Module 6 Nuclear and Particle Physics

Question 2

What is a typical diameter for an atom?

Answer 2

Apx 10^-10m

Question 3

What is a typical diameter for a nucleus?

Answer 3

10^-15 or 10^-14

Question 4

Symbol for proton number?

Answer 4

Z

Question 5

Symbol for nucleon number?

Answer 5

A

Question 6

What is a nucleon?

Answer 6

A particle found in the nucleus of an atom, which includes protons and neutrons

Question 7

Symbol for neutron number?

Answer 7

N

Question 8

What is an isotope?

Answer 8

Same proton number different nucleon number

Question 9

What are the assumptions made for nuclear reactions?

Answer 9

Conservation of the usual stuff (mass, momentum, energy etc)
Nucleon number is conserved
Charge is conserved (bottom number)

Question 10

What is an alpha particle?

Answer 10

A helium nucleus

Question 11

What is a positron?

Answer 11

Same as electron but with a positive charge

Question 12

Describe the apparatus used in Rutherford’s experiment.

Answer 12

A sample of radioactive material which emits alpha particles in a lead block with a narrow hole to produce a beam of alpha particles in a vacuum.

Question 13

Why is a vacuum necessary in Rutherford’s experiment?

Answer 13

To prevent air molecules from interfering with the path of the alpha particles.

Question 14

Why does the gold foil need to be rolled thin?

Answer 14

Allows alpha particles to pass through and be detected as they can be absorbed by paper.

Question 15

Describe the results of the Rutherford experiment.

Answer 15

Most alpha particles travel through the foil undetected, implying the atom is mostly empty space.

Some alpha particles are deflected by small angles, implying the nucleus is positively charged.

Very few particles are detected traveling back from the foil, meaning the nucleus has most of the atom’s mass and is very small compared to the rest of the atom.

Question 16

What is the simple conclusion of Rutherford’s experiment?

Answer 16

Atom contains a nucleus (centre) which is very small, positively charged and contains most of the atom’s mass.

Question 17

How can the zinc sulphide screen be adjusted to gain more accurate results?

Answer 17

Move it closer to the gold foil.

Question 18

What can be used to calculate the closest approach of an alpha particle to a nucleus?

Answer 18

Coulombs Law

Question 19

Describe how the closest approach can be calculated.

Answer 19

At closest approach all KE is converted to electrostatic PE. Qq are the respective charges of the nucleus and the alpha particle.

Question 20

What is the evidence to show that there must be a third force within a nucleus to keep itself intact?

Answer 20

Calculate force due to gravity and Coulomb force separately. Gravity is attractive whereas electrostatic forces are repulsive. Ratio of forceE/forceG is massive meaning gravitational force is negligible.

Question 21

What does strong nuclear force act on?

Answer 21

Neighbouring protons and neutrons equally

Question 22

What is the prefix femto?

Answer 22

10^-15

Question 23

Describe how strong nuclear force varies.

Answer 23

Separation of r>3fm force is negligible.

Separation of 0.5 to 3fm force is very high magnitude and attractive.

Separation of r<0.5fm force is of very high magnitude and repulsive.

Question 24

Explain why neutrons increase nuclear stability.

Answer 24

Strong nuclear force has a short range, only affecting adjacent nucleons and is attractive.

Coulomb force has an infinite range and acts between all protons inside the nucleus and is repulsive.

The more neutrons there are, the more the overall strong nuclear force of attraction is increased without contributing to the Coulomb force.

Question 25

Describe how you would determine PD required for an alpha particle to be accelerated so that it fuses with a nucleus.

Answer 25

Put Qq as charge of nucleus and alpha particle respectively into Coulombs equation for energy (V).

Question 26

Describe a simple experiment to show that the radius of a nucleus is directly proportional to the cube root of the nucleon number.

Answer 26

High energy electrons are accelerated through a PD to a de Broglie wavelength of approx 1fm, fired at samples of nuclei which are diffracted around a nucleus and the pattern is used to find a value of R. Repeated for many different nuclei of known sizes.

Question 27

What is an approximate value for r_0, the radius of one nucleon?

Answer 27

. 1.25fm

Question 28

When plotting a graph of R=r_0A^1/3 in log form, how do you find r_0?

Answer 28

Y intercept is log r_0.

Question 29

How to show that nuclear density is independent of size of nucleus?

Answer 29

Take mass as A x 1.7x10^-27. Substitute r_0A^1/3 for R in equation for volume (is cubed). A cancels out.

Question 30

What are the two main groups of particles?

Answer 30

Hadrons and Leptons

Question 31

What does fundamental mean?

Answer 31

Is not comprised of smaller particles, cannot be split up further.

Question 32

What does the electron family consist of?

Answer 32

Electrons, Positrons, Neutrinos, Anti-neutrinos

Question 33

What are the two subgroups of hadrons?

Answer 33

Baryons and Mesons

Question 34

What is the composition of a baryon?

Answer 34

Three quarks

Question 35

What is the composition of a meson?

Answer 35

Quark antiquark pair

Question 36

Give an example of a meson.

Answer 36

A pion

Question 37

What is different for antiparticles?

Answer 37

Opposite charge and opposite baryon/lepton number.

Question 38

What types of forces do leptons interact with?

Answer 38

Weak nuclear force, Gravity, Electromagnetic

Question 39

What force do leptons not experience?

Answer 39

Strong nuclear forces

Question 40

Give an example of a lepton.

Answer 40

Electron, Neutrino

Question 41

What is the lepton number for a positron?

Answer 41

-1

Question 42

Mass of a neutrino?

Answer 42

Approx 0

Question 43

What are hadrons comprised of?

Answer 43

Quarks

Question 44

What is the baryon number of a quark?

Answer 44

1/3

Question 45

What is the baryon number of a meson?

Answer 45

0

Question 46

What is the notation for an antiparticle?

Answer 46

Put a bar over the symbol (eg. n with a bar on is an antineutron)

Question 47

Which quarks are neutrons made of?

Answer 47

udd

Question 48

Which quarks are protons made of?

Answer 48

uud

Question 49

What does beta minus decay emit?

Answer 49

A fast moving electron and an antineutrino

Question 50

When does beta minus decay occur?

Answer 50

In an unstable nucleus with too many neutrons

Question 51

Give the equation for the quark model of beta minus decay.

Answer 51

udd ⇒ uud + e- + v(bar) In words neutron decays in to proton + electron + anitneutrino

Question 52

How to remember between beta minus and plus decay?

Answer 52

Minus produces a negatively charged electron.

Question 53

When does beta plus decay occur?

Answer 53

When an unstable nucleus has too many protons.

Question 54

What happens during beta plus decay?

Answer 54

A proton is converted into a neutron, a positron, and a neutrino.

Question 55

What is annihilation?

Answer 55

When a particle meets its antiparticle in a head-on collision. Both are destroyed and mass is converted to photon energy using the equation according to E=mc^2.

Question 56

Why do a minimum of two photons need to be produced during annihilation?

Answer 56

To conserve total momentum.

Question 57

What happens to initial KE of particles during annihilation?

Answer 57

Is added to final total photon energy.

Question 58

Why must photons be emitted on the same straight line during annihilation?

Answer 58

So their momentums cancel out (so momentum is conserved).

Question 59

How would you find the frequency of radiation needed to produce a quark?

Answer 59

Calculate the energy needed using E=mc^2. Calculate f using E=hf.

Question 60

What happens during pair production?

Answer 60

A particle and its anti-particle are created directly from energy.

Question 61

When can pair production take place?

Answer 61

Collisions between particles in an accelerator or directly from photons.