Nuclear Energy (not quite done!) Flashcards
Where do stable nuclei lie on the graph of N against Z?
The centre of the band, central belt that curves upwards. For Z < 20, N ~= Z, For Z > 20, N/Z > 1.
When do particles start emitting alpha radiation?
USUALLY when Z > 60 or so, as the strong nuclear force cannot then overcome the electrostatic repulsion between protons.
When does beta minus decay occur?
On isotopes to the left of the stability belt who are too neutron-rich
When does beta plus decay occur?
On isotopes to the right of the stability belt who are too proton-rich
When does electron capture occur?
To the right of the stability belt, as it turns a proton into a neutron and removes an electron.
What do the different decays look like on an N-Z graph?
Alpha is 2 down and 2 left; beta + is 1 up and 1 left, beta - is one down and 1 right.
How are radioactive decay series represented?
Chains of decays on the N-Z graph.
What are excited states in nuclear energy?
Atoms being left in an excited state after a radioactive decay; they then emit gamma radiation before returning to the ground state,
What are metastable states?
Stable states that last for at least 1 nanosecond, can be useful in medicine as they can be sources that only emit gamma.
What is the typical radius of a nucleus?
Around 1fm, 1 x 10 ^-15 m
How can you estimate the nuclear radius using an alpha particle?
Use the distance of closest approach of an alpha particle to a nucleus of charge Qn. EPE will be equal to Ke.
So r = Qn Qa / 4pi e0 x E(k)
How can you determine nuclear radius from diffraction?
First minimum, theta min, is given by sin theta = 1.22 lambda / d where lambda is de broglie of an electron and d is diameter.
How do you determine nuclear radius from nucleon number?
R = R0 A^1/3 , A is nucleon number, R is radius and R0 is 1.05 x 10^-15
What is the mass defect, and what does it allow you to calculate?
The difference in the mass before and after a reaction or decay where energy is released; allows you to calculate the energy released through E = mc^2.
What is the mass defect of a nucleus?
Difference in mass between the separated nucleons and the mass of the nucleus, equal to the energy released when the nucleus forms from all these separate neutrons and protons.
What is nuclear fission?
A large unstable nucleus splitting into 2 smaller nuclei
What is nuclear fusion?
Small nuclei joining together to form a larger nucleus.
What is induced nuclear fusion?
Splitting heavy nuclei by firing slow-moving thermal neutrons at them (in thermal equi. with their surroundings)
What is the binding energy of a nucleus equal to?
mass defect x c^2, deltam x c^2. A measure of the stability of the nucleus - the higher the binding energy the more stable the nucleus.
How can you calculate the energy released from fission or fusion?
The change in binding energy per nucleon.
What is the most stable nucleus?
Iron-56
What does increasing the binding energy do?
Release energy.
What is the equation for fission in a reactor?
n + U -> Kr + Ba + n + n + n
What are some safety features of reactors?
Thick concrete walls to absorb radiation
Rad. fuel rods inserted and removed using remote handling devices
Control rods fully inserted in emergencies
How are spent fuel rods disposed of?
Removed with remote handling devices, placed in cooling ponds. Then reprocessed so some products can be used for other things.
How is radioactive waste disposed of?
Stored, usually in stainless steel containers in concrete vaults to isolate it from the environment.
What are the advantages and disadvantages of nuclear power?
Can produce huge amounts of energy without producing greenhouse gases, but produces waste and is extremely expensive and time-consuming to commission, maintain and decommission.
What are control rods usually made of?
Boron or cadmium, absorb neutrons and so control the rate of the reaction.
