Nuclear Physics Flashcards
Describe Rutherford’s scattering experiment (6)
- Beam of alpha particles was directed at a thin gold leaf
-Curved Fluorescent screen surrounds the gold leaf
-In a Vacuum so that no collisions between air particles and alpha particles can occur
-Most alpha particles pass straight through
-Some alpha particles are reflected back
- From this he deduced that most of the atom is made form empty space, but a large positively charged ‘Nucleus’ at its centre.
Name 3 types of radiation
Alpha, Beta , Gamma
Which type of radiation is the most ionising?
Which type of radiation is the most Penetrating?
Which type of radiation is the least ionising?
Which type of radiation is the least Penetrating?
Alpha
Gamma
Gamma
Alpha
Name a material that can block each type of Radiation
Sheet of paper - Alpha
Thin layer of Aluminium - beta
Several inches of Lead - gamma
Write a general equation that explains electron capture
P + e- ——-> N + electron neutrino
Why is ionising radiation dangerous
- Kills and mutate cells
- lead to tumours and cancerous cells
Explain which type of radiation is most harmful inside the human body
Alpha
Highest ionising power
More cells would be damaged
Very poorly penetrating
So radiation wont be able to leave the body
Give an example of an everyday use for beta decay
Measuring the thickness of a material on a production line
Used as a sensor to alter the positions of equipment relative to changes in the thickness of the material produced.
Beta used as alpha isnt penetrating enough and gamma is too penetrating
What does the inverse square law state?
Which type of radiation follows the inverse square law the best?
The intensity is inversely proportional to the square of the distance from the source
Gamma
What is intensity?
What is its standard unit
The energy per second passing normally through a unit area.
Watts per square meter (Wm^-2)
Describe an Experiment that can be used to show the inverse Square law with gamma rays (6)
- Measure background radiation with Geiger Muller tube without the gamma source in the room
-Place Gamma source at a set distance (1m) away from the GM tube - measure the count rate
- Record 3 measurements and take an average, take away the background radiation from this average.
- Repeat steps 2&3 but with incrementing distances of 10cm away from the initial placment of the source
- Square each of the distances and plot a graph of count rate against 1/ Distance^2
- straight line through origin shows inverse direct proportion ( and inverse)
What is background radiation?
Radiation that is constantly in our surroundings caused by things such as rock, minerals and food
What is the Decay Constant?
What are the units for the Decay Constant?
The probability of a nucleus Decaying per second
S^-1
What is a Half-Life
The time taken for the mass, activity or count rate of an isotope to decrease to half of its initial value
Half Life =
ln(2) / Decay Constant
Number of Nuclei Decayed =
N(0) * e^( -Decay constant/time)
Exponential Decay
What is Activity?
What is it measured in?
What formulas are there to calculate it?
The number of nuclei in an unstable radioactive isotope that decay per second
Bq
Decay Constant * Number of Nuclei left
ln(2) * Number of nuclei/Half Life
Change in Nuclei/ Change in Time
Describe the Desirable properties of a Radioactive a source used in medicinal Tracers
-Gamma Emitting
-Non-ionising radiation (minimal damage to cells)
-Penetrating Radiation (passes out through body easily)
-Short half life —> long enough to be detected —-> short enough to not cause the patient sickness
What does the N and Z graph Show
Describe the graph
Shows the relationship between proton number and neutron number
number of Neutrons (N) against number of protons (Z)
Starts as the line N=Z until N value of 20
The graph then shows exponential growth
Stability line passes through (80,120)
Z values greater then the stability line are proton rich and undergo beta plus decay
N values greaterthen the stability line are neutron rich and undergo beta minus decay
Alpha Emitters are above Z=60 , majority of alpha emitters are above Z=82
On the N-Z, explain why being above or below the stability affects the most probable radiation type.
Below stability line, nuclei isotopes are proton rich —> protons decay into neutrons with a byproduct of a neutrino and positron (beta plus)
Above stability line, nuclei isotopes are Neutron rich —> Neutrons decay into protons with a byproduct of an anti-neutrino and electron (beta minus)
Heavier nuclei above Z=60 , often decay as alpha radiation , as they are rich in protons and neutrons
Alpha particle is fired at a nucleus at a known speed
Describe how you would calculate its closest possible approach to the nucleus
1) Use speed and mass to calculate Kinetic energy of alpha particle
2) Equate kinetic energy losses to gain in electric potential (formula in book)
3) Rearrange for R
How is electron diffraction used to determine the diameter of a nucleus
1) Electron bean fired at a thin sheet of desired atom
2) Diffraction patter produced on screen behind
3) angle of minimum (diffraction) can be used to determine the diameter
What is the proposed relationship between Nuclear radius and Nucleon Number (A)
r = r(O)*A^(1/3)
Radius is directly proportional to cube root of nucleon number
What is the equation to convert mass to its energy equivalent?
E=MC^2
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?
Energy is need to bring the constituent parents of the nucleus together
Therefore the mass equivalent of energy is lost and the total mass decreases
Give the two definitions for binding energy
The work that must be done to separate the nucleus into its constituent nucleons
The energy released when a nucleus is assembled form its constituent nucleons
What is nuclear fission
Where a unstable nucleus splits into 2 smaller daughters nuclei
They binding energy per nucleon increases where fission occurs, therefore the overall process releases energy
What is Nuclear fusion
When two small nuclei fuse together to create a larger nucleus.
