Topic 6 - Radioactivity Flashcards
particle theory
a model that helps explain the properties of solids, liquids and gases
atomic model
models representing how an atom looks and behaves
atomic number
the number of protons
an atoms mass number
total number of protons and neutrons in the nucleus
isotope
atoms of the same element that have the same number of protons but DIFFERENT number of neutrons
explain the ‘plum pudding’ model
- positive orb of energy with electrons inside
- no nucleus
explain Rutherford’s model
- dense positive nucleus with protons and neutrons
- mostly empty space
- electrons orbiting nucleus
where are protons
lives in the middle of the atom known as the nucleus and has a positive charge
where are neutrons
lives in the middle of the atom known as the nucleus and has no charge
electron
orbits around the nucleus and has a negative charge
what happens when an electron falls down an electron shell
it will release energy as light or EM radiation
ionising radiation
radiation that causes electrons to escape
emission spectrum
the spectrum of frequencies (series of colours) of electromagnetic radiation emitted due to electrons making a transition from a high energy state to a lower energy state
absorption spectrum
a spectrum of electromagnetic radiation transmitted through a substance, showing dark lines or bands due to absorption at specific wavelengths.
what are the sources of background radiation
- food and drink
- cosmic rays
- ground and buildings
- medical
- radon gas
what’s the main source of background radiation
radon gas
background radiation
when we are constantly exposed to ionising radiation at a low level from space and from naturally radioactive substances in the environment
how does radon gas contribute to background radiation
this radioactive gas is produced by rocks that contains small amounts of uranium; radon diffuses into the air from rocks and can build up in houses, especially where there is poor ventilation
how does food and drink contribute to background radiation
some foods contribute to exposure background radiation because they contain small amounts of radioactive substances
how does medical contribute to background radiation
hospital treatment such as x-rays gamma scans and cancer treatment
how does cosmic rays contribute to background radiation
because they’re high energy charged particles that stream out the Sun and other stars
how can you measure radioactivity of a source
using a Geiger-Müller (GM) tube
how does a GM tube work
- radiation cools through the tube ionising gas and inside it and allows a short pulse of current to flow
- the GM tube can then be connected to counter to count the pulses of current, or the GM tube may give a click each time the radiation is detected - the account rate is a number of clicks per second or minute
what are the 5 types of radiation
- alpha
- beta+
- beta- (positron)
- gamma
- neutron
why does decay or change happen in the nucleus of a radioactive substance
because the nucleus of a radioactive substance is unstable, which means it can easily change or decay
what happens when decay occurs
radiation is emitted, which causes a nucleus to lose energy and become more stable
what do alpha particles contain
2 protons, 2 neutrons
what is alpha particles relative mass
4
charge of alpha particles
2+
how is alpha particles written as
4
He
2
beta particles
high-energy, high-speed electrons
what’s beta particles relative mass
1/2000
beta particles charge
-1
what can beta particles be written as
0
e
-1
gamma rays
high frequency electromagnetic waves
electric charge of gamma rays
they don’t have a charge
what can all these radioactive waves do
they can penetrate (pass through) materials
what stops alpha particles penetrating
thin piece of paper - very ionising
what stops beta particles penetrating
thin sheet of aluminium - medium ionising
what stops gamma rays penetrating
block of lead - weakly ionising
what happens to an atom when an alpha particle is emitted
the mass number goes down by 4 and the atomic number goes down by 2
what happens in beta- decay
A neutron changes into a proton and an electron, atomic number increases by one, no change to the mass number
- electron is ejected from the atom
what happens in a beta+ decay
a proton becomes a neutron and a positron, the mass number stays the same, the atomic number goes down by 1
half life
the time taken for half the unstable nuclei in a sample of radioactive isotope to decay
- Measure of how long it takes for activity to half
what happens in nuclear fission
large nuclei break up to form smeller nuclei and release energy
nuclear fusion
two small nuclei collide and high speed to form a larger nuclei
when does fusion happen
only happens at very high pressures/temperatures and the nuclei needs to be close together to fuse
what is released in nuclear fission
high amount of energy and neutrons
who came up with the ‘plum pudding’ idea
J.J Thompson
how did Rutherford discover his idea
he fired alpha particles at gold foil
- some bounced back (reflected) because they were repelled by positively charged particles in the gold atom
- some alpha particles went straight through which indicated the atoms and mostly empty space
Bohrs model of atom
Agreed with Rutherford, however he suggested that electrons can only be in a certain fixed orbit around the nucleus
count rate
The number of clicks per second or minute
positron
High energy high-speed particle
positron relative mass
1/2000
positron charge
+1
how are positrons written
0
e
+1
what can be emitted from an unstable nucleus
- alpha particles
- Beta particles
- gamma rays
- positrons
- neutrons
alpha particles
- transfer a lot of energy
- each time they ionise an atom they loose energy
- short penetration distance
- very ionising
measurement used for activity of any radio active substance
Number of nuclear decades per second and is measured in becquerels (Bq)
- One becquerel is one nuclear decay second
What are uses of radioactivity?
