Question 1

Does a radioactive isotope ever lose its radioactivity?
A)yes
B)no
C)sometimes
D)usually

Accepted Answer

A radioactive isotope does not lose its radioactivity naturally. It undergoes radioactive decay over time, which means its nucleus becomes stable by emitting particles or energy in the form of radiation. This process can take anywhere from a few microseconds to billions of years, depending on the isotope's half-life. Once the isotope has undergone decay and become stable, it is no longer radioactive.

Question 2

Which shape is likely to need more material for a critical mass,a cube or a sphere? Why?
A)a sphere because it has the greater surface area to volume ratio
B)a sphere because it has the smaller surface area to volume ratio
C)a cube because it has the greater surface area to volume ratio
D)a cube because it has the smaller surface area to volume ratio

Accepted Answer

A critical mass refers to the minimum amount of a substance required to sustain a chain reaction. In this case, we can assume that the material is evenly distributed throughout the shape. The cube has a larger surface area to volume ratio as compared to the sphere. This means that more of its surface area is exposed to the surroundings, allowing for more opportunities for interaction and possible neutron absorption. Hence, more material is needed to achieve a critical mass in a cube than a sphere.

Question 3

Otto Hahn and Fritz Strassmann discovered fission by bombarding uranium with neutrons.Their discovery was made possible by finding one of the fission products,barium (Ba,atomic no.= 56).What is a reasonable explanation for why they were unable to initially observe the other product,krypton (Kr,atomic no.= 36)?
A)Krypton is a noble gas and it may have diffused out of the sample.
B)The isotope of krypton generated might have a short half-life and had undergone radioactive decay to some other element.
C)Krypton is a noble gas and therefore chemically unreactive,making it difficult to characterize by chemical means.
D)both A and B
E)all of the above

Accepted Answer

Krypton's nature as a noble gas means it could have diffused out of the sample due to its low reactivity (A), and its potential short-lived isotope could have decayed, making it hard to detect (B). Additionally, its chemical inertness (C) would make it difficult to identify through chemical methods.

Question 4

Does the average distance that a neutron travels through fissionable material before escaping increase or decrease when two pieces of fissionable material are assembled into one piece? Does this assembly increase or decrease the probability of an explosion?
A)The average distance increases while the probability of an explosion also increases.
B)The average distance decreases while the probability of an explosion decreases.
C)The average distance increases while the probability of an explosion decreases.
D)The average distance decreases while the probability of an explosion increases.

Accepted Answer

When two pieces of fissionable material are assembled into one piece, the average distance a neutron can travel before escaping increases because there is more material for it to traverse. This assembly also increases the probability of an explosion, as neutrons have a higher chance of causing further fissions in a larger mass of material, potentially leading to a chain reaction.

Question 5

Uranium-235 releases an average of 2.5 neutrons per fission,while plutonium-239 releases an average of 2.7 neutrons per fission.Which of these elements might you therefore expect to have the smaller critical mass?
A)plutonium-239
B)uranium-235
C)The number of neutrons per fission will not effect the size of critical mass.
D)The critical mass of these elements cannot be determined from only the number of neutrons per fission.

Accepted Answer

The number of neutrons released per fission is directly related to the critical mass of the element. The more neutrons released per fission, the smaller the critical mass required for a sustained chain reaction. Since plutonium-239 releases an average of 2.7 neutrons per fission, it requires a smaller critical mass than uranium-235, which only releases an average of 2.5 neutrons per fission. Therefore, the answer is A) plutonium-239.

Question 6

If a nucleus of $\begin{array} { c } 
232\
90
\end{array}$ Th absorbs a neutron and the resulting nucleus undergoes two successive beta decays (emitting electrons),what nucleus results?
A)Americium-232
B)Plutonium-232
C)Thorium-233
D)Uranium-233

Accepted Answer

When a nucleus of Thorium-232 absorbs a neutron, it becomes Thorium-233. After two successive beta decays, it becomes Uranium-233, as each beta decay increases the atomic number by 1 while the mass number remains the same.

Question 7

Why doesn't uranium ore spontaneously undergo a chain reaction?
A)Uranium ore must be "weapons' grade" in order for it to undergo chain reaction.
B)Uranium ore is mostly non-fissionable isotope U-238 and undergoes a chain reaction only if mixed with a moderator to slow down the neutrons.
C)Uranium ore does spontaneously undergo slow chain reaction over time finally resulting in it becoming lead.
D)Uranium ore,mostly U-235,must be enriched with U-238 in order for it to undergo a chain reaction.

Accepted Answer

Uranium ore is mostly made up of the non-fissionable isotope U-238. In order for a chain reaction to occur, the U-238 must be mixed with a moderator to slow down the neutrons so that they can be readily absorbed by the fissionable isotope U-235. Additionally, other factors such as critical mass and containment must also be in place for a sustained chain reaction to occur.

Question 8

The isotope Cesium-137,which has a half-life of 30 years,is a product of nuclear power plants.How long will it take for this isotope to decay to about one-sixteenth its original amount?
A)480 years
B)240 years
C)120 years
D)960 years

Accepted Answer

The answer of The isotope Cesium-137,which has a half-life of...

