P4 Atomic Structure

when was plum pudding model made and by who

1897, JJ Thompson

description of plum pudding model

positive ball of charge with a lot of negative electrons stuck in it.

who did the alpha scattering model

ernest rutherford

in the alpha scattering model, the particles are _______ in a ______

suspended in a vacuum

the alpha scattering experiment is done inside a

scintillation screen

why was gold foil used for the alpha scattering experiment?

it was the only metal which could roll out thin enough without cracking

in the alpha scattering experiment, most particles passed straight through the foil. what does this show?

shows that most of the atom is empty space

in the alpha scattering experiment, small number of particles were deflected by large angles as they passed through foil. what does this show?

shows there’s a concentration of positive charge in atom - like charges repel, positive alpha repelled by positive charge in foil

in the alpha scattering experiment, a very small number of alpha particles bounced straight back. what does this show?

the ‘small amount’ shows that positive charge and mass are concentrated in very small volume of atom.

was discovery of protons and neutrons done by rutherford?

no

was discovery of electrons done by rutherford?

no

was discovery of nucleus done by rutherford?

yes

who and when discovered energy levels

niels bohr, 1913

what happens to electrons when atoms absorb energy

electron at a particular level are pushed up to higher levels (bigger distance from nucleus). in time, they jump back down a lower level releasing light of definite frequencies

who and when proved existence of neutron

james chadwick, 1932

how was neutron discovered

chadwick repeated rutherford’s experiment but with beryllium and a paraffin block instead of gold foil

radius of an atom

about 1×10^-10 metres

atomic mass

total number of protons and neutrons

atomic number

total number of protons

modern periodic table is arranged by…

increasing atomic number

isotope

atom with the same number of protons but a different number of neutrons

is it possible to say which part of a nucleus will decay next and why?

no because it is a random process, but it’s possible to predict how many will decay in a certain time period

half-life

turn it takes for half of unstable nucleus to decay / for the activity to halve.

a nuclear equation describes

an atom changing element due to emitting alpha/beta particles.

irradiation

exposing objects to beams of radiation, which could damage living cells

how can irradiation be used

sterilising equipment, preserve food, killing cancerous tumours

why is sterilising surgical instruments using irradiation beneficial?

destroys bacteria without high temperatures, so equipment is not melted

why is preserving food using irradiation beneficial?

destroys bacteria on food using cobalt-60 without changing food in any significant way or making it radioactive.

how can tumour be destroyed using irradiation

beams (called gamma knife) aimed at tumour from many directions to maximise dose on tumour but minimise dose on surrounding soft tissue.

when using irradiation in medicine, what must be considered?

• nature of decay (alpha/beta/gamma)

• half-life (long enough to be useful but not cause unnecessary damage

• toxicity

irradiation

exposing objects to beams of radiation

contamination

object is exposed to a source of radiation outside the object

how do medical tracers work

radioactive source injected to make soft tissues show up through medical imaging processes. changes in amounts of gamma emitter from different parts would indicate how well isotopes are flowing or if there is a blockage

contamination can be used for

medical tracers, checking for leaks

how can you check for leaks using contamination

gamma emitting source used. where there is leak, contaminated water seeps into ground, causing a build up of gamma emission in area. build up found using geiger muller tube. this makes it easier to find where to dig to fix leak

disadvantages of contamination

• isotopes may not go where they’re wanted

• small amounts of radioisotope may still be left behind

• can damage healthy cells

what is the difference between irradiation and contamination

• contaminated object is radioactive as long as source is on/in it. irradiated isn’t radioactive

• irradiation stops as soon as source is removed, contamination can be difficult to remove completely

effects of radiation on eyes

causes cataracts

effects of radiation on thyroid

radioactive iodine can build up and cause cancer, particularly during growth

effects of radiation on lungs

inhaling radioisotopes can damage DNA

effects of radiation on stomach

radioactive isotopes can sit in stomach and irradiate for a long time

effects of radiation on reproductive organs

high doses can cause sterility or mutations

effects of radiation on skin

radiation can burn skin or cause cancer

effects of radiation on bone marrow

can lead to leukaemia or other blood diseases

how to protect when using radioactive source (7 ways)

• keep sources in a lead lined box when not in use

• wear protective clothing to prevent contamination

• avoid contact with bare skin

• wear face masks to avoid inhaling materials

• limit exposure time

• handle materials using tongs for a safe distance

• monitor exposure using detector badges

background radiation definition

low level of daily radiation which occurs naturally

what unit is used to measure radioactivity

Becquerel (Bq), measure of activity of nucleus

a source that emits one particle per second…

has the activity of 1 Bq.

beta causes less damage than alpha because…

it is less strongly ionising

alpha has less ____ than beta, meaning…

energy, meaning it will travel less far

what unit is used to measure radiation dose

the sievert (Sv)

definition of sievert

amount of damage caused by absorption of 1 joule of energy in each kg of body mass.

what are the processes of nuclear power

nuclear fission and nuclear fusion

nuclear fission process

nucleus splits apart to form 2 daughter nuclei in addition to some individual neutrons. when neutrons collide with other unstable nuclei, they could also undergo fission, starting a chain reaction.

how is the nucleus split in nuclear fission

bonds that hold nucleus are broken and thermal energy is released

nuclear reactors control fission by…

using rods of silver/indium/cadmium/etc to absorb some of stray neutrons so we get a useful reaction rather than a dangerous one.

during nuclear fission, what is released in addition to the daughter nuclei?

a high speed neutron which carries most of the energy form the reaction

in a nuclear reactor, before high speed neutrons collide with other nuclei, …

they need to be slowed down so energy can be passed onto other components in nuclear reactor. this is used to heat water/drive turbines which turn generator etc.

nuclear fusion process

combining 2 small nuclei to make a heavy one, producing huge amounts of energy.

why is nuclear fusion difficult and why is it expensive

both nuclei are positive (like charges) so they repel each other, so they must be moving extremely fast to collide. for this, high temperatures need to be used for high energy in nuclei, so it is very expensive

what must be done on earth to replicate nuclear fusion as in the core of sun

temperature must be 10x hotter than in the core of sun to make up for lack of pressure on earth which would otherwise be present in the core of the sun

why must magnetic fields be used when scientists do fusion reactions

temperature must be 10x hotter than in the core of sun to make up for lack of pressure on earth which would otherwise be present in the core of the sun

why is fusion not used as an energy source in today’s world

cost of reaction > profit, so until tech improves, it is not a viable power source

why must magnetic fields be used when scientists do fusion reactions

temperatures are so high that reaction can vaporise contained walls, so magnetic fields are used to keep reaction contained

why is fusion not used as an energy source in today’s world

cost of reaction > profit, so until tech improves, it is not a viable power source

what does uncontrolled fission lead to

basis of atomic bomb/explosion