TOPIC 3- Radioactivity Flashcards
1
Q
What are alpha particles?
A
Helium nuclei (2 neutrons and 2 protons)
2
Q
Penetration of alpha particles
A
They are stopped quickly by a few cm of air, a thin sheet of paper and skin.
3
Q
Ionising power of alpha particles
A
Strong
4
Q
What’s a beta minus particle?
A
A fast moving electron due to a neutron splitting into a proton and electron.
5
Q
Ionising power of beta particles?
A
Moderate
6
Q
Stopping power of beta minus particles?
A
Go a few m in air and are stopped by aluminium foil.
7
Q
What are beta plus particles?
A
A fast moving positron due to a proton splitting into a neutron/positron.
8
Q
What’s the stopping power of beta plus particles?
A
Can be stopped by aluminium foil but have a shorter range in air due to annihilating when they hit an electron and destroy each other (releasing gamma rays)
9
Q
What’s a neutron particle as a part of neutron radiation?
A
A neutron released to maintain a stable atom.
10
Q
Ionising power of neutron radiation?
A
Low
11
Q
Stopping power of neutron radiation?
A
Concrete/ water
12
Q
What are gamma rays?
A
EM waves with a short wavelength. Produced after nuclear rearrangement (movement of nucleons) which releases energy.
13
Q
Ionising power of gamma rays?
A
Low as they tend to pass through atoms rather than collide. Eventually they hit something and do damage.
14
Q
Stopping power of gamma rays?
A
They penetrate far into materials and km through air. However they can be absorbed by thick sheets of lead/concrete.
15
Q
Ionising power
A
How readily the radiation removes/ gives electrons
16
Q
What happens to the atomic/ mass number of the atom after alpha decay? How is this written in a nuclear equation?
A
The atomic number decreases by 2 and the mass number decreases by 4. It’s written as:
atom before decay > atom after decay + 4 (top) 2 (bottom) (alpha symbol/ He)
17
Q
How are nuclear equations written out?
A
Atom before decay > atom after decay + radiation emitted
The total mass/atomic numbers must be equal on both sides.
18
Q
Mass number
A
Number of protons and neutrons
19
Q
Atomic number
A
Number of protons
20
Q
Isotope
A
Atoms with a different number of neutrons but same number of protons.
21
Q
Relative atomic mass
A
The weighted mean mass of an atom.
22
Q
Why was Geiger and Marsden’s experiment carried out in a vacuum
A
So the air particles weren’t in the way
23
Q
Gold foil experiment method
A
A beam of alpha particles was aimed at v thin gold foil and their passage through detected.
Most atoms passed straight through.
Some were deflected.
Some were deflected straight back
24
Q
What atomic model did this bring in?
A
The plum pudding model.
25
Which conclusions did they get from this?
There’s much free space in the atom (passed straight through).
The nucleus has a positive charge (deflections).
Mass is concentrated in the nucleus. (Straight deflection)
26
First atomic model
DALTON’S BILLIARD BALL
1766-1844
All matter is made of atoms that can’t be broken down.
Different elements are different atoms.
Atoms are rearranged in chemical reactions.
27
2nd atomic model
J.J Thompson’s plum pudding
Electron discovered in 1897.
Atoms were spheres of positive charge w negative electrons spread out within.
28
3rd atomic model
Rutherford’s nuclear atom (from Geiger and Marsden’s experiment)
Central nucleus of atom was discovered in 1911.
29
Present model of atom
Niels Bohr’s model
| Discovered electron orbits.
30
Difference between Rutherford and plum pudding model
Rutherford has neutrons, nucleus and free space.
Mass in center of nucleus.
Electrons were outside nucleus.
31
How are atom quantities written
Standard form
32
Size of nucleus in comparison to whole atom
10 000 times smaller than whole atom
33
Atom overall size
1 * 10 to the -10
| Small molecules are same size
34
What happens if an inner electron absorbs EM radiation w the right amount of energy?