Question 9

Why does plutonium not occur in appreciable amounts in natural ore deposits?
A)Most naturally occurring plutonium deposits have already been depleted in the creation of nuclear weapons.
B)Plutonium is strictly a human-made element.
C)Any plutonium initially in the earth's crust has long since decayed.
D)Plutonium loses electrons to form positively charged particles that have long since washed into the oceans.

Accepted Answer

Plutonium does not occur in appreciable amounts in natural ore deposits primarily because it is a radioactive element with a relatively short half-life in geological terms. Any plutonium that was present in the Earth's crust from the formation of the planet has decayed into other elements over billions of years.

Question 10

Why will nuclear fission probably not be used directly for powering automobiles?
A)Massive shielding would be required to protect against radioactivity exposure.
B)Radioactive wastes could not be adequately controlled.
C)It's more practical for cars to use the electricity generated by nuclear fission power plants.
D)All of the above are true.

Accepted Answer

All of the options listed are valid concerns regarding the use of nuclear fission directly in automobiles. Massive shielding would indeed be necessary to protect passengers and the environment from radiation. Managing radioactive waste from such a small, mobile source would present significant challenges. Additionally, it is more practical and efficient for vehicles to use electricity produced by nuclear fission in stationary power plants, where safety and waste management can be more effectively controlled.

Question 11

How do fission power plants work?
A)The heat from a nuclear reaction is used to boil water.
B)The neutrons from a nuclear reaction undergo fusion with water to produce hydrogen gas,which drives a turbine.
C)The electrons from a nuclear reaction are harnessed to produce an electrical current.
D)The krypton gas generated in the fission process is used to drive a turbine.
E)none of the above

Accepted Answer

In fission power plants, the heat generated by the nuclear reaction is used to boil water, producing steam that drives a turbine, which generates electricity. This is the most common and well-established method for producing power from nuclear reactions, with over 400 nuclear power plants currently in operation around the world using this method.

Question 12

Which of the following is a major advantage of nuclear-fission-based power plants?
A)The amount of energy per kilogram of fuel is greater than any other fuel source.
B)The byproducts of the fission process are radioactive and have very long half-lives.
C)The reactors can be used to produce their own fuel.
D)The power plants are complex and there are many safety requirements to prevent contamination of the environment.
E)A and C

Accepted Answer

The greatest advantage of nuclear-fission-based power plants is that they produce a large amount of energy per kilogram of fuel, which is unmatched by any other fuel source. Additionally, the reactors can be used to produce their own fuel, which provides more long-term sustainability of the energy source.

Question 13

Why is carbon better than lead as a moderator in nuclear reactors?
A)Carbon produces the high energy,high speed neutrons necessary for maintaining the nuclear chain reaction.
B)Carbon slows down the neutrons making them more effective in stimulating the nuclear chain reaction.
C)Lead absorbs the neutrons rather than allowing them to rebound to maintain the nuclear chain reaction.
D)Lead slows down the neutrons making them less effective in stimulating the nuclear chain reaction.

Accepted Answer

Carbon is a better moderator than lead in nuclear reactors because it slows down the neutrons, making them more effective in stimulating the nuclear chain reaction. Lead absorbs the neutrons rather than allowing them to rebound, making it less effective as a moderator. Carbon does not produce high energy, high-speed neutrons necessary for maintaining the nuclear chain reaction.

Question 14

After a uranium fuel rod reaches the end of its fuel cycle (typically 3 years)most of its energy comes from the fissioning of plutonium because
A)fissionable Pu-239 is formed as the U-238 absorbs neutrons from the fissioning U-235.
B)fissionable Pu-239 is formed as the U-235 absorbs neutrons from the fissioning U-238.
C)fissionable Pu-239 is formed as the U-238 absorbs alpha particles from the fissioning U-235.
D)fissionable Pu-239 is formed as the U-235 absorbs alpha particles from the fissioning U-238.

Accepted Answer

During the fuel cycle, U-238 absorbs a neutron from fissioning U-235 to become U-239. This decays to form Pu-239, which is fissionable and can sustain the chain reaction in a nuclear reactor. Therefore, as the fuel rod reaches the end of its cycle, most of its energy comes from the fissioning of Pu-239 formed from the U-238 absorbing neutrons from the fissioning U-235.

Question 15

Which of the following is a major disadvantage of nuclear-fission-based power plants?
A)The reactors can be used to produce their own fuel.
B)The byproducts of the fission process are radioactive and have very long half-lives.
C)The amount of energy per kilogram of fuel is greater than any other fuel source.
D)The power plants are complex and there are many safety requirements to prevent contamination of the environment.
E)B and D

Accepted Answer

The byproducts of the fission process are radioactive and have very long half-lives, making them harmful to the environment and human health. Additionally, nuclear-fission-based power plants are complex and require strict safety measures to prevent accidents that could lead to contamination of the environment. Therefore, B and D are the correct choices. A is a potential advantage of nuclear-fission-based power plants, and C is not a major disadvantage.

