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Physics

John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler

Chapter 31

Nuclear Physics and Radioactivity - all with Video Answers

Educators


Chapter Questions

08:21

Problem 1

find (a) the net electrical charge of the nucleus, (b) the number of neutrons, (c) the number of nucleons, (d) the approximate radius of the nucleus, and (e) the nuclear density.

Yaqub Khan
Yaqub Khan
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00:53

Problem 2

A nucleus contains 18 protons and 22 neutrons. What is the radius of this nucleus?

Mike Gaerlan
Mike Gaerlan
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04:29

Problem 3

In each of the following cases, what element does the symbol X represent and how many neutrons are in the nucleus? Use the periodic table on the inside of the back cover as needed. (a) ${ }_{78}^{195} \mathrm{X}$ (b) ${ }_{16}^{32} \mathrm{X}$ (c) ${ }_{29}^{63} \mathrm{X}$ (d) ${ }_{5}^{11} \mathrm{X}$ (e) ${ }_{94}^{239} \mathrm{X}$

Yaqub Khan
Yaqub Khan
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01:36

Problem 4

By what factor does the nucleon number of a nucleus have to increase in order for the nuclear radius to double?

Mike Gaerlan
Mike Gaerlan
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03:03

Problem 5

In electrically neutral atoms, how many (a) protons are in the uranium ${}_{92}^{238} \mathrm{U}$ nucleus, (b) neutrons are in the mercury ${ }_{80}^{202} \mathrm{Hg}$ nucleus, and (c) electrons are in orbit about the niobium ${ }_{41}^{93} \mathrm{Nb}$ nucleus?

Yaqub Khan
Yaqub Khan
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00:58

Problem 6

The largest stable nucleus has a nucleon number of $209,$ and the smallest has a nucleon number of 1. If each nucleus is assumed to be a sphere, what is the ratio (largest/smallest) of the surface areas of these spheres?

Mike Gaerlan
Mike Gaerlan
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04:30

Problem 7

The ratio $r_{\mathrm{X}} / r_{\mathrm{T}}$ of the radius of an unknown nucleus $\frac{A}{Z} \mathrm{X}$ to the radius of a tritium nucleus ${ }_{1}^{3} \mathrm{T}$ is $\frac{r_{\mathrm{x}}}{r_{\mathrm{T}}}=1.10 .$ Both nuclei contain the same number of neutrons. Identify the unknown nucleus in the form $\frac{A}{Z} \mathrm{X}$. Use the periodic table on the inside of the back cover as needed.

Yaqub Khan
Yaqub Khan
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05:41

Problem 8

An unknown nucleus contains 70 neutrons and has twice the
volume of the nickel ${ }_{28}^{60} \mathrm{Ni}$ nucleus. Identify the unknown nucleus in the $$
\text { form } \frac{A}{Z} X
$$. Use the periodic table on the inside of the back cover as needed.

Yaqub Khan
Yaqub Khan
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01:54

Problem 9

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Ajay Singhal
Ajay Singhal
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01:54

Problem 10

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Ajay Singhal
Ajay Singhal
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07:15

Problem 11

Find the binding energy (in $\mathrm{MeV}$ ) for lithium ${ }_{3}^{7} \mathrm{Li}$ (atomic mass $=$ $7.016003 \mathrm{u})$

Yaqub Khan
Yaqub Khan
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01:27

Problem 12

The binding energy of a nucleus is 225.0 MeV. What is the mass defect of the nucleus in atomic mass units?

Mike Gaerlan
Mike Gaerlan
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03:57

Problem 13

Determine the mass defect (in atomic mass units) for (a) helium ${ }_{2}^{3} \mathrm{He},$ which has an atomic mass of $3.016030 \mathrm{u},$ and $(\mathrm{b})$ the isotope of hydrogen known as tritium ${ }_{1}^{3} \mathrm{T},$ which has an atomic mass of $3.016050 \mathrm{u}$. (c) On the basis of your answers to parts (a) and (b), state which nucleus requires more energy to disassemble it into its separate and stationary constituent nucleons. Give your reasoning.

