3.2.1.2 - Unstable and Stable Nuclei

Question 1

What does the nuclear force do?

Answer 1

It overcomes the electrostatic force of repulsion between the protons in the nucleus and keeps the protons and neutrons together.

Question 2

What kind of effect does the nuclear force have between protons and protons compared to neutrons and protons?

Answer 2

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

Question 3

Why does the nuclear force have a short range?

Answer 3

So it only acts within the nucleus.

Question 4

What is the difference between the range of the strong nuclear force and the range of the electrostatic force?

Answer 4

The range of the strong nuclear is no more than 3-4fm (diameter of a nucleus) while the electrostatic force between two particles has an infinite range.

Question 5

Why are the nuclei stable?

Answer 5

Because of the huge attractive force the strong force can provide.

Question 6

How can we estimate the size of the nucleus?

Answer 6

The separation of the nucleons within any nucleus is virtually independent of how many nucleons there are in that nucleus.

Question 7

Why must the strong nuclear force also be repulsive?

Answer 7

Or else it would crush the nucleus to a point.

Question 8

How far is the strong nuclear force repulsive up to?

Answer 8

Up to 0.5fm

Question 9

After what value does the attractive force of the strong nuclear force drop to 0?

Answer 9

3fm

Question 10

Why will a nucleus emit an alpha or beta decay?

Answer 10

In order for the nucleus to become stable.

Question 11

What does an alpha particle consists of?

Answer 11

2 protons and 2 neutrons.

Question 12

What is the relative charge of an alpha particle?

Answer 12

+2

Question 13

How do we represent alpha particles?

Answer 13

4(on top), 2(on bottom) a.

Question 14

What happens when an alpha particle is emitted?

Answer 14

The proton number decreases by two and the nucleon number decreases by four.

Question 15

What is the result of an alpha emission?

Answer 15

The product nucleus belongs to a different element.

Question 16

When is a beta particle emitted?

Answer 16

In isotopes that are unstable due to being neutron rich.

Question 17

How can we represent beta emission?

Answer 17

0(on top), -1(on bottom) B

Question 18

What happens during beta emission?

Answer 18

One of the neutrons in the nucleus changes into a proton. The proton number increases by one, and the nucleon number stays the same.

Question 19

What else is released during beta decay?

Answer 19

An antineutrino.

Question 20

What does the antineutrino do?

Answer 20

It carries away some energy and momentum.

Question 21

How were neutrinos first hypothesised?

Answer 21

Observations of beta decay.

Question 22

What is a hypothesis?

Answer 22

An untested theory or idea?

Question 23

How were antineutrinos found?

Answer 23

When they reacted with cadmium nuclei which were in a large tank of water.

Question 24

What produces neutrinos?

Answer 24

Nuclear reactors, the sun, beta emitting isotopes.

Question 25

What observation showed that neutrinos may have existed?

Answer 25

During beta emission the energy of particles before and after was less and so didn’t fit the principle of conservation of energy.

Question 26

What did scientists decide this particle have to be?

Answer 26

Neutral (or charge wouldn’t be conserved) and have a zero or almost zero mass (as it hadn’t been detected).

Question 27

What are electrostatic forces caused by?

Answer 27

Protons’ electric charges.

Question 28

What is gravitational force due to?

Answer 28

The masses of the particles.