Question 1

If a nucleus decays by gamma decay to a daughter nucleus, which of the following statements about this decay are correct? (There may be more than one correct choice.)

Accepted Answer

A)  The daughter nucleus has more protons than the original nucleus. 
B)  The daughter nucleus has more neutrons than the original nucleus. 
C)  The daughter nucleus has the same number of nucleons as the original nucleus. 
D)  The daughter nucleus has fewer protons than the original nucleus. 
E)  The daughter nucleus has fewer neutrons than the original nucleus. 
A)  The daughter nucleus has more protons than the original nucleus. 
B)  The daughter nucleus has more neutrons than the original nucleus. 
C)  The daughter nucleus has the same number of nucleons as the original nucleus. 
D)  The daughter nucleus has fewer protons than the original nucleus. 
E)  The daughter nucleus has fewer neutrons than the original nucleus.

Question 2

A radioactive atom has 98 protons and 249 nucleons. If it undergoes alpha decay, what are the number of protons and nucleons, respectively, in the daughter nucleus?

Accepted Answer

A)  100, 245 
B)  94, 247 
C)  96, 245 
D)  96, 247 
E)  100, 249 
A)  100, 245 
B)  94, 247 
C)  96, 245 
D)  96, 247 
E)  100, 249

Question 3

Consider the short-lived neutral isotope represented by   X. Which of the following statements about this isotope are correct? (There may be more than one correct choice.)

Accepted Answer

A)  The isotope has 25 nucleons. 
B)  The isotope has 25 protons. 
C)  The isotope has 25 neutrons. 
D)  The isotope has 15 orbital electrons. 
E)  The isotope has 15 protons.
F) The isotope has 10 neutrons. 
A)  The isotope has 25 nucleons. 
B)  The isotope has 25 protons. 
C)  The isotope has 25 neutrons. 
D)  The isotope has 15 orbital electrons. 
E)  The isotope has 15 protons.
F) The isotope has 10 neutrons.

Question 4

Going from medium mass nuclei to heavy nuclei, the average binding energy per nucleon

Accepted Answer

A)  decreases. 
B)  behaves randomly with no clear pattern. 
C)  does not change. 
D)  increases. 
E)  doubles. 
A)  decreases. 
B)  behaves randomly with no clear pattern. 
C)  does not change. 
D)  increases. 
E)  doubles.

Question 5

Plutonium-239 decays into uranium-235 plus an alpha particle. The energy released in the process is 5.24 MeV. Given the following mass values   He: 4.002603 u  
U: 235.043924 u
What is the mass of  
Pu in atomic mass units? (1 u = 931.494 MeV/c2)

Accepted Answer

A)  239.05215 u 
B)  239.02775 u 
C)  239.00189 u 
D)  238.99919 u 
E)  238.98884 u 
A)  239.05215 u 
B)  239.02775 u 
C)  239.00189 u 
D)  238.99919 u 
E)  238.98884 u

Question 6

Today, the uranium found on Earth contains 0.720% 235U (with a half-life of 0.700 billion years) and 99.28% 238U (with a half-life of 4.50 billion years). At a time 2.20 billion years ago, what percent of the uranium on Earth was 238U (assuming that no other uranium isotopes were present)?

Accepted Answer

A)  95.6% 
B)  2.18% 
C)  6.29% 
D)  8.68% 
E)  4.53% 
A)  95.6% 
B)  2.18% 
C)  6.29% 
D)  8.68% 
E)  4.53%

Question 7

A radioactive isotope decays by β- emission with a half-life of 1.0 min. During the first 1.0 min, a particular sample emits 1000 β- particles. During the next 1.0 min, the number of β- particles this sample will emit will be closest to

Accepted Answer

A)  250. 
B)  500. 
C)  1000. 
D)  1500. 
E)  2000. 
A)  250. 
B)  500. 
C)  1000. 
D)  1500. 
E)  2000.

Question 8

An ancient rock is found to contain 40Ar gas, indicating that 77% of the 40K in the rock has decayed since the rock solidified. Any argon would have boiled out of liquid rock. The half-life of 40K is 1.25 billion years. How long ago did the rock solidify?

