Topic 6 Flashcards
Who made the plum pudding model
J j Thompson
Explain the plum pudding model
Negatively charged electron plums embedded in a uniform positively charged ‘dough’
Shows both positive and negative charges existed in atoms and accounted for the atom being neutral
Rutherfords model
Atom must contain a very small positively charged nucleus which electrons orbit - a bit like planets orbiting the sun
Hypothesis was proved to be correct by Geiger and Marsden who fired alpha particles at gold film
Rutherford scattering
Source of a particles beam of particles at thing gold foil
Surrounded by a circular fluorescent screen
Some a particles are scattered
Most a particles are undeflected
The Bohr model
Niels Bohr showed that electrons had to orbit a positive nucleus in well - defined energy levels or orbits but could move between energy levels if they gained or lost energy
How can unstable nuclei undergo radioactive decay
Beta decay
What are the two types of beta decay
One where an electron is emitted
One where a positron is emitted
What happens in Beta-minus decay
Neutron in nucleus of an unstable atom decays to become a proton and an electron
Proton stays within nucleus but the electron
- which is the B- particle -
Is emitted from the nucleus at High speed as a fast-moving electron
N -> p + e-
The decay of carbon-14 to nitrogen-14 by the emission of a B- particles is an example of
B- decay
The mass number does not change
Proton number increased by 1
14C -> 14N + 0 E
6. 7. -1
What happens in beta-plus decay
Proton in nucleus decays into
Neutron positron
Neutron stays in nucleus
Positron (B+ particle) is emitted from nucleus at a high speed carrying away a positive charge and very small amount of the nuclear mass
P -> n + e+
The decay of sodium-22 into neon-22 by the emission of a positron is an example of
B+ decay
The mass number does not change but the proton number decreases by 1
22Na -> 22Ne + 0B
11. 10. +1
Uses of beta decay
Carbon-14 is an unstable isotope of carbon
It emits B- particles it has a half-life of over 5700 years
Means that it can be used for radiocarbon dating, which involves finding the ages of materials that are thousands of years old.
Positrons can be used in hospitals to form images of patients by the use of PET scans
When unstable nuclei decay
The changes that occur depend on the radiation that is emitted from the nucleus
Alpha radiation changes to the nucleus
Nuclear mass reduced by 4 [-4]
Positive charge reduced by 2 [-2]
Beta - changes to the nucleus
No change [0]
Positive charge increases by 1 [+1]
Beta + changes to the nucleus
No change [0] on mass of nucleus
Positive charge reduced by 1 [-1]
Gamma radiation changes to the nucleus
No effect on either the mass of the charge or a nucleus
Neutron radiation
Mass reduced by 1
No change of nuclear charge
In any nuclear decay the total mass and charge of the nucleus are conserved
Masses and charged on each side of equation must balance
Balancing nuclear decay equations
Searcj YouTube
The activity of a radioactive source is
The number of atoms that decay every second
The unit for activity is the
Becquerel (Bq)
When at atom decays it
Emits radiation but changes into a more stable isotope
The activity of a source depends on how many
Unstable atoms there are in a sample and on the particular isotope
As more + more atoms in a sample decay, there are fewer unstable ones left, so the activity decreases
What’s the half-life of a radioactive isotope
The time it takes for Half of the unstable atom to decay
Time for activity to go down by half
Can you predict when a particular nucleus will decay?
No
But when there is a very large number of nuclei the half-life gives a good prediction of the proportion of nuclei that will decay in a given time
The activity of a radioactive source is 240Bq and it’s half-life is 6 hours.
After 1 half-life the activity will halve to 120Bq
After 2 half-lives it will halve again to 60Bq
After 3 half-lives it will halve again to 30Bq
After 4 half-lives (one day) it will be 15 Bq
Used of gamma rays
Kill cancer cells
Beams of gamma-rays can be directed at cancer cells to kill them
Sterilise surgical instruments
Gamma-rays can be used to sterilise plastic instruments which cannot be sterilised by heating
Diagnose cancer
A tracer solution containing a radioactive isotope that emits gamma-rays is imjected unto 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’
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
Smoke alarms contain a source of
Alpha particles
How to smoke alarms work
Smoke enters the smoke detector
Smoke in the machine will absorb alpha particles and make the current fall
Alpha particles ionise the air and these charged particles move across the gap forming a current
Americium-241 alpha source gives off a constant stream of alpha particles
A detector senses the amount of current
Siren will sound when the current falls
Beta particles being used to control the thickness of paper
If the paper is too thick not as many beta particles get through
The rollers press together harder to make the paper thinner or move apart to make it thicker
Explain why beta particles are used to control the thickness of paper
Alpha particles would not go through the paper at all
Gamma-rays would psd through paper too easily and the amount getting through would hardly change with small changes in the thickness of the paper
What can ionising radiation do
Knock electrons out of atoms, turning the atoms into ions
This can be very harmful to humans
The energy transferred by ionising radiation can remove electrons from atoms to form
Ions
Ions are very reactive and can cause mutations to the DNA in cells
This can lead to cancer
How can ionisation and cellular mutation lead to cancer
Energy transferred by ionising radiation removed electrons from atoms to form ions
Ions are reactive and can cause mutations to the DNA in cells
Damaged DNA can lead to cancer
Ionising radiation can also cause damage to cell tissue in the form of radiation burns. When it’s energy is high enough it can also kill cells
How are people protected once they’ve come into contact with ionising radiation
Limiting the time of exposure
Keep time that a person needs to be in contact with ionising radiation as low as possible
Wearing protective clothing
Wearing a lead apron will absorb much of the ionising radiation
Increasing the distance from the person to the radioactive source
The further a person from, less damaging
How could you determine how much radiation a person has been exposed to
By wearing a film badge
The greater the half-life of an ionising source, the longer it will
Remain dangerous
Precautions of radioactive material
The source is being moved using tongs to keep it as far away from the persons hand as possible. The source is always kept pointing away from people
What’s irradiation
Ionising radiation from an external radioactive source travelling to the body
It is not breathed in, eaten or drunk
Does not refer to non-harmful rays from televisions, light bulbs or other non-ioninisung sources
Irrational
Alpha particles are unlikely to be harmful outside the body as they have a very short range in air (5cm) and are unlikely to reach a person
Irradiation is the exposure of a person to ionising radiation from outside the body. This could be in the form of harmful gamma-rays, beta particles or X-rays
When ionising radiation reached the body, cells may be damaged or killed but you will not become radioactive
Contamination
External contamination occurs when radioactive materials come into contact with a persons hair, skin or clothing.
