Paper 1 Development of the atom and radioactivity Flashcards
before the discovery of the atom
some ancient Greek philosophers believed the atom was the smallest building block of everything
they thought it couldn’t be divided into any smaller parts
the plum pudding model
when Thompson discovered the the electron he developed plum pudding model in 1897
atom is sphere of positive charge with negative electrons embedded inside
rutherford’s experiment
- Rutherford’s shot high-speed alpha particles through thin layer of gold. some went straight through some deflected but some bounced back at very large angles
shows most of the mass of the atom was concentrated in positive nucleus
electrons orbit around nucleus at different distances
Niels Bohr’s model
- adapted rutherford’s saying electrons could only orbit nucleus at specific distances
this agreed with experimental measurements so was accepted as more accurate than rutherford’s
the proton 1919
more experiments conducted in 1919 showing charge of nucleus could be divided into protons. every proton had same positive charge
electrons orbited core nucleus at discrete distances
chadwick’s discovery
proved existence of neutron in 1932
mass of nucleus too large to be made of just protons so another neutral particle must be responsible for the mass
what are radioactive substances
some isotopes have unstable nuclei and will break down.
when this happens they give out radiation and these substances are said to be radioactive
alpha particle
consists of 2 neutrons and 2 protons, same as helium nucleus
beta particle
a high speed electron ejected from the nucleus as a neutron changes into a proton
gamma ray
high energy electromagnetic radiation from the nucleus
what do nuclear equations represent
radioactive decay
alpha decay
causes both mass and charge of the nucleus to decrease
beta decay
doesn’t cause mass of nucleus to change but does cause the charge of the nucleus to increase
emission of gamma rays
doesn’t cause the mass or the charge of the nucleus to change
what happens when alpha, beta of gamma radiation strike atoms in a substance
they can knock an electron from one atom onto another
what is an ion
an atom that’s gained or lost an electron
what are alpha particles like
relatively big, heavy and slow moving
large relative charge (+2)
strongly ionising
bash into a lot of atoms and knock electrons off them before they slow down
what are beta particles like
quite small and move quite fast
moderately ionising because their relative charge is smaller (-1)
what is gamma like
weakly ionising because gamma isn’t charged
what is alpha’s range in air and what stops it
few cm
paper, card + skin
what is beta’s range in air and what stops it
few metres
aluminium (5mm thick)
what is gamma’s range in air and what stops it
infinite
thick shetts of lead or metres of concrete
what damage can ionising radiation cause
damages or kills living cells
damage to the genes in a cell can be passed on and lead to cancer
from the outside which radiation is the safest and which is the most dangerous
alpha as it’s the least penetrating
gamma because it’s the most penetrating
from the inside which radiation is the safest and which is the most dangerous
gamma because it can easily escape
alpha because it can’t escape
what is Alpha used for
smoke detectors. ionises air particles, causing current to flow
if smoke in the air, it binds to the ions reducing the number available to carry a current
the current falls and alarm sounds
why is alpha used for smoke detectors and why not beta or gamma
small range so safest, only one that can be stopped by smoke, most ionising
aren’t used as won’t be stopped by smoke and and won’t ionise the air enough. bigger range so not safe
what is beta used for
test thickness of thin sheets of metal, as particles aren’t immediately absorbed by the material like alpha would be and don’t penetrate as far as gamma
gamma tracers in medicine
gamma is used so that it can be detected on the outside of the body
alpha would be too dangerous as highly ionising
gamma leak detection in pipes
injected into pipe. outside of pipe is checked with Geiger-moller detector to find areas of high radioactivity. this is where the pipe has a leak
useful for underground pipes that’s hard to get to
why would alpha and beta not be used for leak detection in pipes
they would be blocked by the metal and the earth
food irradiation
foods like strawberries can be irradiated with gamma radiation, killing any living bacteria or virus meaning less likely to go off
What is a half life of a radioactive isotope
It’s the average time it takes for the number of nuclei of the isotope in a sample to half, or the time taken for the count rate of the sample to fall to half its initial rate
The more nuclei there are in a sample…
The more a re likely to decay in one half life so the higher the count rate will be
What is net decline of a radioactive substance
The fraction of the nuclei that have decayed in a certain time. it’s a fraction, ration or percentage because it doesn’t have a unit
What is count rate
The time taken for the count rate from a sample containing the radioactive isotope to fall to half its starting level
Radioactive tracers
Tracers used to trace flow of a substance through an organ.
