Nuclear Physics Flashcards
-what did the Rutherford scattering prove?
- what did it contradict?
-the existence of a nucleus
-contradicted Thomson’s plum pudding model, which stated the atom was made up of a sea of positive charge and small areas of electrons embedded
What equipment did Rutherford use?
- alpha source
-gold foil - chamber covered in fluorescent coating
what would the Rutherford experiment show if the plum pudding model was true?
positively charged alpha particles would be deflected by a very small amount when passing through the foil
What were the actual results for the Rutherford experiment and what did they mean?
-most alpha particles passed straight through the foil with no deflection
= atom is mostly empty space
-A small amount of particles were deflected by a large angle
= centre of atom is positively charged
-Very few particles were deflected by more than 90°
=centre of atom is vert dense and small
What are the 3 types of radiation?
-Alpha
-Beta
-Gamma
What is the: (Alpha)
1. Range in Air?
2. Ionising power
3. Deflected by electric and magnetic fields?
4. What is it Absorbed by?
- 2-10cm
- Highly
- Yes
- Paper
What is the: (Beta)
1. Range in Air?
2. Ionising power
3. Deflected by electric and magnetic fields?
4. What is it Absorbed by?
- around 1m
- Weakly
- Yes
- Aluminium foil
What is the: (Gamma)
1. Range in Air?
2. Ionising power
3. Deflected by electric and magnetic fields?
4. What is it Absorbed by?
1.Infinte range
2. Very weak
3. No
4. Several metres of concrete or inches of lead
How would you identify which type of radiation is emitted?
- use Geiger counter to find background radiation
- place source of radiation close to Geiger counter and measure count rate
- Place sheet of paper between the source and the Geiger counter and measure count rate agin, if count rate decreases significantly then the source is alpha radiation
- Repeat with aluminium foil and several inches of lead, if a significant decrease for aluminium foil, then it is beta. if a significant decrease for several inches of lead, then it is gamma
How can these types of radiation be used to monitor the thickness of certain materials while they are being produced?
e.g for the production of aluminium foil, a bet source is placed on one side of the material, while a detector is placed on the other. If the material becomes to thick, less beta radiation will pass through the foil, therefore the reading on the detector decreases causing the roller to move closer; opposite for the material becoming too thin. Same method for alpha and paper, and gamma and steel
what are the applications of gamma radiation?
-sterilise surgical equipment
- radiotherapy
what is the equation for the intensity of radiation? (inverse square law)
I= k / x²
how would you verify the inverse square law?
measure the count rate of a gamma source at different distances from the GM tube, making sure to adjust to the background radiation. then plot graph of corrected count rate to 1/x² which will form a straight line
How can radioactive sources be handled safely?
-use of tongs
-storing in lead-lined container when not in use
-limit exposure
what are examples for sources of background radiation?
-Radon gas
-Cosmics rays
-Rocks
what does random mean?
you can’t predict when the next decay will happen
what is the decay constant, λ?
the probability of a nucleus decaying per unit time
what is the exponential equation for the number of nuclei?
N= N₀e^(-λt)
-what is half-life?
- what is the equation for half life?
-the time taken for the number of nuclei to halve
- T₀.₅=ln2/λ
-what is activity?
-what is the equation for activity?
-the number of nuclei that decay per second
-A=λN
what is the exponential equation for activity?
A=A ₀e^(-λt)
what are the applications of half life?
-dating of objects
-medical diagnosis
why might a nucleus become unstable?
-too many neutrons
-too many protons
-too many nucleons
-too much energy
why, on a Graph of N against Z for stable nuclei, do the number of neutrons and protons not increase uniformly?
because beyond a certain point, the electromagnetic force of repulsion becomes larger than the strong nuclear force keeping the nucleus together, so more neutrons are needed to increase the distance between the protons in order to decrease the magnitude of the electromagnetic force keep the nucleus stable
what is a source of gamma radiation for medial diagnosis?
technetium-99m
what is the equation for the radius of a nucleus?
R=R₀A¹/³
what is binding energy?
the energy required to separate the nucleus into its constituents
what is the value of 1u in kg? and in MeV?
1.661x10⁻²⁷kg
931.5MeV
what is nuclear fission?
the splitting of a large nucleus into two daughter nuclei
what is nuclear fusion?
where two smaller nuclei join together to form one larger nucleus
why does fusion occur only at extremely high temperatures?
it requires a lot of energy to overcome the electrostatic force of repulsion between nuclei
On a fission/ fusion graph, what is on the left and right of the peak?
left is fusion and right is fission
what is nuclear fission used for?
used in nuclear power plants in order to create electricity without the emission of greenhouse gases
what are dangers of nuclear fission in nuclear power plants?
-the daughter nuclei produced in fission are radioactive and will need to be stored underground for thousands of years
-meltdowns can cause devastating harm to the environment
how can fission be induced?
by firing a thermal neutron into a uranium nucleus causing it to become extremely unstable
what is the critical mass?
the minimum mass required to. maintain a steady chain reaction
what are the key features of a nuclear reactor?
-Moderator
-Control rods
-Coolant
what is the function of a moderator?
-an example and why?
this slows down the neutrons released in fission reactions to thermal speeds
-water, as it’s inexpensive and not very reactive, or graphite
what is the function of control rods?
-what are they made of?
absorb neutrons in the reactor in order to control chain reactions. i.e control amount of energy produced
-boron and cadmium
what is the function of coolant?
-an example and why?
absorbs heat released during fission reactions in the core of the reactor and that used is used to make steam which power electricity-generating turbines
-water is used as it has a high specific heat capacity, meaning it can transfer large amounts of thermal energy
what is the fuel used in nuclear reactors?
enriched uranium which consists of U-238 and U-235
what are the safety precautions taken in a nuclear reactor?
- very thick concrete shielding around the reactor which blocks radiation from escaping the reactor and affecting the workers
-in an emergency, the control rods are dropped into the reactor entirely in order to stop fission reactions from occurring
what are the types of waste
-high level?
-low level?
-high level: the daughter nuclei produced which are usually extremely unstable and have a very high activity (spent fuel rods)
-low level: short lived radioactivity such as equipment used
how is radioactive waste processed?
- waste is removed and handled remotely to limit exposure
- material removed from the reactor will be extremely therefore they are placed in cooling ponds for up to a year. cooling ponds tend to be on site
- any usable plutonium or uranium is removed to be recycled
- waste is then vitrified and placed in thick steel casks and stored in deep caverns in geologically stable locations
what are the cons and benefits of nuclear power stations?
-benefits: no polluting gases, reliable, far less fuel required compared to coal
-cons: produce radioactive waste and risk of a nuclear meltdown could have catastrophic consequences
