topic 4 - radioactivity Flashcards
how has the model of the atom changed (Thomson, Rutherford, Bohr
in 1897, Thomson discovered that electrons could be removed from atoms so atoms must consist of smaller components - he proposed the plum pudding model (positive pudding and negative currants)
in 1909, Rutherford’s gold foil experiment demonstrated that most of the mass of an atom was concentrated in a positively charged nucleus and that most of the atom is empty space
Bohr changed this idea slightly a few years later, proposing that electrons were arranged in fixed orbits at set distances from the nucleus (electrons can only exist in these shells)
subatomic particles
neutrons
protons
electrons
neutrons (relative mass and charge)
mass: 1
charge: 0
protons (relative mass and charge)
mass: 1
charge: +1
electrons (relative mass and charge)
mass: 0
charge: -1
electrons moving levels (up)
if an electron absorbs enough EM radiation with the right amount of energy, it can move up to another energy level
if an outer electron absorbs enough radiation, it can move so far that it leaves the atom to become a free electron - ionising the atom
electrons moving levels (down)
electrons quickly move bac to their original position and emit the amount of energy that was absorbed
what can be observed when electrons move levels
visible light is often emitted when electrons move shells
within the nucleus itself, high frequency gamma rays are emitted
isotopes
different forms of the same element
atoms with the same number of protons but a different number of neutrons
radioactive decay
when unstable isotopes decay into other elements and give out radiation as they try to become more stable
it is impossible to predict which unstable nucleus will decay next because the process is completely random
ionising radiation
any radiation that can knock electrons from atoms
3 types of radioactive decay
alpha decay
beta decay (beta-minus and positron)
gamma rays
alpha radiation
when an alpha particle (α) is emitted from the nucleus
an α particle is 2 neutrons and 2 protons (like a helium nucleus)
features of alpha radiation (4)
don’t penetrate far and are stopped quickly
travel a few cm in air
blocked by a thin sheet of paper
strongly ionising due to their size
beta particles
can be electrons ( ß- particle) or positrons (ß+ particle)
beta-minus (ß- particle)
fast moving electron released by nucleus
virtually no mass
relative charge of -1
beta-plus (ß+ particle)
fast moving positron
positron is the antiparticle of the electron
virtually no mass
relative charge of +1
beta particle decay features (4)
absorbed by a thin sheet of aluminium
moderately ionising
ß- travel a few metres in air
ß+ has a smaller range due to when they hit an electron, the two destroy each other and produce gamma rays (this is ANNIHILATION)
gamma rays
once a nucleus has decayed, it undergoes nuclear rearrangement and releases some energy
gamma rays are EM waves with a short wavelength and high frequency
gamma rays features (4)
penetrate far into materials
travel a long distance in air
weakly ionising
absorbed by thick sheets of lead or metres of concrete
background radiation
the low level radiation around us all of the time
sources of background radiation
radioactivity comes from naturally occurring unstable isotopes around us
found in air, some foods, building materials and some rocks
cosmic radiation
radiation due to human activity
cosmic radiation
radiation comes from space in the form of cosmic rays, from the sun
the atmosphere protects us mostly from cosmic radiation
radiation due to human activity
there is radiation due to human activity but this is only a tiny proportion of background radiation (eg. fallout from nuclear explosion/ nuclear waste)
activity
the rate at which a source decays
measured in becquerels (Bq - 1Bq means 1 decay per second)
how to measure/detect radioactive decay
measured with a geiger-muller tube which clicks each time it detects radiation
the tube can be connected to a counter to display the count rate (number of clicks per second)
radiation can also be detected with photographic film - the more radiation it is exposed to, the darker the film becomes
what are the three main dangers
radiation - ionisation of cells
irradiation
contamination
ionisation of cells dangers
radiation can enter living cells and ionise atoms and molecules, leading to tissue damage
what do lower doses of radiation cause
lower doses tend to cause minor damage as opposed to killing cells, which can cause mutant cells which divide uncontrollably into cancer
what do higher doses of radiation cause
higher doses tend to kill cells
if a lot are affected at once this can cause radiation sickness (vomiting, tiredness, hair loss)
how to choose a source
when choosing a source for an application, you need to find a balance between the right level of activity for the right amount of time and that isn’t too dangerous for too long
how hazardous is a source
the lower the activity, the safer the source is to be around
if two sources produce the same amount of activity to begin with, the one with the longer half life is more dangerous
if two sources have different initial activities, the danger changes, even if the initial activity is lower, the source with the longer half life is more dangerous as activity falls more slowly
irradiation
exposure to radiation
irradiating something doesn’t make it radioactive
irradiation as humans
we are always irradiated by background sources
medical staff working with radiation wear photographic film badges to monitor exposure
4 ways of reducing irradiation
- keeping sources in lead-lined boxes
- standing behind barriers
- being in a different room
- using remote controlled sources
contamination
radioactive particles getting onto unwanted objects
dangers of contamination
contaminating atoms may decay, releasing potentially harmful radiation
contamination is especially dangerous if radioactive particles enter the body - once contaminated, you are in danger until contamination is removed or all radioactive atoms have decayed
reducing risk of contamination (2)
gloves and tongs should be used when handling sources
some industrial workers wear suits to stop them from breathing particles in
radiation outside the body
beta and gamma are most dangerous as they can penetrate the body and damage organs
alpha is less dangerous as it can’t penetrate the skin
radiation inside the body
alpha sources are very dangerous as they are highly ionising so strongly damage a localised area
3 uses of nuclear radiation
fire alarms
sterilisation
tracers
how do fire alarms work
a weak source of alpha radiation is place inside, close to two electrodes
this causes ionisation so a current of charged particles flow
in case of a fire, the smoke will absorb the charged particles so the current will drop and the alarm will sound
sterilisation and nuclear radiation
with a high dose of gamma rays, food can be irradiated so it won’t go off as quickly as normal
medical equipment can be sterilised with gamma rays
why is irradiation a good method of sterilisation
good method of sterilisation because there are no high temperatures involved so the object won’t be damaged
source for sterilisation should….
