ATOMIC STRUCTURE Flashcards
what is the alpha scattering experiment
the alpha particles were shot at the gold nucleus some particles were refracted straight back meaning the mass of the atom must be concentrated in the centre, some particles were deflected which means the nucleus was positive. Lastly some of the alpha particles went straight through meaning that the atom was mostly free empty space. this formed the nuclear model which had a positive nucleus and contained mostly free space
Describe the current model of the atom
The centre of an atom is an tiny positively charged nucleus. this is made up of protons and neutrons and is the source of most of the atoms mass. Most of the atom is empty space, Electrons orbit the nucleus at set energy levels
the atomic number of an atom is its….
number of protons
what are isotopes
isotopes are atoms with the same number of protons different number of neutrons
the mass number of an atom is its
number of protons + number of neutrons
what is radioactive decay
when unstable isotopes give out radiation to become more stable
radioactive substances give out radiation what else do they release and why
neutrons to rebalance their atomic and mass numbers
what is ionising radiation
it is radiation that knocks electrons off atoms creating positive ions
what is alpha radiation
is when an alpha particle is emitted from the nucleus
what is an alpha particle
a helium atom
alpha particles are (ionisation and penetration)
strongly ionising because of their size
do not penetrate far into materials and is stopped quickly
what is alpha radiation absorbed by
paper
what is alpha radiation used for and how
alpha radiation is used in smoke detectors
it ionises air particles causing current to flow, if there is smoke in the air it binds to the ions meaning current will stop and the alarm will sound
what is beta radiation
it is a fast moving electron released from the nucleus
what is a beta particle
they have no mass
and it is an electron
beta particles are (ionisation and penetration)
beta particles are moderately ionising
beta particles penetrate moderately far into materials
what is beta radiation absorbed by
by a sheet of aluminium
for every beta particle emitted…..
a neutron in the nucleus has turned into a proton
what are gamma rays (radiation)
gamma rays are waves of electromagnetic radiation released by the nucleus
gamma rays are (ionisation and penetration)
deeply penetrating they penetrate far into materials
they are weakly ionising
what are gamma rays absorbed by
they are absorbed by thick sheets of lead or concrete
in nuclear equations the alpha particle can be written as….
an helium atom 4
2
what type of radiation is given off 8 8
Li—->Be + radiation
3 4
beta
in nuclear equations the beta particles can be written as……
an electron 0
-1
what is the nuclear equation for 219 emitting an alpha
Rn particle
86
write down the equation
219 215 4
Rn ——> + He
86 84 2
do gamma rays change the mass or charge of the nucleus
NO
how is radiation measured and what does it record
Geiger muller tube and counter and it records the count rate
what is half life
half life is the amount of time taken for the number of radioactive nuclei in an isotope to halve
what does a short half life mean and is it dangerous
a short half life means the activity falls quickly because the nuclei are very unstable and rapidly decay. Sources with a short half life are dangerous for the radiation they emit at the start then become safe quickly
what does a long half life mean and is it dangerous
a long half life means the activity falls slowly because most of the nuclei don’t decay for a long time, which means the source will emit small amounts of radiation for a long time. This can be dangerous because nearby areas are exposed to radiation for a very long time
the initial count rate of a sample is 40cps calculate the decline in count rate after three half lives as a ratio
40/2=20 one half life
20/2=10 two half lives
10/2=5 three half lives
5:40= 1:8
sources of background radiation
cosmic rays, air, food, rocks
what is irradiation
when objects are exposed to radiation
what is contamination
contamination is when radioactive particles get onto objects
how to reduce the effects of irradiation
keeping sources in lead lined boxes
reduce effects of contamination
wearing gloves and tongs when handling sources
wearing protective suits
what radiation is dangerous outside the body and why
beta and gamma because they can penetrate the body and get to delicate organs
what radiation isn’t dangerous outside the body
alpha because its cannot penetrate the skin
what radiation is dangerous inside the body
alpha because they do its damage in a very localised area
what radiation is not as dangerous inside the body
beta as radiation is absorbed over a wider area and some passes throughout the body all together
what radiation is least dangerous inside the body
gamma as it has low ionising power and they mostly pass straight through the body
what risks are there using radiation
cancer
how are gamma emitters used as medical tracers
radioactive isotopes are swallowed or injected by a person, the radiation the isotope gives off is detected
how is radiotherapy used to treat cancerous tumours
gamma rays are directed carefully at a tumour because a high dose of gamma rays will kill living cells, the cancerous cells will be destroyed without damaging too many normal healthy cells
why would some patients not want to use medical tracers
medical tracers use radiation and this poses a risk to the human body as it can cause cell damage or cell mutation, patients may think the risks are too serious and want other tests to be performed
what is nuclear fission
nuclear fission is splitting a larger nucleus into smaller one
what has to happen before nuclear fission
the nucleus has to absorb a neutron
what is a chain reaction
when the neutrons released are absorbed by another nucleus causing more fission to occur
what controls the amount of energy produced by fission in a nuclear reactor
it is controlled b how quickly the chain reaction can occur this is done by using control rods which are lowered and raised inside a nuclear reactor to absorb neutrons slow down the chain reaction and control the amount of energy released
how do nuclear weapons work
uncontrolled chain reactions which quickly leads to lots of energy being released as an explosion
what is nuclear fusion
nuclear fusion is when two light nuclei join to form a larger nucleus and a small amount of mass is turned into energy
describe the process of nuclear fission use the information above
nuclear fission is when the nucleus splits into smaller lighter nuclei, the atom has absorbed a neutron and turned into an unstable isotope of the atom, the atom goes through nuclear fission where it splits into daughter nuclei. During nuclear fission it emits neutrons which is absorbed by another nuclei which causes a chain reaction it also emits energy during this fission
explain how the distance at which an electron orbits the nucleus may be changed
electrons absorb energy in the form of electromagnetic radiation
this causes it to move further away from the nucleus
this makes it move to another energy level.
What is the energy released from nuclear fuels inside a nuclear reactor used for?
to generate electricity
Suggest one reason why scientists continue to try to develop a practical nuclear fusion reactor
will give another source of energy
what substances are used as a fuels in some nuclear reactors.
uranium 235 and Plutonium-239
Explain how the energy released by the chain reaction is affected by moving the control rods.
lowering the control rods increases the number of neutrons absorbed so energy released decreases
Energy is released from nuclear fuels by the process of nuclear fission.
This energy is used to generate electricity.
Describe how this energy is used to generate electricity.
(energy) used to heat water and
produce (high pressure) steam
the steam drives a turbine (which turns a generator)
lowering the control rods…..
reduce the amount of energy released as it increases the amount of neutrons that are absorbed meaning there are fewer neutrons causing chain reactions to slow down
where does nuclear fusion happen naturally
the sun
Tritium is radioactive.
After 36 years, only 10 g of tritium remains from an original sample of 80 g.
Calculate the half-life of tritium.
80–40–20–10
36/3=12 years
