PHYS40422: Applied Nuclear Physics Paul Campbell Room Interaction of Radiation with Matter 2.Radiation Detection 3.Biological Effects of Radiation 4.Applications of Nuclear Techniques 5.Nuclear Fission 6.Nuclear Fusion

Chapter 1. The Interaction of Radiation with Matter : 1.2 Neutrons and gamma rays Neutrons – negligible EM interaction (bar weak magnetic). They stop via collisions… Elastic and inelastic possibilities.

The energy loss of neutrons in successive collisions

Nucleus  n to thermalise 1H H C U n is the number of collisions to go from 2 MeV to a thermal energy of eV Logarithmic Energy Decrement

From the collision kinematics we learn: In a light-mass medium the neutrons lose more energy on average in each collision. Each collision leads to big step changes in energy in a light-mass medium. It takes less collisions to reach thermal energies in a light-mass medium. In a heavy-mass medium the neutrons lose little energy on average in each collision. Each collision leads to small step changes in energy in a heavy-mass medium. It takes many collisions to reach thermal energies in a heavy-mass medium.

Some terminology Fast neutrons: E > ~ few MeV Slow neutrons: epithermal neutrons E ~ eV thermal neutrons E ~ 3/2 kT ~ eV at room temperature

Klein-Nishina formula for Angular Distribution in Compton Scattering

Linear Attenuation Coefficient for Al

Linear Attenuation Coefficient for Pb K-shell Edge