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The radiations typically used to image 201Tl are polyenergetic because:

A. electron capture creates multiple gamma ray emissions.

B. 201Hg K- and L-shell electrons have different binding energies.

C. there are multiple gamma ray emissions for 201Hg.

D. 201Tl gamma ray emissions are more abundant than x-ray emissions.

Answer b. The energy of characteristic x-rays is dependent on the binding energies of the shells from which they originate. Since the K and L shells have different binding energies, so will the x-rays that are produced by a vacancy in each shell.

See Chapter 1.

If a nucleus decays by isomeric transition, which of the following might be emitted in the process?

A. A positron

B. An alpha article

C. A conversion electron

D. A neutron

Answer c. In an isomeric transition, only the energy state of the nucleus changes. A conversion electron is ejected in the process of internal conversion when an excited nucleus gives some of its energy to a low-shell electron (typically K or L), ejecting it from the atom. This is one of the two forms of isomeric transition, the other being gamma emission. Positrons are given off when a proton changes into a neutron in positron decay. Alpha particles would decrease the total number of nucleons by 4 (2 neutrons and 2 protons). The emission of a neutron would decrease the number of neutrons by 1.

See Chapter 1.

Photons undergoing Compton scatter in tissue:

A. can be identified by their energy.

B. are less abundant than the photoelectrons.

C. are not considered in radiation safety.

D. are more abundant than Compton electrons.

Answer a. When a photon undergoes Compton scatter, it loses energy relative to its incident energy and is therefore identifiable.

See Chapter 1.

As the thickness of tissue overlying the heart increases:

A. the percentage of transmitted photons increases.

B. the number of photoelectrons decreases.

C. the amount of characteristic x-rays decreases.

D. the ...

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