Accepted Answer

A)  2.6 billion years 
B)  0.50 billion years 
C)  1.8 billion years 
D)  0.30 billion years 
A)  2.6 billion years 
B)  0.50 billion years 
C)  1.8 billion years 
D)  0.30 billion years

Question 9

Rutherfordium-261 has a half-life of 1.08 min. How long will it take for a sample of rutherfordium to lose one-third of its nuclei?

Accepted Answer

A)  1.02 min 
B)  1.62 min 
C)  0.632 min 
D)  2.70 min 
E)  3.24 min 
A)  1.02 min 
B)  1.62 min 
C)  0.632 min 
D)  2.70 min 
E)  3.24 min

Question 10

The decay rate of an isotope is initially R0, but after one half-life has gone by, the rate is R0/2. At the end of the NEXT half-life, what will the decay rate be?

Accepted Answer

A)  0 
B)  R0/16 
C)  R0/e 
D)  R0/4 
E)  R0/e2 
A)  0 
B)  R0/16 
C)  R0/e 
D)  R0/4 
E)  R0/e2

Question 11

An archaeologist finds the 14C in a sample of 3.10 g of material to be decaying at 107 counts per second. A modern 1.00-g sample of the same material decays at 151 counts per second. The half-life of 14C is 5730 y. How old is the sample?

Accepted Answer

A)  12,200 y 
B)  8460 y 
C)  25,100 y 
D)  12,600 y 
A)  12,200 y 
B)  8460 y 
C)  25,100 y 
D)  12,600 y

Question 12

Consider two different isotopes of the same neutral element. Which statements about these isotopes are true? (There may be more than one correct choice.)

Accepted Answer

A)  Both isotopes contain the same number of neutrons. 
B)  Both isotopes contain the same number of protons. 
C)  Both isotopes contain the same number of nucleons. 
D)  Both isotopes contain the same number of orbital electrons. 
E)  The sum of the protons and neutrons is the same for both isotopes. 
A)  Both isotopes contain the same number of neutrons. 
B)  Both isotopes contain the same number of protons. 
C)  Both isotopes contain the same number of nucleons. 
D)  Both isotopes contain the same number of orbital electrons. 
E)  The sum of the protons and neutrons is the same for both isotopes.

Question 13

An air sample is contaminated with 15O, which has a half-life of 2.03 min. One possible way to minimize its hazard is to pass it through a long pipe to allow it to decay inside the pipe until it can be safely released into the atmosphere. If the oxygen moves at a speed of 1.1 m/s in the pipe, how long must the pipe be for the sample to have decayed to 3.0% of its original activity just as it leaves the pipe?

Accepted Answer

A)  680 m 
B)  8.0 m 
C)  7.0 m 
D)  2.0 m 
A)  680 m 
B)  8.0 m 
C)  7.0 m 
D)  2.0 m

Question 14

The half-life of cobalt-60 is 5.3 years, while that of strontium-90 is 28 years. Suppose you have a sample of each, such that they initially contain equal numbers of atoms of these nuclides. How will the activities (number of decays per second) of the samples compare?

Accepted Answer

A)  The activity of the cobalt-60 sample will be greater. 
B)  The activities cannot be compared without more information. 
C)  The activities will be equal. 
D)  The activity of the strontium-90 sample will be greater. 
A)  The activity of the cobalt-60 sample will be greater. 
B)  The activities cannot be compared without more information. 
C)  The activities will be equal. 
D)  The activity of the strontium-90 sample will be greater.

Question 15

How many days are required for a radioactive sample, with a half-life of 5.7 d and an initial activity of 1.07 × 105 Bq, to decay to an activity of 100 Bq?

Accepted Answer

A)  57 d 
B)  46 d 
C)  68 d 
D)  39 d 
A)  57 d 
B)  46 d 
C)  68 d 
D)  39 d

Question 16

The stability of   Fe with respect to alpha, β+, and β- decay is to be determined. Do not consider the possibility of decay by electron capture. The following atomic masses are known:  
He: 4.002603 u  
Cr: 51.944768 u  
Mn: 55.938907 u  
Fe: 55.934939 u  
Co: 55.939841 u
The  
Fe nuclide is

Accepted Answer

A)  not subject to alpha, β+, or β- decay. 
B)  subject to alpha decay only. 
C)  subject to β+decay only. 
D)  subject to β- decay only. 
E)  subject to β+ or β- decay, but not to alpha decay. 
A)  not subject to alpha, β+, or β- decay. 
B)  subject to alpha decay only. 
C)  subject to β+decay only. 
D)  subject to β- decay only. 
E)  subject to β+ or β- decay, but not to alpha decay.

