chapter 26 - Nuclear physics (scuffed quizlet) Flashcards
Einsteins equation
E=mc^2
The two interpretations of Einsteins equation
mass is a form of energy
energy has mass
Explanation of the first interpretation of Einsteins equation that mass is a form of energy
the interaction of an electron-positron pair illustrates how these two particles completely destroy each other (annihilation) and the entire mass of the particles is transformed into two gamma photons.
Explanation of the second interpretation of Einstein’s equation that energy has mass
the change in mass of an object is related to the change in energy by the equation ΔE=Δmc^2 - a moving ball has kinetic energy implying that its mass is greater than its rest mass.
or more simply, a mug of hot tea will decrease in mass as it cools but by an almost negligible amount.
Equation to calculate change in mass of a moving everyday object
Δm = 1/2 mv^2 / c^2
What event can not be explained by the conservation of energy theory
In alpha decay, the parent nucleus emits an alpha particle, creating a daughter nucleus, which recoils in the opposite direction. Both the alpha particle and daughter nucleus have kinetic energy.
How to explain alpha decay with the conservation of mass-energy
the total amount of mass and energy in a system is conserved. Since energy is released in radioactive decay there must be an accompanying decrease in mass. This means the total mass of the alpha particle and the daughter nucleus must be less than the mass of the parent nucleus - said decrease in mass is equivalent to the energy released.
How does a pet scan use annihilation
when a positron and electron see they annihilate each other and their entire mass is transformed into energy in the form of two identical gamma photons- the point of annihilation can be calculated
What occurs in pair production
a single photon vanishes and its energy creates a particle and corresponding antiparticle.
An increase in mass multiplied by c^2 must be …
equal to the minimum kinetic energy of the colliding particles
What is deuterium
an isotope of hydrogen
what is in the nucleus of deuterium
one proton and one neutron
According to Einsteins equation, what happens to the mass of nucleons separated from the deuterium nucleus
when the proton and neutron are separated their total mass when separated must be greater than the mass of the deuterium nucleus
What is the mass defect
the difference between the mass of the completely separated nucleons and the mass of the nucleus
What is the binding energy
the minimum energy required to completely separate a nucleus into its constituent protons and neutrons
How to calculate the binding energy of a nucleus
mass defect of nucleus x c^2
Larger nuclei have
this one is dumb, but ok
larger binding energies
How do we compare how easy it is to break up nuclei
determine the average binding energy per nucleon
The higher the binding energy per nucleon…
the more tightly bound the nucleons are - meaning the nucleus is more stable
What are thermal neutrons
neutrons with mean kinetic energy similar to the thermal energy of particles in a nuclear reactor core.
What is induced fission
where a stable atom’s nucleus absorbs a neutron making it unstable and fissions into two lighter elements
The energy released in a fission reaction is…
the difference between the total binding energies before and after fission
The energy released in a single fission reaction is a combination of…
kinetic energy of the particles produced and the energy of photons and neutrinos emitted
How is the steady production of power from a nuclear reactor controlled
by ensuring that on average one slow neutron survives between successive fission reactions.
Key components of a fission reactor
Fuel rods are spaced evenly within a steel-concrete vessel known as a reactor core.
A coolant is used to remove the thermal energy produced from the fission reaction within the fissile fuel.
The fuel rods are surrounded by the moderator and controls rods can be moved in and out of the core.
What are fuel rods
they contain enriched uranium which consists mainly of uranium-238 with 2-3% uranium-235
What is the moderator in a nuclear fission reactor
a component to slow down the fast neutrons produced in fission reactions to increase the likelihood on the uranium nuclei absorbing the neutrons. In many reactors the moderator and coolant are the same
The material of the moderator must be…
cheap and readily available and must not absorb the neutrons in the reactor
Mean kinetic energy of thermal neutrons
3/2kT
(K= boltzmann Constant)
(T= temp in kelvin)
What are control rods
made of a material whose nuclei readily absorb neutrons. The position of the control rods is automatically adjusted to ensure that exactly one slow neutron survives per fission reaction. They can be pushed further into the reactor core to completely stop the fission reaction.
Environmental impacts of nuclear fission reactors
Neutrons of intermediate kinetic energies are absorbed by uranium-238 nuclei within the fuel rods which quickly decay into plutonium-239 ehich is one of the most hazardous materials produced.
Radioactive waste is hard to dispose of and can have extremely long half-lives
What is Nuclear fusion
a process where small nucleus are combined to make larger nuclei producing enormous amounts of energy
The only way to make nuclei fuse is to …
bring them close together within a few 10^-15 m of each other so that short-range strong nuclear forces can attract them into a larger nucleus
Conditions for nuclear fusion
high temperature and high pressure from high density
proton-proton cycle or hydrogen-burning cycle.
Two protons fuse together to produce a deuterium nucleus, a positron and neutrino to produce 2.2Mev of energy. The two single protons have 0 binding energy and the deuterium nucleus has a binding energy of 2.2Mev (the difference is the energy released in the reaction). The deuterium fuses with a proton to make a helium-3 nuclei and 5.5Mev of energy. The helium-3 combines with another helium-3 to form a helium-4 and two protons and 12.9MeV of energy.
How many times does the proton-proton fusion reaction occur in the sun
9x10^37 times a second
Why are there no fusion reactors yet
it is difficult to maintain high temperatures for long enough to sustain fusion and on confining the extremely hot fuel within a reaction.
