Particles and Radiation

Question 1

Define atomic number, Z.

Answer 1

The number of protons in an atoms nucleus.

Question 2

Define mass number, A.

Answer 2

The number of nucleons in its nucleus (protons+neutrons).

Question 3

Define isotope.

Answer 3

Atoms of the same element with the same proton number, but a different neutron number.

Question 4

Define specific charge.

Answer 4

Charge per unit mass (Ckg^-1).

Question 5

What does the strong nuclear force do?

Answer 5

Overcomes the electrostatic force of repulsion between the protons in the nucleus, and keeps the protons, and neutrons together.

Question 6

What is the specific size of the strong nuclear force’s range?

Answer 6

3-4fm.

Question 7

When is the strong nuclear force attractive?

Answer 7

From 3-4fm to about 0.5fm.

Question 8

When is the strong nuclear force repulsive?

Answer 8

At separations < 0.5fm, that acts to prevent neutrons and protons being pushed into each other.

Question 9

How does the strong nuclear force effect like-nucleons?

Answer 9

It has the same effect between two protons or two neutrons as it does a proton and a neutron.

Question 10

What does alpha radiation consist of?

Answer 10

Alpha particles which each comprise two protons and two neutrons (a He atom).

Question 11

When an unstable nucleus of an element X emits an alpha particle, how is the nucleon number, A, and the atomic number, Z, effected?

Answer 11

The nucleon number decreases by 4 and the atomic number decreases by 2.

Question 12

What does beta radiation consist of?

Answer 12

Fast-moving electrons.

Question 13

What does an unstable nucleus of an element X emit when it has too many neutrons?

Answer 13

A B^- particle, (atomic number increases by 1).

Question 14

What is also emitted during the emission of beta radiation?

Answer 14

An antiparticle with no charge called an antineutrino (represented by a v with a bar across the top).

Question 15

What is gamma radiation?

Answer 15

Electromagnetic radiation emitted by an unstable nucleus.

Question 16

What can gamma radiation pass through?

Answer 16

Thick metal plates.

Question 17

When is gamma radiation emitted?

Answer 17

When the nucleus has too much energy.

Question 18

Why were the neutrino and the antineutrino hypothesised?

Answer 18

To explain why beta particles from an isotope have a range of kinetic energies up to a maximum unlike alpha particles, which are emitted with a fixed proportion of the energy released.

Question 19

When is B^+ radiation emitted?

Answer 19

When the nuclei have too many protons.

Question 20

What speed do electromagnetic waves travel at in a vacuum?

Answer 20

The speed of light, c, (3.00 x 10^8)ms^-1.

Question 21

Electromagnetic waves are emitted as short bursts of waves, each leaving the source in a different direction… What is the name of these bursts?

Answer 21

Photon.

Question 22

What is rest energy?

Answer 22

When a particle is stationary, its rest mass corresponds to rest energy. Rest energy must be included in the conservation of energy.

Question 23

For every type of particle there is corresponding antiparticle that:

Answer 23

• Annihilates the particle and itself if they meet, converting their total mass into photons.
• Has exactly the same rest mass as the particle.
• Has exactly opposite charge to the particle if the particle has a charge.
• Can be produced together with its corresponding particle in a process known as pair production. This can happen when a single photon with sufficient energy passing near a nucleus changes into a particle-antiparticle pair. The nucleus is necessary for conservation of momentum as well as conservation of energy.

Question 24

What happens when a particle and corresponding antiparticle meet?

Answer 24

Their mass, including their rest mass, is all converted into radiation energy so that energy is conserved.

Question 25

What is this process called?

Answer 25

Annihilation.