Particle physics

Question 1

Rutherford’s alpha-scattering experiment

Answer 1

A narrow beam of alpha particles, all of the same kinetic energy, were targeted at a thin piece of gold foil
Particles were scattered by the foil and detected on a zinc sulphide screen

Question 2

Alpha-scattering experiment observations and conclusions

Answer 2

Most passed straight through - about 1 in 2000 were scattered. This shows the atom is mostly empty space and the mass is concentrated in a small region (the nucleus)
Very few were deflected through through angles >90 degrees - about 1 in every 10000. This shows that the nucleus has a positive charge.

Question 3

How did alpha scattering experiment determine radius of nucleus

Answer 3

For alpha particle to collide with gold nucleus, initial kinetic energy = electrical potential energy when separation is d
This gives an upper limit for the distance from the centre - more energetic alpha particles might get closer

Question 4

Isototopes

Answer 4

Nuclei of the same element that have the same number of protons but different numbers of neutrons

Question 5

Atomic mass units

Answer 5

u
1u = 1/12 the mass of a neutral carbon-12 atom
1u = 1.661 x 10^-27 kg

Question 6

Radius of nucleus equation

Answer 6

R = r0 . A1/3

Question 7

Strong nuclear force direction

Answer 7

When distance is less than diameter, force is large and repulsive. This prevents merging
At typical nuclear separation, force is strong and attractive. It gets weaker with force

Question 8

Antiparticles

Answer 8

Every particle has a corresponding antiparticle. If the two meet, they annihilate each other. The masses of both particle and antiparticle are converted into a high-energy pair of photons
Antiparticle has opposite charge to particle
The antiparticle for the electron is the positron

Question 9

Strong nuclear force

Answer 9

Force that is experienced by nucleons. It is the force that holds the nucleus together

Question 10

Fundamental particles

Answer 10

Cannot be divided into smaller bits

Question 11

Hadrons

Answer 11

Particles and antiparticles made up of quarks that are affected by the strong nuclear force

Question 12

Leptons

Answer 12

Particles and antiparticles not affected by the strong nuclear force

Question 13

Quarks

Answer 13

Fundamental particles that make up hadrons

Question 14

Types of quarks

Answer 14

up(u) charm(c) top(t) charge = +2/3
down(d) strange(s) bottom(b) charge = -1/3

Question 15

Baryons

Answer 15

Hadrons made with a combination of 3 quarks or 3 antiquarks
E.g. uud (proton) udd (neutron)

Question 16

Meson

Answer 16

Hadrons with a quark and an antiquark

Question 17

Pions(π)

Answer 17

Mesons made up of only up, antiup, down and antidown quarks

Question 18

Kaons(K)

Answer 18

Mesons made up of up, antiup, down antidown, strange and antistrange quarks

Question 19

Leptons

Answer 19

Electron, muon, tau
electron neutrino, muon neutrino, tau neutrino

Question 20

Beta - decay

Answer 20

Neutron decays into a proton
udd => uud
d=>u

charges must be balanced
d =>u +e-

Lepton numbers must be balanced
d => u+e- + anti electron neutrino

Question 21

Beta + decay

Answer 21

proton decays into a neutron
uud => udd
u=>d

charges must be balanced
u => d +e+

Lepton numbers must be balanced
u => d + e+ + electron neutrino