Atomic structure and radioactivity Flashcards
(192 cards)
1
Q
How large are atoms?
A
Very small, with a radius of about 1 × 10⁻¹⁰ m.
2
Q
Describe the basic structure of an atom.
A
A positively charged nucleus
composed of both protons and neutrons surrounded by negatively charged electrons.
3
Q
The radius of a nucleus is less than _______ of the radius of an atom.
A
1/10 000
4
Q
Where is most of the mass of an atom concentrated?
A
In the nucleus.
5
Q
Why are atoms neutral?
A
The positive charge from the protons cancels out the negative charge from the electrons.
6
Q
How are the electrons of an atom arranged?
A
They orbit the nucleus at different distances from it (different energy levels).
7
Q
How might electron arrangements change?
A
With the absorption or emission of electromagnetic radiation.
8
Q
Explain what happens when atoms absorb electromagnetic radiation.
A
Electrons gain energy and can move to higher energy levels (further from the nucleus).
9
Q
Explain what happens when atoms emit electromagnetic radiation.
A
Electrons lose energy and move down to lower energy levels (closer to the nucleus).
10
Q
Atoms have no overall what?
A
electrical charge
11
Q
What is the number of protons in an atom of an element called?
A
Its atomic number
12
Q
What is the total number of protons and neutrons in an atom called?
A
Its mass number
13
Q
How can atoms turn into ions?
A
If they lose one or more outer electron(s).
14
Q
What are the ways in which electrons can leave an atom?
A
-Absorbing electromagnetic radiation of enough energy so that the outer electrons can escape the pull of the nucleus
-Being hit by a particle such as an alpha or beta particle
15
Q
What are the types of electromagnetic radiation with enough energy to allow outer electrons to escape the pull of the nucleus?
A
-UV
-X-rays
-Gamma-rays
16
Q
What might new experimental evidence lead to?
A
A scientific model being changed or replaced.
17
Q
Before the discovery of the electron, what were atoms thought to be?
A
Tiny spheres that could not be divided.
18
Q
What did the discovery of the electron lead to?
A
The Plum Pudding model (of the atom).
19
Q
What dis the plum pudding model suggest that the atom is?
A
A ball of positive charge with negative electrons embedded in it.
20
Q
What conclusions were drawn from the alpha particle scattering experiment?
A
-The mass of an atom was concentrated at the centre (in the nucleus).
-The nucleus was charged.
21
Q
Which model replaced the Plum pudding model?
A
Rutherford’s nuclear model.
22
Q
How did Niels Bohr adapt Rutherford’s nuclear model?
A
By suggesting that electrons orbit the nucleus at specific distances.
23
Q
The theoretical calculations of Bohr agreed with (and helped explain) what?
A
Other scientists’ experimental observations at the time.
24
Q
What did later experiments by Rutherford et al lead to? (after Bohr)
A
The idea that the positive charge of any
nucleus could be subdivided into a whole number of smaller particles.
And that each particle had the same amount of positive charge.
These particles were named protons.
25
What is a hydrogen nucleus?
A proton!
26
The experimental work of James Chadwick provided the evidence for what?
The existence of neutrons within the nucleus.
27
When did James Chadwick prove the existence of neutrons within the nucleus?
About 20 years after the nucleus became an accepted scientific idea.
28
What is the order of scientists who developed the atomic model?
-Dalton
-Thomson
-Rutherford
-Bohr
-Chadwick
29
Why was Rutherford expecting most of the alpha particles to pass straight through the thin sheet of gold foil? (or be very slightly deflected at most).
Because the positive charge of the atom was thought to be very 'spread out' through the 'pudding' of the atom.
30
What was the alpha particle scattering experiment?
Positively charged alpha particles were fired at an extremely thin sheet of gold foil.
31
Explain how Rutherford's work led to the conclusion that atoms had a small, positive nucleus. (4)
Positive alpha particles were fired at the nucleus.
Most went through undeflected, so most of the atom must be empty space.
There is a small positive nucleus because very few of the alpha particles were deflected backwards.
