Radioactivity - topic 5 Flashcards
what does an atom consist of
protons, neutrons and electrons
charge of a proton
+1
charge of an electron
-1
charge of a neutron
0
mass of proton and neutron
1
mass of an electron
1/2000
what are isotopes
atoms of the same element with the same number of protons but different number of neutrons
mass number
protons + neutrons (top number)
atomic number
number of protons
what is the plum pudding model
large positive proton with negative electrons inside
which experiment disproved the plum pudding model
Rutherford’s gold foil experiment
what is the gold foil experiment
when alpha particles were shot through thin gold foil
findings of the gold foil experiment
majority of alpha particles went through because most of the atom was empty space, some were deflected because centre of atom was positively charged and some alpha particles bounced directly back as the centre had a concentrated mass
the further away the electron from the nucleus …..
the more easily the electron can change its energy level
why do electrons further away from nucleus easily change electron levels
the further away the electron is from the nucleus, the weaker the force of attraction between nucleus and electron
ionisation
when atom with neutral charge becomes positively charged as it loses an electron
what is an ion
atom that loses or gains an electron
radiation
emission of energy in the form of waves or particles through space
unstable atom
contains surplus of energy and is called radioactive
what is used in external radiotherapy
gamma
dangers of radioactivity
tissue damage, skin burns, DNA mutation and sometimes cancer
contamination
where ionising radiation gets in contact with skin or enters their body
safety procedures with radioactive sources
shielding
minimise exposure time
maximise distance
wear protective clothing
use of dosimeters
use materials with short half lives
advantages of nuclear power
alternative to fossil fuels
doesn’t release carbon dioxide
doesn’t cause acid rain
disadvantages of nuclear power
high overall costs
risk of radioactive materials leaking
danger of polluting land and rivers
nuclear fission
high energy neutron collides with isotope. Nuclei absorbs high energy neutron and splits it into 2 smaller daughter nuclei. Daughter nuclei are radioactive and 2 or more neutrons are released which go on to collide with more isotopes causing an uncontrolled chain reaction.
where nuclear fission takes place
inside a nuclear reactor
what is steam released during nuclear fission used for
to power turbines which turn a generator to produce electricity
graphite moderator
slow down neutrons so uranium can absorb them so chain reaction can keep going
control rods
control rate of reaction by absorbing neutrons. Control rods can be lowered into the reactor to slow reaction down.
nuclear fusion
smaller nuclei combine under high pressure and high temperature to form a larger nuclei.
example of nuclear fusion
in the sun
what is needed for nuclear fusion
high temp and pressure
for the nuclei to fuse …
they must overcome the strong electrostatic forces of repulsion
why is high temp needed for nuclear fusion
high temperature means high energy, which is needed to overcome forces of repulsion between nuclei
what is the radius of an atom
1 x 10 ^-10 m
why are atoms neutral
atoms have the same number of protons and electrons
what is the relative mass of a positron
1/2000
what is the relative electric charge of a positron
+1
how far away are electrons from the nucleus
in each atom, electrons orbit the nucleus at different set distances from the nucleus
when do electrons change orbit
when there is absorption or emission of EM radiation
how do atoms form positive ions
by losing outer electrons
what happens when electrons release EM radiation
they lose energy and fall to a lower energy level closer to the nucleus
how are alpha, beta minus, positrons, gamma rays and neutron radiation emitted
they are emitted from unstable nuclei in a random process
what is an alpha particle
a helium nucleus
what is a beta particle
an electron emitted from the nucleus
what is a gamma ray
electromagnetic radiation
what is the ionising power of alpha particles
highly ionising
what is the penetration power of alpha particles
low
what is the ionising power of beta minus particles
moderately ionising
what is the penetrating power of beta minus particles
medium
what is the ionising power of gamma ray
weakly ionising
what is the penetrating power of gamma rays
high
what is the effect on the mass number and atomic number of alpha decay
atomic number decreases by 2 and mass number decreases by 4
what is the effect on the mass number and atomic number of beta minus decay
atomic number increases by 1 and mass number in unchanged
what is the effect on the mass number and atomic number of beta plus decay
mass number does not change, and atomic number decreases by 1
what is the effect on the mass number and atomic number of gamma decay
atomic number and mass number remain unchanged
what is the effect on the mass number and atomic number of neutron emission
mass number decreases by 1 and atomic number stays the same
