Section 4 - Radioactivity Flashcards
What did JJ Thomson find in 1897?
What model did he suggest? What did it look like?
Jj Thomson discovered that electrons could be removed from atoms.
Suggested the plum pudding model, the atoms were like spheres of positive charge with tiny negative electrons stuck in them like in a fruit plum pudding
What did Rutherford do?
What did Rutherford expect?
Rutherford tried firing a Beam of alpha particles at thin gold foil. They expected particles to pass straight through the gold sheet or be slightly deflected..
What actually happened in Rutherfords alpha particle experiment ?
Most of the particles went straight through some were deflected more than expected, very few were deflected back the way they had come , something the plum pudding model couldn’t explain
What 3 things did Rutherford realise as a result of his experiment?
1)Rutherford realised that this meant most of the mass in the atom was concentrated at the centre in a nucleus.
2) most of the atom is empty space
3)the nucleus must have a positive charge since the positive alpha particles were repelled
How did Niels Bohr tweak Rutherfords findings?
Niels Bohr proposed that the electrons were in fixed orbits at set distances from the nucleus. These orbits were callled energy levels
Relative mass of a proton
Charge of a proton
Relative Mass of proton=1
Relative charge of a proton = +1
Relative mass of a neutron
Relative charge of a neutron
Relative mass of a neutron =1
Relative charge of a neutron =0
Relative mass of an electron
Relative charge of an electron
Relative mass of electron = 0.0005
Relative charge of electron =-1
What’s the structure of an atom?
Protons and neutrons in the nucleus
Negative Electrons on fixed shells orbiting the nucleus
Why is an atom neutral ?
Number of protons = the number of electrons
What’s it called if an atom looses an electron?
Positive ion
What’s it callled if an atom gains an electron?
It’s called a negative ion if an atom gains an electron
What can atoms join together to form?
Molecules
What can happen to an electron if it absorbs too much electromagnetic radiation and is “excited”
What happens when the electron falls back to its original energy level?
If an electron is “excited” it will move up a shell.
When an electron falls back to its original energy level, it emits the same amount of energy it absorbed, this can often be seen as visible light .
What happens if an atom looses an electron?
An atom is ionised if it looses an electron.
The atom is now a positive ion because there are more protons than electrons.
What do atoms of the same element have ?
Atoms of the same element all have the same number of protons
What is the number of protons in an atom called?
Atomic number or proton number
What is the mass number of an atom?
Number of protons + neutrons
What are isotopes?
Isotopes are different forms of the same element.
They have the same number of protons but a different Number of neutrons (mass number)
What is radioactive decay?
Unstable isotopes decay into other elements and give oht radiation as they try to become stable.
What are the types of ionising radiation radioactive substances release ?
Alpha
Beta
Gamma
Also neutrons
What are alpha particles.
How well do they penetrate material, how far can they travel
How ionising are they?
-An alpha particle is 2 neutrons and 2 protons. It’s shown as 4/2
-They are not very penetrating and are stopped quickly. They can only travel a few cm in the air
-because of their size they are strongly ionising
What’s a beta- (B-)particle ?
Range and how penetrating is it
How ionising is it
A beta minus particle is a fast moving electron released by the nucleus because a neutron has been changed to a proton . No mass, charge of -1.
It’s 0/-1
Moderately ionising
Range of a few metres absorbed by a sheet of aluminium
What is a beta + particle ?
How ionising is it and what is its range ?
-A beta + particle is a fast moving positron. The positron is the antiparticle of the electron . This means it has the same mass as the electron but a positive 1 charge. 0/1
-smaller range
-moderately ionising
What do gamma rays do?
How penetrative are they?
How far do they Travel?
How ionising are gamma rays ?
-Carry released energy away from the nucleus.
-gamma rays are very penetrative and travel very far
-they are weakly ionising because they pass through rather than collide with ions .
Examples of background radiation?
-radioactivity of naturally occurring isotopes all around us , the air , foods , building materials
-radiation from the sun known as cosmic rays
-radiation due to human activity such as nucleus explosions or radiation of nuclear waste
Is radioactivity random or not?
Radioactivity is a totally random process.
How can you predict how many nuclei will decay in a given period of time?
