What happened in 1804
John Dalton agreed with Democritus that matter was made from atoms that could not be broken and each element was made from a different type of atom.
What happened 100 years after 1804
J.J Thompson discovered electrons could be removed from atoms.
Thompson said their were elcectrons tuck in a mass of positive charge and mad the “plum pudding model”
What happened in 1909- Alpha Scattering
Scientists in Rutherfords lab fired a beam of alpha particles to a thin sheet of gold foil - the alpha scattering experiment, from the PP model they expected to pass straight through or only be slightly defected instead most did pass through but some deflected back the reverse direction.
What did they realise in The Alpha Scattering Experiment?
Nearly all the alpha particles passed through most of the atom was empty space.
Positivley charged nucleus surrounded by a cloud of negative electrons.
Most the mass of an atom must be concentrated in the nucleus.
What did Niehls Bohr say?
Electrons orbiting the nucleus do so at a distance called energy levels.
Then James Chadwick developed the idea of the neutron whichh explained the imbalance between the atomic and mass numbers.
Give the charge of a proton neutron and electron
P= +1 N = 0 E = -1
Give the mass of a proton neutron and electron
P= 1 N = 1 E = 0.0005
What happens is electrons gain EM radiation
They move to higher energy levels
If they release EM radiation they move to lower energy levels.
How does an atom become a positive ion
If one or more of the outer electrons leave
What is an isotope
Atoms with the same number of protons but a different number of neutrons
What do unstable isotopes do
decay into other elements and give out radiations as they try to become stable. This is called radioactive decay.
What is ionsing radiation?
knocks of electrons on atoms creating positive ions
What is alpha radiation
an alpha particle is emmited from a nucleus a charge of +2
What is the alpha particles structure
two protons and two neutrons a helium nuclei
How far do alpha particles penetrate
Dont penetrate very far into materials and are stopped quickly
What are alpha particles stopped by?
A few cm of air
absorbed by a sheet of paper
Are alpha particles ionising
yes strongly because of their density.
What is a beta particle
fast moving electron released by the nucleus hae virually no mass and a charge of -1
Are beta ionising
moderatly
How penetrating are beta
moderately far into material before colliding and have a range in air of a few metres
What is beta stopped by
a few metre of air
absorbed by 5mm of aluminum foil
What happens when a beta particle is emmited
a neutron in the nucleus has changed to a proton
What are gamma waves
Electromagnetic radiation released by the nucleus
How far does gamma penetrate
pass through rather than collide with atoms
eventually they hit something and do damge
What is gamma absorbed by
a few thick sheets of lead
metres of concrete
What do nuclear equations show
radioactive decay
In nuclear equations how is an alpha particle written
4 2 he
In a nuclear equation how is alpha decay calculated
+4 +2
How is a beta particle written in a nuclear equation
0 -1 e
Explain gamma rays in nuclear eqautions
gamma rays are a way of given of excess energy from a nucleus so their is no change,
Whta is a halflife
the time taken for the number radiocative nuclei in an isotope to halve
Where do radioactive substances give out radiation
nuclie of their atoms
Is radioactivity random
yes you cant predict exactly which will decay next or when it will decay
What is background radiation?
low level radiation around us at all times
Where does background radiation come from?
naturally occuring unstable isotopes air food building material rocks under our feet space- cosmic rays sun nuclear waste/explosions measured in sv
What is irradiation
exposure to radiation
Does irradiation near something make something radioactive
no
How to keep radioactive substances
lead lined box behind barriers with remote controlled arms
What happens if unwanted radioactive atoms get on an object
it becomes contamintated these contaminating atoms might decay releasing radiation cauing you harm.
How to stop being contaminated
Gloves and tongs when handling sources
protective suits
Which sources are more damaging outside the body and why
Beta and Gamma because beoth can penetrate through th body and ionise or organs
Alpha is less as it can only penetrates through a few cm of air
Which radiation is most damaging inside the body
Alpha as they damage in localised areas Beta is less damaging as its is wider spread and passes through
Gamma is least as it ALL passes through
Risks of radiation
enters living cells and ionises atoms and molecules inside of them which leads to tissue damage
lower doses tend to minor damge and gives a rise to mutant cells which divdde uncontrolably leading to CANCER
Higher doses tend to kill completley causing radiation sickness leading to HAIR LOSS
Explain how a medical tracer is used
radioactive isotopes are injected into people and their progress around the body can be followed using a external detector a computer conerts this to show where th highest reading is.
How is iodine 123 used as a medical tracer
absorbed by the thyroid gland and gives out radiation which can be detected to indicate whether the thyroid gland is taking iodine as it should
Which isotope is used as a medical tracer
gamma as it passes through without being too ionising
How is radiotherapy used to cure cancers
gamma rays are directed at the right dose to kill cancer cells without damaging to many healthy cells Beta emmiters can be put next to the tumour
Benefits of radioactive materials
tracers are used to diagnose conditions and cancer risk is small
Risks of using radiactivity
prolonged exposure can damage cells but then end result is cancer free it outweighed by the benefit
What is nuclear fission?
Splitting a large unstable nucleus
nuclear reaction which releases energy from large and unstable atoms by splitting them into smaller atoms
When will the nucleus split in fission
when it has absorbed a neutron
In fission when an atom splits what is the product
two lighter elements that have some energy in there kinetic stores
2 or 3 neutrons are also released when fission takes place if any neutrons are slow they can be absorbed by another nucleus causing more fission which is called a CHAIN REACTION
what happens to the energy not transferred to the kinetic enrgy stores of the product?
carried away by gamma rays and in th ekinetic energy stores of the free neutrons can be used to heat water turbines and generators
How to change the amount of energy prodiced by fission?
change how quickly the chain reactions are by control rods which are lowered and raised by a nuclear reactor to absorb neutrons slow reaction and control energy used
What is nuclear fusion
two nuclei collide at high speed and fuse to create a larger heavier nucleus ex
hydrogen nuclei can fuse to become a helium nucleus
What releases more enrgy fission or fusion
fusion
is fussion used
no temp and pressure needed is to high that is it is too expensive
What does a heavier nucleus made by fusion show
it doesnt have as much mass as the two sperate nuclei did some of the mass of the lighter nuclei is converted as energy then released as radiation
State how a nuclear power station works
reactor contain fuel rods
nuclear fission occur in the uranium rods
energy released used to heat water in the boiler turinging it to steam
steam turns turbines
turbine turns generator
generator creates electrical energy
Disadvantages of nuclear power stations
long time to build decomsioning is high nuclear explosion hard to secure safley expensive
State why urainum is better than coal
it produces pollutant gases which harm the environement