It can move up to a higher, empty / partially filled energy level
35
What happen to the electron after excitement?
It will quickly move back to original energy level due to electrostatic forces, emitting same amount of energy it absorbed via EM radiation.
Corresponding wavelength of light to set amount of energy. High energy = shorter wavelength
36
What affects the frequency of EM radiation?
Higher energy = higher frequency
37
What happens to excitement as you move further out from the nucleus?
As you get further out from the nucleus, energy levels get closer together and so difference in between are smaller. TMT excited atoms falling from further out levels will release less energy.
38
What’s released from changes within the nucleus?
High energy, high frequency gamma rays
39
Ionisation
When an outer electron absorbs enough energy, can leave atom (so atom is ionised) < atom is positive ion.
More electrons lost = greater charge
40
What type of radiation is nuclear radiation?
Ionising
| Can knock electrons from atoms
41
Line spectrum
Colour spectrum emitted by different elements as electrons fall back to lower orbits, releasing different wavelengths.
Can be split by prism to produce line spectra
42
Isotopes
Atoms with the same number of protons but different number of neutrons.
Usually only 1 or 2 stable isotopes of each element
43
What do unstable isotopes do?
Decay into other elements by giving out radiation to become more stable.
44
What do radioactive substances give out upon decay?
Ionising radiation
45
Stable atom
Atom with the right balance of protons and neutrons
46
What are alpha particles? Characteristics?
| What are their charge ?
```
(Helium nuclei)
2 neutrons and 2 protons
Mass number 4
Atomic number 2
Big heavy and slow
```
Charge > +2
47
Ionising power of alpha particles ?
| Stopping power of alpha particles?
Strongly ionising (due to size).
Don’t penetrate far
Stopped by few cm of air, paper and skin.
48
Beta minus particle
| Charge?
Is a fast moving electron caused by a neutron splitting into a proton and electron.
Charge -1
Mass number 0
Atomic number 1
49
Ionising power and stopping power of beta minus particles?
Moderately ionising
Stopped by sheet of aluminium
Travel few m in air
50
Beta plus particle.
| Charge?
Fast moving positron caused by splitting of a proton into a neutron and positron.
Charge of +1
51
Ionising and stopping power of beta plus particles?
Moderately ionising.
Positrons have a smaller range as produce gamma rays when hit electrons (annihilation).
Stopped by aluminium foil
52
Neutron particle
| Charge?
Is a neutron released
| 0 charge
53
Ionising and stopping power of neutron particle
Low ionising power
| Stopped by concrete and water.
54
Gamma radiation
| Charge
Is an EM wave due to rearrangement of the nucleons.
| Has 0 charge.
55
Ionising and stopping power Of gamma radiation
Weak ionising power (pass through rather than collide w atoms)
Stopped by lead / concrete as penetrate far and will travel through a long distance in air
56
Nuclear equations are written in the form ?
Atom before decay > Atom after decay + radiation emitted
57
What happens during the nuclear equation of an alpha particle being emitted?
Mass number is decreased by 4.
| Atomic number is decreased by 2.
58
What happens in the nuclear equation of the release of a beta minus?
The mass number doesn’t change.
| The atomic number increases by 1.
59
What happens in the nuclear equation of the release of a beta plus?
The mass number doesn’t change.
| Atomic number decreases by 1.
60
What happens in the nuclear equation of the release of a neutron?
Mass number decreases by 1.
| Atomic number stays the same.
61
Radioactive sources
Objects containing radioactive isotopes that give out radiation from the nuclei of their atoms.
62
Activity
The rate of decay.
63
What’s activity measured in?
Becquerels (Bq)
| 1Bq=1 decay per second
64
How do you measure radioactive activity?
Geiger Muller tube clicks each time it detects radiation, attached to a counter which displays count rate.
Radiation ionises the gas inside, causing charged particles to move across the chamber.
PHOTOGRAPHIC FILM becomes darker when exposed to radiation.