Mike Gaerlan
Mike Gaerlan
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01:22

Problem 14

A 245-kg boulder is dropped into a mine shaft that is $3.0 \times 10^{3} \mathrm{m}$ deep. During the boulder's fall, the system consisting of the earth and the boulder loses a certain amount of gravitational potential energy. It would take an equal amount of energy to "free" the boulder from the shaft by raising it back to the top, so this can be considered the system's binding energy.
(a) Determine the binding energy (in joules) of the earth-boulder system.
(b) How much mass does the earth-boulder system lose when the boulder falls to the bottom of the shaft?

Mike Gaerlan
Mike Gaerlan
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06:29

Problem 15

For lead ${ }_{82}^{206} \mathrm{Pb}$ (atomic mass $=205.974440 \mathrm{u}$ ) obtain (a) the mass defect in atomic mass units, (b) the binding energy (in MeV), and (c) the binding energy per nucleon (in MeV/nucleon).

Yaqub Khan
Yaqub Khan
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06:43

Problem 16

(a) Energy is required to separate a nucleus into its constituent nucleons, as Interactive Figure 31.3 indicates; this energy is the total binding energy of the nucleus. In a similar way one can speak of the energy that binds a single nucleon to the remainder of the nucleus. For example, separating nitrogen ${ }^{14}{ }_{7} \mathrm{N}$ into nitrogen ${ }^{13}{ }_{7} \mathrm{N}$ and a neutron takes energy equal to the binding energy of the neutron, as shown below: Find the energy (in MeV) that binds the neutron to the ${ }^{14}, \mathrm{N}$ nucleus by considering the mass of ${ }_{7}^{13} \mathrm{N}$ (atomic mass $=13.005738 \mathrm{u}$ ) and the mass of ${ }_{0}^{1}$ n (atomic mass $=1.008665 \mathrm{u}$ ), as compared to the mass of ${ }_{7}^{14} \mathrm{N}$ (atomic mass $=$ $14.003074 \mathrm{u}) .$ (b) Similarly, one can speak of the energy that binds a single proton to the ${ }^{14}{ }_{7} \mathrm{N}$ nucleus: Following the procedure outlined in part (a), determine the energy (in MeV) that binds the proton (atomic mass $=1.007825 \mathrm{u}$ ) to the ${ }_{7}^{14} \mathrm{N}$ nucleus. The atomic mass of carbon ${ }_{6}^{13} \mathrm{C}$ is $13.003355 \mathrm{u}$. (c) Which nucleon is more tightly bound, the neutron or the proton?

Declan Nell
Declan Nell
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02:16

Problem 17

Two isotopes of a certain element have binding energies that differ by 5.03 MeV. The isotope with the larger binding energy contains one more neutron than the other isotope. Find the difference in atomic mass between the two isotopes.

Prashant Bana
Prashant Bana
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06:16

Problem 18

A copper penny has a mass of $3.0 \mathrm{g}$. Determine the energy $(\mathrm{in}$ MeV) that would be required to break all the copper nuclei into their constituent protons and neutrons. Ignore the energy that binds the electrons to the nucleus and the energy that binds one atom to another in the structure of the metal. For simplicity, assume that all the copper nuclei are ${ }_{29}^{63} \mathrm{Cu}$ (atomic mass $=62.939598 \mathrm{u})$.

Declan Nell
Declan Nell
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03:05

Problem 19

Essm Write the $\beta^{+}$ decay process for each of the following nuclei, being careful to include $Z$ and $A$ and the proper chemical symbol for each daughter nucleus: (a) ${ }_{9}^{18} \mathrm{F}$ (b) ${ }_{8}^{15} \mathrm{O}$

Yaqub Khan
Yaqub Khan
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00:40

Problem 20

Write the $\beta^{-}$ decay process for carbon ${ }_{6}^{14} \mathrm{C},$ including the chemical symbols as well as the values of $Z$ and $A$ for the parent and daughter nuclei and the $\beta^{-}$ particle.

Mike Gaerlan
Mike Gaerlan
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04:31

Problem 21

$$
\text { Osmium }{ }_{76 }^{191} \text { Os (atomic mass }=190.960920 \mathrm{u} \text { ) is converted into }
$$ iridium ${ }_{77}^{191} $ Ir (atomic mass $=190.960584 \mathrm{u}$ ) via $\beta$ -decay. What is the energy (in MeV) released in this process?