Some were deflected more than expected because they came close to the concentrated, positively charged nucleus.
32
What is the problem with Rutherford's nuclear model?
If electrons were in a 'cloud' around the nucleus of an atom, they should be attracted to the positive nucleus, causing them to rush inward and the atom to collapse.
33
How did Bohr overcome the problem of Rutherford's model (collapsing atoms)
In 1913, he proposed that electrons orbit the nucleus in fixed shells, (no where in between) at a fixed distance from the nucleus, which kept the atom from collapsing.
34
What is the modern day model of the atom called?
The nuclear model.
35
Describe the differences between the nuclear model and the 'plum pudding' model of the atom. (pt 1)
-In the nuclear model, mass is concentrated at the centre of the atom (in the nucleus) , but in the plum pudding model, mass is evenly distributed.
-In the nuclear model, positive charge occupies only a small part of the atom, but in the plum pudding model, positive charge is spread throughout the atom.
36
Describe the differences between the nuclear model and the 'plum pudding' model of the atom. (pt 2)
-In the nuclear model, electrons orbit the nucleus at a fixed distance in shells, but in the plum pudding model, electrons are embedded in the mass of positive charge.
-In the nuclear model, the atom is mainly empty space, but the plum pudding model is a ‘solid’ mass.
37
Some atomic nuclei are...
unstable.
38
How do unstable nuclei change to become more stable?
They give out radiation.
This is a random process.
39
What is the name for the random process in which the nucleus of an atom gives out radiation as it changes to become more stable?
Radioactive decay.
40
Activity
The rate at which a source of unstable nuclei decays.
41
What is the unit for activity?
becquerel (Bq)
42
Count-rate
The number of decays recorded each second by a detector (eg Geiger-Muller tube).
43
How do we calculate activity?
Number of decays ÷ number of SECONDS
44
Explain how the activity of a source relates to how unstable its nuclei are.
A sample of a material with very unstable nuclei will have a high activity because many of the particles will decay each second.
Whereas a material with more stable nuclei will have a lower activity because fewer particles will decay each second.
45
Explain why the activity of a source decreases with time.
Activity is directly related to the number of unstable particles present at the time.
Over time, as more of the unstable nuclei decay and become stable, there are fewer unstable nuclei left.
So, the activity will decrease as fewer unstable nuclei are left to decay each second.
46
What is a Geiger-Muller tube?
A machine used to detect nuclear radiation.
It's connected to a counter/ratemeter which shows the count rate.
47
If count rate decreases, the total amount of radiation absorbed by a material must...
...increase.
48
Number recorded on counter + The amount of radiation detected from the source + what?
Background radiation.
49
Why might an experiment be thought to be valid?
If measurements are made many times/ over a long period of time. (and have similar results).
50
Describe the model now used for the structure of an atom (6).
The nuclear model has:
-A small nucleus which is positively charged overall
-Protons and neutrons (both with a relative mass of 1) contained within the nucleus
-Protons have a relative charge of +1, whilst neutrons have a neutral charge (0)
-Negatively (-1) charged electrons which orbit the nucleus on electron shells
-Which are at fixed distances from the nucleus
51
What can nuclear radiation emitted be?
-An alpha particle (α)
-A beta particle (β)
-A gamma ray (γ)
-A neutron (n)
52
What is an alpha particle (α)?
-Two neutrons and two protons
-It is the same as a helium nucleus
-It has a mass number of 4
-It has an atomic (proton) number of 2
53
What is a beta particle (β)?
-A high speed electron ejected from the nucleus as a neutron turns into a proton
-It has a mass number of 0
-It has a charge of -1
54
What is a gamma ray (γ)?
- Electromagnetic radiation emitted from the nucleus
55
When an alpha particle is emitted, what effect does this have on the nucleus?
-Mass number is reduced by 4
-Positive charge (proton number) is reduced by 2
56
When a beta particle is emitted, what effect does this have on the nucleus?
