Nuclear Physics Flashcards
Describe the Rutherford Scatteing experiment
● Beam of alpha particles directed at thin gold foil
● Occurred in a vacuum so no collisions between air particles and alpha particles
● Was done to determine structure of an atom
In the Rutherford Scattering experiment it was observed that most of the alpha particles passed straight through. What can we infer from that?
Most of the atom consists of empty space
What evidence was there that suggested the nucleus had a positive charge?
Because it caused some of the positive alpha particles to be repelled/deflected (like-charges repel)
Name 3 types of radiation
Alpha, Beta, Gamma
Order Alpha, Gamma and Beta radiation in order of ionising power, starting with the most ionising
Alpha, Beta, Gamma
Order Alpha, Gamma and Beta radiation in order of penetration power, starting with the most penetrating
Gamma, Beta, Alpha
A sheet of paper can block which type of radiation?
Alpha
When a nucleus decays through gamma radiation, how does the atomic number and mass number change?
They remain the same as the number of protons and neutrons doesn’t change
Why is ionising radiation seen as dangerous?
Because it can kill or mutate cells, leading to things such as cancer
Which radiation is more harmful inside a human body, Alpha or Gamma?
Alpha
Give an example of a real life use of Beta decay and explain why Beta is chosen for this
Measuring paper thickness - Alpha is not penetrative enough and Gamma is too penetrative
Which type of radiation follows the inverse square law?
Gamma
What does the inverse square law state?
The intensity is inversely proportional to the square of the distance from the source
What is intensity measured in?
W/m²
What is background radiation?
Radiation that is constantly in the surroundings from sources such as rocks and food
What is the decay constant (λ)?
The probability of a nucleus decaying per second
What are the units for the decay constant (λ)?
S‐¹
What is Half-life?
The time it takes for half of the unstable nuclei in a substance to decay
What equation can you use to work out the half-life of an object?
T½ = ln(2)/λ
Complete the equation, λN = ?
Activity
What is activity measured in?
Becquerels (decays per second)
True or False: Radioactive isotopes decay exponentially?
True
Why is Technetium-99 useful in medicine?
Gamma radiation has a short half life, so it doesn’t stay radioactive for long, and is easy to detect outside patient.
What does the graph of N against Z show?
The relationship between Proton number and Neutron number
Where on the curve does β- decay occur and why?
Above the stability line - nuclei contain too many neutrons
What type of decay occurs below the stability line and why?
β+ as these nuclei contain too many protons
How does the heavier nuclei often decay?
Alpha decay
An Alpha particle is fired at a nucleus, with the KE at the start known. How can you use energy conservation to find closest approach of a particle?
At this point, the KE and PE are equal, so we can rearrange for distance (r)
How is electron diffraction used to determine the diameter of a radius?
● Electron beam fired at thin sheet
● Diffraction pattern produced on screen behind
● Calculate diameter using angle of a minimum
What is the relationship between nuclear radius (R) and nucleon number (A)?
Nuclear radius is directly proportional to the cube root of the nucleon number
True or False: the density of a nucleus is independent of its radius?
True
What equation is used to convert mass to its energy equivalent?
E = mc²
What is the mass defect?
The difference between the total mass of all the nucleons separately compared to the mass of the nucleus
Why is there a mass defect?
Because energy is needed to bring the parts of a nucleus together, therefore the mass equivalent of the energy is lost and the total mass decreases
What is binding energy?
The energy required to separate a nucleus into its constituent parts
What is nuclear fission?
Where a large unstable nucleus splits into 2 smaller nuclei, releasing energy
What is nuclear fusion?
When 2 small nuclei fuse together to create a large nuclei, releasing large amounts of energy
Why is it difficult to make nuclear fusion occur on earth?
There is a large repulsion between the 2 positively-chatged nuclei, therefore a lot of energy is required to overcome the repulsion and fuse them together. It is hard to find a material that can withstand the heat
How is nuclear fission used in nuclear reactors?
Rods of Uranium-235 absorb neutrons and become unstable, causing them to spilt into two daughter nuclei
What is the purpose of a moderator in a nuclear reactor?
To slow down the neutrons so they travel slow enough to be absorbed by the uranium
Why are control rods essential for a nuclear power station?
They stop the chain reaction from getting out of control by absorbing neutrons
Is Boron used as a control rod or a moderator?
Control rod
Give an example of a material that can be used as a moderator in a nuclear reactor?
Water
What is the purpose of using water as a coolant?
It allows heat from the nuclear reactor to escape, stopping the reactor from overheating
What is the critical mass?
The minimum mass of fuel needed for a chain reaction to occur
Which waste products from a nuclear reactor cause the highest risk?
Spent fuel rods
How is high-level waste disposed of?
● First stored in cooling ponds
● Then they are put in sealed steel containers and put deep underwater
What is low-level waste contained in?
They are sealed in containers and put underground until they are safe again
Why is the constant density of nuclear material derived from the equation R =R⁰A⅓ only approximate?
It assumes a uniform distribution of nucleons within the nucleus
How is fission induced?
By firing a thermal neutron into the elements nucleus, causing it to become extremely unstable
What is binding energy (mass defect ) equal to?
Mass of nucleons - Mass of nucleus
In a fission reactor, what do the control rods do?
Absorb excess neutrons to slow down the chain reaction to stop it from getting out of control
In a fission reactor, what does the moderator do?
Slows down the neutrons to allow them to be absorbed easier and to sustain the chain reaction
What provides evidence for the existence of energy levels in nuclei?
The existence of gamma radiation
