Chapter 6.4 - Nuclear and Particle Physics Flashcards
Alpha particle scattering experiment and what it proved
A stream of alpha particles were emitted at a piece of gold foil. Most of the particles went straight through, but some were reflected back. This meant that matter must be mostly empty space with small, dense positively charged pockets (the nucleus)
fm
femtometer - 10-15m
Standard notation for an atom
AZX
Where
A is mass number
Z is proton number
Radius of a nucleus
R = r0A1/3
where
r0 is a constant
A is the mass number
Value of r0
1.4 fm
Strong nuclear force
The force that holds the nucleus together against the repulsion of the electrostatic repulsion
How the strong force varies with distance
Repulsive < 0.5 fm
Attractive enough to overcome electrostatic repulsion at < 3 fm
Hadron
Particles that feel the strong nuclear force (made of quarks)
What is the only stable hadron
Proton
Lepton
Fundamental particles that don’t feel the strong force but do feel the weak nuclear force
Examples of hadrons (2)
proton, neutron
Examples of leptons (2)
Electron, neutrino
Antiparticle and its properties
Every particle has an antiparticle with the same properties, except it will have the opposite charge
Pair production
When energy is transformed into a particle and an antiparticle
How a gamma ray might create antimatter
A high energy photon can turn into a electron and a positron via pair production. The energy of the photon (hf) is transformed into the mass of the two produced particles (leftover energy is put to their kinetic energy)
Annihilation
When a particle meets its antiparticle the mass of both is converted into energy in the form of two photons
Quark
The building block of hadrons
Quark composition of a proton
uud
Quark composition of a neutron
udd
up quark charge
+2/3
down quark charge
-1/3
strange quark charge
-1/3
β- decay
Occurs in a neutron rich atom. Neutron decays to a proton, electron and antineutrino. (d –> u)
β+ decay
Occurs in a proton rich atom. Proton changes into a neutron and emits a positron and a neutrino, (u–>d)
Radioactive decay
When a nucleus stabilises by releasing particles/energy in various forms
Properties of radioactive decay
It is spontaneous and random
What is meant by spontaneous and random
There is no way to know when a nucleus will decay. It can’t be predicted
Alpha radiation
A helium nucleus
β radiation
An electron
γ radiation
A gamma ray
ν (nu)
Symbol for neutrino
Range of β+ radiation
Effectively 0 since it will almost instantly be annihilated by an electron
How to investigate radioactivity
Place a material between a radioactive source and a geiger-muller tube and record the count rate over a period of time. Repeat with different materials
where α emmision occurs
Heavy nuclei
when γ radiation is emitted
When a nucleus has too much energy (often after alpha or beta decay)
Activity
The number of nuclei that decay each second
Decay constant
The rate at which a material will decay
Equation for activity
decay constant * undecayed nuclei
Half life
The average time taken for half of the undecayed nuclei to decay
Experiment to determine half life of an isotope
Calculate the background radiation rate first using a geiger-muller counter. Fill a bottle with uraniuam salt and protactinium-234. Shake the bottle so they mix and then wait for them to seperate again. Once they have seperated take measurements by measuring the count for 10 seconds. Repeat this measurement every say 30 seconds. Plot a graph and determine half life from it
Equations for half life, nuclei and activity
Just use common sense exponential maths
How carbon dating works
Living things take in carbon-14 from the atmosphere and all living things will have the same ratio of carbon-12 to carbon-14. When something dies the carbon-14 decays and is not replenished so the ratio will start to decrease. Therefore how long ago something died (e.g. paper from wood) can be determined. The half life of carbon-14 is about 6000 years so it is not suitable for very long ago (e.g. dinosaurs like if u wanted to know when a stegosaurous died or something like that maybe a pterodactyl idk)
Mass defect
The difference in mass between a nucleus and the sum of the masses of all its protons and neutrons if they were seperated
Binding energy
Equals the mass defect (E=mc2)
Graph of binding energy per nucleon against nucleon numbner
Goes up steeply then peaks and slowly decreases. Peaks at Iron
How to calculate energy released from a fission/fusion reaction
It is equal to the change in binding energy
How fission reactors work
Rods of uranium rich in 235U undergo nuclear fission, producing energy and emitting high energy neutrons. These neutrons go on to collide with other uranium atoms causing them to undergo fission and so on, in a chain reaction. The emitted neutrons are travelling to fast to cause fission so they are slowed down by a moderator such as water. To make sure that the chain reaction remains steady and does not get out of control, control rods made of boron are lowered into the case. These absorb some of the neutrons so that there are not enough to cause the reaction to get out of control. The heat from the reaction is then used to heat water and make steam, which powers a turbine and then a generator
Environmental impact of nuclear waste
Radioactive waste can take a long time to decay to safe levels
Natural distasters pose a risk to nuclear plants (e.g. Fukishima)
How nuclear fusion reactions work
Light nuclei under very high temperatures (much higher than in fission) combine and form a heavier nucleus and release lots of energy