Question 17

A 70-kg laboratory technician absorbs 2.9 mJ of 0.50-MeV gamma rays in a workday. How many gamma-ray photons does the technician absorb in a workday?

Accepted Answer

A)  3.6 × 1010 
B)  3.6 × 109 
C)  3.6 × 108 
D)  1.0 × 109 
E)  1.0 × 108 
A)  3.6 × 1010 
B)  3.6 × 109 
C)  3.6 × 108 
D)  1.0 × 109 
E)  1.0 × 108

Question 18

The stability of   C with respect to alpha, β+, and β- decay is to be determined. Do not consider the possibility of decay by electron capture. The following atomic masses are known:  
He: 4.002603 u  
Be: 7.016928 u  
B: 11.009305 u  
C: 11.011433 u  
N: 11.026742 u
The  
C nuclide is

Accepted Answer

A)  not subject to alpha, β+, or β- decay. 
B)  subject to alpha decay only. 
C)  subject to β+ decay only. 
D)  subject to β- decay only. 
E)  subject to β+ or β- decay, but not to alpha decay. 
A)  not subject to alpha, β+, or β- decay. 
B)  subject to alpha decay only. 
C)  subject to β+ decay only. 
D)  subject to β- decay only. 
E)  subject to β+ or β- decay, but not to alpha decay.

Question 19

Radium-226 decays into radon-222 plus an alpha particle. How much energy is released in this process? 1 u = 931.494 MeV/c2, and the relevant mass values are   He: 4.002603 u  
Rn: 222.017570 u  
Ra: 226.025402 u

Accepted Answer

A)  4.24 MeV 
B)  3.76 MeV 
C)  4.87 MeV 
D)  5.05 MeV 
E)  5.39 MeV 
A)  4.24 MeV 
B)  3.76 MeV 
C)  4.87 MeV 
D)  5.05 MeV 
E)  5.39 MeV

Question 20

Which of the following statements about β+ decay are correct? (There may be more than one correct choice.) During β+ decay

Accepted Answer

A)  an orbital electron is captured by the nucleus. 
B)  a proton is emitted from the nucleus. 
C)  a neutron in the nucleus decays to a proton and an electron. 
D)  a proton in the nucleus decays to a positron and a neutron. 
E)  the atomic number Z of the isotope increases by one unit but the atomic weight A remains unchanged. 
A)  an orbital electron is captured by the nucleus. 
B)  a proton is emitted from the nucleus. 
C)  a neutron in the nucleus decays to a proton and an electron. 
D)  a proton in the nucleus decays to a positron and a neutron. 
E)  the atomic number Z of the isotope increases by one unit but the atomic weight A remains unchanged.

Exam 42: Nuclear Physics

If a nucleus decays by gamma decay to a daughter nucleus, which of the following statements about this decay are correct? (There may be more than one correct choice.)

A radioactive atom has 98 protons and 249 nucleons. If it undergoes alpha decay, what are the number of protons and nucleons, respectively, in the daughter nucleus?

Consider the short-lived neutral isotope represented by X. Which of the following statements about this isotope are correct? (There may be more than one correct choice.)

Going from medium mass nuclei to heavy nuclei, the average binding energy per nucleon

Plutonium-239 decays into uranium-235 plus an alpha particle. The energy released in the process is 5.24 MeV. Given the following mass values He: 4.002603 u U: 235.043924 u What is the mass of Pu in atomic mass units? (1 u = 931.494 MeV/c2)

Today, the uranium found on Earth contains 0.720% 235U (with a half-life of 0.700 billion years) and 99.28% 238U (with a half-life of 4.50 billion years). At a time 2.20 billion years ago, what percent of the uranium on Earth was 238U (assuming that no other uranium isotopes were present)?

A radioactive isotope decays by β- emission with a half-life of 1.0 min. During the first 1.0 min, a particular sample emits 1000 β- particles. During the next 1.0 min, the number of β- particles this sample will emit will be closest to

An ancient rock is found to contain 40Ar gas, indicating that 77% of the 40K in the rock has decayed since the rock solidified. Any argon would have boiled out of liquid rock. The half-life of 40K is 1.25 billion years. How long ago did the rock solidify?

