Radioactivity Flashcards
What are the three types of ionising radiation? Where are they emitted from?
alpha particle
beta particle
gamma rays
they are emitted from unstable nuclei
The ionising radiation are emitted for … reasons. What are the reasons?
The ionising radiation are emitted for different reasons:
in a metastable state
the nucleus is too large
has too many protons
has too many neutrons
What is radiation?
the spontaneos and random emission of energy from unstable nuclei
Can you predict when a nucleus will emit radiation exactly?
No, but you can estimate on average
Can you do anything to the physical properties to affect the rate of radiation?
no
Why are aplha, beta and gamma radiation ionising?
because they ionise matter as they pass through it (knock electrons out of orbit)
ionisng matter requires work to be done by the radiation so they slow down
The more alpha, beta and gamma radiation ionise, the … their penetration through the matieral
The more alpha, beta and gamma radiation ionise, the shorter their penetration through the matieral
What are Alpha Particles made up of? What is this identical to?
2 protons and 2 neutrons (identical to a Helium nucleus)
What is a Beta Particle?
it is an electron
What are Gamma rays?
high frequency, short wavelength electromagnetic rays
What is the mass of an Alpha Particle?
2 protons + 2 neutrons
What is the mass of a Beta Particle?
the mass of an electron
What is the charge of an Alpha Particle?
+ 2 electrons
What is the charge of a Beta Particle?
-1 electron
What is the charge of a Gamma Ray?
no charge
As the heaviness of the ionising radiation increases, the … …
As the heaviness of the ionising radiation increases, the speed decreases
What is the order of heaviness (most to least) and of ionising radiation? Then what is the order of speed (most to least)
Heavy:
alpha
beta
gamma
Speed:
gamma
beta
alpha
Are gamma rays ionising?
not very
What is the speed of gamma rays?
speed of light
The more ionising the ionising radiation the … able to …
The more ionising the ionising radiation the less able to penetrate in materials
What is the order of ionising of the ionising radiation (most to least)? Then, what is the order of penetration in materials (most to least)?
Ionising:
alpha
beta
gamma
Penetration:
gamma
beta
alpha
What can Alpha Particles penetrate?
it cannot even penetrate paper
What can Beta Particles penetrate?
paper
weak Beta Particles can pentrate aluminum foil
What can Gamma Rays penetrate?
paper
aluminium
their energy decreases as they travel through concrete or dense materials like lead
What are Alpha Particles absorbed by?
skin
paper
10 cm in air
What are Beta Particles absorbed by?
a few mm of aluminium
What are Alpha Particles emitted from?
the nucleus of a large, heavy, unstable isotope
What are gamma rays absorbed by?
thick lead
very thick concrete
What are Beta Rays emitted from?
the nucleus when there are too many neutrons for it to be stable
a neutron decyas into a proton and emits a Beta particle
What happens if there are too many protons in the nucleus for it to be stable?
a positive electron (positron) is emitted - this is rare
What are Gamma Rays emitted from?
a nucleus in a high energy state - sometimes called a metastable
How can ionising radiation be detected?
ionising radiations can be detected using a photographic film or a Geiger-Muller detector
What is background radiation?
background radiation is low-level ionisng radiation that is around us all the time due to a mixture of natural and man-made sources
What are four natural sources of background radiation?
Cosmic rays radiation that reaches the Earth from spac
Rocks and soil - some rocks are radioactive and give off radioactive radon gas
The atmosphere - C14 in the air
Living things - plants absorb radioactive materials from the soil and these pass up the food chain
What are five man-made sources of background radiation?
Nuclear power stations - move dangerous when they explode e.g. Chernobyl
X-rays
Nuclear medicine
Nuclear bombing
Nuclear power plants
How do you record background radiation?
connect a Geiger-Muller tube to a Geiger-MUller counter
ensure that there is no other sources of radiation in a room
leave them for 10 minutes
the counted number is the background radiation
Why do we record background radiation before taking any activity measurements?
we need to take away background radiation when measuring anything else so it does not interfere with our results and make them inaccurate
What is the atomic number>
also called the proton number
number of protons which also equals the number of electrons
atomic number = number of protons = number of electrons
What is the mass number?
also known as the nucleon number
the number of protons + number of neutrons
What is an isotope?
