2. Introduction:-
Pair production is a process in which
the energy of a photon is converted
into rest mass.
In this process, the photon disappears
as an electron (negatron) and positron
pair is created.
4. HISTORY OF PAIR PRODUCTION
The pair production phenomena was first predicted by
a British physicist P.A.M. Dirac in 1925.
His work suggested the existence of a sea of particles
below physical matter which remains unobservable.
Dirac’s concept which predicted the positron, the anti
electron, was rather than two separate particles being
produced, an electron is released from an infinite sea
of particles below empty space.
In removing a particle from sea, the remaining
particle would act as the antiparticle.
5. CONT..…
For photon with the energy exceeding 2mc2 or 1.02
MeV, it is possible to create an electron-positron pair
through the interaction of such a quanta with the field
of nucleus.
High energy photon interaction with the nucleus or
near the nucleus causes ionization of the atom to
produce a pair of charged particles (negatron and
positron).
The resulting kinetic energy of the produced charged
particles is equal to E = E’-2mc2
6. CONT…..
In the Born approximation (which is not very accurate for
low energy or high Z) one finds
54
1
183
ln
9
7
4
137
and
0
screening
Complete
54
109
2
ln
9
7
4
137
and
1
screening
No
3
/
1
2
2
3
/
1
2
2
2
2
3
/
1
2
2
Z
f
Z
r
Z
Z
c
m
h
Z
f
c
m
h
r
Z
Z
c
m
h
c
m
e
pair
e
e
e
pair
e
e
7. CONT…..
TOC
1. Photon with sufficient energy passes near
nucleus
2. Energy of photon turns into matter
3. Pair of matter/anti matter is created
4. Nucleus must carry off momentum
Electron
m = 9.11 x 10-31 kg
Charge = -e
Positron
m = 9.11 x 10-31 kg
Charge = +e
Help me! I’m going to be
annihilated presently!
8. Solving pair production
E = hf = hc/
E = mc2
E - Energy
m - mass
c = 3.00 x 108 m/s
1 eV = 1.602 x 10-19 J
9. Applications of Pair Production
1. BRACHYTHERAPY
2. PROTON THERAPY
3. CONFORMAL RADIATION THERAPY
