ATOM AND RADIATION PHYSICS
HW4 (Due, May 5, 2015)
1. The threshold wavelength for tungsten is 2700 Å. What is the maximum kinetic
energy of photoelectrons produced by photons of wavelength 2200 Å?
2. Light of wavelength 1900 Å is incident on a nickel surface (work function 4.9 eV).
(a) Calculate the stopping potential.
(b) What is the cutoff frequency for nickel?
(c) What is the threshold wavelength?
3. A 900-keV photon is Compton scattered at an angle of 115o with respect to its original
direction.
(a) How much energy does the recoil electron receive?
(b) At what angle is the electron scattered?
4. Show that the fractional energy loss of a photon in Compton scattering is given by
5. The Klein–Nishina cross section for the collision of a 1-MeV photon with an electron
is 2.11×10-25 cm2. Calculate, for Compton scattering on aluminum,
(a) the energy-transfer cross section (per electron cm-2)
(b) the energy-scattering cross section (per electron cm-2)
(c) the atomic cross section
(d) the linear attenuation coefficient.
6. An experiment is carried out with monoenergetic photons in the “good” geometry
shown in Fig. 8.7. The relative count rate of the detector is measured with different
thicknesses x of tin used as absorber. The following data are measured:
(a) What is the value of the linear attenuation coefficient?
(b) What is the value of the mass attenuation coefficient?
(c) What is the photon energy?
7. A pencil beam of 200-keV photons is normally incident on a 1.4-cm-thick sheet of
aluminum pressed against a 2-mm-thick sheet of lead behind it.
(a) What fraction of the incident photons penetrate both sheets without interacting?
(b) What would be the difference if the photons came from the other direction,entering
to lead first and then the aluminum?
8. A narrow beam of 104 photons s-1 is normally incident on a 6-mm aluminum sheet.
The beam consists of equal numbers of 200-keV photons and 2-MeV photons.
(a) Calculate the number of photons s-1 of each energy that are
transmitted without interaction through the sheet.
(b) How much energy is removed from the narrow beam per
second by the sheet?
(c) How much energy is absorbed in the sheet per second?
9. A parallel beam of 500-keV photons is normally incident on a sheet of lead 8 mm
thick. The rate of energy transmission is 4×104 MeV s-1.
(a) What fraction of the incident photon energy is absorbed in
the sheet?
(b) How many photons per second are incident on the sheet?
(c) What fraction of the transmitted energy is due to uncollided photons?