Particles

Question 1

Give the charge and mass of a proton

Answer 1

+1.6 x 10^-19 (C)

1.67 x 10^-27 (Kg)

Question 2

Give the charge and mass of a nutron

Answer 2

0

1.67 x 10^-27 (Kg)

Question 3

Give the charge and mass of an electron

Answer 3

-1.6 x 10^-19 (C)

9.11 x 10^-31 (Kg)

Question 4

Give the equation for specific charge

Answer 4

Charge/mass Or Q/m

Question 5

Give the definition for an isotope

Answer 5

Atoms of the same element (same number of protons and electrons) but different number of nutrons

Question 6

What are the forces acting on the nucleus

Answer 6

-Electrostatic repulsion between protons
-Gravity is very weak due to small masses
-Strong nuclear force binds all nucleons together. It is not associated with charge
-The nucleons are held in equilibrium position

Question 7

Give the range of the strong nuclear force

Answer 7

It is repulsive below 0.5 fm
Between 0.5 - 3.0 fm it is attractive
Zero beyond 3.0fm

Question 8

When does alpha decay take place

Answer 8

It only happens in very large nuclei like uranium. This is because nuclei are too massive for the strong nuclear force to keep them stable. An alpha particle is emitted from the unstable nucleus.

Question 9

What is an alpha particle made of?

Answer 9

An alpha particle is made up of two protons and two neutrons ( same as a helium nucleus)

Question 10

What is the range of an alpha particle

Answer 10

They have a very short range - only a few cm in air

Question 11

Why do all alpha particles have the same kinetic energy?

Answer 11

All emitted alpha particles travel at the same speed which means they have the same ke

Question 12

When does beta minus decay occur?

Answer 12

Beta minus decay occurs in nuclei that are neutron rich (high neutron to proton ratio)

Question 13

What happens in beta minus decay?

Answer 13

A neutron in the nucleus changes into a proton. A beta particle (electron) and an electron anti-nutrino is emmitted from the nucleus.

It was first thought that the electron was the only particle emitted however it was found that the total energy after the decay was lees than before. This is why it was suggested that another particle, that had no charge and no mass was emmitted. The energy released is shared between the particles. This means the beta minus particle can have a range of Ke.

Question 14

What is Gamma decay?

Answer 14

Gamma rays are emitted by nuclei that need to loose energy, normaly following alpha or beta decay.

There is no change in the proton or nucleon number and a new element is not formed.

Question 15

What is a Geiger-Muller Tube?

Answer 15

It detects and records radiation. The background radiation is recorded before recording the radiation of a sorce then this is subtracted.

Question 16

How does electromagentic radiation occur?

Answer 16

EM radiation can behave as a wave or a particle. This is known as wave-particle duality

Question 17

What is a photon?

Answer 17

It is a fundamental particle. A photon is a massless “packet” or a “quantum” of electromagentic energy. This means that the energy is not transferred continously, but as discrete packets of energy.

Question 18

How much energy does a photon have?

Answer 18

The energy of a photon is directly propertional to the frequency of the radiation.

E = hf

The photon energy equation can be combined with the wave speed equation v = fλ

this gives us another for of the photon energy equation: E=hc/λ

Question 19

Give the definition for an electron volt

Answer 19

The energy gained by an electron that is travelling through a potential differance of one volt.

Question 20

Why is an electron volt used?

Answer 20

When dealing with small energy values, it is often more useful to use an alternative energy unit to joules. e.g electron volts(eV)

Question 21

How do you convert from electon-volts to joules?

Answer 21

x1.6x20^-19

Question 22

How do you convert from joules to electron-volts?

Answer 22

÷ 1.6x10^-19

Question 23

What is antimatter/antiparticles?

Answer 23

for every particle ther is a corresponding antiparticle.
They have the same mass and rest energy.
They have the opposite charge.
They also have other opporsite properties such as baryon number, lepton number and strangness.

Question 24

What is energy mass equivelance?

Answer 24

-energy can be converted into mass
-mass can be converted to energy

Question 25

What is pair production?

Answer 25

When energy is converted into mass, then you get equal amounts of matter and antimatter. This ensures that charge is conserved.

Pair production is when a photon interacts with a nucleus and the energy of the photon is used to create a particle-antiparticle pair.

Question 26

What photon is used in pair production and why?

Answer 26

• The energy of a photon must be above a certain value to provide the total rest enery of the particle-antiparticle pair.

-Only gamma ray photons have enough energy to undergo pair production
-Electron-positron pairs are more likely to be produced than any other pair as they have a relatively low mass (and low rest energy)