7 Atoms and radioactivity Flashcards
(141 cards)
1
Q
What are atoms made up of?
A
- Electrons.
- Protons.
- Neutrons.
2
Q
Where can electrons be found?
A
Orbiting the nucleus of the atom.
3
Q
What is an electron?
A
A very small particle with very little mass/
4
Q
What is the charge of a proton?
A
Positive.
5
Q
How can we tell how many protons an element has?
A
The atomic number.
6
Q
What is the charge of an electron?
A
Negative.
7
Q
What is the amount of protons equal to?
A
The amount of neutrons.
8
Q
What is the nucleus made up of?
A
Protons and neutrons.
9
Q
So, what is the atomic number sometimes called?
A
The proton number.
10
Q
What is the charge of a neutron?
A
Neutral or uncharged.
11
Q
Why are they called nucleons?
A
Because they are found in the nucleus of the atom.
12
Q
Why are atoms neutral?
A
They are neutral because the number of positive charges (protons) is balanced by the number of negative charges (electrons), so they cancel each other out.
13
Q
What are protons and neutrons called?
A
Nucleons.
14
Q
What does the chemical behaviour and properties of a particular element refer to?
A
How the atoms combine with other atoms.
15
Q
So what does the chemical behaviour and properties of a particular element depend on?
A
The number of electrons in the atom (In its outer shell).
16
Q
What happens even though atoms may gain or lose electrons?
A
The number of protons is always the same.
17
Q
What is the symbol that we use for the atomic number?
A
Z.
18
Q
What is the mass number?
A
The total number of protons and neutrons in the atom.
19
Q
What is the symbol that we use for the mass number?
A
A.
20
Q
What notation do we use to represent elements?
A
Top number = Mass number.
Bottom number = Atomic number.
X = Element.
21
Q
What do the number of protons do?
A
They identify the element.
22
Q
What can happen to the number of neutrons?
A
They can vary slightly.
23
Q
What are atoms of an element with different numbers of neutrons called?
A
Isotopes.
24
Q
What do neutrons affect?
A
The mass of the atom.
25
So, what will be the characteristics of atoms that are isotopes?
They will have the same atomic number but different mass numbers.
26
What is hydrogen2 called?
Deuterium.
27
What is hydrogen3 called?
Tritium.
28
What are the differences between isotopes of an element?
- Physical properties.
- Stability of the nucleus.
29
What do we mean by the physical properties being different?
isotopes of an element have different physical properties from other isotopes of the same element. One obvious difference is the mass.
30
What do we mean by the stability of the nucleus?
We are referring to how the protons are held in the nucleus by the nuclear force.
31
What is a characteristic of this force?
This force is very strong and acts over a very small distance. It is strong enough to hold the nucleus together against the electric force repelling the protons away from each other.
32
What is important to remember in terms of the attractions of the sub-atomic particles?
Remember that protons carry positive charge and like charges repel.
33
What will affect the balance between these forces?
The presence of neutrons in the nucleus affects the balance between these forces.
34
So, what will make the nucleus unstable?
Too many or too few neutrons will make the nucleus unstable.
35
What happens to unstable nuclei?
They will eventually decay.
36
What is produced through the decay of an unstable nucleus?
When the nucleus of an atom decays it gives out energy and may also give out alpha or beta particles.
37
What is another thing that unstable nuclei give out during decay?
They give out ionising radiation.
38
What does ionising radiation do?
Ionising radiation causes atoms to gain or lose electric charge, forming ions.
39
What can we say about the decay in nuclei?
Unstable nuclei decay at random.
40
What does this randomness mean for us?
This means that it is not possible to predict which unstable nucleus in a piece of radioactive material will decay, or when decay will happen.
41
So, what can we do to predict the probability that a certain proportion of radioactive material will decay in a given time?
We shall see that we can make measurements that will enable us to predict the probability that a certain proportion of a radioactive material will decay in a given time.
42
What happens when a neutral atom (or molecule) is hit by ionising radiation?
It loses an electron and becomes a positively charged ion.
43
What is a diagram that shows this?
44
What are the three basic types of ionising radiation?
- Alpha. (α)
- Beta. (β)
- Gamma. (γ)
45
What does alpha-radiation consist of?
Fast moving particles that are thrown out of unstable nuclei while they decay.
46
What are these fast-moving particles called?
Alpha particles.
47
What are alpha particles?
They are helium nuclei - helium atoms without their orbiting electrons.
48
What is a diagram that shows an alpha particle and the notation that is used to denote it in equations?
4
2 He
49
What is the mass of alpha particles?
They have a relatively large mass. They are made up of four nucleons and so have a mass number of 4.
50
What is the charge of alpha particles?
They are also charged because of the two protons that they carry. The relative charge of an alpha particle is +2.
51
What is the approximate range of alpha particles?
Alpha particles have a short range.
52
What are we referring to when we say 'the range'?
The range of ionising radiation is the distance it can travel through matter.
53
What is the range of alpha particles in relation to materials?
Alpha particles can only travel a few centimeters in air and cannot penetrate more than a few millimeters of paper.