Yaqub Khan
Yaqub Khan
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03:27

Problem 22

$$\text { Find the energy that is released when a nucleus of lead }{ }_{ 82}^{211} \text {} \mathrm{Pb} \text { (atomic mass } $$$$ \begin{aligned} &\text { }=210.988735 \text { u) undergoes } \beta^{-} \text {decay to become bismuth }{ }_{83}^{211} \mathrm{Bi} \text { (atomic mass }\\ &\text { }=210.987255 \mathrm{u}). \end{aligned}$$

Yaqub Khan
Yaqub Khan
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03:47

Problem 23

$$
\text { Find the energy (in MeV) released when } \alpha \text { decay converts radium }
$$ $\frac{226}{88} \mathrm{Ra}$ (atomic mass $\left.=226.02540 \mathrm{u}\right)$ into radon ${ }_{86}^{222} \mathrm{Rn}$ (atomic mass $=$ $222.01757 \mathrm{u}) .$ The atomic mass of an $\alpha$ particle is $4.002603 \mathrm{u}$.

Yaqub Khan
Yaqub Khan
Numerade Educator
01:05

Problem 24

$$
\text { Lead }{ }_{82}^{207} \mathrm{Pb} \text { is a stable daughter nucleus that can result from either }
$$ an $\alpha$ decay or a $\beta^{-}$ decay. Write the decay processes, including the chemical symbols and values for $Z$ and $A$ of the parent nuclei, for (a) the $\alpha$ decay and
(b) the $\beta^{-}$ decay.

Mike Gaerlan
Mike Gaerlan
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04:24

Problem 25

$$
\text { In the form } \frac{A}{Z} X, \text { identify the daughter nucleus that results when }
$$ (a) plutonium ${ }_{94}^{242}$ Pu undergoes $\alpha$ decay, (b) sodium $_{11}^{24}$ Na undergoes $\beta^{-}$ decay, and (c) nitrogen ${ }_{7}^{13} \mathrm{N}$ undergoes $\beta^{+}$ decay.

Yaqub Khan
Yaqub Khan
Numerade Educator
03:07

Problem 26

$$
\text { When uranium }{ }_{92}^{235} \mathrm{U} \text { decays, it emits (among other things) a } \gamma
$$ ray that has a wavelength of $1.14 \times 10^{-11} \mathrm{m} .$ Determine the energy (in $\mathrm{MeV}$ ) of this $\gamma$ ray.

Yaqub Khan
Yaqub Khan
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04:38

Problem 27

$$
\text { Polonium }{ }_{84}^{210} \mathrm{Po} \text { (atomic mass } \left.=209.982848 \mathrm{u}\right) \text { undergoes }
$$ $\alpha$ decay. Assuming that all the released energy is in the form of kinetic energy of the $\alpha$ particle (atomic mass $=4.002603 \mathrm{u}$ ) and ignoring the recoil of the daughter nucleus (lead $\left.{ }_{82}^{206} \mathrm{Pb}, 205.974440 \mathrm{u}\right),$ find the speed of the $\alpha$ particle. Ignore relativistic effects.

Yaqub Khan
Yaqub Khan
Numerade Educator
07:39

Problem 28

$$
\text { Radon }{ }_{86}^{220} \mathrm{Rn} \text { produces a daughter nucleus that is radioactive. The }
$$ daughter, in turn, produces its own radioactive daughter, and so on. This process continues until lead ${ }_{\mathrm{} 82}^{208} \mathrm{Pb}$ is reached. What are the total number $N_{a}$ of $\alpha$ particles and the total number $N_{\beta}$ of $\beta^{-}$ particles that are generated in this series of radioactive decays?

Yaqub Khan
Yaqub Khan
Numerade Educator
06:47

Problem 29

$$
\text { Review Conceptual Example } 5 \text { as background for this problem. The }
$$ $a$ decay of uranium ${ }_{92}^{238} \mathrm{U}$ produces thorium ${ }_{90}^{234} \mathrm{Th}$ (atomic mass $\left.=234.0436 \mathrm{u}\right)$ In Example $4,$ the energy released in this decay is determined to be 4.3 MeV. Determine how much of this energy is carried away by the recoiling ${ }_{90}^{234} \mathrm{Th}$ daughter nucleus and how much by the $\alpha$ particle (atomic mass $=$ $4.002603 \mathrm{u}) .$ Assume that the energy of each particle is kinetic energy, and ignore the small amount of energy carried away by the $\gamma$ ray that is also emitted. In addition, ignore relativistic effects.