atoms of an element with the same number of same protons number but different number of neutrons (so a different mass number)
What is carbon-14
an unstable isotope of carbon
it is radioactive - the nucleus is unstable so it decyas and emits radiation
What does nuclear radiation cause? How?
nuclear radiation causes ionisation by bashing into atoms and knocking electrons off them. Atoms (with no overall charge) are turned into ions (which are charge) - ionisation
this requires the radiation to do work and therefore it transfers some of its energy to the ion pair
What do electric and magnetic fields do to alpha particles?
because they’re electrically charged (with a positive charge), alpha particles are deflected (their direction changes) by electric and magnetic fields
What does emitting an alpha particle do to the atomic number and the mass number?
emmitting an alpha particle decreases the atomic number of the nucleus by 2 and the mass number by 4
What do electric and magnetic fields do to beta particles?
Because they’re charged (negatively), beta particles are deflected by an electric and magnetic fields
What does emmiting a beta particle do to the atomic number and the mass number?
emmiting a beta particle increases the atomic number by 1 but the mass number stays the same
What does emmiting gamma ray radiation do to the atomic number and the mass number
emmiting gamma ray radiation has no effect on the atomic number or the mass number
What happens to the activity of a radioactive source over a period of time?
the activity of a radioactive source decreases over a period of time
What happens each time a decay happens?
each time a decay happens and an alpha particle, beta particle or gamma ray is given out, it means one more radioactive nucleus has disappeared - hence why radioactivity decreases over time
The older a sample becomes, the more/less radiation it will emit
The older a sample becomes, the less radiation it will emit
Does radioactivity ever reach zero?
no - this is why we have to use the idea of half-life to measure how quickly the activity drops off
What is radioactivity measure in?
becquerels (Bq)
What does 1 Bq equal?
1 Bq = 1 decay per second
What is the defintion of half-life?
the time taken for the activity of a radioactive isotope to halve
or the time taken for the amount of radioactive isotope to halve
Is the half-life always the same?
no - the half-life is different for different radioactive isotopes
What does a short half-life mean?
a short half-life means the activity falls quickly because lots of nuclei decay quickly
What does a long half-life mean?
a long half-life means the activity falls more slowly because most of the nuclei don’t deacy for a long time - they just sit there, basically unstable, but kind of biding their time
The activity of a radioisoptope is 640 Bq. Two hours later it has falled to 40 Bq. find the half-life of the sample
Initial count: 640
After one half-life: 640 ÷ 2 = 320
After two half-lives: 320 ÷ 2 = 160
After three half-lives: 160 ÷ 2 = 80
After four half-lives: 80 ÷ 2 = 40
There are four half-lives for the activity tot fall from 640 to 40
Two hours = four half-lives
1 hour = two half-lives
30 mins = one half life
the half-life = 30 minutes
How does a thickness control machine work?
The machine can be used to produce thin sheets of paper, aluminium and lead
The thickness is controlled by the amount of radiation received by the detector that has passed through the material
The detector is attached to the pressure control, which can move two rollers closer together or further apart, depending on the amount of radiation received by the detector
Describe what would happen to the thickness control equipment if the material produced was too thick
if the material is too thick, less radiation arrives at the detector
the detector sends a signal to the pressure control that the level of radiation is too low
the pressure control makes the gap between the rollers smaller
the smaller gap makes the material thinner until the amount of radiation at the detector increases to its normal level
Describe what would happen to the thickness control equipment if the material produced was too thin
if the material is too thin, more radiation arrives at the detector
the detector sends a signal to the pressure control that the level of radiation is too high
the pressure control makes the gap between the rollers bigger
the bigger gap makes the material thicker until the amount of radiation at the detector decreases to its normal level
Explain why radiation emitted from the source must have a greater activity than the background radiation during thickness control?
if the activity of the source is too low then the detector cannot tell the difference between it and the background radiation - the equipment would not function properly
Which radiation and half-life is best for controlling paper by the thickness control machine? Why?
alpha, beta or gamma
20 seconds, 150 years or 1,000, 000 years
Alpha - Alpha particles will be absorbed by the paper. Beta and Gamma rays are too penetrating so the pressure control would not be able to sense if the paper was too thick or too thin
150 years - 20 seconds is too short; the emitter would have to be changed too often
1 million years is too long; the activity is too low and the detector would not be able to pick up the radiation emitted from the material and so the equipment would not function properly
Which radiation and half-life is best for controlling aluminium by the thickness control machine? Why?