-No change to the mass number
-Positive charge increases by 1 (atomic number)
57
When gamma rays are emitted, what effect does this have on the nucleus?
-It has no effect on either the mass or the charge of a nucleus as only energy (in the form of electromagnetic radiation ) is emitted.
58
When a neutron is emitted, what effect does this have on the nucleus?
-Mass number decreases by 1
-No change to the atomic (proton number)
59
When unstable elements undergo radioactive decay, what do they change into?
Other elements.
60
Ionising power of a neutron
Not directly ionising
61
Ionising power of an alpha particle
Very/highly ionising
62
Ionising power of a beta particle
Moderately ionising
63
Ionising power of gamma-rays
Weakly ionising
64
Range of alpha particles in air
around 5cm
65
Range of beta particles in air
a few metres
66
Range of gamma rays in air
a few kilometres
67
Penetration through materials - alpha particles
Can be stopped by a thin sheet of paper
68
Penetration through materials - beta particles
Can be stopped by aluminium 3mm thick
69
Penetration through materials - gamma rays
Can be stopped by thick lead or concrete
70
Doo neutrons have a high penetrating power?
Yes.
This is due to them having no charge and not interacting strongly with matter.
71
Neutrons can travel through ______ for long distances before being stopped.
Humans and buildings
72
How do alpha particles, beta particles, and gamma rays ionise atoms?
By colliding with them, causing them to lose electrons.
73
Explain why alpha particles are the most ionising radiation.
They have the greatest mass and the greatest charge, so can remove electrons more easily from the shells of atoms.
74
Explain why radioactive decay is a random process.
You cannot predict when a nucleus will decay by emitting radiation.
75
Explain why alpha particles are much more dangerous inside than outside the body.
Alpha particles are highly ionising and readily absorbed by nearby cells, which can lead to mutations when inside the body.
Outside the body, they have a very short range and are unlikely to reach the body and cause harm to cells.
76
State three uses of gamma rays (ionising radiation).
-To kill cancer cells (radiotherapy)
-To diagnose cancer (and other medical problems using tracers)
-To sterilise surgical equipment
-To preserve food
-In smoke alarms
77
How is radiation used to kill cancer cells?
Beams of gamma-rays can be directed at cancer cells to kill them.
78
How is radiation used to sterilise surgical equipment?
Gamma rays can be used to sterilise plastic instruments which cannot be sterilised by heating.
79
How is radiation used to diagnose cancer?
A tracer solution containing a radioactive isotope that emits gamma rays is injected into the body and taken up by cells which are growing abnormally.
The places in the body where the tracer collects are detected with a 'gamma camera'.
80
How is radiation used to preserve food?
Food irradiated with gamma rays will last longer as microbes are killed by the high-energy gamma rays.
The food does not become radioactive.
81
What do smoke alarms contain?
A source of alpha particles.
82
How is radiation used in smoke alarms?
-Alpha particles ionise the air and form a current within the smoke alarm
-When smoke enters the alarm, it absorbs alpha particles so the current falls
-This is detected by a detector
-This triggers a siren to sound
83
Explain why beta particles are used to control the thickness of paper.
Alpha particles wouldn't go through the paper at all.
Gamma rays would pass through too easily, and the amount getting through would hardly change with small changes in the thickness of the paper.
84
Why would a radioactive isotope with a long half life, and that emits gamma radiation be suitable for irradiating food?
-Long half life
-Gamma radiation can penetrate deeper into the food
-To penetrate bacteria in the food and kill it
85
Suggest one reason why some people may be concerned about the safety of eating irradiated food.
They may be concerned that the food is still radioactive.
86
Explain why the radiation in smoke alarms is not dangerous to people in homes.
It contains alpha particles which have a short range in air and so cannot reach the body.
87
Suggest how ionising radiation can be used to find cracks in underground pipes.
Water is injected with a gamma source.
When water reaches a crack, it will pass out of the pipe into the surrounding ground.
So, a higher reading of gamma rays is detected at the surface above the crack in the pipe.
88
The government may not support factories manufacturing what?
