Malignant tumors are commonlytreated with targeted x-ray radiation therapy. To generate these medicalx rays, a linear accelerator directs a high-energy beam of electronstoward a metal target—typically tungsten. As they near the tungsten nuclei,the electrons are deflected and accelerated, emitting high-energyphotons via bremsstrahlung. The resulting x rays are collimated into abeam that is directed at the tumor. The photons can deposit energy inthe tumor through Compton and photoelectric interactions. A typicaltumor has 108 cells/cm3, and in a full treatment, 4 MeV photons mayproduce a dose of 70 Gy in 35 fractional exposures on different days.The gray (Gy) is a measure of the absorbed energy dose of radiation perunit mass of tissue: 1 Gy = 1 J/kg. The high-energy photons can undergo Compton scattering off electrons in the tumor. The energy imparted by a photon is a maximum when the photon scatters straight back from the electron. In this process, what is the maximum energy that a photon with the energy described in the passage can give to an electron? (a) 3.8 MeV; (b) 2.0 MeV; (c) 0.40 MeV; (d) 0.23 MeV.
Malignant tumors are commonly
treated with targeted x-ray radiation therapy. To generate these medical
x rays, a linear accelerator directs a high-energy beam of electrons
toward a metal target—typically tungsten. As they near the tungsten nuclei,
the electrons are deflected and accelerated, emitting high-energy
photons via bremsstrahlung. The resulting x rays are collimated into a
beam that is directed at the tumor. The photons can deposit energy in
the tumor through Compton and photoelectric interactions. A typical
tumor has 108 cells/cm3, and in a full treatment, 4 MeV photons may
produce a dose of 70 Gy in 35 fractional exposures on different days.
The gray (Gy) is a measure of the absorbed energy dose of radiation per
unit mass of tissue: 1 Gy = 1 J/kg. The high-energy photons can undergo Compton scattering off
electrons in the tumor. The energy imparted by a photon is a maximum
when the photon scatters straight back from the electron. In this process,
what is the maximum energy that a photon with the energy described
in the passage can give to an electron? (a) 3.8 MeV; (b) 2.0 MeV;
(c) 0.40 MeV; (d) 0.23 MeV.
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