The new nucleus has a larger binding energy per nucleon, then the old nuclei together Therefore energy is released in this process
Why is it difficult to create nuclear fusion on earth
Lots of electromagnetic repulsion between two positively charged nuclei, therefore a lot of energy is required to overcome the IM forces to fuse them.
Hard to find a material that can withstand the heat and remain cost effective
High Temperature High pressure
Describe the process of nuclear fission in a reactor
Rods of a radioactive isotope absorb neutrons and become unstable and split into two daughter nuclei. The process emits more 2/3 neutrons.
In a nuclear reactor what is the purpose of a moderator
Give an Example
Slows down neutrons so they travel slow enough to be absorbed by the uranium
Does this through elastic collisions between moderator and neutrons.
Water
In a nuclear reactor what is the purpose of the control rods?
-Stop the chain reaction from being out of control
-Boron Absorbs neutrons so that only 1 neutron is released per fission reaction.
-If not the reactor would overheat as turn into a uncontrollable chain reaction.
Why is water used as a coolant?
Allows heat from the reactor to escape, to prevent overheating
What is the critical mass?
The minimum mass of fuel needed for a chain reaction to occur
Which waste product form a nuclear reactor poses the highest risk
Spent Fuel Rods
How is High Level waste disposed of?
Firstly theyre stored in cooling pods’
Then placed in sealed steel containers and put deep beneath water or Deep underground
How is low level waste disposed of
Sealed in containers and put underground until safe to retrieve
Describe the relation ship between nuclear radius and nuclear density
Both are independent
Nuclear density is constant throughout all elements
Explain why a student should subtract background radiation from their count rate results
Reduces the amount of systematic error within their results, as background radiation will always inflate your results.
State examples of Background radiation (6)
Radon (gas) / Radioactive rocks / cosmic rays / radioactive isotopes in living organisms / nuclear waste / medical sources
Calculate the time taken for 2.5g or uranium- 236 to be created from 5g of neptunium-236
The likelihood of a neptunium atom decaying into uranium-236 is 0.873
Half life of Neptunium is 1.5X10^5 years
5.448x10^21 is the number of molecules left of N-236
7.31 X 10^21 is the number of molecules that have decayed
Both are alpha particle emitters, Radiation is very ionising from both, meaning they can damage and kill cells within bodies
Radon is a gas. This leaves it with a higher contamination risk then Radium which is solid at room temperature, as it can be breathed in.
Radon being colourless and odourless makes it very hard to detect, increasing contamination risk.
Radon has a much shorter half life then radium meaning in the same time , it will emit more ionising radiation then radium, delivering a high dose of radiation and possibly damaging the body
If a nuclear equilibrium is met between two elements, and the rate of production of one and decay of another is equal. What is the same about the two elements.
Activity of both are equal
What safety measures are in place within Nuclear Power Plants
CARESS
C- Concrete vessel and building to store reactor to absorb ionising Radiation
A-Air expelled from nuclear power plants is filtered to remove radioactive isotopes
R-Remote Handling to reduce exposure of employees
E-Emergency Shutdown Procedures
S-Steel Vessel for core reactor
S-Spent fuel rods placed in lead lined containers and placed under water
Explain what would happen to the nuclear chain reaction within a reaction if the moderator was removed
Speed of Neutrons would be too quick for uranium to absorb, so the rate of fission reaction would significantly decrease.
State 1 factor that affects how efficient a material would be as a moderator
Size of the Materials particles
Particles of similar mass to a neutron mass are most efficient
Why is there an imbalance between proton and neutron numbers, with larger atomic numbers
Protons are the only nucleon that feel the electromagnetic force.
Greater amount of electromagnetic repulsive forces between protons, requires a much greater amount of neutrons.
To increase the magnitude of the strong force, so it can overcome the electromagnetic force which acts over a much larger range.
Explain 2 origins for electromagnetic radiation
Excited electrons, de-excite releasing to lower energy levels, with the energy difference released as electromagnetic radiation.
Excited Nucleus emits gamma radiation as it de-excites
State benefits for Nuclear Power
- Small amounts of fossil fuels used, so little greenhouse gas emissions
-Small amounts of fuel consumed ti generate large amounts of energy
-Continuous Energy production Compared with Renewables
-Produces isotopes that can be used as medical Tracers
Explain how you would reduce systematic error from the inverse square law experiment
-Measure background radiation prior to the radioactive source being within the room, take this value away from, each value measured.
-Check the ginger counter/ stopwatch has no zero error
-Place source in lead container
Explain how you would reduce % uncertainty from the inverse square law experiment.
Measure the Intensity over a longer period of time.
Which type of radiation is most optimal for sterilising hospital equipment and why?
Gamma
Most penetrating radiation as all the sides of the equipment can be irradiated without removing any packaging
Explain why you don’t have to worry about irradiated hospital equipment becoming radioactive
The become radioactive the nucleus has to become affected,
Radiation emitted only affects outer electrons and not the nucleus
Explain possible reasons why results sometimes wont follow the inverse square law.
Dead time in GM detector
Distance between sources are incorrect
Didn’t account for background radiation prior to getting results
Source may not be a pure gamma emitter
Explain any problems in disposing of nuclear waste
Waste to too hot initially, so hast to be placed in cooling ponds to remove the heat
Initially the waste is highly radioactive and only can be remotely handled
Waste will be radioactive for many centuries, so long term storage has too be in geologically stable areas