Irradiated food (because they may see this as unsafe).
89
Why is it important that people eating at a restaurant are given menus which state which ingredients have been irradiated?
They might feel vulnerable and not want to eat irradiated food due to the risk of tumours (due to ionisation of cells).
90
What are nuclear equations used to represent?
Radioactive decay.
91
In a nuclear equation, how may an alpha particle be represented?
By the symbol: ⁴₂He
92
In a nuclear equation, how may an beta particle be represented?
By the symbol ⁰₋₁e
93
Give an example of a nuclear equation for alpha radiation.
²¹⁹₈₆radon → ²¹⁵polonium ₈₄ + ⁴₂He
94
Give an example of a nuclear equation for beta radiation.
¹⁴₆carbon → ¹⁴₇nitrogen + ⁰₋₁e
95
What is the half life of a radioactive isotope?
The time it takes for the number of nuclei of the isotope in a sample to halve.
or
The time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.
96
When answering questions...
look to see if its part ii or iii or iv - there might be important information elsewhere!!!
97
What doe net decline tell you?
What ratio of a radioactive material has decayed after each half life.
After 1 half life, the net decline is 1/2.
After 2 half lives, the net decline is 3/4. (1/2+1/4)
After 3 half lives, the net decline is 7/8 (1/2 + 1/4 + 1/8)
98
When is background radiation around us?
All the time
99
Where does background radiation come from?
* natural sources such as rocks and cosmic rays from space
* man-made sources such as the fallout from nuclear weapons testing and nuclear accidents, medical
100
What can the level of background radiation and radiation dose a person receives be affected by?
Their occupation and/or location.
101
What is the unit for radiation dose? (helpful but not required to know)
sieverts (Sv)
102
1000 millisieverts (mSv) = how many sieverts?
1
103
What is radioactive contamination?
The unwanted presence of materials
containing radioactive atoms on other materials.
(or on/inside human bodies)
104
What is the hazard from contamination due to?
The decay of the contaminating atoms.
105
What affects the level of hazard posed by contamination?
The type of radiation emitted.
106
What is irradiation?
The process of exposing an object/person to ionising radiation from outside of the body.
This could be in the form of harmful gamma rays, beta particles, or x-rays.
(its not eaten, drunk, or breathed in, - it's an external radioactive source and doesn't touch the skin).
107
What does irradiation NOT refer to?
Non-harmful rays from televisions, light-bulbs, or other non-ionising sources.
108
What happens when ionising radiation reaches the body?
Cells may be damaged or killed, but you/
the irradiated object will not become radioactive.
109
When dos external contamination occur?
When radioactive materials come into contact with a person's skin, hair, or clothing.
110
When does internal contamination occur?
When a radioactive source is eaten or drunk.
111
Why do some nuts/plants/fruits/alcoholic drinks have low levels of radioactivity?
Due to the radioactive minerals they are exposed to during their growth or manufacture.
112
Explain why alpha particles are more likely to cause damage inside than outside the body.
Alpha particles are highly ionising due to their charge and mass...
...and will cause damage inside the body as they have a short range and will come into contact with cells.
Outside the body, they are unlikely to reach the body because they have a range of only 5cm in air.
So, they cannot easily reach the body to cause and infection in cells.
113
Explain why background radiation is a mixture of contamination and irradiation.
Some sources of background radiation do not come into contact with the body, such as cosmic rays from the sun and medical X-rays.
But other sources such as radon gas and radioisotopes in food are taken into the body.
114
How is ionising radiation harmful to humans?
It can knock electrons out of atoms, turning the atoms into ions.
115
What is a possible risk of health caused by a radioactive source?
-The cell could divide uncontrollably and become cancerous
-The DNA could mutate
-The DNA could be destroyed
116
What safety precautions can be taken when handling radioactive substances?
-Wear overalls
-Store the radioactive substance in a lead-lined box
-Use tongs when picking up the radioactive substance
117
What are the factors that affect the amount of radiation you receive?