small amount of radioactive material put into patients body (by injection or ingestion)
Tracer given enough time to travel through body before gamma camera is positioned to detect the radiation from outside the body
multiple images takes to show progress of tracer over time by measuring activity over time
Gamma cameras
Can be used to image internal organs
as with tracing, a radioactive isotope (gamma emitting) is injected into the patient. The isotope is chosen because it concentrates in the organ
How do gamma cameras work
Made of a crystal scintillator (sodium iodide) which produces a burst of light
light picked up by photo multiplier tubes which convert energy into an electrical signal. this fed into computer to get an image
Lead grid acts as collimator which only allows rays aligned with the holes to hit the crystal making the image sharper
What does ionising mean
Means atoms are turned into ions by gaining or losing an electron
What is ionising radiation
The high frequency end of the electromagnetic spectrum (UV, gamma, x-rays) and gamma and beta radiation
What are the dangers of ionising radiation
Can damage living cells if small dose, large dose can kill cells this leads to cancer
What is gamma radiotherapy
Gamma radiation is used in narrow beam to destroy cancer cells in a tumour .
the radiation emitted is from the isotope of cobalt
How does gamma radiotherapy work
Individual beams that cross over at the target so individual beams less intense and don’t damage healthy cells.
destroys cells by ionising them and gamma because can penetrate further into the body
What is that half life of the isotope used in gamma radiotherapy
5 years because it needs to last a long time so that it doesn’t need to be replaced and so the dose the patient receives doesn’t decrease
Gamma knife
used to accurately focus many beams of gamma radiation on one or more brain tumours
each beam low intensity but with 200 beams can be accurately concentrated on small volume
Radioactive implants
Small seeds or tiny rods used to attack tumour from inside the body. sources place inside tumour or in nearby tissue
with low dose rate the implants can stay in for hours or days
What is irradiation
When something has been irradiated, the irradiation stops as soon as the source of radiation has been removed
What is contamination
When contamination has occurred the source of ionising radiation itself is transferred such as when radiation isotopes in sold liquid or gas are introduced into the environment
What is nuclear fission
Splitting of a large nucleus into 2 smaller nuclei (daughters) releasing energy
Which nuclei are usually split in fission reactions
Uranium-235 or plutonium-239
the numbers are the mass number so the number of protons and electrons the element has
What is induced fission
When a neutron is fired at the nucleus, causing it to split
What is released in nuclear fission and how is it a chain reaction
2 or 3 neutrons released
energy in form of radiation and kinetic energy
Neutrons released may cause further and further fission resulting in a chain reaction
What is the energy released in fission used for
Used to heat water, turning the it into steam
steam turns turbine which turns generator which transforms kinetic energy into electrical energy
level of energy produced must remain constant for output of power station to be constant
What is nuclear fusion
Happens when 2 nuclei collide and fuse together, forming a larger nucleus releasing energy in the process
the colliding energy need enough kinetic energy otherwise they’ll repel and not fuse
How does fusion work in a fusion reactor
Heated by passing and electric current through it
gas becomes so hot it forms a plasma of small nuclei
plasma contained using a magnetic field to prevent it from touching container walls otherwise will cool down and fusion stops
When hydrogen nuclei fuse together helium is formed as one of the products
Example of nuclear fusion
process powering the sun and stars
in the core of the sun, hydrogen is converted into helium by fusion providing enough energy to keep sun burning an sustain life on earth
Ads of fission
Concentrated source of energy so more J/kg
no polluting gases
supply of uranium for many years
reliable 24/7
Disads of fission
Produces radioactive waste
chain reaction to control with severe consequences
expensive
Ads of fusion
Produces very little radioactive waste-safer
no chain reaction to control
very concentrated source of energy
fuel readily available (hydrogen in water)
renewable and cheap
Disads of fusion
Not yet viable
fusion on earth needs more energy input than the energy output