Internal contamination occurs when a radioactive source is eaten or drunk. Some nuts, plants, fruits and alcoholic drinks have low levels of radioactivity. This is due to the radioactive minerals that they are exposed to during their growth or manufacture
Ionising radiation can be used internally and externally to diagnose
Illnesses and treat cancer
Medical tracers are substances that are used in
Biological processes in the body and contain s radioisotope
Patient can eat or drink this substance or inject
Ionising radiation emitted by tracer can be detected and the biological process monitored
Doctors can diagnose the nature and location of any health problems
Example of medical travers
Fluorodeoxyglucose (FDG)
Radioactive form of glucose that is commonly used as a tracer
Once it is in the blood it travels to the tissues that use glucose
When part of the brain is affected, less radioactivity is detected because glucose is not being used
What are PET scanners used to produce
3D colour images of the internal workings of the patient
Explain PET scanners
The tracer is a radioactive material that decays quickly by emitting positrons
When these positrons come into contact with electrons in the body, the two particles annihilate each other resulting in formations of gamma- rays
These gamma-days are detected by the PER scanner and processed by a computer and an image is then displayed on a computer screen
As the travers decay quickly they need to be produced close to where they are used
Treating tumours internally
Cancer tumours can be treated internally by using a radioactive source that is inside the patient.
Source enters patient by:
- injecting the radioisotope into the patient
- the patient eating or drinking something which contains the radioisotope in solid or liquid form
In the treatment of thyroid cancer the radioactive Elelemt
Iodine - 131 is used
It’s swallowed in a capsule
Taken up by the thyroid gland but not other parts of the body
Ionising radiation is likely to kill the thyroid cancer without affecting other cells surrounding it
Treating tumours externally
Several beams of gamma rays are fired, from different positions, towards the cancer
Each beam is not energetic enough to kill the tumour but damaged it
By moving the beam the amount of ionising radiation received by the surrounding tissues is reduced
Explain why internal treatments are used to treat cancer tumours
When internal treatments are used
The ionising radiation can be targeted at the tumour
Most of ionising radiation goes to the tumour and damage to surrounding areas is reduced
With external treatment the ionising radiation has to pass through healthy tissue which can be damaged
Electrical energy can be generated in
Power stations that use nuclear fuel ⛽️
Energy from the nucleus
All nuclear reactions can be a source of energy :
Radioactive decay- can be in the form of alpha or beta particles or gamma rays (electromagnetic waves)
Nuclear fusion - the funding of hydrogen nuclei in the sun releases enormous amounts of light and heat, some of which we receive on earth
Nuclear fission- uranium nuclei are split by slow-moving neutrons in a nuclear reactor, resulting in the release of enormous amounts of thermal energy
Nuclear power and waste
Nuclear power is a highly efficient way of producing electrical energy, much less nuclear fuel is needed compared with coal, oil or gas to produced the same amount of electrical energy
However nuclear power stations do produce radioactive nuclear waste which needs to be dealt with. Some of it is radioactive for thousands of years
Advantages of nuclear power
Don’t produce carbon dioxide so don’t contribute to climate change
Supplied of nuclear fuel will last longer than supplies of fossil fuels
(Construction processed produce carbon dioxide so it will be added to atmosphere when the power station is built and when fuel rods are made)
Disadvantages of nuclear power
Difficult and expensive to store nuclear waste safely
An accident in a nuclear power station can spread radioactive material over a large area
Many people think that nuclear power is dangerous and do not want new nuclear power stations to be built
(Nuclear power stations do not make the local areas more radioactive when they are working its only in an accident)
Explain the disadvantages of nuclear power (3 marks)
Nuclear radiation is very dangerous
Nuclear accident could kill many people
Much radioactive waste which is difficult and expensive to store and some of it is radioactive for many thousands of years
Public perception surrounding nuclear power as a form of energy means that people often distrust it because of previous accidents such as chernobyl and Fukushima
The fission of uranium-235 results in the release of a
Large quantity of energy which is used to heat water in power stations
What happens in nuclear fission
A large unstable nucleus splits into two smaller ones
Eg uranium-235 nucleus splits up when it absorbs a neutron
The fission of uranium-235 produces two daughter nuclei, two or more neutrons, and also releases energy
The daughter nuclei are also radioactive
Describe how a xhain reaction of nuclear fission can be controlled
A chain reaction can be controlled by using a different material to absorb some of the neutrons
This slows the reaction down because there are fewer neutrons to cause more nuclei to undergo fission
Chain reactions
Neutrons released by fission of U-235 may be absorbed by other nuclei each of these nuclei may undergo fission and produce even more neutrons
If this is not controlled there will be a nuclear explosion