54
Why is the range of alpha particles limited?
Because they react with atoms along their paths, causing ions to form.
55
What happens then, in terms of energy to the alpha particles, as they react with atoms along their paths?
They rapidly give up the energy that they had when they were ejected from the unstable nucleus.
56
What are the two types of beta particles?
- Beta minus.
- Beta plus.
57
What are beta minus particles? (β^-)
They are very fast moving electrons that are ejected by a decaying nucleus.
58
Why is it wierd that electrons are ejected from a decaying nucleus?
The nucleus of an atom contains protons and neutrons, so where does the electron come from.
59
What does the stability of a nucleus depend on?
It depends on the proportion of protons and neutrons it contains
60
What is the result of radioactive decay?
It is to change the balance of protons and neutrons in the nucleus to make it more stable.
61
What does beta minus decay specifically involve?
Beta minus decay involves a neutron in the nucleus splitting into a proton and an electron.
62
After the splitting of the nucleus (during decay) into a proton and electron, how is the electron ejected?
The proton remains in the nucleus and the electron is ejected at high speed as a beta minus particle.
63
What is the mass of beta particles?
Beta particles are very light - they only have 0.000125 times the mass of an alpha particle?
64
What is the relative charge of a beta minus particle?
-1
65
What is the relative charge of a beta plus particle?
+1
66
What is known about the way that beta particles interact with matter?
They interact with matter in their paths less frequently than alpha particles.
67
Why does this happen?
This is because they are smaller and carry less charge.
68
Due to the fact that they are smaller and carry less charge, what is their range?
This means that beta particles have a greater range than alpha particles.
69
What are Beta particle's penetrating power?
Beta particles can travel long distances through air, pass through paper easily and are only absorbed by denser materials like aluminium.
70
What amount of aluminium will stop beta particles?
A millimetre or two of aluminium foil will stop all but the most energetic beta particles.
71
What are Gamma rays?
They are electromagnetic waves with very short wavelengths.
72
What happens to their mass and charge because they are waves?
They have no mass and no charge.
73
How do Gamma rays react with other atoms?
They are weakly ionising and interact only occasionally with atoms in their paths.
74
What is the penetrating power of Gamma rays?
They are extremely penetrating and pass through all but the very densest materials with ease.
75
What can stop Gamma rays?
It takes several centimetres-thick of lead, or a meter of so of concrete, to stop gamma radiation.
76
What are neutrons emitted by?
Radioactive material.
77
What is the mass of a neutron?
They have roughly the same mass as a proton but have no electric charge.
78
What is the symbol used for a neutron in radioactive decay equations?
1
0 n
79
What happens if a neutron is emmitted by a nucleus?
Its mass number goes down by 1, but the atomic number is unchanged.
80
What happens if a neutron is absorbed by a nucleus?
Its mass number goes up by 1 but the atomic number is unchanged.
81
What does ionising radiation do?
It causes uncharged atoms to lose electrons.
82
What is an ion?
An atom that has lost (or gained) electrons and has an overall charge.
83
How are ions formed?
The three types of radioactive emission can all form ions?
84
What are the three types of radioactive emission?
- Alpha particles.
- Beta particles.
- Gamma rays.
85
What is emission?
Something emitted from a system.
86
What happens as ionising radiation passes through matter?
Its energy is absorbed.
87
Due to the fact that its energy is absorbed, what does it mean about its penetration?
This means that radiation can only penetrate matter up to a certain thickness.
88
What does penetration power depend on?
This depends on the type of radiation and the density of the materials that it is passing through.
89
What do the characteristics of these particles depend on?
The energy of the radiation.
90
What is alpha radiation's ionising power?
Strong.
91
What is alpha radiation's penetrating power?
Weak.
92
What is an example of alpha radiation's range in air?
5 - 8cm.
93
What is alpha radiation stopped by?
Paper.
94
What is beta radiation's ionising power?
Medium.
95
What is beta radiation's penetrating power?
Medium.
96
What is an example beta radiation's range in air?
500-1000 cm.
97
What is beta radiation stopped by?
Thin aluminium.
98
What is gamma radiation's ionising power?
Weak.
99
What is gamma radiation's penetrating power?
Strong.
100
What is an example of alpha radiation's range in air?
Virtually infinite.
101
What is alpha radiation stopped by?
Thick lead sheet.
102
What is the apparatus needed to investigate the penetrating powers of different kinds of radiation?
- Radioactive source.
- Paper, aluminium, or lead sheets.
- GM tube.
- Counter.
- Stopwatch.
103
What is the GM tube?
The Geiger-Müller tube is a detector of radiation.
104
How must we take precautions when we investigate the penetrating powers of different kinds of radiation?
- Radioactive sources must be stored in lead-lined boxes and kept in a metal cupboard with a radiation warning label.
- The source must be handled with tongs away from the body.
105
What is something you need to do before you investigate the penetrating powers of different kinds of radiation?
Before the source is removed from its storage container, measure the background radiation count by connecting a Geiger-Müller tube to a counter.
106
What must you do after you have connected the Geiger-Müller tube to a counter?
