radioactivity Flashcards
Describe how the radius of an atom compares to the size of its nucleus?
The radius of a nucleus is about 10,000 times smaller than the radius of the atom
Each atom its electrons orbit the nucleus at what distances from the nucleus
Different set distances
How do electrons change orbit when there is an absorption or emission of electromagnetic radiation?
1) An inner electron can move up to a higher energy level if it absorbs EM radiation with the right amount of energy.
2) When it does move up, it moves to an empty or partially filled shell and is said to be ‘excited’
3) the electron will then quickly fall back to its original energy level, and on doing so will emit (lose) the same amount of energy is absorbed - energy is carried away by EM radiation
A higher energy means what?
A higher frequency of EM radiation
If an atom loses an electron?
It ionises
What happens when an atom is ionised if it loses an electron?
1) if an outer electron absorbs radiation with other energy, it can move so far that it leaves the atom
2) it is now a free electron and the atom is said to have been ionised
3) the atom is now a positive ion - its positive because there are now more protons then electrons
4) an atom can lose more than one electron- the more electrons it loses, the greater it’s positive charge
What is a type of radiation that ionises atoms?
Nuclear radiation
What is radioactive decay?
Other unstable systems isotopes tend to decay into other elements and give out radiation as they try to become more stable
What are types of ionising radiation radioactive substances spit out when they decay?
Alpha
Beta
Gamma
What is alpha radiation
when an alpha particle is emitted from the nucleus
What is an a particle? (Alpha particle)
Two neutrons and two protons
Explain alpha particles (penetration, absorption)
- They don’t penetrate far and stopped quickly
- Travel a few cm in the air and absorbed by a thin sheet of paper
- strongly ionising because of their size
What is the change and mass of beta minus particles?
Mass = none
Charge. = -1
The position is the the anti..
Antiparticle to the electron (exactly same mass as the electron, but a positive (+1) charge
What is a beta minus particle?
A fast moving electron released by the nucleus
Information on beta minus particles (range in air, absorption)
- moderately ionising
- range in air of a few meters
- absorbed by a sheet of aluminium (5mm thick)
What is annihilation?
Positions have a smaller range, because when they hit an electron the two destroy eachother and produce gamma rays
What is annihilation used for
Medical imaging
After a nucleus decays, what process does it go through?
Nuclear arrangement and releases some energy
Information on gamma rays
- penetrate far into materials without being stopped
- travel far in air
- weakly ionising because they pass through rather than collide with atoms
- absorbed by thick sheets of lead or metres of concrete
What is a gamma ray ?
EM waves with a short wavelength
How are nuclear equations written
Atom before decay - atom after decay + radiation emitted
What is a rule of nuclear equations?
Total mass and atomic numbers must be equal on both sides
What is a rule of nuclear equations?
Total mass and atomic numbers must be equal on both sides
What does alpha decay do to the charge and mass of the nucleus?
Mass number decreases by 4 (increases)
Atomic number decreases by 2 (increases)
What does beta minus decay do to the charge of the nucleus?
A neutron changes into a proton and an electron
- mass number doesn’t change
- atomic number increases by 1 (loses 1)
What does positron emission do to the charge of the nucleus?
In beta plus decay, a proton changes into a neutron and a positron
- mass number doesn’t changed
- atomic number decreases by 1
What does neutron emission do to the mass of the nucleus?
A nucleus emits a neutron
- mass number decreases by 1 (increases by 1)
- atomic number stays the same
What do gamma rays don’t change in a nucleus
Charge and mass
What do gamma rays do in terms of energy?
Getting rid of excess energy from an atom - nucleus goes from an excited state to a more stable by emitting a gamma ray
Mass and atomic number stays the same
What is meant by activity in half-life ?
The rate at which a source decays is called its activity
What is activity measured in ?
Becquerels (Bq)
1 Bq is 1 decay per second
What is a Geiger muller tube?
It clicks each time it detects radiation- tube is attached to a counter, which displays the number of clicks per second
The radioactivity of a source ….. overtime
Decreases
What happens when a radioactive nucleus decays?
One more radioactive nucleus disappears. As the unstable nuclei all steadily appear, the acidity as a whole will decrease
What is half life
Average time taken for the number of radioactive nuclei in an isotope to halve
What does a short half life mean
Activity falls quickly, because nuclei are very unstable and rapidly decay. Sources with a shirt half life are dangerous because of high amount of radiation they emit at the start but they quickly become sfae
What does it mean by a long half life?
the activity falls more slowly because most of the nuclei don’t decay for a long time
the source just sits there, releasing small amounts of radiation for a long time.
This can be dangerous because nearby areas are exposed to radiation for years
What is background radiation?
Low level radiation that’s around us all the time
What does background radiation come from?
- naturally occurring unstable isotopes - the the air, foods, building materials
- space. (cosmic rays) - come from the sun and the Earth’s atmosphere protects us from the radiation
- human activity - nuclear waste
What is irradiation
Exposure to radiation
How do we stop sources being irradiated?
Keep sources in lead-lined boxes, standing behind barriers in a different room and using remote controlled arms
What is contamination ?
Radioactive particles getting into objects
How does contamination work?
Contaminating atoms might decay, that release radiation and cause harm
How to avoid contamination?
Gloves and tongs should be used, as well as protective suits
How does radiation damage cells
By ionisation
How does radiation damage cells by ionisation?
Enter living cells and ionise atoms and molecules within.them leading to tissue damage
What source is the most dangerous to the inside of the body
Alpha sources
How do alpha sources damage the body ?
Strongly ionising
What radiation is the most dangerous outside the body and why?
Beta and gamma
Can penetrate the body and get to delicate organs
What does low doses of radiation cause?
Cancer but minor damage
What does high doses of radiation cause ?
Kills cells completely and cause radiation sickness (vomiting, tiredness and hair loss)
Give three sources of background radiation
Cosmic rays, rocks, fallout from nuclear explosions