Question 16

Which of the following statements about chain reactions is true?
A)The key requirement for a chain reaction is that more neutrons are produced than are absorbed.
B)Three or more neutrons must be released to sustain a chain reaction.
C)Only uranium isotopes are capable of supporting a chain reaction.
D)It is not possible to stop or control a chain reaction once it has been started.
E)A chain reaction will only take place when a critical mass of material has been assembled.

Accepted Answer

The key requirement for a chain reaction is that more neutrons are produced than are absorbed. This allows the reaction to continue and potentially accelerate.

Answer: E
 A chain reaction will only take place when a critical mass of material has been assembled. This is the minimum amount of material required for the self-sustaining reaction to occur.

Question 17

Which of the following statements about fission is true?
A)The amount of energy released in the fission of large nuclei is very large.
B)The amount of energy released in the fusion of small nuclei is very large.
C)Bombarding a nucleus with neutrons always leads to fission.
D)The fragments of a fusion reaction are always the same size.
E)none of the above

Accepted Answer

Fission is the process of splitting a large nucleus into smaller fragments. This process releases a large amount of energy, which is why it is used in nuclear power plants and as a weapon. The amount of energy released in the fusion of small nuclei (answer B) is also very large, but this is a different process than fission. Bombarding a nucleus with neutrons (answer C) can lead to fission, but it is not the only way to initiate the process. Finally, the fragments of a fusion reaction (answer D) can vary in size depending on the nuclei involved.

Question 18

A neutron makes a better nuclear bullet than a proton or an electron because it
A)has the greatest mass.
B)carries no electrical charge.
C)can be accelerated by electromagnetic fields.
D)all of the above

Accepted Answer

Neutrons carry no electrical charge, which allows them to penetrate the electrostatic defenses of an atom's nucleus more easily than charged particles like protons or electrons. This property makes them more effective in initiating nuclear reactions.

Question 19

The original reactor built in 1942 was just "barely" critical because the natural uranium that was used contained less than 1% of the fissionable isotope U-235 (half life 713 million years).What if,in 1942,the Earth had been 9 billion years old instead of 4.5 billion years old? Would this reactor have reached critical stage with natural uranium? Why?
A)No.The age of the Earth has nothing to do with the reactor reaching critical stage with U-235.
B)No.1% of the fissionable isotope U-235 is insufficient for the reactor to reach critical stage no matter what the age of the Earth.
C)Yes.If the Earth had been twice as old there would have then been twice as much fissionable U-235 present and the reactor would have reached critical stage.
D)No.The increased age of the Earth would mean that there would be a much smaller percentage of U-235,thus not enough for the reactor to reach critical stage.

Accepted Answer

The age of the Earth has no direct relation to the reactor reaching critical stage with natural uranium. However, since U-235 has a half-life of 713 million years, if the Earth had been 9 billion years old instead of 4.5 billion years old, there would have been more time for radioactive decay to occur, resulting in a smaller percentage of U-235. Therefore, there would not be enough U-235 for the reactor to reach critical stage even if the Earth were older. Choice D is the best answer.

Question 20

Which of the following statements best describes a critical mass?
A)A critical mass is the minimum amount of material that will undergo nuclear detonation.
B)A critical mass is the minimum amount of material that will spontaneously undergo a chain reaction.
C)A critical mass cannot be assembled from smaller,noncritical pieces of material.
D)A critical mass will detonate when it is separated into subcritical pieces.
E)none of the above

Accepted Answer

The answer of Which of the following statements best describes...

Quiz 13: The Atomic Nucleus and Radioactivity

Does a radioactive isotope ever lose its radioactivity?

Which shape is likely to need more material for a critical mass,a cube or a sphere? Why?

Does the average distance that a neutron travels through fissionable material before escaping increase or decrease when two pieces of fissionable material are assembled into one piece? Does this assembly increase or decrease the probability of an explosion?

Uranium-235 releases an average of 2.5 neutrons per fission,while plutonium-239 releases an average of 2.7 neutrons per fission.Which of these elements might you therefore expect to have the smaller critical mass?

If a nucleus of $\begin{array} { c } 232\\90\end{array}$ Th absorbs a neutron and the resulting nucleus undergoes two successive beta decays (emitting electrons) ,what nucleus results?

Why doesn't uranium ore spontaneously undergo a chain reaction?

The isotope Cesium-137,which has a half-life of 30 years,is a product of nuclear power plants.How long will it take for this isotope to decay to about one-sixteenth its original amount?

Why does plutonium not occur in appreciable amounts in natural ore deposits?

Why will nuclear fission probably not be used directly for powering automobiles?

How do fission power plants work?

Which of the following is a major advantage of nuclear-fission-based power plants?

Why is carbon better than lead as a moderator in nuclear reactors?

After a uranium fuel rod reaches the end of its fuel cycle (typically 3 years) most of its energy comes from the fissioning of plutonium because

Which of the following is a major disadvantage of nuclear-fission-based power plants?

Which of the following statements about chain reactions is true?

Which of the following statements about fission is true?

A neutron makes a better nuclear bullet than a proton or an electron because it

Which of the following statements best describes a critical mass?