Particle Physics

Question 1

what is nucleon number?

Answer 1

number of protons and neutrons in a nucleus

Question 2

what is an isotope?

Answer 2

an atom of an element with the same proton number but a different number of neutrons

Question 3

how does the number of neutrons affect how stable an atom is?

Answer 3

more neutrons makes an atom more unstable

Question 4

how to calculate specific charge
units?

Answer 4

charge/mass
Ckg^-1

Question 5

how does the affect of the strong nuclear force vary with distance?

Answer 5

attractive from 0.5fm to 3fm
repulsive at distances less than 0.5fm
has almost no effect beyond 3fm

Question 6

what particles are affected by the strong nuclear force?

Answer 6

nucleons (protons and neutrons)

Question 7

alpha radiation
- what is its range in air?
- what is is stopped/deflected by?
- what is its speed compared to speed of light?
- what is the relative charge on an alpha particle?

Answer 7

range is 5-10cm in air

stopped by paper or thin foil and easily deflected by a magnetic field

travels at around 10% speed of light

charge is +2 (helium nucleus)

Question 8

beta radiation
-what is relative charge on a beta particle?
- what is the speed of a beta particle compared to speed of light?
- what is it stopped/deflected by?

Answer 8

• relative charge is +-1e
• travels up to 98% speed of light
• stopped by a few mm of aluminium and deflected less than alpha particles in a magnetic field

Question 9

gamma radiation
- what is a gamma ray made of?
-what is the charge of a gamma wave?
-what speed does it travel at?
-what is it stopped/deflected by?

Answer 9

• made electromagnetic photons
  -uncharged (and massless)
  -travels at the speed of light
  -stopped by several cm of lead or a few metres of concrete. not deflected by a magnetic field

Question 10

general equation of beta - decay

Answer 10

nucleus ->(new nucleus with one extra proton) + (beta - particle) + anti-electron neutrino

Question 11

antiparticles
-differences and similarities between particles and antiparticles

-one identical particle and antiparticle
-one non-identical particle and anti-particle

Answer 11

similarities
-same mass
-same lifetime (for unstable particles)

differences
-opposite (but equal) charge

-identical particle and antiparticle is photons
-non identical particle and antiparticle are neutrinos/antineutrinos or electron/positron

Question 12

what happens during annihilation?

Answer 12

particle meeting its antiparticle
all the mass is transferred to energy in the form of photons

Question 13

what happens during pair production?
what are the conditions for pair production?

Answer 13

a gamma ray passing close to a nucleus can split to form an electron and positron

energy of the gamma ray must be high enough to produce the mass of the electron and postiton

Question 14

what is one electron volt (eV) in joules?

Answer 14

1.6e-16 J

Question 15

state the quark compositions of
- mesons
- baryons
-leptons

Answer 15

mesons are a quark-anti-quark pair

baryons are a combination of three quarks or antiquarks

leptons are fundamental particles

Question 16

rules for Feynman diagrams

Answer 16

• normal particles are straight lines
  -exchange particles are wiggly lines
  w bosons must have an arrow to show direction
• time runs upward (starting particles at bottom, final particles at top)
  -charge must be conserved
• baryons on left, leptons on right

Question 17

Feynman diagrams

exchange particle for electron collision

Answer 17

virtual photon

Question 18

what does the Feynman diagram for beta - decay look like?
beta + decay??

Answer 18

neutron to a proton with a W- boson exchange particle decaying to an electron and antineutrino

beta + is the opposite charges, with a proton decaying to a Neuton

Question 19

what is the quark composition of
- a proton
-a neutron

Answer 19

proton- up, up, down
neutron- up, down, down

Question 20

pions
quark composition of
- pion +
-pion 0
-pion -

Answer 20

pion + is up, antidown

pion 0 is up, antiup (or down, antidown)

pion - is antiup, down

Question 21

pions
antiparticles, and what they decay to for Pion+, pion- and pion0

Answer 21

pion+ and pion- are antiparticles
unstable and decay to muons and electron neutrinos via weak interaction

pion0 is its own antiparticle. has a very short lifetime as it annihilates

Question 22

general quark composition of a kaon?

Answer 22

quark-antiquark pair
has a strange quark

Question 23

quark composition and strangeness of
kaon+
kaon0
kaon-

Answer 23

kaon+ up, antistrange
strangeness of +1

kaon- strange, antiup
strangeness of -1

kaon0 down, antistrange
strangeness of +1

Question 24

which 5 quantities must always be conserved?

Answer 24

energy/mass
momentum
charge
lepton number
baryon number

Question 25

conditions for strong and weak interactions

Answer 25

strong interaction- strangeness in conserved

weak interaction- strangeness is not conserved

Question 26

what is the only stable baryon?

Answer 26

proton