Particle physics flashcards (not the big grid of facts)

Question 1

What is the formula for specific charge?

Answer 1

charge/mass

Question 2

Which force binds the nucleus together?
And which other forces act on the nucleus?

Answer 2

The strong nuclear force.
The other forces are: the electromagnetic force and gravitational attraction.

Question 3

Why must the strong nuclear force be repulsive at very small separations?

Answer 3

If it was attractive it would crush the nucleus to a point.

Question 4

Between what nucleon separation is the strong nuclear force repulsive?

Answer 4

0-0.5 fm

Question 5

Between what nucleon separation is the strong nuclear force attractive?

Answer 5

0.5-3 fm

Question 6

What happens to the proton number and the nucleon number after alpha decay takes place?

Answer 6

The proton number decreases by 2.
The nucleon number decreases by 4.

Question 7

How do we know that alpha particles have a very short range?

Answer 7

By observing the tracks left by alpha particles in a cloud chamber.

Question 8

In what kind of nucleus does beta minus decay take place?

Answer 8

Neutron rich nuclei

Question 9

What is beta minus decay?

Answer 9

The emission of an electron from the nucleus, along with an antrineutrino.
One neutron is changed into a proton.

Question 10

How were neutrinos discovered?

Answer 10

It was observed that the energy of the particles after the beta decay was less than it was before, which didn’t fit with the principle of conservation of energy. Pauli suggested that another particle was also being emitted, and was carrying away the missing energy. This particle must be neutral, or charge wouldn’t be conserved in beta decay, and had to have 0 or almost 0 mass, as it had never been detected. The neutrino was observed 25 years later, proving his hypothesis.

Question 11

What is pair production?

Answer 11

High energy photons can produce a particle and its antiparticle.
When energy is converted into mass, you get equal amounts of matter and antimatter.
Eg if you fire two protons at each other at high speeds, you’ll end up with lots of energy at the point of impact, which may be converted into more particles. If an extra proton is formed, then there will also be an antiproton to go with it.

Question 12

What is annihilation?

Answer 12

When a particle meets its antiparticle. All of the mass of the particle and antiparticle gets converted back to energy. Antiparticles can usually only exist for a fraction of a second before this happens, so you don’t get them in ordinary matter. An annihilation is between a particle-antiparticle pair, which both have a rest energy of mass E0. Both photons need to have minimum energy, Emin, which, when added together, equals at least 2E0, so
2Emin=2E0
Emin = hf min = E0

Question 13

What are forces caused by?

Answer 13

Particle exchange

Question 14

What are exchange particles called?

Answer 14

Gauge bosons

Question 15

What is the repulsion between two protons caused by?

Answer 15

The exchange of virtual photons, which are the gauge bosons of the electromagnetic force.

Question 16

What is the gauge boson of the electromagnetic force?

Answer 16

Virtual photon

Question 17

What is the gauge boson of the weak nuclear force?

Answer 17

W+
W-

Question 18

What is the gauge boson of the strong nuclear force?

Answer 18

pions
(+,-,0)

Question 19

The larger the mass of the gauge boson…

Answer 19

…the shorter the range of the force.

Question 20

Draw the Feynman diagram for two electrons repelling each other.

Answer 20

An electron stays an electron (on the left and the right) and emits a virtual photon.

Question 21

Draw the Feynman diagram for two positrons repelling each other

Answer 21

A positron on the left and right stays a positron, a virtual photon is emitted between them.

Question 22

Write out the word equation thing for electron capture.

Answer 22

proton + electron –> neutron + electron neutrino

Question 23

Which force makes electron capture happen, and what is it?

Answer 23

The weak interaction
When a proton captures an electron

Question 24

Draw the Feynman diagram for electron capture

Answer 24

On the left:
A proton turns into a neutron and emits a W+ boson.
On the right:
An electron turns into an electron neutrino.

Question 25

What is the difference between electron capture and an electron-proton collision?

Answer 25

A W- boson goes from the electron to the proton.

Question 26

Write out the word equation for beta minus decay.

Answer 26

neutron –> proton + electron + electron antineutrino

Question 27

Write out the word equation for beta plus decay.

Answer 27

proton –> neutron + positron + electron neutrino

Question 28

Draw the Feynman diagram for beta minus decay

Answer 28

udd becomes uud, which emits a W- boson, which turns into an electron and an electron antineutrino.

Question 29

Draw the Feynman diagram for beta plus decay.

Answer 29

uud becomes udd, which emits a W+ boson, which turns into a positron and an electron neutrino.

Question 30

Which particles are affected by the electromagnetic force?

Answer 30

Charged particles only

Question 31

Which particles are affected by the weak interaction?

Answer 31

All types

Question 32

Which particles are affected by the strong interactions?

Answer 32

Hadrons only

Question 33

What is the only stable baryon?

Answer 33

Protons. All baryons (except protons) decay into protons.

Question 34

Write 2 facts about mesons.

Answer 34

1 - all mesons are unstable
2 - all mesons have baryon number B=0

Question 35

What do kaons decay into?

Answer 35

Pions

Question 36

Where were pions and kaons discovered?

Answer 36

Cosmic rays

Question 37

Are muons stable or unstable?

Answer 37

Unstable - they decay into electrons

Question 38

By which force are strange particles created and destroyed, and what does that mean happens?

Answer 38

Created - strong interaction
Destroyed - weak interaction
This means that strange particles are always produced in pairs.

Question 39

What are baryons made of?

Answer 39

3 quarks

Question 40

What are mesons made of?

Answer 40

A quark and an antiquark

Question 41

What are the properties conserved in particle interactions, and under what circumstances?

Answer 41

• charge: always
• baryon number: always
• strangeness: in the strong interaction
• lepton number: Le or Lu are conserved
• mass-energy
• momentum

Question 42

What can strangeness change by?

Answer 42

In the weak interaction, strangeness can change by +1, -1, or 0