-How radioactive the substance is
-Distance from the source
-How long you’re exposed for
118
What factors determine how harmful the radiation is?
-The type of radiation
-The amount of radiation you receive
-Where you’re exposed to the radiation
119
What century was Chadwick?
20th
120
What does a gamma ray consist of?
electromagnetic radiation
121
What is the source of a beta particle?
A neutron decaying into a proton and an electron.
122
How does limiting the time a person is exposed to ionising radiation protect them?
The time they need to be in contact with the ionising radiation is kept as low as possible.
123
How does wearing a lead apron protect a person from ionising radiation?
It will absorb much of the ionising radiation.
124
The further a person is from ionising radiation...
...the less damage it will do.
125
The greater the half-life of a radioactive source...
...the longer it will remain dangerous.
126
Describe two precautions taken by dentists to reduce their exposure to ionising radiation when taking an X-ray.
-They go out the room in which the X-ray is taking place
-They keep the X-ray pulse as short as possible (this also minimises the patient's exposure)
127
What is the amount of energy the human body is exposed to from a radioactive source called?
The dose
(in medicine this needs to be high enough to form an x-ray image but low enough to be safe for the patient and doctor/dentist)
128
Explain why peer review is important in the scientific community.
It is important for scientists to analyse or test other scientists' claims to see if new knowledge or understanding of the area of science can be developed/improved for the benefit of science and people.
129
Suggest why ionising radiation is more dangerous than non-ionising radiation.
Ionising radiation ionises atoms, making them more reactive and allowing change to DNA to occur.
Whereas non-ionising radiation cannot do this as there is not enough energy to ionise atoms.
130
Describe three precautions that can be taken to avoid unnecessary exposure to ionising radiation. (3)
-A short exposure time
-As low a dose as possible
-Using protective clothing
131
Why is it important for the findings of
studies into the effects of radiation on humans to be published?
So that people are informed of the impact of radiation on their bodies.
132
Radioactive isotopes have a ____ ____ range of half-life values.
very wide
133
When is the threat of a radioactive isotope higher to human health?
-if it has a long half-life
-if you are exposed to a high dosage
-this is because living cells will be exposed to dangerous radiation for a longer amount of time
134
The background radiation dose is very low, (about 0.003 mSv / hr) so...
...the risk to human health is also low.
135
A radiation dose of what will lead to death?
0.1 sieverts (Sv)
136
What is radon?
A radioactive gas produced when uranium in rock decays.
It can build up in homes and other buildings.
137
What is nuclear radiation used in medicine for?
* the exploration of internal organs
* the control or destruction of unwanted tissue.
138
What is a medical tracer?
A substance used in biological processes in the body and that contains a radioisotope
139
What are the properties of a medical tracer?
-An isotope of an element or part of a compound that is absorbed by the body
-Usually an emitter of gamma rays
-Have a half-life long enough to form a useful image, but short enough so that its nuclei are mostly decayed after the image is taken
140
Why do we want medical radioisotopes to have a short half life?
So it is long enough to give a useful image/to irradiate a tumour, but short enough to limit a patients exposure time to radiation as to not kill healthy cells.
141
What type of radiation is used for medicine?
Gamma rays ad they penetrate deeper into the body than alpha and beta particles from an external source.
Alpha particles would pose risk to a patient as it is highly ionising so could kill healthy cells/cause mutations.
142
Rutherford’s model
-The atom is mostly empty space
-The nucleus is positively charged
-The nucleus is small
143
How do medical tracers enter the body?
-It can be injected into the body
-The patient can eat or drink the substance
144
How can doctors use medical tracers to diagnose the nature and location of any health problems?
The ionising radiation emitted by the medical tracer can be detected and the biological processes monitored.
145
Give an example of how medical tracers are used to diagnose health problems.
FDG is commonly used as a tracer.
It travels in the blood to tissues that use glucose.
When part of the brain is affected, glucose is not being used. (or not as much)
So less radioactivity will be detected.
146
What is FDG?
Fluorodeoxyglucose is a radioactive form of glucose commonly used as a tracer.