should have a long half life so it doesn’t need replacing often
and be a strong emitter of gamma rays
tracers use medicine
some radioactive isotopes can be used as a tracer
a medical tracer is injected or swallowed and its progress can be followed using an external detector
this can be used to detect/diagnose medical conditions
all isotopes put into the body can never be alpha because only beta and gamma can reach the detector and are weakly ionising
tracers use industry
industry uses gamma emitting tracers to detect leaks underground
beta radiation is used in thickness control - direct radiation through the product and put a detector on the other side, paper rollers can then be adapted
PET scanning
a technique to show tissue or organ function
positron emission tomography
can identify active tumours by showing metabolic activity in tissue
cancer cells have a much higher metabolism than normal cells
PET scanning process (6)
1) inject a patient with a substance used by the body, such as glucose, containing a positron emitting radioactive isotope with a short half life
2) in about 1/2 hour it moves to the organs
3) positrons emitted meet electrons in an organ and annihilate, emitting high energy gamma rays in opposite directions
4) detectors around the body detect pairs of gamma ways and the tumour will lie along the same line
5) by detecting at least 3 pairs, the tumour can be located using triangulation
6) distribution of radioactivity matches up with metabolic rate, more of the injected substance is used up by cells with a high metabolism
isotopes used in PET scanning
need to have a short half life so they may need to be made nearby
some hospitals have their own cyclotron
if isotopes were made offsite then their activity could be too low, making them no longer useful
radiotherapy
treatment that exposes patients to targeted doses of radiation that can be used to kill cancer cells
can be delivered internally or externally
internal radiotherapy
radioactive material is placed in the body into/near a tumour
can be alpha or beta emitters
radioactive isotopes have short half-lives
alpha emitters internal radiotherapy
alpha emitters are usually injected near to a tumour as they are strongly ionising and will do lots of damage to the nearby cancerous cells
beta emitters internal radiotherapy
beta emitters are often used in implants to be near to a tumour
radiation can penetrate the implant’s casing and then damage nearby cells
however their long range may damager other healthy, nearby cells
external radiotherpy
gamma rays are aimed at the tumour so radiation is focused on the tumour
sources used in external radiotherapy should have long half lives so they don’t need to be replaced often
reducing risk to patients and staff in external radiotherapy
sometimes shielding can be placed on other areas of the body, but sometimes damage is done to healthy cells nearby
machines are often surrounded by shielding and kept in a separate room to reduce the risk to staff and patients
nuclear power stations
powered by nuclear reactors that created controlled chain reactions
process in a nuclear power station (could be unnecessary but not sure) (6)
1) energy released by fission is transferred to the thermal energy store of the moderator
2) this is transferred to the thermal energy store of the coolant
3) this is transferred to the thermal energy store of the cold water in the boiler
4) water boils and energy is transferred to the kinetic energy store of the steam
5) the steam turns the turbine, transferring kinetic energy to the turbine and then the generator
6) the generator generates electricity, energy is transferred away from the generator electrically
what is the perception of nuclear power like
there is a negative public perception of nuclear power
what are 6 advantages of nuclear power
+ pretty safe way of generating electricity
+ very reliable energy resource
+ reduces need for fossil fuels
+ doesn’t make carbon dioxide or sulfur dioxide (which are generated through the combustion of fossil fuels)
+ huge amounts of energy can be generated from a relatively small amount of nuclear reactivity
+ nuclear fuel is cheap and readily available
what are 3 disadvantages of nuclear power
- danger of nuclear waste leaking out and polluting land, rivers and oceans
- risk of leaks from the power station or major disaster
- overall high cost -> initial cost of power plant is expensive -> final decommissioning can take decades to do safely
