Deck 15: Modern Physics

Question 1

A uranium nucleus has 92 protons. How many neutrons does a uranium-235 nucleus have?

A) 92
B) 143
C) 235
D) 327

Answer 1

143

Question 2

Which of the following is not a criterion to make a nuclear bomb?

A) Fissionable material
B) Excess production of neutrons
C) Nuclear chain reaction
D) Sufficient number of electrons to propagate the chain reaction.

Answer 2

Sufficient number of electrons to propagate the chain reaction.

Question 3

Radioactive isotope technetium-99m has a half-life of 6 hours. What fraction of a sample of technetium-99m remains after 24 hours?

A) ¼
B) 1/6
C) 1/16
D) 1/24

Answer 3

1/16

Question 4

What percentage of an atom's mass is in its nucleus?

A) Over 99.9%
B) Over 99% but less than 99.9%
C) Over 90% but less than 99%
D) Less than 90%

Question 5

What two Japanese cities were attacked with nuclear bombs during World War II?

A) Tokyo and Hiroshima
B) Hirohito and Yokohama
C) Hiroshima and Nagasaki
D) Tokyo and Kyoto

Question 6

Nuclear reactions are how much more energetic than chemical reactions?

A) 10 times
B) 10 thousand times
C) 10 million times
D) 10 billion times

Question 7

The nuclear bombs developed during World War II used what principle?

A) Nuclear fusion
B) Nuclear fission
C) Nuclear magnetic resonance
D) Nuclear force

Question 8

What is needed for a nuclear chain reaction?

A) Subcritical mass
B) Critical mass
C) Supercritical mass
D) Infinite mass

Question 9

In a well-designed water-cooled thermal fission reactor, the water is acting as a moderator for the neutrons. If some of this water is lost, the chain reaction in the reactor core will slow down because neutrons in the reactor core will

A) remain positively charged and will not be able to cause uranium 235 nuclei to fission.
B) not be magnetic enough to stick to uranium 235 nuclei and cause them to fission.
C) be traveling too fast and will be absorbed by uranium 238 nuclei.
D) be traveling too slowly and will be unable to cause uranium 235 nuclei to fission.

Question 10

When uranium undergoes fission, it releases an enormous amount of energy. That energy was stored in the uranium nuclei as

A) kinetic energy in the nucleons.
B) electrostatic potential energy-from the electrostatic forces between nucleons.
C) gravitational potential energy-from the gravitational forces between nucleons.
D) nuclear potential energy-from the nuclear forces between nucleons.

Question 11

Fission chain reactions in uranium are sustained by neutrons, each of which is released by one fission and may induce a subsequent fission. Each fission also releases other particles, which include protons. However, proton-containing fission fragments are not as effective at causing subsequent fissions because they

A) are not massive enough to cause fissions in uranium.
B) are repelled as they try to approach other uranium nuclei.
C) do not exert any forces on the uranium nuclei they encounter.
D) are not hot enough to make a uranium nucleus boil.

Question 12

For a nuclear weapon to explode normally, the fissionable material in its core must be assembled very quickly. For technical reasons, a nuclear bomb developed by a terrorist group would probably not achieve such rapid assembly. As a result of its slow assembly, such a bomb would

A) explode powerfully, but at a relatively unpredictable moment. To shorten the time window over which the explosion could occur, external nuclear triggers would be needed.
B) not explode because there would not be enough momentum present to push the neutrons into the fissionable nuclei of its core.
C) overheat and push itself apart during the assembly, producing only a weak explosion.
D) not explode because there would not be enough energy present to push the neutrons into the fissionable nuclei of its core.

Question 13

The energy that is released by a nuclear weapon was put into the weapon's fissionable core in the process of

A) heating and melting the fissionable materials when the core is being fabricated.
B) assembling each of the core's fissionable nuclei from smaller nuclear pieces.
C) separating the core's fissionable nuclei from the non-fissionable nuclei with which they are normally found.
D) raising the core's fissionable materials from deep in the earth where they were mined.

Question 14

The fallout from a nuclear explosion and the waste from a nuclear reactor contain radioactive isotopes. The atoms of these isotopes

A) have unstable nuclei but are chemically indistinguishable from stable atoms.
B) have unstable nuclei and are chemically unstable.
C) are chemically unstable but their nuclei are indistinguishable from stable atoms.
D) emit a steady stream of X-ray radiation.