Declan Nell
Declan Nell
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01:56

Problem 30

$$
\text { An isotope of beryllium (atomic mass }=7.017 \text { u) emits a } \gamma \text { , }
$$ ray and recoils with a speed of $2.19 \times 10^{4} \mathrm{m} / \mathrm{s} .$ Assuming that the beryllium nucleus is stationary to begin with, find the wavelength of the $\gamma$ ray.

Dading Chen
Dading Chen
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04:49

Problem 31

$$
\text { Find the energy (in MeV) released when } \beta^{+} \text {decay converts }
$$ sodium ${ }_{11}^{22} \mathrm{Na}$ (atomic mass $=21.994434 \mathrm{u}$ ) into neon $\frac{22}{10} \mathrm{Ne}$ (atomic mass $=$ $21.991383 \mathrm{u}) .$ Notice that the atomic mass for $\frac{22}{11} \mathrm{Na}$ includes the mass of 11 electrons, whereas the atomic mass for $\frac{22}{10} \mathrm{Ne}$ includes the mass of only 10 electrons.

Yaqub Khan
Yaqub Khan
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02:33

Problem 32

In 9.0 days the number of radioactive nuclei decreases to one-eighth the number present initially. What is the half-life (in days) of the material?

Mike Gaerlan
Mike Gaerlan
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01:54

Problem 33

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Ajay Singhal
Ajay Singhal
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01:16

Problem 34

The ${ }_{15}^{32} \mathrm{P}$ isotope of phosphorus has a half-life of 14.28 days. What is its decay constant in units of $s^{-1} ?$

Yaqub Khan
Yaqub Khan
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03:51

Problem 35

$$
\text { Strontium }{ }_{38}^{90} \mathrm{Sr} \text { has a half-life of } 29.1 \text { yr. It is chemically similar}
$$ to calcium, enters the body through the food chain, and collects in the bones. Consequently, ${ }_{38}^{90} \mathrm{Sr}$ is a particularly serious health hazard. How long (in years) will it take for $99.9900 \%$ of the ${ }_{38}^{90} \mathrm{Sr}$ released in a nuclear reactor accident to disappear?

Yaqub Khan
Yaqub Khan
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04:23

Problem 36

$$
\text { Two radioactive waste products from nuclear reactors are strontium }
$$${ }_{38}^{90} \mathrm{Sr}\left(T_{1 / 2}=29.1 \mathrm{yr}\right)$ and cesium ${ }_{55}^{134} \mathrm{Cs}\left(T_{1 / 2}=2.06 \mathrm{yr}\right) .$ These two species
are present initially in a ratio of $N_{0.S\mathrm{r}} / N_{0 . C \mathrm{s}}=7.80 \times 10^{-3} .$ What is the ratio $N_{\mathrm{Sr}} / N_{\mathrm{C}}$ fifteen years later?

Yaqub Khan
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01:54

Problem 37

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Ajay Singhal
Ajay Singhal
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03:34

Problem 38

Iodine ${ }_{53}^{131} \mathrm{I}$ is used in diagnostic and therapeutic techniques in the treatment of thyroid disorders. This isotope has a half-life of 8.04 days. What percentage of an initial sample of ${ }_{53}^{131}$I remains after 30.0 days?

Yaqub Khan
Yaqub Khan
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01:43

Problem 39

The number of radioactive nuclei present at the start of an experiment is $4.60 \times 10^{15} .$ The number present twenty days later is $8.14 \times 10^{14}$ What is the half-life (in days) of the nuclei?

Mike Gaerlan
Mike Gaerlan
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01:54

Problem 40

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Ajay Singhal
Ajay Singhal
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05:28

Problem 41

A device used in radiation therapy for cancer contains $0.50 \mathrm{g}$ of cobalt ${ }_{27}^{60} \mathrm{Co}(59.933819 \mathrm{u}) .$ The half-life of ${ }_{27}^{60} \mathrm{Co}$ is $5.27 \mathrm{yr} .$ Determine the activity of the radioactive material.

