P7 Radioactivity Flashcards
what is the radius of an atom?
1 x 10^-10 m
what is the radius of the nucleus?
less than 1/10000 of the radius of the atom
what does the nucleus contain?
protons - positive particles
neutrons - neutral particles
what is the overall charge of the nucleus?
positive overall charge due to the protons
where are electrons found?
in energy levels orbiting the nucleus
how is the energy of the energy level and the distance from the nucleus related?
energy levels further from the nucleus are at a higher energy than those closer
how can electrons move from energy levels?
if an electron absorbs EM radiation the electron can move from a lower energy level to a higher one
the atom can then emit EM radiation and the electron returns back to the lower energy level
what is the atomic number?
the number of protons
all atoms of each element have the same number of protons (same atomic number)
how is an atom neutral overall?
the number of electrons equals the number of protons
this means the negative charge on the electrons cancels out the positive charge of the protons
what does the mass number of an atom equal?
it equals the number of protons and neutrons in the atom
what is an isotope?
atoms of the same element with different numbers of neutrons
what is an ion?
atoms which lose electrons to become positively charged
what did the ancient Greeks think about atoms?
everything is made of atoms
atoms are tiny spheres that cannot be divided
what happened in 1897?
electrons were discovered
this showed that atoms must have an internal structure
what did the plum-pudding model suggest?
an atom is a ball of positive charge with negative electrons embedded in it
why was gold foil used in the alpha scattering experiment?
it can be hammered out very thin (a few atoms thick)
what did scientists do during the alpha scattering experiment?
fire positive alpha particles at gold foil
what were the observations made during the alpha scattering experiment?
most alpha particles passed straight through the foil
some particles were deflected
some particles bounced straight back off the foil
what told the scientists that atoms are mostly empty space? (in the alpha scattering experiment)
most of the particles passed straight through the gold foil
this meant the plum-pudding model had to be wrong
if some alpha particles were deflected, what does this mean?
the centre of the atom must have a positive charge that repelled the alpha particles
if some alpha particles bounced back, what does this say about the structure of an atom?
the mass of the atom must be concentrated in the centre. this central mass is known as the nucleus
what did Niels Bohr propose about electrons?
electrons orbit the nucleus at specific distances known as energy levels or shells
what did James Chadwick discover?
the nucleus contains neutral particles called neutrons
what is radioactive decay?
some isotopes have an unstable nucleus.
in order to become stable, the nucleus gives out radiation
can scientists predict when a nucleus will decay?
no
radioactive decay is completely random
what is the activity?
the rate at which a source of unstable nuclei decay
what is the symbol/unit for activity?
the becquerel (Bq)
1 Bq = 1 decay per second
what is the count rate?
the number of decays recorded each second by a detector
what is an alpha particle?
a radioactive particle with the structure of 2 protons and 2 neutrons (the same as a helium nucleus)
what is a beta particle?
an electron ejected from the nucleus at high speeds
how is a beta particle formed?
when a neutron turns into a proton and an electron
what is gamma radiation?
a type of electromagnetic radiation from the nucleus
what other radiation type is given out by the nucleus?
a neutron
what happens to the atomic number during alpha decay?
it decreases by 2
what happens to the mass number during alpha decay?
it decreases by 4
what is the rule for beta decay?
the atomic number increases by 1 but the mass number stays the same
what happens to the mass/atomic number during gamma decay?
they are not changed
what are alpha particles’ range in air? (and why)
alpha particles are large
they can travel around 5 cm before colliding with air particles and stop
what are beta particles’ range in air?
up to a metre
what are gamma rays’ range in air?
several metres before stopping
what are the penetrating powers of the three types of radiation?
alpha - stopped by paper
beta - stopped by a few mm of aluminium
gamma - stopped by thick lead or concrete
what is ionising?
when radiation collides with atoms, it can cause the atoms to lose electrons and form ions
what are the ionising powers of radiation types?
alpha - very strongly ionising
beta - quite strongly ionising
gamma - weakly ionising
what is half life?
the time it takes for the number of radioactive nuclei in an isotope in a sample to halve
half life is also the time it takes for the count rate (or activity) for a sample containing the isotope to fall to half its initial level
what is the risk of ionising radiation?
it can increase the risk of cancer in humans
what is irradiation?
exposing an object to nuclear radiation
the object does not become radioactive
how is irradiation used to sterilise objects?
the object is exposed to gamma radiation
this kills any bacteria present
what are the precautions when working with ionising radiation?
shielding - using gloves, lead apron, lead glass screen/container
monitoring - measure how much radiation has been received
what is radioactive contamination?
when unwanted radioactive isotopes end up on other materials
why is radioactive contamination hazardous?
the radioactive atoms decay and emit ionising radiation
how are alpha particles dangerous?
very strongly ionising
can cause a lot of damage if inhaled or swallowed
which radiation types can pass through the skin?
alpha - stopped by dead skin cells
beta - can penetrate skin
gamma - can penetrate body by likely to pass straight through
what does peer reviewing allow?
it allows other scientists to check the findings of other scientists
what is background radiation?
the low level nuclear radiation that is always present from natural or man-made sources
what are some natural forms of background radiation?
rocks
cosmic rays
what are cosmic rays?
very high energy particles which travel through space and crash into the earth’s atomosphere
what are some man made sources of background radiation?
fall out from nuclear weapons testing
nuclear accidents
what affects your exposure to background radiation?
location and occupation
what is radiation dose measured in?
sieverts (Sv)
or
milisieverts (mSv) = 1/1000 of a Sv
what are some features that a radioactive isotope must have to be used in medical tracers?
must emit a radiation type which can pass out of the body (beta/gamma)
not be strongly ionising to minimise damage to tissue
must not decay into another radioactive isotope
short half life so the isotope is not present in the body after a long time
how does radiotherapy work?
gamma rays pass into the body and destroy a tumour
what is the problem with radiotherapy?
healthy tissue may also be damaged when the gamma rays pass through the body
how can the damage to healthy tissue be reduced in radiotherapy?
the radioactive isotope can be implanted into the body
this means the radiation is targeted precisely to the tumour
