P6 Radioactivity Flashcards
What does it mean for an electron to become excited?
Move to a higher energy level
When can electrons in a gas become excited?
When the gas is heated / current is passed through it
After becoming excited electrons fall back down to their shell and lose energy. This is emitted as?
An electromagnetic wave in a random direction
The bigger the fall, the more…
Energy lost
Energetic EM wave emitted
Every element has different ____ levels. Therefore if there is an unknown gas we can ____ it and see which ___ it emits
Energy
Heat
Wavelengths
All EM waves except what can be emitted in this way?
Gamma
When light of all colours is shone through a cold gas, most wavelengths…
Go straight through
Electrons can only absorb light with…
Just the right energy to move them up to another energy shell
After electrons absorb light they’ll then fall back down, emitting…
An identical wavelength (colour) of light in a random direction
An electron can gain enough energy to ___ ___ from the atom. This is known as ____ and we say the atom has been ____
Break free
Ionisation
Ionised
Some isotopes contain too many ____, this makes them ___ and therefore radioactive. We call them _____
Neutrons
Unstable
Radioisotopes
Radioactive substances consist of unstable ___ which ___, emitting alpha / beta / gamma
Nuclei
Decay
What is an alpha particle?
Two protons and two neutrons
The same as a helium nucleus
A beta particle is?
A high energy electron
What is gamma?
An electromagnetic wave, high frequency, short wavelength
Absorbing what can make a material radioactive?
Neutrons
Losing a gamma ray has what effect on a nucleus?
The nucleus stays the same but has less energy
How is a beta particle formed?
A neutron turns into a proton + electron
Alpha is how ionising?
Highly
Beta is how ionising?
Moderately
Gamma is how ionising?
Weakly
Alpha is how penetrating?
Weakly
Beta is how penetrating?
Moderately
Gamma is how penetrating?
Highly
Alpha can be stopped by…
Paper
5cm of air
Beta can be stopped by…
3-5mm of aluminium
Gamma can be stopped by…
Thick lead
Metres of concrete
Why is ionisation of living things potentially dangerous?
Ionisation within living cells can damage DNA —> cell mutation / death
What is irradiation?
When the radiation from a material damages the cells. You can move away from the source and end the irradiation
What is contamination?
If some of the radioactive material itself is swallowed or inhaled, it emits radiation inside the body, causing damage
List the precautions your teacher took while handling radioactive sources
Wearing lab coat and gloves to avoid contamination
Tongs and source holder to increase distance between source + people
Experiment done quickly to limit time close to source
Pointed sources away from students
What is background radiation?
Radiation all around us
What is half-life?
The half-life of a radioactive element is the time it takes for half the nuclei in a sample to decay
Carbon-__ is made in the upper atmosphere by ___ __ and decays elsewhere at the same rate
14
Neutron capture
Living organisms take in ___ including some of the radioactive C-14
Carbon
When organisms die they stop taking in C02 (plants) or ____ (animals) so the amount of C-14 in them starts _____ as it radioactively decays
Glucose
Decreasing
C-14 has a half life of….
5730 years
The ratio of C-14 to C-__ in living objects can be compared to the artefact and therefore it can be ___
12
Dated
How is radioactivity used to treat cancer?
An x-ray or gamma source is rotated around patient’s body, aiming x-rays / gamma rays at tumour. This ensures the tumour gets large amount of radiation (hopefully cells die) while healthy cells receive lowest amount possible
What radiations are emitted from medical tracers we use? Why?
Usually gamma - most penetrating, least ionising
Sometimes beta
Why is alpha never used for medical tracers?
Would cause damage (most ionising) and wouldn’t be detected (least penetrating)
How do we get medical tracers into patient?
Injection, ingestion, inhalation (3 Is)
Radioactive iodine behaves the same as non-radioactive iodine. This is good because?
Our body won’t reject it
An appropriate half-life for a medical tracer might be…
4-6 hours
What is nuclear fission?
The process of splitting a heavy nucleus to form 2 or more small nuclei, releasing large quantities of energy
What is a chain reaction?
A reaction where the product of the first reaction causes further reactions to take place
A ___ moving neutron is absorbed by the nucleus of a ____-235 atom
Slow
Uranium
The uranium nucleus splits into two smaller, still _____ nuclei, releasing ____ and ____
Radioactive
Heat
Gamma
When the uranium nucleus splits, 2 or 3 ___ are also released; these could be ___ by other uranium nuclei causing further ____ reactions
Neutrons
Absorbed
Fission
Advantages of nuclear power?
Produces no C02
Stores more energy per kg than any other fuel (4 million times more than coal)
Reliable, produces 24/7
Disadvantages of nuclear power?
Generate nuclear waste that emit alpha, beta and gamma, and stay radioactive for millions of years - has to be treated, sealed and buried
Closing power station is expensive because some parts have become radioactive by absorbing neutrons
Nuclear accidents are rare but have serious consequences
What is nuclear fusion?
The process of joining together two lighter nuclei to form one large nucleus, releasing large quantities of energy
What happens if we bring two protons (hydrogen nuclei) together?
They repel
In order to fuse, protons must move very fast. What must the temp of the substance be?
Extremely hot
How do we increase the likelihood of successful collisions?
Increase pressure and density
What does E= delta m c2 mean
Energy = change in mass x speed of light squared
Energy and mass are…
Interchangeable
If we can recreate nuclear fusion in a controlled way, we could produce energy that:
Produces no C02
Produces no long half-life waste
Is inherently safe - if something goes wrong the temp drops, and the reaction stops
What is an absorption spectrum?
A continuous spectrum with dark lines where particular wavelengths / frequencies of EM waves have been absorbed
Where does background radiation come from?
The air, rocks, the sun, space and artificial sources
Define radioactive decay
A random process by which an unstable nucleus loses energy by emission of radiation or a particle
What is an emission spectrum?
A set of wavelengths / frequencies of EM waves emitted by an atom when excited electrons move to lower energy levels