Yaqub Khan
Yaqub Khan
Numerade Educator
07:38

Problem 42

$$
\text { A one-gram sample of radium }{ }_{ 88}^{224} \mathrm{Ra} \text { (atomic mass }=224.020186 \mathrm{u} \text {, }
$$ $T_{1 / 2}=3.66$ days $)$ contains $2.69 \times 10^{21}$ nuclei and undergoes $a$ decay to produce radon ${ }_{86}^{220} \mathrm{Rn}$ (atomic mass $=220.011368 \mathrm{u}$ ). The atomic mass of an $\alpha$ particle is $4.002603 \mathrm{u}$. The latent heat of fusion for water is $33.5 \times 10^{4} \mathrm{J} / \mathrm{kg}$. With the energy released in 3.66 days, how many kilograms of ice could be melted at $0^{\circ} \mathrm{C} ?$

Declan Nell
Declan Nell
Numerade Educator
05:48

Problem 43

$$
\text { The isotope }{ }_{79}^{198} \mathrm{Au} \text { (atomic mass }=197.968 \mathrm{u} \text { ) of gold has }
$$ a half-life of 2.69 days and is used in cancer therapy. What mass (in grams) of this isotope is required to produce an activity of $315 \mathrm { }^{\circ}{C} ?$

Yaqub Khan
Yaqub Khan
Numerade Educator
03:02

Problem 44

$$
\text { Outside the nucleus, the neutron itself is radioactive and decays }
$$ into a proton, an electron, and an antineutrino. The half-life of a neutron (mass $=1.675 \times 10^{-27} \mathrm{kg}$ ) outside the nucleus is 10.4 min. On average, over what distance (in meters) would a beam of 5.00 -eV neutrons travel before the number of neutrons decreased to $75.0 \%$ of its initial value?

Mike Gaerlan
Mike Gaerlan
Numerade Educator
02:12

Problem 45

Two radioactive nuclei A and B are present in equal numbers to begin with. Three days later, there are three times as many A nuclei as there are $\mathrm{B}$ nuclei. The half-life of species $\mathrm{B}$ is 1.50 days. Find the half-life of species A.

Mike Gaerlan
Mike Gaerlan
Numerade Educator
05:06

Problem 46

$$
\text { A sample has a }{ }_{6}^{14} \mathrm{C} \text { activity of } 0.0061 \mathrm{Bq} \text { per gram of carbon. (a) Find }
$$ the age of the sample, assuming that the activity per gram of carbon in a living organism has been constant at a value of 0.23 Bq. (b) Evidence suggests that the value of $0.23 \mathrm{Bq}$ might have been as much as $40 \%$ larger. Repeat part
(a), taking into account this $40 \%$ increase.

Yaqub Khan
Yaqub Khan
Numerade Educator
01:24

Problem 47

Review Multiple-Concept Example 10 for help in approaching this problem. An archaeological specimen containing $9.2 \mathrm{g}$ of carbon has an activity of 1.6 Bq. How old (in years) is the specimen?

Mike Gaerlan
Mike Gaerlan
Numerade Educator
02:35

Problem 48

$$
\text { The half-life for the } \alpha \text { decay of uranium }{ }_{92 }^{238} \mathrm{U} \text { is } 4.47 \times \mathrm{}
$$ $10^{9}$
ye Determine the age (in years) of a rock specimen that contains $60.0 \%$ of its original number of ${ }_{92}^{238} \mathrm{U}$ atoms.

Yaqub Khan
Yaqub Khan
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01:54

Problem 49

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Ajay Singhal
Ajay Singhal
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03:38

Problem 50

$$
\text { Multiple-Concept Example } 10 \text { reviews most of the concepts that}
$$ are needed to solve this problem. Material found with a mummy in the arid highlands of southern Peru has a ${ }_{6}^{14} \mathrm{C}$ activity per gram of carbon that is $78.5 \%$ of the activity present initially. How long ago (in years) did this individual die?

Yaqub Khan
Yaqub Khan
Numerade Educator
09:39

Problem 51

When any radioactive dating method is used, experimental error in the measurement of the sample's activity leads to error in the estimated age. In an application of the radiocarbon dating technique to certain fossils, an activity of 0.100 Bq per gram of carbon is measured to within an accuracy of $\pm 10.0 \% .$ Find the age of the fossils and the maximum error (in years) in the value obtained. Assume that there is no error in the 5730 -year half-life of ${ }_{6}^{14} \mathrm{C}$ nor in the value of 0.23 Bq per gram of carbon in a living organism.