- Food can be irritated with gamma rays to kill bacteria
- surgical instruments need to be sterilised to kill microorganisms (heat them)
- radioactive detecting (radioactive isotopes can be used as tracers)
- Diagnose cancer using tracers in the body
- Treat cancer
- Checking thickness of paper
- Smoke alarms
Explain how radioactivity is used in radioactive detecting
- When radiation passes inside a detector, it causes ionisation of gas atoms separating atoms into positive ions and electrons
- separated electrons and positive irons are attracted to the electrodes causing a current to flow
- This is converted into electrical signals which are then measured as the amount of radiation
explain how radioactivity is used to check thickness of paper
- when paper is too thin more bait particles penetrate the paper and the detector records a higher count rate
- A computer senses that the account rate has risen and reduces the force supplied to the rollers to make the paper thicker
- when the paper is too thick, the opposite happens
explain how radioactivity works in smoke alarms
- smoke alarms contain a source of alpha particles, usually a radioactive isotope called americium-241
- The detector has an electrical circuit with an air gap between two electrically charged plates
-The alpha particles ionise the air molecules and these ions then move across the gap forming a current - Smoking the device will slow down the ions and so make the current fall
- The detective senses the amount of current if the current falls the siren sounds
two dangers of radiation on the body
- large amount of ionising radiation can cause tissue damage such as reddened skin
- small amount of ionising radiation over a long period of time can cause damage of the DNA inside a cell (mutation)
-> may cause cancer
explain two precautions to handle radioactive sources
- handle with tongs because the intensity of radiation decreases with distance from the source
- Don’t point sources at people
- Store in lead line containers as lead is an effective radiation shielding material because of its density
when is someone irradiated and how it stops
- someone is irradiated when they’re supposed to alpha beta or gamma radiation from nearby radioactive materials
- Once a person moves away the irradiation stops
When does someone become contaminated and how will it stop?
- someone becomes contaminated if they get particles of radioactive material on their skin or inside their body
- This will continue until the material has all decayed until the source of contamination is removed (which is not always possible)
Explain some medical ways to use gamma ray tracers - gamma cameras
- They can be injected into the bloodstream, swallowed, inhaled or injected directly into an organ
- Can be found to find sources of internal bleeding
- gamma cameras are used to detect tumours
how do gamma cameras find internal bleeding
gamma cameras detect the area of highest gamma radiation which is where the bleeding is occurring
how do gamma cameras detect tumours?
Tracer is made using radioactive glucose molecules because very active cells such as cancer cells take up glucose more quickly than other cells
gamma camera
- gamma cameras image the radiation from a tracer introduced into the patient’s body
-> the text grammar is emitted by radioactive isotopes in the body
radioactive tracers
they contain an radioactive isotope attached to molecule that will be taken up by a particular organ in the body to track the movement of a substance or it’s location
what do radioactive isotopes used in medical tracers need to have a short half life?
