Chapter 34: Nuclear Fission and Fusion

Physics Test Review

Why doesn't a chain reaction normally occur in uranium mines?

uranium atoms don’t fission easily, only occurring for rare isotope U-235; other isotopes are too “impure”

Why is a chain reaction more likely to occur in a big piece of uranium than in a small piece?

ratio surface area to mass is higher in a small piece than in a large one

What is meant by the idea of a critical mass?

mass greater than a certain amount; the minimum mass of fissionable material in a reactor or nuclear bomb that will sustain a chain reaction

Which will leak more neutrons: two separate pieces of uranium or the same pieces stuck together?

two separate pieces

What were the two methods used to separate U-235 from U-238 in the Manhattan Project during World War II?

diffusion and magnetic separation of uranium ions shot into a magnetic field

What are the three possible fates of neutrons in uranium metal?

1. may cause fission of a U-235 atom
2. escape from the metal into non-fissionable surroundings or
3. be absorbed by U-238 without causing fission

What are the four main components of a fission reactor?

1. nuclear fuel
2. control rods
3. a moderator
4. a fluid

What components are the safeguards to prevent a reactor from generating energy out of control?

control rods

What isotope is produced when U-238 absorbs a neutron?

U-239

What isotope is produced when U-239 emits a beta particle?

^^239-92 U ***—beta→*** 0/-1 e + 239-93 Np^^

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Np-239

What isotope is produced when Np-239 emits a beta particle?

^^239-93 Np —beta→ 0/-1 e + 239-94 Pu^^

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Pu-239

What do U-235 and Pu-239 have in common?

they both will undergo fission when it captures a neutron

What is the effect of placing small amounts of fissionable isotopes with large amounts of U-238?

neutron transmutes U-238 to U-239 then to Np-239 to Pu-239

Name two isotopes that undergo nuclear fission.

U-235 and Pu-239

What element reacts in a breeder reactor to breed nuclear fuel?

U-238

In what way is a nuclear reactor similar to a conventional fossil-fuel plant?

boil water to produce steam for a turbine

Cite three main advantages of fission power. Cite four main drawbacks.

advantages:


1. providing plentiful electricity
2. saving many billions of tons of coal, oil, and natural gas
3. eliminating the megatons of sulfur oxides and other poisons

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drawbacks:


1. problem of storing radioactive wastes
2. the production of plutonium and the danger of nuclear weapons proliferation
3. the low-level release of radioactive materials into the air and ground water
4. the risk of an accidental release of large amounts of radioactivity

What celebrated equation shows the equivalence of mass and energy?

E = mc^2

Is work required to pull a nucleon out of an atomic nucleus? Does the nucleon, once outside, have more energy than it did when it was inside the nucleus? In what form is this energy?

yes; yes; increased mass

Which ions of like charge and equal speed are least deflected in a mass spectrometer?

more massive ions

What is the basic difference between the graphs in Figure 34.15 and Figure 34.16?

34\.15 shows mass vs. atomic #

34\.16 shows mass per nucleon vs. atomic #

In which element is the mass per nucleon greatest? Least?

greatest: hydrogen

least: iron

How does the mass per nucleon in uranium compare with the mass per nucleon in its fission fragments?

it decreases in fission fragments

What becomes of the "lost" mass per nucleon in fission and fusion reactions?

it becomes energy

If the graph in Figure 34.16 is seen as an energy valley, what can be said about the energy of nuclear transformations that progress toward iron?

there would be less mass per nucleon

When a pair of hydrogen nuclei are fused to create helium, how does the mass of the resulting helium nucleus compare with the sum of the nuclear masses before fusion?

it’s less than the sum of the masses of the hydrogen nuclei

For helium to release energy, should it be fissioned or fused?

fused

What isotopes of hydrogen fuse best at "moderate" temperatures?

H-2 and H-3

Which isotope of hydrogen--deuterium or tritium-is abundant and which is scarce?

abundant: deuterium

scarce: tritium

What kind of nuclear power is responsible for sunshine?

thermonuclear fusion

Assume that all of the following nuclei undergo fission into a pair of equal or nearly equal mass fragments. Using the periodic table and Figure 34.16 as your guide, rank from greatest to least the reduction in mass per nucleon for these nuclei after fission.


1. (a) Uranium
2. (b) Silver
3. (c) Gold
4. (d) Iron

a, b, c, d