterons results in
high energy neutrons. This reaction that has been used as a source of
high-energy neutrons .
9. • The deuteron is not captured by the nucleus but
passes close to it.
• The proton is stripped off from the deuteron and the
neutron continues to travel with high speed.
10. NEUTRON BOMBARDMENT
• Neutrons have good penetration:
• no electric charge
• Ie , they do not have to possess high kinetic energies , to penetrate the
nucleus.
• slow neutrons or thermal neutrons (neutrons with energy equal to the energy
of thermal agitation in a material, 0.025 eV) : Effective in nuclear
transformation.
• An example of a slow neutron capture is the n,α reaction with boron:
11. • An ionization chamber is filled with boron gas.
• The α particle released by the n,α reaction with boron produces the
ionization detected by the chamber.
• n,γ reaction: the compound nucleus is raised to one of its excited
states and then immediately returns to its normal state with the
emission of a γ-ray photon.
• These γ-rays, called capture γ-rays
12. • Products of the n,γ reaction, in most cases, have been found to be
radioactive, emitting β particles. Typical examples are,
13. • the n,p reaction, also yields β emitters.
• The example of a fast neutron n,p reaction is the production of 32P:
• In the case of an n,p reaction, if this mass difference exceeds
0.000840 u (mass difference between a neutron and a proton), then
only fast neutrons will be effective in producing the reaction.
14. PHOTODISINTEGRATION
• An interaction of a high-energy photon with an atomic nucleus can
lead to a nuclear reaction and to the emission of one or more
nucleons.
• In most cases, emission of neutrons by the nuclei.
• The above reaction has a definite threshold, 10.86 MeV.
15. • Because the rest energies of many nuclei are known for a very high
accuracy,
• the photodisintegration process can be used as a basis for energy
calibration of machines producing high-energy photons.
16. FISSION
• This type of reaction is produced by bombarding certain high-atomic-
number nuclei by neutrons.
• The nucleus, after absorbing the neutron, splits into nuclei of lower
atomic number as well as additional neutrons.
• The product nuclei of a fission reaction, called fragments, consist of
many possible combinations of A and Z.
17.
18. The fission yield curve shows maximum yield at approximately A
of 90 and 140.
19. • The energy released Q, appears as the kinetic energy of the product
particles as well as γ-rays.
• The additional neutrons released in the process may also interact
with other 235U nuclei, thereby creating the possibility of a chain
reaction.
• To induce a chain reaction, neutrons have to be slowed down to
thermal energies by collision with nuclei of low Z material (e.g.,
graphite, water, heavy water) called moderators.
20. • the energy released per fission reaction is enormous.
• The process, therefore, has become a major energy source as in the
case of nuclear reactors.
• In a nuclear reactor, the chain reactions are controlled.
• In a nuclear bomb, on the other hand, the chain reaction is
uncontrolled to cause explosion.
21. FUSION
• Reverse of nuclear fission.
• nuclei are combined to produce one nucleus.
• For a fusion reaction to occur, the nuclei must be brought sufficiently
close together so that the repulsive Coulomb forces are overcome
and the shortrange nuclear forces can initiate the fusion reaction.
• This is accomplished by heating low Z nuclei to very high
temperatures (>10 7 K), which are comparable with the inner core
temperature of the sun.
• In practice, fission reactions have been used as starters for the
fusion reactions.
