Flashcards in Radioactivity Deck (101):
What are the similarities between Rutherford’s gold foil experiment and Thompson’s plum pudding model?
Both contain positive and negative sub atomic particles
What are the differences between Rutherford’s gold foil experiment and Thompson’s plum pudding model?
-Rutherford discovered the atoms was mostly empty space, Thompson believe an atom was solid
-Rutherford discovered that the atom has a nucleus
-Rutherford had electrons outside the nucleus, Thompson had them anywhere
-Rutherford - the mass was contained, Thompson had mass everywhere
What did Bohr add to the atom analogy?
Electron shells at set distances from the nucleus, and explained the lines in emission and absorption spectrum
What is the atomic number?
The number of protons (equal to that of electrons)
What is the mass number?
The number of protons and neutrons
What is an isotope?
Atoms of the same element (so they have the same number of protons) but they have different numbers of neutrons
What is relative atomic mass?
The weighed down mass of an atom (taking into account the mass of isotopes)
What is the standard configuration of an electron shell?
Why can electrons emit em radiation?
-an inner electron can move to a higher energy level by absorbing EM radiation with the right amount of energy, it will then quickly fall back and emit the same amount of energy as EM radiation
-The shells further away are closer together so energy emitted when electrons fall between them is less
What happens to electrons in a neon tube?
-Neon atoms absorb energy transferred by electricity as electrons jump to higher shells.
-When the electrons fall back again they emit energy as electromagnetic radiation that we can see.
What is an emission spectrum?
That each colour is a different wavelength of light. This is different for each element.
What does electrical voltage do?
Makes electrons move within atoms of a gas
What is an ionisation?
When an atoms gains to much energy, one of the electrons escapes from the atom. This atom is now called a positive ion
What is the radiation that allows electrons to escape called?
Ionising radiation as it knocks electrons out of atoms
What is radiation?
Energy that is emitted from a source as waves or particles
What is nuclear radiation?
Radiation (energy) that is emitted from the nucleus of an atom
Are energy and mass interchangeable?
What are the 4 main types of nuclear radiation?
What happens if an atom or isotope is unstable?
It try’s to become stable by ejecting mass or energy to become stable, we call these atoms radioactive
What is activity?
The number of decays per second(Measured in becquerels)
Overtime it will go down as the nucleus can only decay once p, however once it decays the new nucleus can
What is count rate?
The number of counts per minute (very similar to activity)
What happens in neutron decay?
An unstable nucleus will emit only one neutron at a time (become more stable) radioactivity is entirely random.
-Mass number down by one
-atomic number stays the same
What happens in alpha decay?
Unstable nucleus will eject a whole alpha particle (2 protons, 2 neutrons)
-mass number down by 4
-atomic number down by 2
What happens in beta minus decay?
Within the unstable nucleus, one neutron changes into a proton and an electron is emitted
- Mass number stays the same
- atomic number increases by 1
What happens in beta plus?
A proton turns into a neutron and a positron is emitted
- atomic number decrease by one
- mass number stays the same
What is a positron?
An anti electron
What happens in gamma decay?
When atoms decay, protons and neutrons in nucleus sometimes rearrange themselves (nuclear rearrangement), this releases energy
- atomic and mass number stays the same
How can you detect background radiation?
Smell, taste, hearing, tough, infrared sensor, thermometer, Geiger counter
What is background radiation?
Radioactivity is a natural occurrence that we are exposed to radiation in low levels all the time.
-the amount your exposed to is called absorbed radiation dose
How does the Geiger- muller tube work?
The GM tube works by detecting when gas inside the chamber is ionised by radiation
Every click/ beep is one incident of radiation
How was radioactivity discovered?
By Henri Becquerel when he realised some substances turn photographic film dark.
Scientists use this to identify presence of radiation
What is background count?
Average reading of background radiation in a particular area at a particular time (probably an hour)
What is stage 1 of the radiation of a potato?
Leave the Geiger counter in the room for 1 hour (or desired time)to measure background radiation - no potato present
What is stage 2 of the radiation of a potato?
Repeat and calculate the mean average background count rate
What is stage 3 of the radiation of a potato?