Rutherfordium-261 has a half-life of 1.08 min. How long will it take for a sample of rutherfordium to lose one-third of its nuclei?

The decay rate of an isotope is initially R0, but after one half-life has gone by, the rate is R0/2. At the end of the NEXT half-life, what will the decay rate be?

An archaeologist finds the 14C in a sample of 3.10 g of material to be decaying at 107 counts per second. A modern 1.00-g sample of the same material decays at 151 counts per second. The half-life of 14C is 5730 y. How old is the sample?

Consider two different isotopes of the same neutral element. Which statements about these isotopes are true? (There may be more than one correct choice.)

The half-life of cobalt-60 is 5.3 years, while that of strontium-90 is 28 years. Suppose you have a sample of each, such that they initially contain equal numbers of atoms of these nuclides. How will the activities (number of decays per second) of the samples compare?

How many days are required for a radioactive sample, with a half-life of 5.7 d and an initial activity of 1.07 × 105 Bq, to decay to an activity of 100 Bq?

The stability of Fe with respect to alpha, β+, and β- decay is to be determined. Do not consider the possibility of decay by electron capture. The following atomic masses are known: He: 4.002603 u Cr: 51.944768 u Mn: 55.938907 u Fe: 55.934939 u Co: 55.939841 u The Fe nuclide is

A 70-kg laboratory technician absorbs 2.9 mJ of 0.50-MeV gamma rays in a workday. How many gamma-ray photons does the technician absorb in a workday?

The stability of C with respect to alpha, β+, and β- decay is to be determined. Do not consider the possibility of decay by electron capture. The following atomic masses are known: He: 4.002603 u Be: 7.016928 u B: 11.009305 u C: 11.011433 u N: 11.026742 u The C nuclide is

Radium-226 decays into radon-222 plus an alpha particle. How much energy is released in this process? 1 u = 931.494 MeV/c2, and the relevant mass values are He: 4.002603 u Rn: 222.017570 u Ra: 226.025402 u

Which of the following statements about β+ decay are correct? (There may be more than one correct choice.) During β+ decay

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Plutonium-239 decays into uranium-235 plus an alpha particle. The energy released in the process is 5.24 MeV. Given the following mass values He: 4.002603 u U: 235.043924 u What is the mass of Pu in atomic mass units? (1 u = 931.494 MeV/c²)

A radioactive isotope decays by β^- emission with a half-life of 1.0 min. During the first 1.0 min, a particular sample emits 1000 β^- particles. During the next 1.0 min, the number of β^- particles this sample will emit will be closest to

An ancient rock is found to contain ⁴⁰Ar gas, indicating that 77% of the ⁴⁰K in the rock has decayed since the rock solidified. Any argon would have boiled out of liquid rock. The half-life of ⁴⁰K is 1.25 billion years. How long ago did the rock solidify?

The decay rate of an isotope is initially R₀, but after one half-life has gone by, the rate is R₀/2. At the end of the NEXT half-life, what will the decay rate be?

An archaeologist finds the ¹⁴C in a sample of 3.10 g of material to be decaying at 107 counts per second. A modern 1.00-g sample of the same material decays at 151 counts per second. The half-life of ¹⁴C is 5730 y. How old is the sample?

How many days are required for a radioactive sample, with a half-life of 5.7 d and an initial activity of 1.07 × 10⁵ Bq, to decay to an activity of 100 Bq?

The stability of Fe with respect to alpha, β⁺, and β^-decay is to be determined. Do not consider the possibility of decay by electron capture. The following atomic masses are known: He: 4.002603 u Cr: 51.944768 u Mn: 55.938907 u Fe: 55.934939 u Co: 55.939841 u The Fe nuclide is

The stability of C with respect to alpha, β⁺, and β^-decay is to be determined. Do not consider the possibility of decay by electron capture. The following atomic masses are known: He: 4.002603 u Be: 7.016928 u B: 11.009305 u C: 11.011433 u N: 11.026742 u The C nuclide is

Radium-226 decays into radon-222 plus an alpha particle. How much energy is released in this process? 1 u = 931.494 MeV/c², and the relevant mass values are He: 4.002603 u Rn: 222.017570 u Ra: 226.025402 u

Which of the following statements about β⁺ decay are correct? (There may be more than one correct choice.) During β⁺ decay