Topic 6- Radioactivity

Question 1

What did J.J. Thomson discover about electrons in 1897

Answer 1

He discovered that electrons could be removed from atoms, so atoms must be made up of smaller bits

Question 2

What did J.J. Thomson suggest about atoms

Answer 2

He suggested the ‘plum-pudding’ model - that atoms were spheres of positive charge with tiny negative electrons stuck in them like fruit in a plum pudding

Question 3

How long did the “plum pudding” model theory last

Answer 3

Until 1909

Question 4

Who disproved the “plum pudding” model and how

Answer 4

Rutherford and Marsden tried firing a beam of alpha particles at thin gold foil. From the plum-pudding model, they expected the particles to pass straight through the gold sheet, or only be slightly deflected

But although most of the particles did go straight through the sheet, some were deflected more than expected, and few were deflected straight back the way they had come - something the plum-pudding model couldn’t explain

Rutherford realised this meant that most of the mass of the atom was concentrated at the centre in a tiny nucleus

He also realised that most of an atom is empty space, and that the nucleus must have a positive charge, since it repelled the positive alpha particles

This lead to the creation of the nuclear model of the atom

Question 5

Who tweaked Rutherford’s idea a few years later and what did he propose

Answer 5

Niels Bohr and he proposed a model where the electrons were at fixed orbits at set distances from the nucleus. These distances were called energy levels

Question 6

What did Neil Bohr suggest about the electron and whatsthe model called

Answer 6

He suggested that electrons can only exist in these fixed orbits (shells),and not anywhere in between and the model is called the Bohr model

Question 7

What’s our current model of the atom like

Answer 7

Positively charged nucleus surrounded by negatively-charged electrons

Virtually all the mass of the atom is in the nucleus. The nucleus is tiny - about 10000 Tim’s smaller than the whole atom. The nucleus contains positively charged protons and neutrally charged neutrons. The rest of the atom is mostly empty space

The negative electrons whizz around the outside of the nucleus in fixed orbits called energy levels or shells. They give the atom its overall side of around 1x10^-10m

The atoms are neutral so the number of protons = number of electrons. This is because protons and electrons have an equal but opposite relative charge.

Question 8

What happens if an atom looses an electron

Answer 8

It becomes a positive ion

Question 9

What happens if an atom gains an electron

Answer 9

It becomes a negative ion

Question 10

What do atoms join together to form

Answer 10

A molecule

Question 11

What is a protons relative mass and relative charge

Answer 11

Relative mass is 1

Relative charge is +1

Question 12

What is an electrons prelative mass and relative charge

Answer 12

Relative mass is 0.0005

Relative charge is -1

Question 13

What is a neutrons relative mass and relative charge

Answer 13

Relative mass is 1

Relative charge is 0

Question 14

How do electrons in an atom sit

Answer 14

On different energy levels (shells)

Question 15

Is each energy level a different distance away from its nucleus

Answer 15

Yes

Question 16

How can an inner electron move up to a higher energy level

Answer 16

If it absorbs a enough Electromagnetic (EM) radiation with the right amount of energy

Question 17

What happens when an inner electron moves up an energy level

Answer 17

It moves to an empty space or partially filled space and is said to be ‘exited’

Question 18

What happens after the electron falls back into its original energy level

Answer 18

It will emit(lose) the same amount of energy it absorbed. The energy is them carried away by EM radiation

Question 19

As you move further out from the nucleus what happends to the energy levels

Answer 19

They come closer together (so the difference in energy between two levels next to each other gets smaller)

Question 20

Would an exited electron release more or less energy when falling from the third energy level to the second then an exited electron falling from the second energy level to the first

Answer 20

Less energy will be released. So the frequency of the generated radiation decreases as you get further from the nucleus

Question 21

What do changes in the nucleus itself lead to produce

Answer 21

The production High energy, high frequency gamma rays

Question 22

What can happen if an outer electron absorbs radiation with enough energy

Answer 22

It can move so far that it leaves the atom. It then becomes a free electron and the atom is said to have been ionised. The atom is now a positive ion. It’s positive as there are now more protons then electrons. An atom can lose more then. One electron. The more electrons it loses, the greater it’s positive charge

Question 23

What is ionising radiation

Answer 23

Any radiation that can knock electrons off of atoms.how likely it is that each type of radiation will ionise an atom varies

Question 24

What’s an isotope

Answer 24

A different form of the same element. Atoms with the same number of protons but with a different number of neutrons (a different mass number)

Question 25

What is the number of protons in an atom called

Answer 25

It’s atomic number air proton number

Question 26

What is the mass (nucleon) number of a an atom

Answer 26

The proton number + the number of neutrons in the nucleus

Question 27

Finish this m All elements have different isotopes but

Answer 27

But there’s only one or two stable ones

Question 28

What happens to unstable isotopes

Answer 28

They tend to decay into other elements and give out radiation as they try to become more stable.