147
Exposure to low levels of radiation over long periods can lead to cancer. Why is this?
Radiation can cause mutations in our DNA which may cause our cells to divide uncontrollably.
148
Radiotherapy
The use of small targeted doses of radiation to kill cancerous cells.
149
How do we reduce the amount of ionising radiation received by tissue surrounding a tumour?
By moving the beams of gamma-rays.
150
Destroying unwanted tissue externally (external radiotherapy)
When treating a tumour externally, cancerous cells are exposed to beams of gamma-rays from outside of the body, from lots of different angles.
This way, the cancer site gets the highest dose of radiation.
Each beam is not energetic enough to kill the tumour, but damages it.
151
Why are gamma rays used to destroy unwanted tissue externally?
They penetrate deeper into the body than alpha and beta particles from an external source.
152
What does destroying unwanted tissue internally (internal radiotherapy) involve?
-The placing of seeds, ribbon, or capsules inside the patient's body near to the tumour (brachytherapy)
or
-The radioisotope can be injected, swallowed, or enter the body via an intravenous drip.
153
What is the medical term for internal radiotherapy?
Brachytherapy
154
How can a radioactive source enter the patient?
-It can be injected into the patient
-The patient can eat or drink something which contains the radioisotope in solid or liquid form
155
Destroying unwanted tissues internally (internal radiotherapy)
Once inside the body, radioisotopes travel through the body, locating and killing cancer cells
The radiation source usually emits beta particles or gamma-rays and is placed inside or near the cancer cells.
156
What type of radioisotopes are used for destroying unwanted tissue internally?
-Ones with half lives log enough to irradiate the tumour over a given time
-But short enough to limit the dose to the patient so long-term harm isn't caused
-This could be a few hours, days, or weeks depending on the type of cancer being treated
157
Iodine-131
-Used in internal radiotherapy to treat thyroid cancer
-Has a half-life of 8 days
-Is a beta emitter
158
Why should gamma rays used to destroy unwanted tissue externally come from a source with a long half life?
So that it does not need to be constantly replaced.
159
Give an example of an external source with a long half-life.
Cobalt - 60, which has a half life of between 5 and 6 years.
160
Does a patient become radioactive after treatment using external sources of radiotherapy?
No. Gamma rays are used for irradiating the patient.
161
Does a patient become radioactive after treatment using internal sources of radiotherapy?
Yes as they have been contaminated with radioactive material which can emit particles that will leave the body.
162
Why can the position of the tracer be detected from outside the body?
Because it emits radiation.
163
If a tracer is injected...
...it will travel to parts of the body through the blood.
164
If the tracer is swallowed...
...it may be absorbed through the persons intestine and then travel via the bloodstream.
165
Side effects of radiotherapy
Patient feels sick and the radiation can kills healthy cells.
166
Give an example of an alpha source used in smoke alarms.
Americium-241.
This alpha source gives off a constant stream of alpha particles, which ionise the air and move across the gap in the smoke detector, forming a current.
167
Nuclear fission
The splitting of a large and unstable nucleus, (e.g. uranium or plutonium) into smaller nuclei.
168
Fission can occur…
…by an atom’s nucleus absorbing a neutron and becoming even more unstable.
169
What happens in a nuclear fission chain reaction? (steps 1 and 2)
-It starts with an unstable nucleus like uranium- 235.
-A neutron is then fired at the unstable nucleus, and causes the nucleus to split apart.
170
What happens in a nuclear fission chain reaction? (steps 3 and 4)
-The unstable nucleus splits into two ‘daughter’ nuclei, roughly equal in size, and emits two or three neutrons and gamma rays.
-The neutrons that were released may go on to form a chain reaction: if they are absorbed by other unstable nuclei, this repeats the process.
-The daughter nuclei are also radioactive.
171
How do nuclear power stations generate electricity?
-Whenever unstable uranium or plutonium nuclei split apart they release lots of gamma radiation.
-This gamma radiation is then used to heat liquid water into steam.
