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aqqa A-level physics year 1 (yr12) particles and nuclides/fundamental particles : chapter 1/2
Particle Forces
force |
affects |
exchange particles |
range |
strong nuclear |
hadrons |
pion/gluon |
none- >4fm, attrac 0.5<x<4fm, repul <0.5fm |
em |
charged particles |
photons |
infinite |
weak nuclear |
all |
W+/-/ |
10-18 |
gravity |
all |
graviton |
infinite |
the strong nuclear force holds nucleons together in a nucleus. the repulsion at <0.5fm stops the nucleus imploding.
specific charge
specific charge:
charge to mass ratio
for an atom, is the charge (typically proton number unless an ion then the charge eg 2+ only) over the overall mass (proton and neutron number) |
nuclear decay equations
unstable nuclei decay to become more stable emitting radiation.
these can ionise other atoms/molecules which can be dangerous
Alpha decay (larger nuclei):
4 on the top, 2 on the bottom
Beta decay (smaller nuclei):
+ - p>n
- - n>p
**make sure lepton numbers are balenced
eg. beta- decay has anti electron neutrino
gamma radiation:
is a high energy EM wave that can be emitted but this isnt due to decay but due to nucleus being in an metastable state (excess energy)
in a decay equation you would write the product number at the top with a small m
in a separate equation you take the element with the m and write it out with the product being without the m and the gamma ray |
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conservation
charge, energy and momentum, baryon/lepton number must all be conserved in any interaction.
strangeness doesnt need to be conserved, only in strong interaction
rules:
- particle decay > strangeness is not always conserved
- pair production > strangeness is always conserved
strangeness:
- strange particles are produced by strong interaction
- to conserve strangeness they are always created in pairs
eg. p + p = us-s
- they decay via weak interaction but don't need to be created in pairs (don't have to be conserved)
proving conservation: (Relating to particle interactions)
B+/- --> occurs in a neutron (decay) - B+ = p>n
electron scatter --> come close and repel due to charge
P-N bond --> occurs in nuecleus due to strong force (also em however em is weaker than strong)
electron capture --> electron captured by a proton, therefore exchange particle is always from the proton (W+)
E-P collision --> electron collides with proton so exchange particle comes from the electron (w-) |
Annihilation and pair production
these are possible due to the fact that mass can be converted ubti energy and vice versa
Annihilation:
particle and antiparticle collide- mass is converted to two photons
minimum energy/frequency:
2mc2 = 2hf
if the particles have kinetic energy this is added to the photons energy
Pair production:
a photon of sufficient energy is converted into a particle and its antiparticle
minimum freq photon for this:
hf = 2mc2
if photon has more than minimum needed, it is converted into Ek |
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