Atomic structure Flashcards
what is the radius of an atom?
1 x 10^-10 metres
when does the energy level of an electron change?`
when the atom emits or absorbs electromagnetic radiation
what is the radius of a nucleus
1/1000 the radius of an atom
what happens when atoms absorb electromagnetic radiation
electrons to a higher energy level
what happens when atoms emit electromagnetic radiation
electrons drop to a lower energy level
What is radioactive decay?
when isotopes are unstable and decay into other elements and give out radiation as they try to become more stable
what does the type of radiation depend on?
why the nucleus is unstable and is spontaneous
what are 4 types of nucleur radiation?
alpa beta gamma neutron
What is ionising radiation?
radiation that creates positive ions. *the ionising power of radiation source is how easily it can do this
What is activity?
the rate at which a source of unstable nuclei decays.
what is activity measured in?
becquerel (Bq)
What is the count-rate?
the number of decays recorded each second by a detector (eg Geiger-Muller tube).
What do alpha particles consist of?
two neutrons and two protons the same as a helium nucleus
What is alpha radiation?
when an alpha particle is emitted from the nucleus
What are the features of alpha radiation?
- they don’t penetrate very far into materials and are stopped quickly
- they can only travel a few cms in air and are absorbed by a sheet of paper
- because of their size they are strong ionising
What is a beta particle?
a high-speed electron ejected from the nucleus as a neutron turns into a proton
What are features of beta radiation?
- they are moderately ionising
- they penetrate moderately far into materials before colliding and have a range in air of a few metres.
- they are absorbed by a sheet of aluminium
what is a gamma ray?
electromagnetic radiation from the nucleus
What are features of gamma radiation?
- they penetrate far into material without being stopped and will travel a long distance through air
- they are weakly ionising because they pass through rather than collide with atoms
* eventually they hit something and do damage
- they can be absorbed bu thick sheets of lead or metres of concrete
What happens during beta decay?
a neutron in the nucleus turns into a proton and releases a fast-moving electron
because the nucleus has lost a neutron and gained a proton the mass doesnt change
Gamma rays don’t change the charge or mass of the nucleus.
What do they do instead?
They get rid of excess energy from a nucleus
Radioactive decay is spontaneous, however, with a _______________ it is possible to predict how many decay in a certain time period
large enough number of nuclei
What is half-life?
the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.
What can the half-life be used for?
to make predictions about radioactive sources, even though their decays are random
- can also be used to find the rate at which a source decays (activity)
The radioactivity of a source decreases over ______
time
What happens each time a radioactive nucleus decays?
the activity as a whole will decrease
What does it suggest if an isotope has a short half-life?
- the activity falls quickly
- the nuclei are very unstable
- emit radiation very quickly s exposure can be hazardous
- they quickly became safe
- don’t remain radioactive for long
long half-life means:
- the activity falls more slowly
- they are more stable and remain radioactive for a long time
- emit radiation slowly so exposure is less hazardous
What is radioactive contamination?
the unwanted presence of materials containing radioactive atoms on other materials.
Why is radioactive contamination harmful?
because when the contaminating atoms decay, they release radiation which could cause you harm
What precautions are taken against the hazards of radioactive contamination?
- Gloves and tongs should be used when handling sources to avoid particles getting stuck to your skin or under your nails
Protective suits can be worn to stop you breathing in the contamination
What is irradiation?
The process of exposing an object to nuclear radiation. The irradiated object does not become radioactive.
How can you reduce of effects of irradiation?
- keep radioactive sources in lead-lined boxes,
- standing behind barriers
- being in a different room
- not handling sources with bare arms
- using sources of the lowest activity possible for the shortest amount of time possible
What are the hazards associated with irradiation?
- Outside the body, beta and gamma sources are the most dangerous. This is because the beta and gamma can penetrate the body and get to delicate organs
- Alpha is less dangerous because it has the least penetration and therefore can’t penetrate the skin and is easily blocked by a small gap
- Alpha wouldn’t be dangerous unless entered into, but an area with gamma can irradiate people near by
What are the hazards associated with contamination?
- Alpha is the most dangerous inside the body because they are the most ionising and they do all their damage in a very localised area
- Beta sources are less damaging inside the body as radiation is absorbed over a wider area and some passes out of the body altogether
- Gamma sources are the least dangerous because they just pass straight out- the lowest ionising power
What are the uses of nuclear radiation? (3)
- medical tracers
- looking for damages or blockages in the intestine
- treating tumours
Why would a gamma source make the best tracer?
- they can penetrate the body and be detected on the outside
- they are the least ionising
What is nuclear fission?
the splitting of a large and unstable nucleus
In nuclear fission, what must the unstable nucleus do first?
It must absorb a neutron before it will spilt
What happens during nuclear fission
1) nucleus splits into two smaller nuclei
2) emits 2 or 3 neutrons plus gamma rays
All products of fission have kinetic energy
How do neutrons from nuclear fission create chain reactions?
the neutrons that are emitted fro Nuclear fission can be absorbed by another nucleus which will cause more fission to occur
What is the deal with nuclear reactors and chain reactions
in a nuclear reactor, a controlled chain reaction is used to release constant and steady energy
What are explosions caused by a nuclear weapon caused by?
uncontrolled chain reaction
What is nuclear fusion?
the joining of two light nuclei, by colliding at high speed, to form a heavier nucleus.
In this process, some of the mass may be converted into the energy of radiation.
some of this energy may be emitted as radiation
Nuclear fusion requires very high temperatures and pressures to:
overcome electrostatic repulsion
bring the positive nuclei close enough together for fusion to take place