-As the steam rises it turns turbines, and the kinetic energy of those turbine is converted into electricity by a generator.
172
How can we ensure safety in nuclear reactors?
To keep the reaction stable, we can lower control rods into a nuclear reactor which absorb neutrons and slow down the chain reaction.
173
What are the main pros of nuclear power?
Nuclear power plants don’t produce any greenhouse gas (CO2).
Nuclear power plants can produce large and steady electric power.
Nuclear fuel such as uranium or plutonium is relatively cheap.
174
State and explain three major cons of nuclear power
-Nuclear power stations are very expensive to build.
-The nuclear waste is radioactive so must be stored safely in underground bunkers for a long period of time, which is very expensive.
-There is a risk of the nuclear chain reaction getting out of control and causing a nuclear meltdown.
175
Explain what happens in the process of nuclear fusion.
Two unstable lighter nuclei fuse to make a single heavier nucleus which is more stable.
When this occurs, energy is emitted in the form of electromagnetic radiation.
The energy emitted comes from some of the mass converting to energy.
176
Why does fusion only happen in stars?
What elements fuse to make what?
It only occurs at very high temperatures and pressures in order to overcome the repulsion of the positively charged nuclei.
Most of the fusion occurring in stars is hydrogen nuclei fusing to become helium nuclei. (this is the stars' source of energy).
177
Nuclear fission simple
Slow moving neutrons are absorbed by a nucleus, which becomes unstable and splits.
178
Explain why radioisotopes that emit alpha particles are not used as medical tracers.
A single high-energy beam would destroy all the cells that it came into contact with when fired at the body because it has a much higher energy.
Whereas many low-energy beams will not have enough photon energy by themselves to harm healthy cells.
However, when they are focused at a point, the energies of the individual beams add up to become a large energy that can kill a cam=ncer tumor.
179
Explain why several low-energy gamma-ray beams are used instead of a single high-energy beam when treating cancer with gamma rays from an external source. (4)
Alpha particles are highly ionising, so absorption by tissues can lead to cellular mutations.
Alpha particles emitted from a tracer in the body would be absorbed by the tissue around the tracer and so could not be detected from outside the body.
180
Gamma rays can be used to...
...form images of the internal workings of the body and control/destroy cancer cells.
181
What are the 2 smaller nuclei gained from nuclear fission called?
daughter nuclei
182
What do all of the fission products have?
Kinetic energy
183
The explosion caused by a nuclear weapon is
caused by what?
An uncontrolled chain reaction.
184
Students should be able to draw/interpret diagrams representing...
...nuclear fission and how a chain reaction may occur.
185
Controlled chain reaction
Only one neutron from each fission can cause another fission.
186
Why are high temperature and pressures needed to make nuclear fusion worthwhile?
So the nuclei are moving fast enough to overcome the electrostatic repulsion between the positively charged nuclei.
187
Why is the mass of the products slightly less than the mass of the reactants in nuclear fusion?
The difference in mass is released as thermal energy.
188
Explain the difference between a chain reaction and a controlled chain reaction.
In a chain reaction, the number of atoms undergoing fission increases very rapidly and can cause an explosion.
In a controlled chain reaction, some of the neutrons are absorbed by a different material so only one neutron from each fission can cause another atom to fission.
189
Explain why neutrons in a nuclear reaction need to be slow moving.
So they can be easily absorbed by nuclei causing the nucleus to become unstable.
190
Explain why only one neutron should be absorbed by a uranium-235 nucleus.
Because otherwise the reaction would become out of control leading to an explosion.
191
Calculate the volume of the patient's blood question steps:
1. calculate the dilution by dividing the counts per minute of the solution by the counts per minute of the blood
2.multipy this by 10 or however many cm³ of the solution has been injected
e.g. 7350/15 x 10
192
Why might a method of estimating blood volume using a radioactive isotope diluted in the blood not be completely accurate?
-Some radiation absorbed by organs
-Some radiation absorbed into urine
-Count rate decreases, so may be divided incorrectly - wrong estimate