Yaqub Khan
Yaqub Khan
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01:54

Problem 52

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Ajay Singhal
Ajay Singhal
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01:54

Problem 53

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Ajay Singhal
Ajay Singhal
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03:36

Problem 54

In a nucleus, each proton experiences a repulsive electrostatic force from each of the other protons. In a nucleus of gold ${ }_{ 79}^{197}$Au, what is the magnitude of the least possible electrostatic force of repulsion that one proton can exert on another?

Yaqub Khan
Yaqub Khan
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00:59

Problem 55

When a sample from a meteorite is analyzed, it is determined that $93.8 \%$ of the original mass of a certain radioactive isotope is still present. Based on this finding, the age of the meteorite is calculated to be $4.51 \times 10^{9} \mathrm{yr}$. What is the half-life (in yr) of the isotope used to date the meteorite?

Mike Gaerlan
Mike Gaerlan
Numerade Educator
05:44

Problem 56

$$
\text { The } \beta^{-} \text {decay of phosphorus } \frac{32}{15} \mathrm{P} \text { (atomic mass } \left.=31.973907 \mathrm{u}\right)
$$ produces a daughter nucleus that is sulfur $\frac{32}{16} \mathrm{S}$ (atomic mass $=31.972070 \mathrm{u}$ ), a $\beta^{-}$ particle, and an antineutrino. The kinetic energy of the $\beta^{-}$ particle is 0.90 MeV. Find the maximum possible energy (in MeV) that the antineutrino could carry away.

Declan Nell
Declan Nell
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04:05

Problem 57

Complete the following decay processes by stating what the symbol $X$ represents $\left(X=a, \beta^{-}, \beta^{+},\right.$ or $\left.\gamma\right)$
(a) ${ }^{211} \mathrm{Pb} \rightarrow{ }_{83}^{211} \mathrm{Bi}+\mathrm{X}$
(b) ${ }_{6}^{11} \mathrm{C} \rightarrow{ }_{5}^{11} \mathrm{B}+\mathrm{X}$
(c) $\frac{231}{90} T h^{*} \rightarrow \frac{231}{90} T h+X$
(d) ${ }_{84}^{210} \mathrm{Po} \rightarrow \frac{206}{\mathrm{8} 2 \mathrm{}}+\mathrm{X}$

Yaqub Khan
Yaqub Khan
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01:54

Problem 58

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Ajay Singhal
Ajay Singhal
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01:54

Problem 59

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Ajay Singhal
Ajay Singhal
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03:50

Problem 60

$$
\text { A sample of ore containing radioactive strontium }{ }_{38}^{90} \mathrm{Sr} \text { has an }
$$ activity of $6.0 \times 10^{5} \mathrm{Bq} .$ The atomic mass of strontium is $89.908 \mathrm{u},$ and its half-life is 29.1 yr. How many grams of strontium are in the sample?

Yaqub Khan
Yaqub Khan
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01:54

Problem 61

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Ajay Singhal
Ajay Singhal
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05:46

Problem 62

In a radioactive decay series similar to that shown in Figure $31.15,$ thorium ${ }_{90}^{228} \mathrm{Th}$ (atomic mass $\left.=228.028715 \mathrm{u}\right)$ undergoes four successive $\alpha$ decays, producing a daughter nucleus. (a) Determine the symbol $4 \mathrm{X}$ for the nucleus produced by four successive $\alpha$ decays of ${ }_{90}^{23} \mathrm{Th} .$
(b) What is the total amount of energy (in MeV) released in this series of $\alpha$ decays? The mass of the daughter nucleus can be obtained by using the result of part
(a) and consulting Appendix $F$ at the back of the book. The mass of a single $\alpha$ particle is $4.002603 \mathrm{u}$.

