Stable And Unstable Nuclei

Question 1

What are the forces that act in the nucleus?

Answer 1

Electromagnetic

Gravitational

Strong nuclear

Question 2

What does the electromagnetic force do?

Answer 2

Causes positively charged protons in the nucleus to repel each other

Question 3

What does the gravitational force do?

Answer 3

Causes all the nucleons in the nucleus to attract each other due to their mass

Question 4

What does the strong nuclear force do?

Answer 4

Holds the nucleus together

Question 5

Why is there a strong nuclear force?

Answer 5

The repulsion from the electromagnetic force is much bigger than the gravitational attraction so the nucleons would fly apart without the strong nuclear force

Question 6

Is the strong nuclear force stronger than the electromagnetic force?

Answer 6

Yes

Question 7

What is the range of the string nuclear force?

Answer 7

Very short

A few femtometres

Question 8

At very small separations, is the strong nuclear force attractive or repulsive?

Answer 8

Repulsive

Question 9

When is the strong nuclear force repulsive?

Answer 9

For very small separations of nucleons

Less than about 0.5fm

Question 10

When does the strong nuclear force become attractive?

Answer 10

As nucleon separation increases past about 0.5fm

Question 11

When does the strong nuclear force reach maximum attractive value and then falls rapidly towards 0?

Answer 11

After about 3fm

Question 12

How far does the electromagnetic repulsive force extend over?

Answer 12

Much larger range than the strong nuclear force

Question 13

What is nuclear decay?

Answer 13

When unstable nuclei will emit particles to become more stable

Question 14

When does alpha decay happen?

Answer 14

In very big atoms

Question 15

Why does alpha decay happen?

Answer 15

The nuclei of the atoms are too big for the strong nuclear force to keep them stable

Question 16

What happens to the atoms during alpha decay?

What happens to the proton and nucleon number~?

Answer 16

They emit an alpha particle

Proton number decreases by 2

Nucleon number decreases by 4

Question 17

What is the range of alpha particles?

Answer 17

Very short range (only a few cm in air)

Question 18

How can alpha decay be seen?

Answer 18

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

OR

Using a Geiger/spark counter

Question 19

What do Geiger and Spark counters measure?

Answer 19

Amount of ionising radiation

Question 20

What is beta minus decay?

Answer 20

Emission of an electron from the nucleus along with an antineutrino particle

Question 21

When does beta minus decay happen?

Answer 21

In isotopes that are ‘neutron rich’

Question 22

What happens when a nucleus ejects a beta particle?

Answer 22

1 of the neutrons is changed into a proton

Proton number increases by 1

Nucleon number stays the same

Question 23

What does the antineutrino particle released in beta minus decay carry away?

Answer 23

Some energy and momentum

Question 24

How far can beta particles travel in air?

Answer 24

Several metres