atomic structure Flashcards
what is the plum pudding model and who created it
spheres of positive charge with tiny balls of negative electrons stuck in them J.J Thomson
what experiment did rutherford do
fired a beam of alpha particles at a sheet of gold foil
what were the results of rutherfords experiment
most particles went through
some deflected more than expected
a few deflected back
what did scientists relies after rutherfords experiment
most of the mass must be concentrated
the nucleus must have a positive charge
as most atoms passed they relised most of the atom was empty
what did Niels Bohr discover
electrons orbiting the nucleus do at certain distances
what did james chadwick discover
neutron which explained imbalance between atomic mass and mass number
what is the atomic number
number of protons
what is the mass number
number of protons and neutrons
what are isotopes
are atoms with the same number of protons but a different number of neurons
what is ionising radiation
radiation that knocks electrons off atoms creating positive ions
what is ionising power
how easily it can knock off an atom
what happens to unstable isotopes
decay into other elements and give out radiation
what is an alpha particle
ionising power and how far it penetrates
2 neutrons and 2 protons / helium nucleus
don’t penetrate far and stopped by paper
strongly ionising
what is a beta
ionisong power and how far it penetrates
a fast moving electron released by nucleus
absorbed by aluminium and moderate ionising
what happends to the neutron and proton when beta particle is released
for every beta emitted a nuetron turns into a proton
what is gamma
ionising power and how far it penetrates
waves of electromagnetic radiation
penetrate far and stopped by lead
weak ionising
how is radioactivity measured
geiger-muller tube
what is half life
time it takes for the amount of radiation emitted by a source to half
what is the activity of a radioactive source
rate at which a source decays measured in Bq(becquerels)
what does short half life mean
activity falls quickly as nuclei is very unstable and decay fast
they are dangerous because of high radiation but quickely become safe
what does long half life mean
activity falls slowely
source just sits there releasing a small amount of radiation so very dangerous
how do you measure half life of a graph
finding the time interval on the bottom axis corresponding to a halving of the activity
which three places does background radiation come from
naturally occurring unstable isotopes
space
human activity
what is irradiation
exposure to radiation
how do you decrease the amount of irradiation
lead-lined boxes and standing behind barriers
what is contamination
radioactive particles getting into objects
how do you stop contamination
gloves and tongs
what radiation is most dangerous on the out side and why
beta and gamma because they can penetrate to the organs (irradiation)
why is alpha not as dangerous outside the body
does not penetrate skin
what radiation is most dangerous inside the body and why
alpha as it does damage in a localised area
why are beta and gamma less dangerous inside the body
beta is absorbed over a wide area and gamma just passes out
what are the risks of radiation
enter living cells and ionise there atoms
lower dose can cause minor damage like giving rise to mutant cells which then divide uncontrollable(cancer)
higher doses kill
how is gamma used in medical tracers
gamma isotopes are injected into people and their progress around the body can be traced using an external detector.
A computer converts the reading to a display showing where strongest reading is from
why is gamma used in medical tracers
passes straight through
what is radiotherapy
gamma rays are directed carefully and at the right dosage to kill the cancer cell
what is fission
release of energy from large atoms by splitting them into smaller atoms
what is the process of fission
neutron hits the atom splitting into two lighter elements that are the same size
2 or 3 neutrons are released and if moving slowly anougth they are absorbed and cause a chain reaction
where does the energy come from in fission
energy in gamma and kinetic energy stores of the free neutrons
how are the chain reactions controlled in fission
control rods that are lowerd and raised inside a nuclear reactor to absorb neutrons
what is fusion
joining small nuclei
process of fusion
2 light nuclei collide at high speed and fuse to create a larger heavier nucleus
the heavier nucleus produced does not have as much mass as some is converted into energy
what releases more energy fusion or fission
fusion
why is fusion so hard and expensive to build
high temp and pressure
