2. Particles and Radiation Flashcards
Equation for specific charge:
Specific charge = charge / mass
Therefore the specific charge is the charge-mass ratio.
What is an isotope and it’s uses?
Atoms with the same number of protons but different numbers of neutrons.
Carbon dating: by comparing how much carbon-14 is in the dead organism with the amount in a living one and knowing it’s half life.
What is the strong nuclear force?
The force which keeps nuclei stable by countering the electrostatic force of repulsion between the protons.
Over what range does the strong force act?
It’s repulsive for distances below 0.5 fm, and the attractive until about 3 fm.
What are unstable nuclei?
Nuclei which contain too many protons, neutrons, or both, thereby causing the strong force to be unable to keep them stable. So they will decay.
What decay occurs in nuclei with too many protons and neutrons?
Alpha decay, where 2 protons and 2 neutrons are ejected in the form of an alpha particle (α): the nucleon number decreases by 4, the proton number decreases by 2.
What decay occurs in neutron rich nuclei?
Beta-minus decay, where a neutron is converted into a proton and a fast moving electron (β) and neutrino (ν^-) pair which are ejected from the nuclei: the proton number increases by 1, the nucleon number stays the same.
How were neutrinos hypothesised?
Without them energy would not have been conserved during beta-minus decay.
What is an antiparticle?
Something which has the same rest energy and mass as it’s particle counterpart, but the opposite of every other property.
What is annihilation?
What occurs when a particle and antiparticle collide. Their masses are converted into energy. This energy combined with their kinetic energy will form two photons moving in opposite direction in order to conserve momentum.
What’s an application of annihilation?
PET scanners, a positron emitting radioisotope is introduced into a patient. When the positrons are released, they will annihilate with the electrons already in the system and release gamma photons which can be easily detected allowing 3D images of inside the body to be taken.
What is pair production?
Where a photon is converted into an equal amount of matter and antimatter.
What are the fundamental forces?
Gravity, electromagnetic, weak nuclear, and strong nuclear.
What causes forces between particles?
Exchange particles: these carry energy and momentum between particles.
Strong force: exchange particle, range, acts on:
Gluon, 3x10^15, hadrons
Weak: exchange particle, range, acts on:
W boson (W+ or W-), 10^-18, all particles
Electromagnetic: exchange particle, range, acts on:
Virtual photon (γ), infinite, charged particles
Gravity: (exchange particle), range, acts on:
(Graviton), infinite, particles with mass
What is the weak nuclear force responsible for?
Beta decay, electron capture, and electron-proton collisions.
Interaction diagrams (page 6 on PMT)
What are leptons?
Fundamental particles. They do not experience the strong nuclear force.
What are hadrons?
Particles made of quarks.
What are baryons?
Hadrons formed from 3 quarks.
What are mesons?
Hadrons formed from a quark and an anti-quark.
What is the baryon number?
An indication as to whether something is: a baryon (1), an antibaryon (-1), or not a baryon (0). The baryon number is always conserved in particle interactions.
What will happen to all baryons?
They will decay into the only stable baryon: the proton.
What is the lepton number?
An indication as to whether something is: a lepton (1), an antilepton (-1), or not a lepton (0). The lepton number is always conserved in particle interactions.
What are the types of lepton number?
Electron lepton number and muon lepton number.
What is a muon described as?
A “heavy electron”, they also decay into electrons.
What are strange particles?
Strangeness (s) proves that particles are always created in pairs.
Particles which are produced by the strong nuclear interaction but decay by the weak interaction (kaons decay into pions).
Strangeness is conserved in strong interactions but can change by +1, 0, or -1 in the weak.
What’s needed to investigate particle physics?
Particle accelerators: scientific investigations rely on collaboration of scientists internationally.
How do you represent antiquarks?
With a line above their usual symbols.
What must be conserved in particle interactions?
-energy and momentum
-charge
-baryon number
-lepton number
(-strangeness during strong interactions)
What is the photoelectric effect and what does it prove?
It’s where photoelectrons are emitted from the surface of a metal after light above the threshold frequency is shone at it.
It proves that EM waves travel in discrete packets called photons, which have energy that is directly proportional to frequency. Each electron can absorb a single photon. If the intensity of the light is increased and the frequency is above the threshold, more photoelectrons are emitted per second.
What is the work function?
The minimum energy needed for electrons to be emitted from the surface of a metal, φ.
What is the stopping potential?
The potential difference you would need to apply across a metal to stop the photoelectrons with the maximum kinetic energy.
Ek(max) = eVs (where e is the charge of an electron and Vs in the stopping potential)
What happens if electrons gain energy?
Excitation where electron move up in energy level, or ionisation where electrons are removed from the atom entirely.
How do fluorescent tubes work?
Fluorescent tubes are filled with mercury vapour, across which a high voltage is applied, thereby accelerating free electrons through the tube, which collide with the mercury atoms causing the electrons to become excited. When they de-excite they release UV photons, which the fluorescent (phosphorus) coating on the inside of the tube absorb causing their electrons to become excited which de-excite and release photons of visible light.
What is an electron volt?
A measure of energy which is equal to the charge of an electron.
What do line spectra show?
The different wavelengths of light coming from a source. This proves that electrons can only transition between discrete energy levels.
You can also get line absorption spectra which show every colour of light with black lines representing where it has been absorbed.
What are some experiments to prove the wave-particle duality of light?
Wave: diffraction and interference.
Particle: photoelectric effect.
What is an experiment to prove the wave like properties of electrons?
Electron diffraction, it will show an interference pattern: a large white spot in the middle with concentric circles becoming ever fainter.
How do scientific views change?
Knowledge and understanding of any scientific concept changes over time in accordance to the experimental evidence gathered, which must first be peer-reviewed by the community to become validated, and eventually accepted.
Threshold frequency; photon explanation of threshold frequency.
Why does increasing the momentum of the particle change the amount of diffraction?
De Broglie wavelength…
