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Flashcards in topic 6 Deck (54)
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6.2- size of atoms

radios of a nucleus is 1x10^-15
radius of an atom is 1x10^-10


6.17- plum pudding model

jj thomson- discovered electrons
said atoms were spheres of positive charge with negative electrons inside


6.17 - Rutherford alpha

experimented what happened to positive alpha particles when fired at gold foil
discovered most of alpha particles passed through but some bounced back- the plum pudding model couldn't explain this
he said that most of the mass was in a central nucleus, electrons were outside the nucleus and that most of the atom is empty space the nucleus must have a positive charge since it repelled the alpha particles


bohr model

rutherfords discover was changed slightly by Bohr- he said electrons were in shells as set distances from the nucleus and electrons could only exist in shells and not anywhere in-between


6.3- nucleus of isotopes

same atomic number as the nucleus had same number of protons but different mass numbers due to a different number of neutrons


6.6- charges of an atom

have equal numbers of protons and electrons and so an atom is neutral
a nucleus has a positive charge


6.5charges of subatomic particles

proton- +1, mass of 1
neutron- 0, 1
electron- -1, mass of 1/1835


6.7- how do electrons orbit a nucleus

at set distances from the nucleus called shells


6.8 how do electrons change orbit

electrons can change orbit when they absorb or emit EM radiation
the part of EM radiation emitted depends on the energy of the atom and the energy levels that the shell moves between, a higher energy means a higher freq of EM radiation


6.9- formation of ions

atoms can form a positive charge by losing outer electrons
ionising radiation causes atoms to be formed


6.12- what is background radiation

low levels of radiation that is around us from a number of sources


6.13- where does background radiation come from

radon gas- radioactive gas produced rocks that contain small amounts of uranium
hospital treatments
the sun


6.14- how can photographic film be used to measure radioactivity

film becomes darker as more radiation reaches it
dosimeter babes check how much radiation people have been exposed to


6.14- how can a geiger muller tube be used to measure radioactivity

radiation passing through the tube ionises gas inside and allows a short pulse of current to flow
the GM tube is connected to s counter that counts the pulses of current or clicks when radiation is detected
the count rate is the number of clicks per second/ minute


6.14- how to measure radioactivity of a source

measure levels of background radios first. take several readings and find a mean. subtract this from the measurements of the source


6.10 what does an unstable nucleus emit

an unstable nucleus emits alpha, beta minus, positron, gamma rays and neutron radiation at a random process


what radiation is ionising

alpha, beta minus, position and gamma


what is alpha radiation

a helium nucleus
mass of 4
charge of 2
strongly ionising
short penetration distance, a few cm
stopped by paper


6.15 what are the different particles emitted

an alpha particle is a helium nucleus
a beta particle is an electron emitted from a nucleus
a gamma ray is EM radiation
positrons are particles with same mass as an electron but a charge of +1
mass number deceases by 4
atomic number decreases by 2


6.18 what is beta - decay

neutron changes into a proton and an electron
atomic number increases by 1


6.19 what is positron (beta +) decay

proton becomes a neurone and a positron
atomic number decreases by 1


what is beta radiation

less ionising than alpha
travel a few m
stopped by aluminium


what is gamma radiation

gamma rays emitted by a nucleus
don't change mass or atomic number
don't have a charge
travel few km
weakly ionising
stopped by lead or concrete


what is neutron decay

nucleus emits a neutron
mass number decreases by 1


6.21 why do atoms emit gamma radiation

nuclei that have undergone radioactive decay often undergo nuclear rearrangement with a loss of energy as gamma radiation


6.23- how does the activity of a source decrease over time

each time a radioactive atom decays, one more radioactive nucleus disappears. as the unstable nucleus disappear the activity will decreases


6.25- what is half life

is the time taken for half the undecayed nuclei to decay or the activity of a source to decay by half


6.26- use of half life

it cannot be predicted when a particular nucleus will decay but half-life enables the activity of a nuclei to be predicted during the decay process.
a short hl means the activity falls quickly because the nuclei are unstable and decay rapidly.
a long hf means the activity fall slowly because most of the nuclei don't decay for a long time,


6.29 fire alarms

contains a source of alpha particles
the alpha particles ionise molecules in the air.
ions are attracted to plates with opposite charges so a current flows
when smoke gets into the air gap it slows down the ions and current slows down
if the current drops below a certain level the alarm goes off


6.28 irradiating food

gamma rays irradiate food to kill bacteria
makes it last longer