P4 - Atoms & Radiation Flashcards
How did Rutherford discover the nucleus
Alpha Scattering Experiment:
fired a beam of alpha particles at thin gold foil. most particles went straight through the sheet but a few were deflected back and a few of those were deflected back the way they came from.
this made scientists realise that most of the mass of an atom must be concentrated at the centre in a tiny nucleus - this created the first nuclear model
Who discovered the plum pudding model and what was it?
J.J Thomson
- way to remember is that “pudding” and “thomson” have the same amount of letters
the plum pudding model meant that an atom was a ball of positive charge (dough) with negatively charged electrons (currents) mixed in with the “dough”
Who discovered the modern model of the atom and what was it
Niels Bohr
it meant that electrons orbited the nucleus at fixed distances
then James Chadwick discovered some particles in the nucleus have no charge at all which he then names neutrons.
What are the subatomic particles
- Protons
- ELectrons
- Neutrons
What is the relative charge of a proton and where are they found in an atom
Their charge is +1
They are found in the nucleus
What is the relative charge of a electron and where are they found in an atom
Their charge is -1
They are found in fixed orbits around the nucleus (shells)
What is the relative charge of a neutron and where are they found in an atom
Their charge is 0
They are found in the nucleus
What happens if electrons emit or absorb electromagnetic radiation (EM radiation)
- If they emit EM radiation then they drop to a lower energy level/shell that’s closer to the nucleus
- If they absorb EM radiation then they move up to a higher energy level/shell that is further away from the nucleus
What happens to an atom if it gains one or more electrons
it becomes a negative ion
(because its in debt which is negative)
What happens to an atom if it loses one or more electrons
it becomes a positive ion
(gets rid of the surplus (yipee))
Why do normal atoms have no overall charge
because: number of electrons = number of protons
so they cancel out to be neutral
What is the mass number (top number)
total number of protons and neutrons in an atom
What is the atomic number (bottom number)
number of protons in an atom
What are isotopes
atoms with the same number of protons but different number of neutrons
What is radioactive decay
when an unstable nucleus decays into another element and gives out radiation to become more stable
What is ionising radiation
alpha (α), beta (β) and gamma (γ) - radiation that knocks electrons off atoms, creating positive ions
Give the characteristics of alpha particles
e.g:
- what is consists of
- what it is absorbed by
- what its range in the air is
- its ionising power
- an example of its use
- consists of 2 neutrons and 2 protons
(helium nucleus) - it is absorbed by a sheet of paper
- its range in the air is a few centimeters
- its ionising power is strong
- an example of its use is smoke detectors
Give the characteristics of beta particles
e.g:
- what is consists of
- what it is absorbed by
- what its range in the air is
- its ionising power
- an example of its use
- it consists of a fast moving electron from
nucleus - is it absorbed by a sheet of aluminium
- its range in the air is a few metres
- its ionising power is moderate
- an example of its use it for material
thickness testing
Give the characteristics of gamma particles
e.g:
- what is consists of
- what it is absorbed by
- what its range in the air is
- its ionising power
- an example of its use
- it consists of electromagnetic radiation
from nucleus with a short wavelength - it is absorbed by a thick sheet of lead
- its range in the air is longer distances
- its ionising power is weak
- an example of its use is for medical tracers
What are the 3 primary ways of detecting radiation (+ information of how they work)
- Cloud chamber
- a container full of alcohol vapor
- ionising radiation enters the air and leaves a trail of ionised molecules
- the alcohol vapor condenses on the ionised air molecules showing the trail of radiation - Photographic film
- a bright spot appears wherever the ionising radiation hits the film - Geiger counter
- ionising radiation enters a tube of low pressure gases
- it ionises the atoms in the gas, knocking the electrons out of the atoms
- the gas can now conduct electricity and completes an electric circuit. current flows between both electrodes
- the current produces a clicking noise
the count-rate is the number of decays recorded each second
What are the charges and masses of alpha beta and gamma
- alpha - charge = +2, mass = 4
- beta - charge = -1, mass = 0 (electron)
- gamma - charge = 0, mass = 0
In Nuclear equations, what does an alpha particle do
mass decreases by -4 (top number)
charge decreases by -2 (bottom number)
(on the right hand side of the equation after you have minused the 4 and 2, you add a helium atom to represent the alpha particle:
4 at the top, 2 at the bottom of H)
In Nuclear equations, what does a beta particle do
mass doesn’t change
charge increases by +1 (bottom number)
(on the right hand side after you had added the 1 at the bottom, you need to also add an electron by writing “e” with a 0 at the top and a -1 an the bottom of it”)
In Nuclear equations, what does a gamma particle do
mass and charge stay the same
What is half-life
the time taken for the number of nuclei f an isotope in a sample to halve
- you can measure half life by using a graph
What is meant by activity
the rate at which a source decays, measured in becquerels (Bq)
What is meant by count-rate
the number of radiation counts reaching a detector per second
What is radioactive contamination
getting unwanted radioactive atoms onto or into an object
What is irradiation
the exposure of an object to nuclear radiation (this doesn’t make the object radioactive)
Why can ionising radiation be dangerous
- it can cause cell damage:
- it can damage cells and complex chemical structures like DNA
- the cell damage from ionising radiation can cause mutations which can lead to cancer
What are some preventative methods of reducing the risks with ionising radiation
- reduced exposure
- washing hands (handling)
- store radioactive substances in lead-lined boxes and locked in steel cabinets away from people
- not eat or drink when using a radioactive source and sources should be kept at an arms length away from people, not inside pockets.
- wearing protective clothing like lead aprons if you work with radioactive sources often
- standing behind a protective screen if you work with radioactive sources often
What is the most dangerous form of radiation inside the body
alpha as it is the most ionising.
Why are beta and gamma not so harmful
because they penetrate easier so they pass through the body
What do scientists do to check each other’s work, theories and findings?
peer review
What is the radius of an atom
1 x 10^-10