what happens in beta minus decay
a neutron turns into a proton plus an electron
what happens in beta plus decay
a proton becomes a neutron plus a positron
how can you measure and detect radioactivity
with a geiger muller tube or photographic film
how do you use a geiger muller tube
place the object in front of the geiger muller tube and then count the number of ticks from the object and take into consideration the radiation from the background. Then repeat and average
how does photographic film work
the more radiation the film is exposed to, the darker it becomes
why can you not predict radioactive decay
because it is entirely random, so you cannot predict when or which nucelus in a sample will decay next but you can find out the half life
what is half life
the time it taken for the activity of a source to decay by half
what does half life enable you to work out
the activity of a very large number of nuclei to be predicted during the decay process
what is activity measured in
becquerels, Bq
how does the activity of a sample decrease over time
each time a radioactive nucleus decays to become a stable nucleus, the activity will decrease
what is background radiation
low level radiation that is present at all times, all around us, wherever we go
where does background radiation come from
cosmic rays, from space
man made sources
naturally occurring unstable isotopes all around us
what are the dangers of ionising radiation
tissue damage and cell mutations, cancer
what is irradiation
if radiation from a radioactive source reaches an object
what is contamination
if unwanted radioactive atoms get onto and into a material
what are the precautions to reduce the risk of harm from irradiation
keep radioactive sources in lead lined boxes
wearing shielding
stay as far away from the source as possible
monitor exposure
what are the precautions to reduce the risk of harm from contamination
gloves and tongs should be used
wear protective suits
chose sources with appropriate half lives
what is the effect of half life on potential danger of a source
the lower the activity of a radioactive source, the safer it is to be around because the activity of a source with a short half life will have fallen more
what type of radiation is used in fire alarms
alpha radiation
what type of radiation is used in gauging thickness
beta radiation
what type of radiation is used in sterilisation
gamma
what type of radiation is used in tracers
gamma
why are isotopes used in PET scanners made near by
they have short half lives so need to be used as quickly as possible
how can tumours be treated externally
using gamma radiation aimed at the tumour from a source outside the body
how can tumours be treated internally
placing a radioactive material inside the body into or near a tumour
difference in half lives of sources used in external and internal tumour treatment
in external treatment, half life is long and in internal treatment, half life is short
what happens in the fission of uranium-235
a slow moving neutron is fired at a large, unstable U-235 nucleus.
The neutron is absorbed by the nucleus , which makes the atom unstable and causes it to split
When the atoms splits, it forms two identical daughter nuclei which are radioactive
Two or more neutrons are also released and if any of the neutrons are moving slowly enough to be absorbed by another nucleus, the can cause more fission to occur
what do graphite moderators do
control the speed of neutrons and slow down fast moving neutrons
why are graphite moderators important
they allow more fissions and the chain reaction to continue as they make sure the neutrons are moving slow enough to be absorbed
what do control rods do
they absorb excess neutrons to prevent the chain reactions from getting out of control
what is the difference between nuclear fusion and fission
in fusion, two daughter nuclei fuse to create a larger nucleus and in fission it is the opposite
what is nuclear fusion
the creation of larger nuclei resulting in a loss of mass from smaller nuclei accompanied by a release of energy
why does fusion only happen at high temperatures and high pressure
because the positively charged nuclei have to get very close to fuse, so the strong force due to electrostatic repulsion has to be overcome and this takes a lot of energy which comes from high temperatures
how is thermal energy from a chain reaction used in the generation of electricity in a nuclear power station
energy released by chain reaction is transferred to the thermal energy of the moderator
some of this energy is then transferred to the thermal energy store of the coolant
the coolant flows around the boiler and transfers energy to the thermal energy store of cold water passing through the boiler
this causes water to boil, generating steam
this steam causes a turbine connected to a generator and the turning generator produces electricity
what are the advantages of using nuclear power
no acid rain
no carbon dioxide emission
what are the disadvantages of using nuclear power
nuclear waste can leak out and pollute land, river and oceans
high cost of setting up power plant and decommissioning it
nuclear waste cannot be disposed of safely