Based on the half life of the source
What is activity of a radioactive source measured in.
What is one Bq?
Becquerels (Bq)
1Bq is one decay per second
What can activity of a radioactive source be measured with?
-A gieger-müller tube
-Photographic film( the more radiation it’s exposed to, the darker it turns )
What are the 2 definition of half life ?
- the average time taken for the number of radioactive nuclei of an isotope to half.
-the time taken for the activity to half
What’s more dangerous out of two sources that produce the same type of radiation at the start but have short and long half lives?why
The one with the longer half life is more dangerous because after any period of time the source with the shorter half life will have fallen more than the activity of the source with the longer half life
How does radiation damage cells ?
Radiation can enter living cells and ionise atoms and molecules within them. This can lead to tissue damadge.
What can lower doses of radiation lead to?
Cancer. It can cause cells to mutate and divide uncontrollably
What do higher doses of radiation lead to?
Higher doses kill cells completely, causing vomitting sickness and hair loss if all cells are affected at once.
What is irridation?
Exposure to radiation.
Does irridating something make it radioactive?
Irradating something doesn’t make something radioactive.
How to reduce the effects of irradiation ?
Using a lead lined box.
What is contamination? Radioactivity
Contamination is radiative particles getting into /onto objects
How may radiation cause harm?
Radiation may enter living cells and ionise atoms and molecules within them.
How to reduce change of contamination happening ?
-Using gloves and tongs to handle the substances.
-wearing a protective suit to stop urself from inhaling the particles
Why are alpha particles the most dangerous is they get in the body?
Because they are the most ionising and least penetrative, this means they won’t be able to get out the body and will cause harm
What radiation do smoke alarms use?
Alpha
How can gamma rays be used?
-To sterilise food.
High doses of gamma rays killl microbes.
-to sterilise medical equipment
How is radiation used in tracers?
What should the radioactive isotope be and what should its half life be like?
Certain radioactive isotopes can be swallowed by a patient and its progress around the body is followed by an external detector. This can be used to diagnose medical conditions.
-should be gamma or beta particles, so they can escape the body (never alpha ) should have a relatively short half life
What can pet scanning help do
What does it stand for
Positron emission tomography can help diagnose illnesses
How do pet scans work?
1) inject the patient with a substance that the body uses eg:glucose. Containing a positron emitting radioactive isotope with a short half life so it can acts as a tracer
2)positrons meet electrons in the organ and annihilate , releasing high energy gamma rays
3)detector around the body detect pairs of gamma rays
4)
What can radiation be used for?
Targeted doses of radiation can be used to kill cancer cells.
2 ways radiation can be delivered …
Externally or internally
How is radiation delivered internally ?
What the half time for the substances like?
1)Radioactive material placed in the body by a tumor
2)alpha emitters are usually injected near the tumor, as they are strongly ionising they do lots of damadge to the cancerous cells.
- the half life of the substances is normally short to limit the time the radioactive substance spends in the body.
How is radiation used to treat cancer externally?
What are their half lives like?
-gamma rays are aimed at the tumor.
-the sources used in external therapy normally have long half lives so they don’t need to be replaced often
What is nuclear fission?
What atoms does it release energy from ?
Nuclear fission is the splitting up of big atomic nuclei. It is a type of nuclear reaction that is used to release energy from uranium or plutonium atoms .
How does nuclear fissions chain reaction work?
1)A slow moving neutron is fired at a large, unstable nucleus- often Uranium-235. The neutron gets absorbed by the nucleus - this makes the atom unstable and causes it to split
2)when the U-235 atom splits it forms two new lighter elements (daughter nuclei) and energy is released
3-there are lots of different pairs the atoms of uranium can split into, eg: krypton -91 and barium -143. But all these new nuclei are radioactive
4)each time uranium splits up it also splits out two or more neutrons which can hit other uranium nuclei causing them to split and so on
Why can a neutron be absorbed by the nucleus of an atom?
Because it has no positive or negative charge meaning it won’t be repelled.
Where must chain reactions be controlled and why?
What is used to control nuclear fission?
In reactors as it could lead to a meltdown
Control rods are used to control the process
What is nuclear fusion ?
What happens in it ?
-Joining small nuclei.
