Interaction of radiation with matter: computer exercises
Charged particles – Range module
1) Estimate the time required for 5 MeV alpha particles to slow down and stop in
Plexiglas. Repeat for the same particles in air.
2) What is the range of a beam of 10 MeV protons in Graphite? Estimate the energy
remaining in a beam of 10 MeV protons after passing through 100 µm of graphite (see
hint).
3) Estimate the range of 10 MeV electron in aluminium.
Hint: If a particle tries to penetrate a thickness of the given material that is less than the
range, it will penetrate it with reduced energy. Here is the key point: The energy that the
particle will have coming out of the range is EXACTLY the energy that is required to
penetrate the "rest" of the range. For example, if a given particle of given initial energy
has a range that is 3 cm (in a given material), and it penetrates a 2 cm thickness of that
same material, it will exit the 2 cm thickness with EXACTLY the energy that is required
to penetrate 1 cm of that material.
Photon dosimetry and shielding – Dose module
1) Irradiators are g-sources (e.g. 137Cs, 60Co) used for food irradiation, radiation induced
mutation, sterilization, medicine purposes, etc…
A 60Co gamma ray irradiation containing a 2TBq source is directed at a 30 cm thick concrete
wall. The wall is situated at 7.5 m from the source. What the exposure rate behind the wall?
2) Radiation regulations impose an exposure rate outside the room of 7.5 µSv/h max. What
thickness of wall would we then need?
3) We want to restrict the exposure rate inside the room (@1m from the irradiator) to 10
µSv/h using lead. Calculate the required thickness.
4) 99mTc is used in radioactive isotope medical tests, for example as a radioactive tracer that
medical equipment can detect in the body. It is well suited to the role because it emits readily
detectable 140 keV gamma rays, and it has a short half-life of 6.01 hours (meaning it has
almost completely decayed to 99Tc in 24 hours). A patient is injected 30 mCi of 99mTc. He is
considered as an unshielded source during the time there is radioactivity in his body. Thus the
staff is exposed to radiation. What is the equivalent dose rate that a staff member can be
exposed to? (Medium is tissue, 1 cm thick @1 m distance)