Radiation Physics Board Practice Questions
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524 Terms
A student asks what the atomic number Z counts. What is the answer?
The number of protons in the nucleus
What does the mass number A represent?
Protons plus neutrons
A nuclide has A = 131 and Z = 53. How is its neutron number found?
N = A − Z
Which change turns an atom into a different element?
A change in the number of protons
What are protons and neutrons together called?
Nucleons
A technologist reads the notation ¹²³₅₃I. What do the superscript and subscript show?
Mass number (top) and atomic number (bottom)
Which electron shell has the highest binding energy?
The K shell
Why is electron binding energy written as a negative number?
Energy must be supplied to remove the electron
An atom loses one electron. What does it become?
A positive ion
What is the removal of an orbital electron from an atom called?
Ionization
How do the masses of protons and neutrons compare with the electron?
About 2,000 times heavier than an electron
About how much smaller is the nucleus than the whole atom?
About 10,000 times smaller (10⁻¹² vs 10⁻⁸ cm)
Which particle carries no electrical charge?
Neutron
Up to about Z = 20, what proton-to-neutron balance do stable nuclei have?
About equal numbers of protons and neutrons
Above about Z = 20, what do stable nuclei need?
More neutrons than protons
Why do heavier nuclei need extra neutrons to stay stable?
Neutrons add nuclear binding without adding proton repulsion
Which quantity best predicts stability when comparing isotopes of one element?
Binding energy per nucleon
Where does nuclear binding energy come from?
The mass defect converted to energy (E = mc²)
C-12 and C-13 are stable. Adding one more neutron gives C-14. What is C-14?
Radioactive (too many neutrons)
A nucleus has too many neutrons. Which decay is expected?
Beta-minus decay
A nucleus has too many protons. Which decay modes are expected?
Positron decay or electron capture
A very heavy nucleus (such as Ra-223) is unstable. Which decay mode is typical?
Alpha decay
A nucleus is in an excited metastable state. How does it usually release its extra energy?
Gamma emission (isomeric transition)
What is the rest-mass energy of an electron?
0.511 MeV
Why are PET annihilation photons always 511 keV?
Each equals the rest-mass energy of an electron or positron
In E = mc², what is c?
The speed of light (3 × 10⁸ m/s)
About what fraction of an atom's mass is in the nucleus?
More than 99%
A student says the atom is 'mostly solid'. What is the best correction?
The atom is mostly empty space around a tiny nucleus
A technologist reviews ¹³¹₅₃I on a package label. How many protons does it have?
53
A student says two atoms with 53 protons can be different elements. What is the correct reply?
No; 53 protons always means iodine
A student asks why a positron emitter must have at least 1.022 MeV available. What is the answer?
Twice the 0.511 MeV electron rest mass is needed
A technologist sees the notation Tc-99. What does the 99 represent?
The mass number (protons + neutrons)
A nucleus contains 43 protons and 56 neutrons. What is its mass number?
99
A physicist describes an atom gaining an extra electron. What does it become?
A negative ion
A physicist explains the 'mass defect.' What is it?
The mass lost when nucleons bind, released as binding energy
I-123 and I-131 are both iodine. What relationship do they share?
Isotopes (same Z, different N)
Mo-99 and Tc-99 both have A = 99 but different Z. What are they?
Isobars
Tc-99m and Tc-99 have the same Z and A but different energy states. What are they?
Isomers
Two nuclides have the same number of neutrons but different numbers of protons. What are they?
Isotones
A student uses a letter trick for the iso words. Which pairing is correct?
isotoNe = same Neutrons
What does the 'm' in Tc-99m stand for?
Metastable
Tc-99m decays to Tc-99. Which decay process is this?
Isomeric transition
Which pair are isotopes?
C-12 and C-14
Which nuclide is an isotone of Tc-99 (Z = 43, N = 56)?
Mo-98
In beta-minus decay, the parent and daughter keep the same A. What are parent and daughter?
Isobars
Besides gamma emission, how else can a metastable nucleus such as Tc-99m de-excite?
Internal conversion
Positron decay and electron capture each turn a proton into a neutron. Are parent and daughter isotopes?
No; Z changes, so they are isobars
Alpha decay changes Z by −2 and A by −4. How are parent and daughter related?
They are different elements and not isobars
A generator contains Mo-99 that decays to Tc-99m. Are Mo-99 and Tc-99m isotopes?
No; they are different elements with the same mass number
A student must identify the pair with the same neutron number. Which pair is it?
C-14 and O-16
A student uses the letter trick for isobar. Which number stays the same?
Mass number (A)
A pharmacist describes In-111 and In-113m as having the same Z but different A. What are they?
Isotopes
A technologist sets up a Tc-99m scan. What are its physical half-life and main photon energy?