alpha, beta or gamma
20 seconds, 150 years or 1,000, 000 years
Beta - Alpha particles would be absorbed by the aluminium; no radiation would reach the detector. Gamma rays are too penetrating so the pressure control would not be able to sense if the aluminium was too thick or too thin
150 years - 20 seconds is too short; the emitter would have to be changed too often
1 million years is too long; the activity is too low and the detector would not be able to pick up the radiation emitted from the material and so the equipment would not function properly
Which radiation and half-life is best for controlling lead by the thickness control machine? Why?
alpha, beta or gamma
20 seconds, 150 years or 1,000, 000 years
Gamma - Alpha and Beta particles would be absorbed by the lead; no radiation woudl reach the detector so the pressure control would not be able to sense if the lead was too thick or too thin
150 years - 20 seconds is too short; the emitter would have to be changed too often
1 million years is too long; the activity is too low and the detector would not be able to pick up the radiation emitted from the material and so the equipment would not function properly
What is the activity of a radioactive susbtance?
the activity of a radioactive susbtance is the number of atoms that decay per unit of time
In a radioactivity experiment, the count rate of a radioactive substance decreased from 800 counts per second. The half-life of the substance was 40 minutes. What was the count rate after 40 minutes?
400 counts per second (halved)
In a radioactivity experiment, the count rate of a radioactive substance decreased from 800 counts per second. The half-life of the substance was 40 minutes. How long would it take for the count rate of the substance todecrease from 800 counts per second to 100 counts per second?
800 to 400 = 40 mins
400 to 200 = 40 mins
200 to 100 = 40 mins
40 + 40 + 40 = 120 mins
= 120 minutes
Balance this nuclear equation:
88226Ra → 86226Ra
88226Ra → 86224Ra + 24He (alpha particles are Helium nuclei)
atomic number decreases by 2, mass number decreased by 4
alpha-emission
Balance this nuclear equation:
75187Re → 76187Os
75187Re → 76187Os + -10e
mass number stays the same, atomic number decreases by 1
beta-emission
Balance this nuclear equation:
4399Tc → 4399Tc
4399Tc → 4399Tc + 00γ
atomic number and mass number stay the same
gamma-emission
What happens if you choose a short half-life?
radiation will decrease quickly toa level lower than background radiation
What happens if you choose a very long half-life?
activity continues for longer but may be difficult to spot above background radiation
What are the uses of radioactivity?
medical tracers
non-medical tracers
radiotherapy
smoke detectors
archaeological specimens and rocks
What source of radiation is used in medal tracers? Why?
Would you use a half-life of 10 mins, 6 hours or 5 months? Why?
Beta and gamma radiation is used in medical tracers because they penetrate the skin and other body tissues - this makes them suitable as medical tracers
6 hours: you would want the blood flow to be able to take it all around the body allowing you to take many pictures. 10 mins is too short for the information and you might want to take repeated readings. 5 months is too long for a person to be radioactive - dangeorus
How does medical tracing work?
A source which emits beta or gamma radiation is injected into the patient (or swallowed). The radiation penetrates the body tissues and can be detected externally. As the source moves around the body, the radiographer uses a detector to monitor its progress or get a ‘snapshot’ of its distribution
A computer converts the reading to an on-screen display showing where the radiation is coming from. Doctors use this method to check whether the organs of the body are working as they should
Why would you not use an alpha source is medical tracers?
they would be stopped by the boyd’s tissues, so you would never detect it externally
the strong ionising power makes alpha really harmful if it gets inside of you
How do smoke detectors work?
The alpha radiation ionises the air particles inside the smoke detector. This allows a small electric current to flow
If there is a fire, smoke particles going into the detector are hit by alpha radiation. This reduces the ionisation of the air particles causing the current to drop
The drop in current is detected by the smoke detector, setting off the alarm
Which source of radiation is used in a smoke detector?
Would you use a half-life of 20 mins, 4 months, 10 years or 1000 years? Why?