Question 29

What’s the process of when unstable isotopes decay into other elements and give out radiation as they try to become more stable called

Answer 29

Radioactive decay

Question 30

What do radioactive substances spit out

Answer 30

One or more types of ionising radiation when they decay: alpha, beta, gamma. They can also emit neutrons

Question 31

What’s an alpha particle

Answer 31

A helium nucleus

Question 32

What’s alpha radiation

Answer 32

When an alpha particle is emitted from the nucleus (2 neutrons and 2 protons)

Question 33

What are the properties of alpha particles

Answer 33

Don’t penetrate very far into materials and are stopped quickly - they can only travel a few cm in air and are absorbed by a thin sheet of paper They are strongly ionising due to their size

Question 34

What’s a beta minus particle

Answer 34

A fast moving electron released by the nucleus. Beta minus particles have virtually no mass and a relative charge of negative one (-1)

Question 35

What’s a beta plus particle

Answer 35

A fast moving positron. The positron is an anti particle of the electron. This means that it has exactly the same mass as the electron, but a positive charge (+1)

Question 36

How ionising are the beta particles

Answer 36

Moderately ionising

Question 37

How are beta minus particles absorbed

Answer 37

Beta minus particles have a range in air of a few meters and are absorbed by a sheet of Aluminium (around 5mm thick)

Question 38

Explain positrons

Answer 38

Positrons have a smaller range, because when they hit an electron the two destroy each other and produce gamma rays - this is called annihilation and it’s used in PET scanners

Question 39

What are gamma rays

Answer 39

EM waves with a short wavelength released by the nucleus

Question 40

What happens after a nucleus has decayed

Answer 40

It often undergoes nuclear rearrangement and releases some energy

Question 41

How do gamma rays penetrate

Answer 41

Penetrate Far into materials without being stopped and will travel a long distance through air

Question 42

How ionising are gamma regs and why

Answer 42

Weakly ionising because they tend to pass through rather then collide with atoms . Eventually they hit something and do damage

Question 43

How are gamma rays absorbed

Answer 43

By thick sheets of less | Or by meters of concrete

Question 44

What are nuclear equations a way of showing

Answer 44

Radioactive decay by using elements symbols

Question 45

What form is radioactive decay written in

Answer 45

Atom before decay—>atom after decay + radiation emitted

Question 46

What’s the golden rule to remember about nuclear equations

Answer 46

The total mass and atomic mass must be equal on both sides

Question 47

What happens when a nucleus emits an alpha particle

Answer 47

The nucleus loses 2 protons and 2 neutrons So the mass number decreases by 4 And atomic number decreases by 2

Question 48

What happens in beta minus decay

Answer 48

A neutron changes into a proton and electron so: The mass number does not change - as it’s lost a neutron but gained a proton The atomic number increases by 1 - because it has one more proton

Question 49

What happens in beta plus decay (positron emission)

Answer 49

In beta plus decay, a proton changes into a neutron and a positron, so: The mass number doesn’t change - as it’s lost a proton but gained a neutron The atomic number decreases by 1 - because it has one less proton

Question 50

What happens when a nucleus emits a neutron (neutron emission)

Answer 50

The mass number decreases by 1 - as it has lost a neutron | The atomic number stays the same

Question 51

What are gamma rays a way of getting rid of

Answer 51

Excess energy from an atom - the nucleus goes from an exited state to a more stable state by emitting a gamma ray

Question 52

What happens the the mass and atomic numbers after a gamma ray has been emitted

Answer 52

The mass and atomic numbers stay the same

Question 53

What do radioactive sources contain that give out radiation from the nuclei of their atoms

Answer 53

Radioactive isotopes

Question 54

How is ,how quickly unstable nuclei unstable Nuclei decay measured

Answer 54

Using activity and half-life

Question 55

What does it mean by ‘the process of radioactivity entirely random’

Answer 55

This means if you you have 1000 unstable nuclei you can’t say when anyone of them are going to decay, or which one will decay next

Question 56

If there is lots of nuclei what can you predict

Answer 56

How many will have decayed in a given time based on the half-life of the source.

Question 57

What is the rate of which a source decays at called

Answer 57

It’s activity

Question 58

How is activity measured

Answer 58

In becquerels(Bq). 1 Bq is 1 decay per second

Question 59

What’s another way activity can be measured

Answer 59

Using a Geiger-muller tube, which clicks each time it detects radiation. The tube is attached to a counter, which displays the number of clicks per second (the count rate)

Question 60

What’s another way to detect radiation

Answer 60

Using a photographic film. The more radiation the films exposed to, the darker it becomes (just like when you expose it to light)