65
Why does the radioactivity of a source decrease over time?
Each time a nucleus decays, one more radioactive nucleus disappears so the activity as a whole will decrease.
Can be number of hours or millions of years.
66
Half-life
The average time taken for the number of radioactive nuclei in an isotope to decrease by half.
67
Why are sources with a short half-life dangerous?
As the nuclei is v unstable and so will rapidly decay, emitting a high amount of radiation.
However quickly becomes safe.
68
Why are sources with a long half-life dangerous?
Means areas can be exposed to radiation for millions of years.
69
Where does background radiation come from?
Naturally occurring unstable isotopes in air, some food, building materials, rocks.
Cosmic rays from space (eg sun)
Human activity (nuclear explosions/waste)
70
Absorbed radiation dose
The amount of radiation you are exposed to .
| Varies depending on where you live and work.
71
IRRADIATION
exposure to radiation.
72
Prevention of irradiation
Lead-lined boxes, barriers, different rooms, remote control arms.
Photographic film badges monitor exposure.
73
CONTAMINATION
Radioactive particles getting on/in objects.
| Is dangerous as can then decay, releasing radiation to cause you harm.
74
Why’s contamination dangerous?
As can get inside body and release radiation to do you harm.
75
How do you remove contamination?
By waiting until decayed or removing (isn’t always possible).
76
Prevention of contamination
Gloves, tongs, protective suits, booties
77
What happens when radiation enters living cells?
It can ionise atoms and molecules within, leading to tissue damage.
78
Lower doses of radiation
Cause minor damage, don’t damage cells, can give rise to mutant cells dividing uncontrollably.
79
How do fire alarms use radiation?
A weak source of alpha radiation is placed in a smoke detector, close to 2 electrodes.
Source causes ionisation and so a current of changed particles to flow.
Smoke will absorb charged particles and so breaks the current to set off the alarm.
80
How are gamma rays used in sterilisation?
Food can be irradiated with a high dose of gamma rays which kill microbes so that they last longer.
Medical equipment can be sterilised with gamma (not boiled).
This is better than boiling as it doesn’t involve high temperatures so fresh fruit and plastic can be sterilised without being damaged.
81
What type of source is needed for sterilisation?
A strong emitter of gamma rays with a reasonably long half-life (so doesn’t need replacing).
82
How is radiation used in tracers?
A medical tracer (containing a radioactive source) is injected/ingested by a patient. Its progress around the body is followed by a doctor. Used to detect and diagnose medical conditions.
BETA/GAMMA emitters are used so radiation passes out the body without damage and have a short half-life so last over a few hours.
Gamma emitting tracers are used in industry to detect leaks in underground pipes.
83
How is radiation used in Thickness gauges?
Beta radiation is used in thickness control.
Directs radiation through substance (paper) and have detector on other side linked to a control unit.
When detected radiation changes, paper is too thin/fat so control units stabilise.
84
Why do thickness gauges need beta sources?
Because paper will partially block radiation.
85
What does PET scanning stand for?
Positron
Emission
Tomography
86
What’s PET scanning and what’s it used for?
A technique used to show tissue/organ function and can be used to diagnose medical conditions.
Can detect cancer by showing metabolic activity of tissue, Cancer cells have a much higher metabolism than healthy cells.
87
How does PET scanning work?
1 Patient is injected with a substance containing a positron-emitting isotope with a short half-life so it acts as a tracer. Tracer moves through organs and is detected.
2 positrons emitted meet electrons in an organ and annihilate to emit high-energy gamma rays in opposite directions. Detectors around the body detect each pair of gamma rays. Triangulation can be used to locate tumours.
3 Distribution of radioactivity corresponds with metabolic activity as more radioactive substance is taken up by the cells dividing uncontrollably.
4 isotopes used have short half-lives so the hospital must be close to where it’s made.
88
Internal radiation therapy
When a radioactive material is placed inside the body onto or near a tumour via injection/implantation.