other parts of the body are affected as little as possible
what is used in internal radiotherapy
uses a beta emitter placed close to a tumour
what is used in external radiotherapy
Uses beams of gamma rays x-rays or protons directed at the tumour from outside the body
nuclear fission
a large nuclei (uranium-235) breaks up to form smaller nuclei and release energy
name a nucleus fuel
uranium-235
+ and - of nuclear power station
- produce waste that will stay radioactive for millions of years
- very expensive to decommission
+ low greenhouse gas emissions
benefits of nuclear fuel
- store a lot more energy per kg
- do not burn so don’t need air to allow them to release energy
fossil fuel power station + and -
- burning fossil fuel produce CO2 - contribute to climate change
+ cost efficient
explain what happens in nuclear fission and what is release
when a uranium-235 absorbs a neutron, it immediately splits into two smaller daughter nuclei; two more neutrons are released - neutron store a lot of kinetic energy cause they’re moving at high speeds
Uncontrolled nuclear fission chain reaction
When the neutrons released or absorbed by another uranium-235 nuclei - these nuclei will become more unstable and release more neutrons when they’re nuclear splits; these neutrons can be absorbed by more uranium nuclei and so on
how to stop a chain nuclear fission reaction
Other materials absorb some of the neutrons
function of control rods in a nuclear reactor
to control the rate of fission by absorbing neutrons (control the chain reaction)
where are control rods in a nuclear reactor
placed between the fuels in the reactor core
explain the function of fuel rods in a nuclear reactor
they power nuclear reactors
- in a nuclear reactor the fuel is made as into fuel rods and as fission reactions occur, neutrons leave fuel rods at high speed
what increases the chances of a neutron being absorbed by a uranium-235 nucleus
If the neutrons are moving slowly
what increases the chances of a neutron being absorbed by a uranium-235 nucleus
If the neutrons are moving slow slowly
where are fuel rods inserted
- inside a reactor core - into holes in a material called a moderator
function of moderator in a nuclear reactor
to slow down neutrons produced by fission that the chain reaction can be sustained which makes it more likely for fission to occur
how to generate electricity from a nuclear reactor
- Energy released from the reactor core is transferred into a coolant
- The hot coolant is pumped to a heat exchanger which is used to make steam
- The steam drives a turbine which turns a generator to produce electricity
what is the lost mass from nuclear fusion converted into
energy
- The mass of the new nucleus formed is slightly less than the total of the masses of the two smaller nuclei
electrostatic repulsion
the protons in the nuclei are positively charged so like charges repel
when can electrostatic repulsion be overcome so that nuclei can fuse
If the nuclei is close enough or is travelling fast enough
+ and - of building a commercial fusion power station (fusion nuclear reactor)
- difficult to sustain the extreme temperatures and pressures required for fusion
- The recipe produce a lot more energy than fission reactors
+ a few problems with safely disposing of radioactive waste materials from fusion reactors
What is a property that an isotope must have to be suitable to use in an RTG?
Have a long half life as the Rover needs to operate for a long time on Mars
state the SI unit for the activity of a radioactive source
becquerel (Bq)
if the number of protons int he nucleus and the number of neutrons in the nucleus DO NOT change how DOES the nucleus change when it emits a gamma ray
becomes more stable OR emits/looses energy OR rearrangement of particles
if the number of protons int he nucleus and the number of neutrons in the nucleus DO NOT change how DOES the nucleus change when it emits a gamma ray
becomes more stable OR emits/looses energy OR rearrangement of particles
How does the brightness of a main sequence star change with its temperature?
As the temperature increases, The brightness increases
How does the brightness of a main sequence star change with its mass?
As the brightness increase the mass increases
Explain how the PET scanner used to detect cancerous tumours can give the location of the tumour
- The isotope that is injected into the patient and absorbed by the tumour and emits a positron which annihilates
- Two gamma rays are produced in opposite directions
- gamma rays are detected by radiation detector at almost the same time
- The time difference is the distance difference
Explain why the radioactive isotope injected into the patient when detecting a cancerous tumour should be produced near to the place where it is to be used
Must be used a short time after production as half-life is short as the activity decreases rapidly
Differences between irridation and radioactive contamination
- irradiation stops when source is removed
- irradiation does not make an object radioactive
- irradiation can be stopped by shielding
- irradiation source is outside the object
Explain how to determine a value for the background radiation count rate
- Use a GM tube to detect the background radiation then attach to a counter which can count the amount of radiation -> measure the number of counts in a certain amount of time (measured in Bq)
- Divide number of counts by time
- Repeat reading and calculate average value
