7 Radioactivity and Particles Flashcards
what is a becquerel
the amount of times something decays per second
1 Bq = 1 decay per second
what is a nucleon
a particle in the nucleus of a atom
proton and neutrons aka the mass number
what does the atomic number refer to
the number of protons an atom has
what does the mass number refer to
the weight of a atom
the number of protons and neutrons
what is a isotope
a element with the same number of protons (and electrons) but a different number of neutrons
how are alpha, beta and gamma particles emitted
from a unstable nucleus in a random process
what are alpha, beta and gamma particles
highly ionising radiations
what is a alpha radiation particle
a helium nucleus -> 2 protons + 2 neutrons
what is a beta particle
an fast moving electron
what is a gamma radiation
a gamma ray which is a type of electromagnet wave
what is the nature of a alpha particle
highly ionising
low penetration -> stopped by paper or a few cm of air
2+
what is the nature of a beta particle
medium ionising
medium penetration -> stopped by a few mm of aluminum + a few meters of air
1-
what is the nature of a gamma ray
low ionising
high penetration -> stopped by a few mm of lead
practical: investigate the penetration powers of different types of radiation using radioactive souces
Connect the Geiger-Müller tube to the counter and, without any sources present, measure background radiation over a one minute period
Repeat this three times, and take an average
Now place a radioactive source a fixed distance of 3 cm away from the tube and take another reading over a one minute interval
Now take a set of absorbers: some paper, several different thicknesses of aluminium (increasing in 0.5mm intervals) and different thickness of lead
One at a time, place these absorbers between the source and the tube and take another reading over a one minute interval
Repeat the above experiment for other radioactive sources
analysis of results
if the count over that interval falls to background levels (allow for a little random variation), then the radiation has all been absorbed
Note that some sources will emit more than one type of radiation
If the radiation is stopped by paper, the source will be emitting alpha
If the radiation is stopped by a few mm of aluminium (about 5 or 6) then the source is emitting beta
If some radiation is still able to penetrate a few mm of lead (5 or 6) then the source is emitting gamma
what happens to the mass number of an atom if it decays by emitting one alpha particle
mass number decreases by 4
atomic number decreases by 2
what happens to the mass number of an atom if it decays by emitting one beta particle
mass number stays the same (a neutron turns into proton)
atomic number increases by one
what happens to the mass number of an atom if it decays by emitting a gamma ray
mass number stays the same
atomic number stays the same
what happens to the mass number of an atom if it decays by emitting one neutron
mass number decreases by 1
atomic number stays the same
what can detect ionising radiation
geiger-muller detector
photographic film
what are the backround causes of radiation
radon gas - 50% - natural
rocks and building materials - 15% - natural
medical (xrays…) - 13% - man
food - 11% - natural
cosmic rays - 10% - natural
does radioactivity decrease over time
yes
what is radioactivity measured in
becquerel
what does half life mean
The time taken for half of nuclei of a radioactive source to decay
is the half life of every element the same
no
uses of radioactivity in industry
sterilizing food
determining the age of ancient artefacts
checking the thickness of materials
smoke alarms
uses of radioactivity in medicine
sterilising medical equipment
Diagnosis and Treatment of Cancer
what is the difference between contamination and irradiation
Contamination is when the radioactive substance itself gets on or in you, and that does make you radioactive
irradiation is:
The process of exposing a material to ionising radiation
Irradiating a substance does not make it radioactive
what are the dangers of ionising radiations
can cause mutations in living organisms - ratiation enters nucleus of cell and destroys DNA and when it reforms it may mutate
can cause damage to cells and tissue
the problens arising from the disposal of radioactive waste and how these risks can be reduced (bury the radioactive material however some of them have long half lives
what can nucleur reactions (fusion, fission, radioactive decay) be a source of
energy
how can uranium 235 be split
by fission
a neutron is fired at the U235 nucleus which makes it unstable
the nucleus splits (fission)
energy is released as kinetic energy of the fission products
what is uranium 235 split into
2 smaller radioactive daughter nuclei (not always identical)
a few neutrons
energy
the combined mass of the 2 daughter nuclei equal the parents
how can a chain reaction be set up with U235
Only one extra neutron is required to induce a uranium-235 nucleus to split by fission
so one neutron is fired at the U235 nucleus which then splits into two daughter nuclei which decay and produce more neutrons
During the fission, it produces two or three neutrons which move away at high speed
Each of these new neutrons hits a different U235 nuclues which starts another fission reaction, which again creates further excess neutrons
what is a chain reaction
a sequence of reactions where a reactive product or by-product causes additional reactions to take place
what is a control rod
absorb excess neutrons which increase or decrease the rate of fission
control rods can be moved in and out of the reacter
what is a moderator
slows down high speed neutrons
which increases the rate of reaction and making it more efficient
what is the purpose of shielding
The purpose of shielding is to absorb hazardous radiation
The daughter nuclei formed during fission, and the neutrons emitted, are radioactive
The reactor is surrounded by a steel and concrete wall that can be nearly 2 metres thick
This absorbs the emissions from the reactions
It ensures that the environment around the reactor is safe
what is the difference between fission and fusion
fission splits a larger nucleus into 2 smaller ones and releasing neutrons
can happen at low temperatures and pressures
fusion is 2 smaller nuclei combining into one larger one
cannot happen at low temperatures and pressures
very difficult to make a practical fusion station
what is fusion
2 smaller nuclei joined to form a larger one
this larger one is not as big as the total mass of the 2 smaller nuclei as the missing mass is given off as energy
what produces energy for stars
fusion
what conditions are needed for nuclear fusion
high temperatures
high pressures
high kinetic energy
these are needed to overcome the electrostatic repulsion of the 2 nuclei
