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chapter 24 - particle physics Flashcards

(34 cards)

1
Q

plum pudding model

A

atom contained neg electrons embedded in a sea of uniform pos charge

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2
Q

Rutherfords alpha scattering experiment

A
  • fired a narrow beam of alpha particles with the same KE at at piece of thin gold foil - so particles are defelected once - one layer of atoms
  • alpha was scattered by foil and detected on a screen - when they hit the screen produced a speck of light
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3
Q

Rutherfords alpha scattering experiment observations/ conclusion

A
  • most passed through with little scattering - mostly empty space
  • very few were deflected by large angles- mass was mostly concentrated in a small volume - of positive charge
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4
Q

size of atom/ nucleus

A

the fraction of the particles scattered a lot = the fraction of the atom taken up by the nucleus
nucleus radius = 10^-14
atom radius = 10^-10m
1mm dot on a 100m running track

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5
Q

how is radius of atom estimated

A

use distance of closest approach - fire alpha particle directly at it
KE > EPE - where it stops
1/2mv^2 = kQq/r^2
solve for r

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6
Q

neutrons discovered

A

Chadiwck noticed that alpha particles hitting beryllium nuclei knock off neutrons

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7
Q

nuclear model of atom

A

nucleus contains positive protons and uncharged neutrons
proton and neutron have about the same mass

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8
Q

isotopes

A

same number of protons with different number of neutrons
isotopes of same element undergo same reactions

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9
Q

atomic mass unit

A

one atomic mass unit is 1/12 the mass of a neutral C-12 atom

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10
Q

nuclear size

A

radius depends on nucleon number (A)
R = r0A^1/3
where r0 = 1.2fm (10^-15) - radius of a hydrogen nucleus (one proton)

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11
Q

strong nuclear force

A

acts between all nucleons
short range force (effective over a few fentometres)
attractive to 3fm
and repulsive below 0.5fm
large - much more than electrostatic

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12
Q

antimatter

A

every particle has a corresponding antiparticle
has same mass and opposite charge
if the two meet they destroy each other - annihilation - mass of poth particles are converted into a high energy pair of photons
symbol is bar over letter

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13
Q

fundamental forces

A

weak nuclear force - responsible for beta decay
strong nuclear - experienced by nucleons
electromagnetic - experienced by static and moving charges
gravitional - experienced by masses

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14
Q

weak nuclear force

A

responsible for beta decay within unstable nuclei

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15
Q

fundamental particles

A

has no internal structure - cant be divided smaller
eg quarks, electrons, neutrinos (leptons)

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16
Q

hadrons

A

affected by strong nuclear force
decay by weak nuclear force
if charged exoerience EM force
made up of quarks
heavy
eg protons, neutrons, mesons

17
Q

2 types of subatomic particle

A

hadrons
leptons

18
Q

leptons

A

not affected by strong nuckear force
if charged experience EM force
fundamental particels
light
eg electrons, neutrinos, muons
electron, muon tau charge -1
neutrinos charge 0
all lepton number 1

19
Q

quarks

A

make up hadrons - fundamental particle
6 quarks with antiquarks
up, down
charm, strange
top, bottom

20
Q

up quark

A

charge + 2/3
baryon +1/3
lepton 0

21
Q

down quark

A

charge -1/3
baryon +1/3
lepton 0

22
Q

strange quark

A

charge -1/3
baryon +1/3
lepton 0

23
Q

antiquarks

A

same mag of charge/ baryon but opposite sign

24
Q

class of quarks

A

up, down
charm, strange
top, bottom
2/3, -1/3 charge
1/3, 1/3 baryon
increase in mass/ energy as you go down

25
protons
+1 charge uud
26
neutrons
neutral charge udd
27
2 types of hadrons
mesons baryons
28
baryons
- all hadrons with 3 quarks eg proton, neutrons
29
mesons
- hadrons made of a quark and antiquark eg pion, kaon
30
neutrino
no charge - tiny mass leptons 3 types - electron, muon and tau each also has its own antineutrino
31
beta decay
due to weak nuclear force either beta - or beta +
32
beta - decay
neutron changes to proton and electron neutron > proton + electron + anti electron neutrino d > u + e- + anti electron neutrino
33
beta + decay
proton changes to a neutron and positron proton > neutron + positron + electron neutrino u > d + e+1 + electron neutrino
34
conservation
in particle interactions have to conserve: - charge - baryon number - lepton number - stangeness (-1 strange, 0 for every other quark)