1) Atoms, Radiation, and Radioactivity
1.
The binding energy of the K-shell and L-shell in an atom is 33 keV and 5 keV, respectively. If a K-shell electron is captured by the nucleus and an L-shell electron jumps to the K-shell, the emitted characteristic x-ray carries energy of
A) 38 keV
B) 28 keV
C) 33 keV
D) 5 keV
Answer:
B) 28 keV
Feedback: The energy of the x-ray is equal to the difference in the binding energies between the L and K shells, that is, 33 – 5 = 28 keV.
2.If a radionuclide decays at 1% per day (λ = 0.01/day), how long will it take to decay to half of its original activity?
A) 100 days
B) 37 days
C) 50 days
D) 70 days
Answer:
D) 70 days
3.
100 mCi I-125 (T1/2 = 60 days) decays to 70 mCi in about _____ days.
A) 7
B) 15
C) 30
D) 60
Answer:
C) 30
4.
If the biological and physical half lives of a radionuclide are both 3 hours, the effective half life is ____ hours.
A) 0.5
B) 1
C) 1.5
D) 2
Answer:
C) 1.5
Feedback:
Teff = Tphy·Tbio /( Tphy+Tbio) = 3·3/(3+3) = 1.5 h.
5.
The characteristics that affect the binding energy of an orbital electron include
A) electron size
B) neutron number of the nucleus
C) orbit location (K shell, L shell, etc)
D) density of the material
Answer:
C) orbit location (K shell, L shell, etc)
Feedback: The binding energy of an electron is due to electric force between the electron and nucleus. Since the electric force depends on the distance between the electron and nucleus, the binding energy is affected by the location of orbits that determines the distance. Other factors are not related to electric force and binding energy.
6.
Which of the following occurs one month after a radium source (T1/2 = 1620 y) is sealed in a tube with its child radon (T1/2 = 4.8 d)?
A) Transient equilibrium
B) Secular equilibrium
C) Equilibrium has not yet occurred
D) Equilibrium will never reach
Answer:
B) Secular equilibrium
Feedback: Because the half life of the parent nucleus (1620 y) is much longer than that of the child nucleus (4.8 d).
7.
The maximum number of electrons in any inner shell is
A) always 8.
B) always 2.
C) 2n2, where n is the shell number.
D) none of the above.
Answer:
C) 2n2, where n is the shell number.
Feedback: The maximum number of electrons in an inner shell is determined by the Pauli Exclusion Principle.
8.Positron emission occurs in radionuclides that have excess of _____.A) electrons
B) positrons
C) neutrons
D) protons
Answer:
D) protons
Feedback: According to the electric charge conservation law, emission of a positron occurs only when a proton in the nucleus transforms to a neutron. The transformation is caused by excessive number of protons in the nucleus. Transformation of a neutron to a proton produces an electron, not a positron. There are no electrons or positrons in a nucleus. Only at the moment of nuclear decay, they are created and ejected instantaneously out of the nucleus.
9.
113Sn50 and 113In49 are
A) isotopes
B) isomers
C) isobars
D) none of above
Answer:
C) isobars
Feedback:
Because 113Sn50 and 113In49 have the same mass number 113.
10.
In β+ decay of potassium to 40Ar18, A and Z of potassium are
A) A = 40, Z = 18
B) A = 40, Z = 19
C) A = 41, Z = 18
D) A = 41, Z = 19
Answer:
B) A = 40, Z = 19
Feedback: In β+ decay, a proton is converted to a neutron. Therefore potassium has 19 protons (Z = 19). Since the total number of the nucleons is unchanged in the decay, the mass number A remains same (A = 40).
11.
The time required for the radioactivity to decay to 10% is between
A) 1 and 2 half lives.
B) 2 and 3 half lives.
C) 3 and 4 half lives.
D) 4 and 5 half lives.
Answer:
C) 3 and 4 half lives.
Feedback:
The activity decays to (1/2)3 = 1/8 in 3 half lives and to (1/2)4 = 1/16 in 4 half lives.
12.
If 30 mCi Tc-99m is to be administrated to a patient at 12 pm, how much Tc-99m should be prepared at 6 am in the morning?
A) 90 mCi
B) 60 mCi
C) 30 mCi
D) 15 mCi
Answer:
B) 60 mCi
Feedback: 60 mCi decays to 30 mCi from 6 am to 12 pm (a half live for Tc-99m).
13.A radium source (T1/2 = 1620 y) has been sealed in a tube with its child radon (T1/2 = 4.8 d) for three months. What is the ratio of the current radon activity versus that of 5 days later?
A) about half
B) about twice
C) about same
D) about one quarter
Answer:
C) about same
Feedback: Because radium and radon are in secular equilibrium, the radon activity is equal to the radium activity that is almost unchanged in several days due to its long half life.
14.
The largest volume within an atom is occupied by
A) nucleus
B) neutrinos
C) electrons
D) empty space
Answer:
D) empty space
Feedback: The nucleus and electrons are very small as compared to the atom. Neutrinos do not exist in the atom under normal circumstances.
15.
The current activity of an I-131 source (I-131 decay constant λ = 0.0036/hr) is 10 mCi. What is the activity the I-131 source had 4 days earlier?
A) 20 mCi
B) 14 mCi
C) 5 mCi
D) 7 mCi
Answer:
B) 14 mCi
Feedback:
Using A(0)=A(τ) eλτ = 4×24 = 96 hr, we obtain A(0) = 10 ⋅e0.0036⋅96 ≈ 14 mCi