Shielding

1
Shielding

• Biological shielding
• Reactor shielding

2
Build-up factors

• Attenuation is easy because you assume that the
  g-rays disappear with each interaction
• Where m is the total attenuation coefficient at E0

3
What really happens

• Compton effect - the photon is scattered with a
  loss of energy
• Pair production incident photon is absorbed
  x-rays are produced
• Photoelectric effect - 0.511 keV (annihilation
  radiation is inevitable)

4
The shield

• Before

• After

f(E)
f(E)
E0
E0
5
So here comes the fudge

• Ok its not really a fudge factor. Several very
  talented scientist solved the really ugly problem
  for several materials and geometries to get
• Bm(ma) - build-up factor

6
Build-up flux

• Planar (mono) source

• Point (isentropic) source

7
Definitions

• fb- build-up flux
• fu- uncollided flux
• f0 - initial flux
• Bm(ma) or BR(mR) - build-up factor
• Table 10.1 for a plane
• Table 10.2 for isotropic point source

8
Biological shield

• Exposure rate mR/hr

9
Other geometries

• Infinite planar
• Disc
• Line
• Internal source - results from neutron activation
  of the shield
• Multilayered shields

10
Reactor shielding

• Slow the fast neutrons down to an energy where
  the absorption cross sections is larger
• Coolant activation
• Gamma rays

• Point water kernel
• Removal cross section
• Half thickness
• Mean free paths thick
• Radiation streaming

11
Why is it so so hard

• Many energies
• Every direction
• In the real world Nuclear engineers use MONTE
  CARLO