Neutrons - hdbk11080110

DOE-HDBK-1108-97

Radiological Training for Accelerator Facilities

Student's Guide

than protons or heavier particles. Some machines, called light sources, accelerate electrons

and positrons specifically for the purpose of producing synchrotron radiation.

Neutrons

EO-16

DISCUSS special instruments and measurement techniques.

Neutrons can be produced through nuclear interactions of the primary or secondary beam

with matter. They can also be produced by interaction of high-energy photons with matter

(photonuetron reaction). The photoneutron reaction typically requires photons with energy

in excess of 10 MeV. Neutron radiation is a concern within any area where the beam can

interact with matter, such as targets, beamline components, etc.

Neutrons do not lose energy by direct ionization like charged particles. They gradually lose

their energy through collisions with atoms in material. The most effective shielding is

material that contains hydrogen, such as concrete, earth, or water. When a neutron collides

with a hydrogen nucleus containing one proton, the neutron transfers energy to the proton

(like two billiard balls colliding). The proton is easily stopped because it is a charged

particle.

Labyrinth designs are often used to "trap" neutrons as they ricochet.

Location of potential sources of neutron radiation exposure. (Facility Specific)

Muons

Muons are short-lived particles that are physically similar to electrons, but about 200 times

heavier.

Muons are produced by several mechanisms and require photon energies greater than 212

MeV or proton energies greater than 140 MeV. Muons are not usually seen in significant

amounts at machines with energies less than 1 giga volt (GeV = 1x109 eV).