Essential Physics

Section 4 review


Applications of nuclear physics include medical diagnostic imaging (both PET and MRI), radiation therapy, and nuclear power. Fission reactions, continually maintained by a nuclear chain reaction, are at the heart of a nuclear power plant. Fusion is another kind of nuclear reaction and it occurs in the core of the Sun. Fusion is not yet a proven source for regular energy production on the Earth. The standard model is the modern consensus of elementary particles (including bosons such as light) and how the particles interact with each other. There are four fundamental forces of nature—gravitational, electromagnetic, weak, and strong—and all but gravity are encompassed in the standard model.
Vocabulary words	nuclear energy, control rods, nuclear waste, positron, dose, rem, Geiger counter, ionization, radiotherapy
Review problems and questions

List three applications of nuclear physics.
Some examples are the following: PET medical diagnostic imaging, MRI medical diagnostic imaging, radiation therapy, and nuclear power.
Compare the advantages and disadvantages of electrical generation by nuclear power versus burning coal.
Some comparisons between the two sources of energy are the following: Nuclear fuel has much higher energy content per unit mass, Coal burning produces carbon emission (exhaust) that goes into the environment, whereas nuclear power does not, Because the fuel for nuclear fission is radioactive, nuclear power plants must be designed with its safety in mind, whereas coal plants do not use radioactive fuel, Both heat water as part of spinning a turbine, Nuclear power generates waste that must be stored for the long term in a safe manner, whereas coal power does not, Natural stores of uranium appear sufficient to last for a long time, whereas coal resources may be more limited, Nuclear power can be operated safely in small confines such as a submarine, whereas coal is less practical for such applications.
What are some of the challenges encountered by researchers who are trying to develop nuclear power using fusion?
It is difficult to achieve the very high temperatures required to initiate a fusion reaction, and it is difficult to confine the hot, ionized gas.
Which of the two following reactions is a fission reaction and which is a fusion reaction? ${}_{1}^{2}H + {}_{1}^{3}H \to {}_{2}^{4}H e + {}_{0}^{1}n$ ${}_{0}^{1}n + {}_{92}^{235}U \to {}_{56}^{144}B a + {}_{36}^{89}K r + 3 {}_{0}^{1}n$
This a fusion reaction, because the two isotopes of hydrogen are combining to create a larger nucleus of helium. This is a fission reaction, because the heavy nucleus of uranium is being split into two lighter nuclei of barium and krypton.
Which of the two reactions above is most likely to be found inside a nuclear power plant, and which is most likely to be found in the core of the Sun?
The fission reaction b is most likely to be found in the core of a nuclear power plant’s reactor. The fusion reaction a is most likely to be found in the core of the Sun.
In a fission reaction, will the combined binding energies of the nuclei in the products differ from the binding energy of the original nucleus? If so, explain the origin of the difference. In a fusion reaction, will the binding energy of the resulting nucleus differ from the combined binding energies of the original nuclei? If so, explain the origin of the difference.
The combined binding energies of the product nuclei will be less than the binding energy of the original nucleus. The difference in binding energies is released by the fission reaction. Similarly, the binding energy of the product nucleus will be less than the combined binding energies of the original nuclei. The difference in binding energies is released by the fusion reaction.
Describe the role of control rods in a nuclear power plant.
Inside the nuclear reactor itself, if the nuclear reactions were allowed to proceed unchecked then the reactions would quickly lead to an ever-increasing reaction rate, followed by energy runaway and likely a meltdown. The control rods absorb some of the neutrons created by the nuclear reactions, thereby slowing down the reaction rate and keeping the temperature inside the reactor at a stable level.
Describe what happens if an electron collides with a positron.
They undergo pair annihilation, in which the masses of the two particles are converted into two high-energy, gamma-ray photons.
Which scientific instrument is the best choice to detect the presence of radioactivity? a galvanometer a rem a magnetic resonance imager a Geiger counter
The correct answer is d. A Geiger counter is used to detect radioactivity.
A quark is a type of particle that is never seen directly or in isolation. What are the six types of quarks? What common particles are composed of three quarks?
The six types of quarks come in pairs: up and down, charm and strange, and top and bottom. Protons and neutrons are each composed of three quarks.
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