Declan Nell
Declan Nell
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02:59

Problem 63

$$
\text { What is the wavelength (in vacuum) of the } 0.186-\text { MeV } \gamma \text { -ray }
$$$$
\text { photon emitted by }{ }_{88}^{226} \mathrm{Ra} ?
$$

Yaqub Khan
Yaqub Khan
Numerade Educator
05:46

Problem 64

$$
\text { Thorium }{ }_{90}^{28} \text { Th produces a daughter nucleus that is radioactive. }
$$ The daughter, in turn, produces its own radioactive daughter, and so on. This process continues until bismuth ${ }^{} \frac{212}{83} \mathrm{B} i$ is reached. Concepts:
(i) How many of the 90 protons in the thorium nucleus are carried off by the $\alpha$ particles?
(ii) How many protons are left behind when the $\beta^{-}$ particles are emitted?
(iii) How many of the 228 nucleons in the thorium nucleus are carried off by the $\alpha$ particles?
(iv) Does the departure of a $\beta^{-}$ particle alter the number of nucleons? Calculations: What are the total number $N_{a}$ of $\alpha$ particles and the total number $N_{\rho}$ of $\beta^{-}$ particles that are generated in this series of radioactive decays?

Declan Nell
Declan Nell
Numerade Educator
07:54

Problem 65

$$
\text { A one-gram sample of thorium }{ }_{90}^{228} \text { Th contains } 2.64 \times
$$$10^{21}$ atoms and undergoes $\alpha$ decay with a half-life of 1.913 yr $\left(1.677 \times 10^{4} \mathrm{h}\right)$ Each disintegration releases an energy of 5.52 MeV $\left(8.83 \times 10^{-13} \mathrm{J}\right) .$ Assume that all of the energy is used to heat a $3.8-\mathrm{kg}$ sample of water. Concepts: (i) How much heat $Q$ is needed to raise the temperature of a mass $m$ of water by $\Delta T$ degrees?
(ii) The energy released by each disintegration is $E$. What is the total energy $E_{\text {tural }}$ released by a number $n$ of disintegrations?
(iii) What is the number $n$ of disintegrations that occur during a time $t ?$ Calculations: Find the change in temperature of the $3.8-\mathrm{kg}$ sample of water that occurs in one hour.

Declan Nell
Declan Nell
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03:26

Problem 66

A Radioisotope Thermoelectric Generator. You and your team are designing a thermoelectric generator that converts the thermal energy released during the decay of a radioactive material into electrical energy. Such devices are used in deep-space probes such as Voyager $1,$ which was launched in $1977 .$ Its radioisotope thermoelectric generators are expected to function until the year $2025 .$ The isotope that your team will use is ${ }^{2}{ }_{94}^{28} \mathrm{Pu}$ (atomic mass $=238.049553$ u), which has a half-life of 87.7 years.
(a) If 'gi Pu undergoes alpha decay, what is the daughter nucleus?
(b) Assuming the daughter nucleus found in (a) has an atomic mass of $234.0409468 \mathrm{u}$ calculate the energy released in the decay in joules (the atomic weight of an alpha particle is 4.002603 u). (c) How many atoms are in one gram of $\frac{238}{94}$ Pu?
(d) How many atoms in one gram of ${ }^{238}$ Pu decay after one year?
(e) How much energy is released from one gram of ${ }_{94}^{238}$ Pu during one year? (f) What is the average power output of one gram during one year (in watts)?

Ze-Han Lee
Ze-Han Lee
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04:21

Problem 67

Radioactive Dating of a Mystery Object. In a science fiction movie, a strange object is discovered buried deep in the ice of western Antarctica. It appears to be a radioisotope thermoelectric device from a spacecraft, the function of which is to convert thermal energy released in the decay of its radioactive contents into electrical energy. The radioactive material is identified as americium-241 ( ${ }_{95}^{241} \mathrm{Am}$ ), which has a half-life of 432 years. (a) If ${ }_{95}^{24}$ Am undergoes alpha decay, what is its daughter nucleus? (b) What is the activity you would expect for $1.00 \mathrm{g}$ of ${ }_{95}^{241} \mathrm{Am}$ (in Bq)? (c) In the movie, $1.00 \mathrm{g}$ of material is extracted from the device, and the activity is measured to be $4.00 \times 10^{10}$ Bq. Assuming the device was initially loaded with $100 \%^{241} \mathrm{Am}$ how old is the device? Express your answer in years.

Ren Jie Tuieng
Ren Jie Tuieng
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