6.02 hours and 140 keV
A Mo-99/Tc-99m generator arrives Monday. Its weekly yield depends on Mo-99's half-life. What is it?
66 hours
Which photon energies are associated with the Mo-99 parent?
740 and 780 keV
A patient is scheduled for an I-123 thyroid scan. What are its half-life and photon energy?
13.2 hours and 159 keV
By which decay mode does I-123 decay?
Electron capture
A patient receives I-131 therapy. What are its half-life and main gamma energy?
8.02 days and 364 keV
By which decay mode does I-131 decay?
Beta-minus decay
A patient is scheduled for a Ga-67 infection scan. What is its half-life?
About 78 hours
Which photon energies does Ga-67 emit?
93, 184 and 296–300 keV
A patient receives In-111 labeled WBCs. What are the half-life and photon energies?
2.8 days, 171 and 245 keV
A patient is scheduled for Tl-201 cardiac imaging. What is its half-life?
About 73 hours
Which photons are mainly used to image Tl-201?
Mercury characteristic x-rays at 69–83 keV
By which decay mode does Tl-201 decay?
Electron capture
A patient is scheduled for a Xe-133 ventilation study. What are its half-life and photon energy?
About 5.3 days and 81 keV
By which decay mode does Xe-133 decay?
Beta-minus decay
A patient receives F-18 FDG. What is the physical half-life of F-18?
About 110 minutes
A cardiac PET team must start imaging within minutes of a Rb-82 infusion. What half-life drives this?
About 75–76 seconds
What is the half-life of Sr-82, the parent in the Rb-82 generator?
About 25–25.5 days
A Ga-68 DOTATATE dose is labeled at 9:00, and the technologist must inject promptly. What half-life is the reason?
About 68 minutes
A patient is scheduled for Y-90 radioembolization (SIRT). What is the half-life of Y-90?
About 64 hours
How is a pure beta emitter like Y-90 imaged after therapy?
Through bremsstrahlung x-rays (or a PET surrogate)
A patient receives Lu-177 therapy. What are its half-life and usable gamma?
About 6.7 days with a 208 keV gamma
A bone-pain patient receives Sr-89 and asks how long it stays radioactive. What is its physical half-life?
About 50.5 days
What kind of emitter is Sr-89?
A pure beta emitter
A patient with prostate cancer bone metastases receives Ra-223. What does it emit?
Alpha particles
A Ra-223 dose is shipped from the vendor several days before treatment. What half-life does the shipping schedule depend on?
About 11.4 days
What are the half-life and photon energy of Co-57, used for camera floods?
About 271 days and 122 keV
The hot lab's dose calibrator accuracy source is Cs-137. What are its half-life and photon energy?
About 30 years and 662 keV
Which decay mode do PET radionuclides such as F-18, Ga-68 and Rb-82 use?
Positron (beta-plus) emission
A question pairs 135/167 keV with I-123. What is the trap?
Those energies belong to Tl-201; I-123 is 159 keV
Which group decays by electron capture?
I-123, Ga-67, In-111 and Tl-201
Which group decays by beta-minus?
I-131, Y-90, Lu-177 and Sr-89
A technologist chooses an energy window and collimator. Which property guides that choice?
The principal photon energy of the isotope
Which isotope has the shortest physical half-life?
Rb-82
Which isotope has the longest physical half-life of these?
Sr-89
Why is Tc-99m an ideal imaging isotope?
A single 140 keV gamma, minimal particulate emission and a 6-hour half-life
A technologist sets the camera window for I-131 imaging. What photopeak is used?
364 keV
An In-111 WBC study is acquired with only a 171 keV window. What is the effect?
Fewer counts, because the 245 keV photons are not collected
Post-therapy SPECT is ordered to confirm Lu-177 PSMA uptake. Which photopeak window is used?
208 keV
A Co-57 flood source (T½ about 271 days) is 1 year old. About what fraction of its original activity remains?
About 40%
A Co-57 flood sheet (T½ about 271 days) is 2 years old. What should the technologist expect?
Longer flood times; about 15% of the original activity remains
A department buys a Cs-137 reference source. Why does it need little decay correction from month to month?
Its half-life is about 30 years
A board question pairs 245 keV with Ga-67. What is the error?
245 keV belongs to In-111; Ga-67 is 93/184/296–300 keV
A technologist chooses between I-123 and I-131 for a diagnostic thyroid scan with low dose. Which property favors I-123?
No beta emission and a shorter half-life
How can Y-90 microsphere distribution be imaged with PET?
Through Y-90's very small positron (internal pair production) branch
Why is staff exposure from a Ra-223 therapy patient low?
Alpha range is micrometers, and the administered activity is very small
A camera protocol lists windows at 93, 184 and 296–300 keV. Which isotope is the study using?
Ga-67
A lung ventilation study uses a gas imaged at 81 keV. Which isotope is it?
Xe-133