89
How are alpha emitters used in internal radiation therapy?
Normally injected near to tumour.
| Are strongly ionising so do much damage to nearby area in a limited area because they have a short range.
90
How are beta emitters used in internal radiation therapy?
Often used in implants placed inside/next to a tumour as they can penetrate casing of implant before damaging nearby cancerous cells. Have longer range than alpha so can damage healthy cells further from cancerous.
91
What are the half-lives used in internal radiation therapy? Why?
Short as so to limit the time that a radioactive substance is inside the patient’s body.
92
How can tumours be treated externally?
Gamma rays aimed at the tumour are able to penetrate through the patient’s body, carefully focussed on the tumour.
Can damage healthy cells despite shielding.
Have long half-lives
93
NUCLEAR FISSION
A type of nuclear reaction used to release energy from uranium/plutonium atoms. Huge amounts of energy are released via a chain reaction.//
When a large atom splits into two smaller atoms induced by a neutron.
94
Chain reaction of nuclear fission
Slow moving neutron is fired at a large and unstable nucleus (uranium 235). Neutron is absorbed by nucleus, causing it to split, forming 2 ‘daughter nuclei’ (which are radioactive too) as well as much energy. Each time it splits, 2 or 3 more neutrons are released which can hit other nuclei, causing them to split in a chain reaction.
95
How does a nuclear reactor use nuclear fission?
The fission forms an uncontrollable chain reaction which releases energy as heat, which then evaporated water, turning a turbine that produces electricity.
If it’s not moderated, will explode.
96
Control rod
| What’s it made of?
Boron.
| Absorbs neutrons. Placed in between fuel rods and lowered/raised into reactor to control chain reaction.
97
Moderator
| What’s it made of?
Graphite
| Slows down the speed of neutrons.
98
Coolant
Is a liquid / gas that reduces the temperature.
99
How do nuclear generators produce energy?
Energy released is transferred to the thermal energy store of the moderator, then transferred to thermal energy store of coolant, then transferred to the thermal energy store of cold water passing through the boiler, causing water to boil, energy being transferred to kinetic energy store of steam and so turbine. Turbine transfers kinetic energy store of generator, transferring energy away electrically.
100
Nuclear fusion
Two light nuclei colliding at high speed and join to create a larger, heavier nucleus.
(Eg hydrogen nuclei can fuse to produce a helium nucleus).
Heavier nucleus’ excess mass is converted to energy, released as radiation.
101
How does nuclear fusion occur?
```
High temperatures (150million°C) and high pressures as positively charged nuclei have to get v close ( 1*10 to the power of -15) and overcome electrostatic repulsion.
V fast moving particles mean will get v close to one another.
```
102
How do you increase KE of the nuclei?
By increasing temp and pressure
103
How are stars made?
Over billions of years, star combines protons (hydrogen) to create helium 4 in a temp of 15 million °C.
Stars use gravity to speed up particles
104
How is fusion carried out in a lab?
Deuterium and tritium are put together with EM force at 150 million °C to produce helium. Fusion reactors are hard and expensive to build.
105
Positives of fusion
Produces much energy.
No CO 2
Little waste
106
Negatives of fusion
Uses too much energy and pressure in production to actually profit in any energy made
107
Negatives of nuclear power overall
Negative public perception.
Nuclear waste is difficult to dispose of (long half-life), there’s danger of pollution.
Always risk of leak from power station to create major catastrophe.
Overall cost is high due to initial cost of power plant and decommissioning.
108
Positives of nuclear power
Generally safe.
V reliable
Reduces need for fossil fuels
Clean source of energy
Huge amounts of energy from small amount of material.
Nuclear fuel is cheap and readily available.
109
Difference between fusion and fission
2 hydrogen atoms fuse into helium (Fusion) however Neuton is pushed into uranium 234 in fission.
Energy is released from electrostatic repulsion in fusion chain reaction releases energy in fission.
Fusion is inefficient
