Atomic and Nuclear Physics

Question 1

Describe the model of the atom:

Answer 1

There is a tiny, dense, positively charged nucleus at the centre of ‘empty space’ with an electron cloud

Question 2

To what order is the diameter of the atom?

Answer 2

~10^-10

Question 3

To what order is the diameter of the nucleus?

Answer 3

~10^-15

Question 4

What is the charge of a proton?

Answer 4

+1.6 x 10^-19 C

Question 5

What is the charge of a neutron?

Answer 5

0C

Question 6

What is the charge of a electron?

Answer 6

-1.6 x 10^-19 C

Question 7

How would an isotope be defined?

Answer 7

A form of an element that has the same number of protons but a different number of neutrons compared to the most abundant form.

Question 8

What is the nucleon number?

Answer 8

The number of protons and neutrons in the nucleus of an atom

Question 9

A radioactive substance contains unstable nuclei. What do unstable nuclei have?

Answer 9

An inbalance of energy between the nucleons

Question 10

How does a particle become more stable?

Answer 10

By improving the balance of energy between the nucleons.

Question 11

How is the balance of energy between the nucleons improved?

Answer 11

By emitting energy from the nucleus in the form of: -Mass -Electromagnetic radiation (carried by photons)

Question 12

Alpha Decay is a mechanism of radioactive decay, what does it do?

Answer 12

Ejects two protons and two neutrons (as a single particle) from the nucleus

Question 13

What is Beta decay?

Answer 13

The emission of an electron from the nucleus- a neutron turns into a proton and emits an electron

Question 14

What is gamma decay?

Answer 14

The emission of high frequency (high energy) electromagnetic radiation from the nucleus

Question 15

What does ionising ability indicate?

Answer 15

How much each radiation type interacts with matter

Question 16

What is the relative charge of an alpha particle?

Answer 16

+2 (two protons)

Question 17

What is the relative charge of a beta particle?

Answer 17

-1 (one electron)

Question 18

What is the relative charge of a gamma particle?

Answer 18

0

Question 19

What is the relative mass if an alpha particle?

Answer 19

7000

Question 20

What is the relative mass of a beta particle?

Answer 20

1

Question 21

What is the relative mass of a gamma particle?

Answer 21

0

Question 22

What is the range in air for alpha radiation?

Answer 22

a few centimetres

Question 23

What is the range in air for beta radiation?

Answer 23

of the order of a metre

Question 24

What is the range in air for gamma radiation?

Answer 24

infinite

Question 25

What is alpha radiation stopped by?

Answer 25

-Paper -Skin

Question 26

What is beta radiation stopped by?

Answer 26

a few millimetres of aluminium

Question 27

What is gamma radiation stopped by?

Answer 27

Many centimetres of lead or metres of concrete (sometimes combination)

Question 28

What is the ionising ability of alpha radiation?

Answer 28

Very high

Question 29

What is the ionising ability of beta radiation?

Answer 29

Low (medium)

Question 30

What is the ionising ability of gamma radiation?

Answer 30

Very low

Question 31

What type of process is radioactive decay?

Answer 31

random

Question 32

What does a Geiger counter detect?

Answer 32

Emitted waves or particles from a sample

Question 33

What does a Geiger counter display to show the radiation?

Answer 33

A count rate

Question 34

What did Rutherford observe happen to alpha particles in his gold leaf experiment in 1911?

Answer 34

That some alpha particles went through the thin metal foil but others were scattered by large angles

Question 35

What was Rutherfords new model?

Answer 35

Most the atom is empty space but there is a small, massive, positively charged nucleus in the centre of the atom with electrons orbiting around it

Question 36

How did Rutherford's model fit in with his observations made in the experiment?

Answer 36

Most of the alpha particles went through the foil, so most the atom is empty space. Some alpha particles were scattered back, so there is a very small, dense, positively charged nucleus at the centre of the atom which repels the positive alpha particles

Question 37

Compare the changes in the nucleus with alpha and beta decay

Answer 37

In alpha decay, the nucleus loses 4 particles, 2 protons and 2 neutrons so the nucleon number decreases by 4. In beta decay, the nucleon number remains the same as the nucleus loses 1 neutron but gains 1 proton

Question 38

Compare gamma emission and neutron emission

Answer 38

In both, an uncharged particle/wave are emitted and the element remains the same. In gamma however, an electromagnetic wave is emitted and the mass of the atom stays the same. In neutron emission, a particle is emitted so the mass decreases.

Question 39

Define irradiation

Answer 39

A process by which a substance is exposed to radiation (and is therefore not the actual source of radiation)

Question 40

How can we tell if alpha radiation is being emitted by a sample?

Answer 40

Set up a Geiger counter so it is detecting radiation from the sample.. Put a sheet of paper between the counter and sample. If the count rate of the counter goes down, the sample is emitting alpha radiation

Question 41

How can we tell if beta radiation is being emitted by a sample?

Answer 41

Set up the same process as for alpha radiation but if the count rate doesn't go down for a sheet of paper, but does go down for a sheet of aluminium, the sample is emitting beta radiation.

Question 42

How can we tell if gamma radiation is being emitted by a sample?

Answer 42

If the count rate on the Geiger counter remains the same if paper and aluminum have been put between the counter and sample, the sample is emitting gamma radiation.

Question 43

Timeline of model of atom discovery:

Answer 43

1897 - J.J. Thompson discovers electrons 1911 - Ernest rutherford creates nuclear model 1913 - Bohr discovers the energy levels for electrons 1924 - de Broglie establishes wave nature of electrons 1932 - Chadwick discovers the existence of the neutron

Question 44

What does gamma radiation have a high something of?

Answer 44

Penetration ability

Question 45

What are two hazards associated with handling radioactive materials?

Answer 45

Irradiation Contamination

Question 46

What is radioactive contamination?

Answer 46

Particles of radioactive material left on an object

Question 47

What kind of process is radioactive decay? Why?

Answer 47

Random process as it is impossible to predict which specific nuclei will undergo decay at any particular instant

Question 48

How can patterns still emerge from the randomness of radioactive decay?

Answer 48

Because of the enormous numbers of radioactive nuclei presentin even a small sample

Question 49

What is activity?

Answer 49

The number of decays per second

Question 50

What is the activity of a sample dependent on?

Answer 50

The number of radioactive nuclei in the sample

Question 51

What is activity measured in?

Answer 51

Becquerel, Bq

Question 52

What does 1Bq represent?

Answer 52

One decay per second

Question 53

What is the relationship between the activity and number of radioactive nuclei in a sample?

Answer 53

Directly proportional

Question 54

Define the half-life of a substance:

Answer 54

the time taken for the number of radioactive nuclei in a sample to reduce by half

Question 55

Is half-life independent or dependent of the size of the sample?

Answer 55

Independent

Question 56

What is the variation between the half lives of substances?

Answer 56

From billions of years to billionths of a second

Question 57

What type of decay (related to maths) is the decay of radioactive substances?

Answer 57

A true exponential