Question 15

Most nuclear reactors in the United States are thermal fission reactors, reactors that slow their fission neutrons by sending those neutrons through materials known as moderators. Water is a common moderator. When a fast moving neutron enters water, it usually slows down because it

A) drags the water molecules with it and experiences water resistance.
B) pushes and pulls on the electrons in the water molecules and transfers most of its energy to those electrons.
C) creates bubbles in the water as it passes and those bubbles carry away most of its energy and momentum.
D) collides with the water nuclei and transfers most of its energy and momentum to those nuclei.

Question 16

The fallout from a nuclear explosion and the waste from a nuclear reactor contain radioactive isotopes. For example, iodine-131 (a fission byproduct) is radioactive while iodine-127 (normal iodine) is not. An atom of iodine-131 differs from an atom of iodine-127 because the iodine-131 atom has more

A) protons in its nucleus.
B) gamma rays in its nucleus.
C) electrons in its orbitals.
D) neutrons in its nucleus.

Question 17

When a free neutron collides with a uranium-235 nucleus and causes that nucleus to fission, the collision fragments contain a total of 2.5 free neutrons, on average, including the original free neutron. The critical mass for uranium-235 is about 50 kilograms. Suppose that another radioactive material, fundamentium-999, undergoes fission when struck by a neutron and the collision fragments contain a total of 0.5 neutrons, on average, including the original free neutron. What would be the critical mass of fundamentium-999?

A) Infinite. No chain reaction could occur in fundamentium-999.
B) About 10 kilograms
C) About 50 kilograms
D) About 250 kilograms

Question 18

A uranium-235 nucleus undergoes fission during a nuclear explosion. If you were to collect all the fragments of that original uranium-235 nucleus, you would find that their total combined mass is

A) about 0.1% more than that of the original uranium-235 nucleus.
B) less than that of the original uranium-235 nucleus.
C) exactly the same as that of the original uranium-235 nucleus.
D) about 1.0% more than that of the original uranium-235 nucleus.

Question 19

In many circumstances it is very important to have control of a fission nuclear chain reaction with a moderator. A moderator must therefore have a profound effect on the motion of

A) electrons.
B) protons.
C) neutrons.
D) photons.

Question 20

Identify and briefly discuss three physical properties that isotopes of an element or compounds formed by isotopes of an element have in common.

Question 21

Please explain why neutrons propagate nuclear chain reactions, and not protons or electrons.
Why neutrons:
Why not protons:
Why not electrons:

Question 22

The two main developments essential to the making of the atomic bomb are

A) relativity and quantum physics.
B) relativity and classical mechanics.
C) quantum mechanics and optical storage.
D) semiconductor physics and relativity.

Question 23

A uranium nucleus has 143 neutrons. How many protons does a uranium-235 nucleus have?

A) 92
B) 143
C) 235
D) 327

Question 24

A Radioactive isotope has 1/64 of the original material left after 10 minutes. Its half life is

A) 5 minutes
B) 10 minutes
C) 2 minutes
D) 2 seconds

Question 25

Isotopes do not share

A) atomic number
B) atomic mass number
C) number of protons
D) chemical behavior
AMS: B
DIFFICULTY LEVEL: M

Question 26

Uranium - 235 and Uranium - 238

A) should behave different chemically but the same optically.
B) should behave similarly chemically and optically.
C) should be different both chemically and optically.
D) should behave similarly chemically but not optically.

Question 27

You are talking with your distant cousin over coffee, and they express worry that things like UV light or microwaves could make food or other things radioactive. How would you correctly and scientifically respond to your cousin?

Question 28

What is not needed for a nuclear chain reaction?

A) Fissionable material.
B) Critical mass.
C) Excess electrons.
D) Neutron moderators

Question 29

Which of the following does a moderator not have an effect on?

A) electron speed
B) neutron speed
C) energy produced
D) cooling water temperature

Question 30

Candle wax is

A) a good chain reaction moderator because of the wax molecular structure.
B) a good chain reaction moderator because it has nuclei that slow neutrons down.
C) a poor chain reaction moderator.
D) of no consequence to a nuclear reaction.

Question 31

Candle wax is not commercially used as a chain reaction moderator because

A) this would deprive the world of candles.
B) it chemically decomposes under intense radiation.
C) it melts too easily.
D) it is too thick.