Write down the number of counts after 5 minutes. Repeat this three times and find the average background radiation count.
107
What is the first step to investigate the penetrating powers of different kinds of radiation?
Take a source of alpha radiation and set it up at a measured distance (between 2 and 4cm) from the GM tube.
108
What is the second step to investigate the penetrating powers of different kinds of radiation?
Measure the counts detected in a 5 minute period.
109
What should you do after you have measured the counts detected in a 5 minute period?
Repeat the count with a sheet of thick paper in front of the source.
110
What should you find in relation to the count?
You should find that the counts have dropped to the background radiation count. This shows that alpha radiation does not pass through paper.
111
What is the third step to investigate the penetrating powers of different kinds of radiation?
Now replace the alpha source with a beta source.
112
What do you do after replacing the alpha source with a beta source?
After measuring the new count for 5 minutes place thin sheets of aluminium between the source and detector.
113
What do you find that depends on the thickness of the aluminium sheet?
When the thickness of the aluminium sheet is 1-2mm thick you will find that the count has dropped to the background radiation level.
114
What does the count dropping to the background radiation show?
This shows that beta radiation is blocked by just a few millimeters of aluminium.
115
What is the fourth step to investigate the penetrating powers of different kinds of radiation?
Finally, carry out the same steps using a gamma radiation source.
116
What will you find out about gamma radiation?
It is only blocked when a few centimeters of lead are placed between the source and the detector.
117
What will decay by emitting radiation?
An unstable atom, or its nucleus.
118
When will the atomic number change?
If the decay process involves the nucleus ejecting either an alpha or a beta particle.
119
What does alpha or beta decay then mean in terms of elements?
This means that alpha or beta decay causes the original element to transform into a different element.
120
What is a photo showing an example of alpha decay in an equation?
222 218 4
88 Ra ---> 86 Ra + 2 He + energy
121
What is the word equation for alpha decay?
Radium atom --> Radon atom + α particle + energy
122
What is an explanation of this equation?
The radioactive isotope radium-222 decays to the elements radon by the emission of an alpha particle. Radon is a radioactice gas that also decays by emitting an alpha particle.
123
Why is this equation balanced?
- The total numbers of protons and neutrons on each side of the equation are the same.
- The number of protons in the nucleus on each side of the equation is the same.
124
What is the general form of the alpha decay equation?
A A-4 4
Z Y ---> Z-2 W + 2 He + energy
125
What is the helium in this equation?
An alpha particle (α)
126
What is a general rule-of thumb when writing alpha decay equations?
Element Y is transferred into element W by the emission of an alpha particle. Element W is two places before. element Y in the periodic table. The alpha particle, a helium nucleus, carries away four nucleons, which reduces the mass number (A), by four. Two of these nucleons are protons so the atomic number of the new element is two less than the original element, Z-2. Notice that the mass number and the atomic number are conserved through this equation - that is, the total numbers of nucleons and protons on each side of the equation are the same.
127
What is an example of beta minus decay?
14. ---> 14 + 0 + energy
6 C 7 N -1e
128
What is the word equation for beta minus decay?
Carbon-14 atom --> Nitrogen-14 atom + Beta particle, β- + energy. (also an antineutrino).
129
What is an explanation of the equation of beta minus decay?
The radioactive isotope of carbon, carbon-14, decays to form the stable isotope of the gas nitrogen, by emitting a beta particle. Remember that the beta minus particle is formed when a neutron splits to form a proton and an electron.
130
What is a photo that shows a beta minus particle?
131
What is the general form of the beta minus decay equation?
A ---> A + 0 + energy
Z Y Z+1 Y -1 e
132
What is the 'e' element in this equation?
Beta minus particle β-.
133
What is a general rule-of thumb when writing beta minus decay equations?
In B- decay, element X is transformed into element Y by the emission of a beta minus particle. Element Y is the next element in the periodic table after element X. The beta particle, an electron, has practically no mass so the mass number, A, is the same in X and Y. As the - particle has a charge of -1, the atomic number of the new element is increased to Z + 1. Again the mass number and the atomic number are conserved through this equation.
134
What is an example of neutron decay?
5 ---> 4 + 1
2 He 2 He 0 n
135
What is the word equation for this neutron decay?
Helium-5 atom ---> Helium-4 atom + neutron.
136
What is an explanation of this equation of neutron decay?
As a neutron has no electric charge, the total positive charge is unchanged by the emission of a neutron - the Z number is 2 before and after the decay. The total number of particles (protons and neutrons) in the nucleus of the helium atom has decreased by 1 because of emission of the neutron.
137
What is Gamma decay?
After an unstable nucleus has emitted an alpha or beta particle it sometimes has surplus energy.
138
What happens to this surplus energy?
It emits this energy as gamma radiation.
139
What happens when a nucleus emits a gamma ray?
There is no change to either the atomic number or the mass number of the nucleus.
140
Why is there no change?
This is because gamma rays are pure energy, so they do not have any mass or charge.
141
When are alpha particles, beta particles and gamma rays emitted?
They are ionising radiations emitted from unstable nuclei in a random process.