You would chose alpha because they are more likely to be absorbed by smoke particles. Beta is more penetrating than alpha and would pass straight through the smoke. Gamma is even more penetrating. Gamme and beta would not affect the charge and so the smoke detector wouldn’t set of the alarm
10 years - 20 mins and 4 months need to be replaced quickly but 1000 would mean too little radiation coming out - not active enough to detect its radiation from the background radiation
How does radiotherapy work?
gamma radiation is used to destroy unwanted cells (cancerous cells.)
How do industrial tracers work?
Squirt a gamma radiation source into an underground pipe, let it flow along and fl along the outside with a detector
Gamma radiation will penetrate through a metal pipe, but some of it getts absorbed - exaclty how much depends on the thickness of the pope and what it’s made of
If there’s a crack in the pipe, the gamma-source will collect outside the pope, and your detector will show extra high radioactivity at that point
the isotope used myst be a gamma emitter so that the radiation can be detected through any rocks or eatyh surrounding the pipe - alpha and beta particles would be tooo easily absorbed
it should also have a short half-life so as not to cause long-term hazard if it collects somewhere
What is working out the age of rocks, fossils and archaeological specimens called?
radioactive dating of archaeological specimens and rocks
How do scientists date of archaeological specimens and rocks?
by measuring the amount of a radioactive isotope left in a sample, and knowing its half life, you can work out how long the thing has been around
What can radiation do to living organisms?
cause mutations
damage cells and tissues
Radiation can both … and … cancer
Radiation can both cause and cure cancer
Which radiation is most dangerous externally? Why?
beta and gamma can penetrate the skin and soft tissue to reach organs inside the body
this makes beta and gamma radiation more hazardous than alpha when outside of the body
Which radiation is most dangerous internally?
alpha radiation can’t penetrate the skin, but it’s very dangerous if it gets inside the body
alpha sources do all their damage in very localised area
if betta or gamma radiation get inside the body (e.g. by being swallowed or breathed in), their radiation mostly passes striaght out without doing much damage
What happens when radiation enters your body?
when radiation enters your body, it will collide with molecules in your cells
these collisions cause ionisation, which damages or destroys the molecules
What do lower doeses of radiation tend to do inside the body?
lower doses tend to cause minor damage without killing the cell
this can cause mutations in cells which then divide uncontrollably - this is cancer
What do higher doeses of radiation tend to do inside the body?
higher doses tend to kill cells completely, causing radiation sickness if a large part of your body is affected at the same time
What doee the extent of the harmful affects of radiation depend on?
the extent of the harmful affects of radiation depends on how much exposure you have to the radiation, and its energy and penetration
When can radiation be used to treat cancer? How does this work?
once cancer has started, patients can be given radiotherapy to kill the cancer cells and stop them dividing
this involves using a high dose of gamma rays, carefully directed to zap the cells in the tumour while minimising the dose to the rest of the body
Most radioactive waste from nuclear power stations and hospitals is ‘high-level’/’low-level’
Give two examples of this
How do you dispose of this waste?
Most radioactive waste from nuclear power stations and hospitals is ‘low-level’ (slightly radioactive)
e.g. clothing, syringes
this kind of waste can be disposed of by burying it in secure landfill sites
‘High-level’ waste is/is not very dangerous
How do you dispose of it?
‘High-level’ waste is very dangerous
A lot of its stays highly radioactive for tens of thousands of years, and so has to be treated very carefully
it is often sealed into glass blocks, which are sealed in metal caniseters - these could then be buried deep underground
What is the problem with disposing high-level waste?
it is difficult to find suitable places to bury high-level waste
the site has to be geologically stable (e.g. not suffer from earthquakers), since big movements in the rock could disturb the canisters and allow radioactive material to leak out
if this material gets into the groundwater, it could contaminate the soil, the plants, rivers etc… and get into our drinking water
How do you minimise your exposure when working with radioactive sources?
never allow skin contact with a source, and always hold it with tongs at arm’s length
keep the source pointed away from the body and avoid looking directly at it
store radioactive sources in a sealed lead box whenever not being used
What extra precautions do people who regularly work with radioactivity need to take?
medical workers who use radioactivity need to wear lead aprons and stand behind lead screens during procedures
industrial nuclear workers wear full protective suits to prevent tiny radioactive particles being inhaled or lodging on the skin or under fingernails etc…
workers can also use remote-controlled robot arms to carry out tasks in highly radioactive areas
Is it possible to predict when an atom might decay?
yes
