Question

1. What thickness of concrete and of lead are needed to reduce the intensity of narrow 500 keV photon beam to one-fourth its value? Compare the thickness in cm and in g/cm2. Repeat for 1.5 MeV photons.

2. A 3 MeV point source of grams is located at the center of a 6.0 cm diameter iron sphere. The lead sphere is surrounded by a spherical shell of lead 3 cm thick (The resulting sphere is a radius 6.0 cm).

a) What is the radius of the sphere in which half the gammas undergo a first interaction?

b) What fraction of the gammas undergo a first collision in the lead?

3. Calculate the mass attenuation coefficient of silica glass (SiO2, ?=2.21 g.cm3) for 3 MeV ?-rays.

4. At 1 MeV the Compton cross section per electron is 0.2112 barn and the Compton energy absorption cross section per electron is 0.0929 barn.

a) What is the average energy of the recoiling electron in a Compton interaction at this energy?

b) Computer the Compton mass attenuation and mass absorption coefficients at 1 MeV for i) aluminum ii) water

5. Drive the following relationship for a photon scattered by a free electron at rest.

E?= E / 1+ (E/m0c2 )(1?cos?)

where E? = final energy of the photon

E = initial energy of the photon

6. Photons from a 3 MeV gamma source are normally incident on plane aluminum foil of 1 mm thick.

a) What is the maximum electron kinetic energy expected from scattering interaction of photons with the foil?

b) What is the minimum photon energy expected?

Answer 1