Record the count rate for 1 type of potato
What is stage 4 of the radiation of a potato?
Repeat and calculate the mean average
What is stage 5 of the radiation of a potato?
Subtract the mean background count from your readings
Is nuclear random/spontaneous?
Yes- it cannot be influence by anything
How can we predict if a radioactive sample is to be safe?
By knowing how old the sample is and its half life we can work out of its activity levels are dangerous
What is half life?
The time taken for the activity if a substance it reduce by half.
Doesn’t matter at what point as will always half in the same time
What can ions in DNA do?
Ionise cells which can lead to cancerous uncontrolled growth
-small does cause minor damages without killing the cell giving rise to mutant cells which divide uncontrollably
-higher doses kill cells completely and can cause radiation sickness
How do alpha and beta particles ionise?
By either attracting (alpha) or repelling (beta) electrons.
What are some ways of handling activity?
-Never tough directly - use tongs
-keep source in lead lined containers
-don’t point sources at yourself or other people
-always wear gloves
- wear eye protection
What is irradiation?
When someone is exposed to radiation (alpha,beta,gamma) from a nearby source
What is contamination?
When someone gets particles of a radioactive source on that person of inside their body
How do you reduce irradiation exposure?
Use distance or barriers to stop it
Lead lined containers
Ring or photographic film badges to monitor exposure
How do you reduce contamination?
Wait till the source finishes decaying (time-half life)
Gloves and tongs when handling the source
What do people who have to work with radiation use?
Ring or film badges to monitor the amount they are exposed to
What happened to Alexander litvinenko?
He was poisoned with radioactive isotopes - contaminated with polonium-210 in his tea as punishment for leaving Russia
What does polonium-210 have?
84 protons and 126 neutrons
It emits alpha radiation so has a charge of +2
What happens to litvinenko’s body?
-immune system broke down
-rapidly lost hair
-multiple organs failed
-Bone marrow was contaminated
What are uses of alpha radiation and how does it work?
Smoke detectors (contain a weak source of alpha)
-alpha particles ionise the air as it is unstable
-when smoke is present it interacts with the ions- ionisation reduced
-less current is flowing through the air causing it to sound
What is a use of beta and how does it work?
Regulating paper thickness
- Beta minus passes through the paper and some of it is absorbed
- if the Geiger counter (detector) doesn’t detect enough radiation a signal will tell rollers that more pressure should be applied
- if too much eradication is detected a signal is sent to the rollers telling them to move further apart
How do you use gamma to locate leaks?
- The radioactive material is put into one end of the pipe
- radiation detector used to track progress through the pipe
- the leak or blockage is found by finding where the amount of radiation detected decreases
How do you use gamma to sterilise food and medical equipment?
-ionising radiation can kill bacteria, gamma used to kill bacteria so food lasts longer and is safer
- gamma rays kill bacteria on equipment, makes then safe to use
How does internal radiotherapy work?
-A radioactive source (usually beta) is placed next to or within a tumour.
- usually dine with surgery - rare form of radiotherapy
- a beta source is used of gamma as it doesn’t penetrate as far due to its shorter half life. Practices are also done in a close vacantly so it will ionise sooner
How does external radiotherapy work?
Most radiotherapy is external
- radiation, usually gamma or X-rays, are directed in a beam at the
- sometimes this is a strong static beam or sometimes several lower strength beams from several directions
How do radioactive tracers work?
- Radioactive isotope is attached to molecules the body would normally use.(Could be injected into the blood or swallowed)
-isotope emits gamma rays that are detected by gamma cameras
- used for detecting blood leaks and cancer, etc
How do PET scans work?
-beta plus source attached to a glucose molecule
-inject the radioactive molecule into the patient
- the radioactive molecule travels to a place where lots of respiration is taking place
How do PET scans work?
Stage 4 and 5
-positron is emitted by the radioactive molecule and annihilates with an electron
-the annihilation produces 2 gamma rays in opposite directions
How do PET scans work?
Stages 6 and 7
-photons (gamma rays) are detected by the ring detector and a 3D image is produced
- The half life of the beta plus source is very short so patients activity count decreases rapidly and they are safe to go home
How is radiation used for diagnosis in medicine?