Question 32

Identify and briefly discuss three physical properties that isotopes of an element or compounds formed by isotopes of an element do not have in common.

Question 33

The three major nuclear reactor accidents are

A) Windscale Pile 1 (1957), Three Mile Island (1979) and Chernobyl (1986).
B) Windscale Pile 2 (1957), Three Mile Island (1979) and Chernobyl (1986).
C) Windscale Mile 1 (1957), Three Pile Island (1979) and Chernobyl (1986).
D) Windscale Pile 1 (1967), Three Mile Island (1989) and Chernobyl (1996).

Question 34

When an x-ray photon is absorbed in a tumor, it may cause the tumor cell to die because the photon

A) causes the cell to crystallize into a brittle solid that cannot tolerate any deformation.
B) carries enough energy to damage molecules and cause chemical injury to the cell.
C) magnetizes the cell and causes it to stick to passing killer cells of the immune system.
D) polarizes the cell and causes its vertical electric field to become horizontal.

Question 35

What occurs whenever a charged particle accelerates?

A) X-ray fluorescence
B) Characteristic x-rays
C) Compton scattering
D) Bremsstrahlung

Question 36

Some of the X-rays emitted by an X-ray imaging machine are fluorescence X-rays and are formed when individual atoms in the machine undergo radiative transitions. While the mercury atoms in a fluorescent lamp also undergo radiative transitions, those mercury atoms emit ultraviolet light, not X-rays. The reason for this difference is that

A) mercury atoms aren't massive enough to emit X-rays, whereas the atoms in an X-ray machine are.
B) the electrons in the imaging machine atoms experience much larger changes in energy during their radiative transitions than the electrons in the mercury atoms do.
C) the electrons in the imaging machine atoms experience much smaller changes in energy during their radiative transitions than the electrons in the mercury atoms do.
D) the atoms in an X-ray machine are packed together in a solid and can amplify each other's waves much more effectively than the gaseous mercury atoms in a fluorescent lamp can.

Question 37

The X-rays used in medical imaging travel through tissue relatively easily but are mostly absorbed by bone. This is because

A) only neutrons can absorb X-rays and the atoms in bone have many more neutrons than those in tissue.
B) the atoms in bone are slightly radioactive and the passing X-rays cause them to undergo fission. Since the atoms in tissue are not radioactive, they cannot undergo fission.
C) solids, such as bone, are much better at absorbing X-ray photons than are liquids, such as those in tissue.
D) the atoms in bone generally have more tightly bound electrons than those in tissue and are thus able to absorb higher energy photons.

Question 38

Imaging x-rays go easily through living tissue but not so easily through bone. This is primarily because the calcium atoms in bone have

A) many more neutrons in their nuclei than the atoms in tissue have.
B) many more electrons than the atoms in tissue have.
C) an odd number of electrons while those in tissue have even numbers of electrons.
D) an even number of electrons while those in tissue have odd numbers of electrons.

Question 39

Please describe why metals are not allowed near an MRI machine while it is in use.

Question 40

What would happen to the effectiveness of MRI imaging if all the hydrogen in our bodies were in equivalent environments?

Question 41

X-rays were discovered in

A) 1985
B) 1895
C) 1905
D) 1921

Question 42

In a common X-ray tube, electrons accelerate from the

A) anode to cathode
B) cathode to anode
C) hot anode to anode
D) hot cathode to cathode

Question 43

X-rays are considered a form of radiation. Briefly discuss one reason why this fits in with other types of radiation and one reason why it does not.

Question 44

The photoelectric effect is what makes X-ray imaging possible because

A) it is valid in only high energy environments.
B) it is valid in only low energy environments.
C) it involves electromagnetic radiation knocking an electron all the way out of an atom.
D) it involves an atom absorbing an electron.

Question 45

Discuss, appropriate to your comfort level, an instance where medical imaging helped or saved the life of someone you know. Please include a brief discussion of the physics behind the type of imaging you chose. You may feel free to use a famous incident or make up one as long as the physics is included

Question 46

Suppose your physics teacher came to class after a 10 day long vacation at a medieval chained library convention. Groggy from the intense experience, they proceed to lecture about nuclear reactions and say that "neutrinos are what propagate nuclear chain reactions and if you moderate them you moderate the reaction". Please comment on the validity of their comment.