-It’s the opposite of nuclear fission.
-two light nuclei collide at high speed and join to create a larger , heavier nucleus
Why does the new nucleus in nuclear fusion not have enough mass as the two separate nuclei?
Because some of the mass is converted into energy and released
What’s nuclear fusion the energy source of?
Stars
What’s the big problem with fusion?
Why
It can only happen at really high pressures and temperatures.
This is because positively charged nuclei have to get very close to fuse so the large force due to electrostatic repulsion has to be overcome.
It’s hard to create those condition and no material can withstand that kind of temperature.
What type of radiation is used in thickness control?
Beta
Where are gamma emitting tracers used?
-To detect leaks in underground pipes.
-detect and diagnose medical conditions in the body by using tracers
What happens if you get a smaller dose of ionising radiation?
Can cause mutant cells which divide uncontrollably , this is cancer.
What happens if you get a higher dose of ionising radiation?
Cells are killed completely causing radiation sickness if a lot of cells are effected at once
What radioactive substance is more dangerous if they start of with the same activity. Long half life or short half life? Why?
Long half life because at any point the actitivty of the source with the shorter half life will have fallen more than the material with the longer half life. You won’t be receiving a dose for very long from a material with a short half life.
Why is alpha radiation the most dangerous when inside the body but not when outside ?
When alpha radiation is fired at a body it can’t penetrate through the skin, however when it’s inside the body, it can’t get out and it’s very ionising.
What type of radioactive decay is used in internal therapy? Why?
Beta because it can escape and isn’t too highly penetrating so the chances of it effecting other tissue is reduced.
What type of decay is used in external therapy and why?
Gamma is used in external therapy because it can penetrate through the skin and tissue.
What type of half life should external therapy have, CET scans? Why?
Long half lives so they dont have to ger replaced often.
What half lives should external diagnosic materials have such as gamma cameras?
They should have short half lives as they are only imaging and don’t need to be on for long
What type of radiation is used to check the thickness of paper?
Beta
What’s the device used to detect radiation?
Geiger muller tube
What does the moderator do in nuclear fission ?
The moderator is a material that slows down neutrons so the neighbouring u-235 nuclei can absorb them
What does nuclear fusion produce ?
Helium
hydrogen as energy
Why does nuclear fusion not happen at room temp?
The hydrogen nuclei needed to be slammed together at high speeds to overcome the strong electrostatic forces of repulsion
Differences between fission and fusion?
-Fission is splitting of a nucleus into daughter nuclei , fusion is the joining of two smaller nuclei to make a larger nucleus
-in fusion there must be a very high temp for the positively charged nucleuses to collide and overcome the strong electrostatic forces of repulsion. Fission doesn’t need a high temp
-fission produces radioactive waste, fusion doesn’t other than the odd neutron
What are nuclear power stations controlled by?
Nuclear power stations are powered by nuclear reactors that create controlled chain reactions
How do we get energy out of nuclear fission?
energy from fission, thermal energy store of the moderator, thermal energy store of coolant, thermal energy store of cold water passing through boiler, water boils and energy is transferred into the kinetic energy of steam which turns a turbine and generates energy.
Pros of nuclear power….
-pretty safe way of generating electricity
-very reliable
-doesn’t need fossils fuels that release CO2.
- huge amount of power can be generated.
Cons of nuclear power…
-radioactive waste could leak out and pollute rivers and lakes
- cost is very high to build
-dismantling a power plant takes decades
-
How is the graphite core and movable rods used to maintain and control the chain reaction?
Neutrons released in a chain. Slower neutrons are needed for fission.
Graphite cords is the moderator and slows down the neutrons. Moveable rods absorb the neutrons. They make fewer neutrons available for fission.
How could you show how far beta particles travel through the air?
Take measurement without source
Place source in front of detector
Increase the distance and measure it
Take reading
The differences between radio and gamma rays being produced ?
Radio waves often produced intentionally But Gamma ways are often accidents
Radio waves are produced in electrical circuits. Gamma rays may result from decay
Radio waves are produced by free electrons . Gamma rays produced in the nucleus
In fusion hydrogen turns into what
Helium
In fusion what is hydrogen turned into
Helium
In fusion what is hydrogen turned into
Helium