- X-rays and CT scans
- PET scans
How is radiation used for treatment in medicine?
- palliative care, stop the spread of tumours to extend their life span or pain management to keep people’s last weeks more comfortable.
What is fission?
When a large atom splits into two smaller atoms ( different daughter nuclei) and three neutrons. It is started by an incident neutron.
What does having extra neutrons at the end if fission mean?
They can induce fission in other atoms - creates a chain reaction
How is fission used for nuclear power?
Stages 1, 2 and 3
- fission creates heat energy
- heats water pm causing it to evaporate and produce steam
- steam rises and turns a turbine
How is fission used for nuclear power?
Stages 4 and 5
- as the turbine rotates, a coil of wire is rotated within a magnetic field
- this produces a current and electricity is created
What do control rods (boron) do?
Absorb neutrons- slows it down and limits reaction.
What does a moderator (graphite) do?
Controls and Slows neutrons down so they can be absorbed
What does a coolant do?
Transfer heat energy from the reactive to the heat exchanger. Also used to cool the reaction
What is the temperature in the reactor core?
Correct- leave control rods in the same place
Too high- move control rods down slightly
Too low - move control rods up slightly
What is fusion?
Joining two small atoms to make one larger atom
Where is the only place fusion naturally happens?
On the sun and stars - this is how they get their energy and how all the element other then hydrogen were created
Over billions if years a star combines protons together (main ingredient hydrogen) to create helium-4
On earth, how do scientists jump start a reaction?
By using two isotopes of hydrogen?
Deuterium and tritium
What does fusion produce?
What is good about fusion?
- abundant fuel
- lots if energy
- no CO2
- little waste
Why don’t we use fusion to produce energy?
We have to out to much energy in (heat and pressure) compared to how much we get out
What distance and speed do particles have to be in to fuse?
1x10-15m and 1,000,000 m/s
What is electrostatic repulsion
When positive charges repel each other
What do we increase by heating the particles up?
Kinetic energy - the faster they travel the closer they will get before repelling
Stars use gravity to speed up particles
What do scientists use to accelerate the fuel?
Electromagnetic force as it is a lot stronger then gravity
What accelerates deuterium and tritium?
A magnetic field
What does fusion need very high pressures?
We have less fuel so need a faster rate of reaction
What is the average size of an atom?
1.2 x 10-10m
How strong is alpha’s ionising power?
How strong is betas ionising power?
Moderate but positions have a smaller range because when they hit an electron the two in annihilate and produce gamma rays
How strong is gamma’s ionising power?
What stops alpha?
Paper, skin, cm of air
What stops beta?
Mm of aluminium foil or meters of air
What stops gamma ?
Cm of lead or tarmac
What is more stable: a shorter or longer half life?
Why does the radioactivity of a source decrease over time?
As there are only a certain number of un-decayed nuclei and as more decay there are fewer left
What are some advantages of nuclear energy?
Does not produce CO2
Produces a lot of energy as electricity
What are some disadvantages of nucleur energy?
Dangerous for people and environment
Has to be stored carefully
Expensive to install
What happens when electrons gain energy?
An inner electron can move up to a higher energy level to a partially filled electron shell if it absorbs electromagnetic radiation with the right amount of energy
What happens when electrons fall back to there original energy level?
They emit the same amount of energy they absorbed. This energy is then carried away by electromagnetic radiation
What conclusions did Rutherford come to?
-as most alpha particles passed through it shoes mass was concentrated in the centre of the atom and that it was mostly empty space
-as some where deflected it showed the nucleus was positive as it repelled positive alpha particles
What were Rutherford observations and conclusions?
-most particles passed through to the other side showing it was mostly empty space
-a few particles bounced directly back and some were deflected showing Mass was concentrated in the centre and nucleus had a positive charge as it repelled positive particles
What are the human and space causes of background radiation?
Cosmic rays usually from the sun contribute greatly but we are protected form much of it due to the atmosphere
Human activity like nuclear explosions and waste account for a small part
What radiation is more dangerous to the body?
-Outside the body gamma or beta as it can penetrate through skin to reach tissues and organs
-inside the body alpha as it is highly ionising so causes damage in a localised area