Separate Physics - 6.4 Flashcards
What is the size of an atom?
Very small – a radius of about 1x10-10 m
Describe the basic structure of an atom
A positively charged nucleus (protons and neutrons) orbited by negatively charged electrons
What is the radius of the nucleus
1/10’000th the radius of an atom (but contains most of the mass)
Describe electrons within energy levels
Electrons are arranged at different distances (energy levels) from the nucleus
How can electron arrangements change?
- Absorption of electromagnetic radiation (higher energy level)
- Emission of electromagnetic radiation (lower energy level)
What is the overall electrical charge of an atom?
No overall charge – electron and proton numbers are equal
How many protons do an atom of the same element have?
The same number
What is the atomic number?
The number of protons in an atom
What is the mass number?
The number of protons and neutrons in an atom
Draw the modern model of an atom
What is an isotope?
Atoms of the same element with different numbers of neutrons
What happens to an atom if it loses one or more outer electron(s)?
It becomes a positive ion
Before the discovery of the electron, what were atoms thought to be (as suggested by Dalton)?
Tiny spheres that could not be divided
What was the Plum Pudding model?
The atom was suggested to be a ball of positive charge with negative electrons embedded in it
What did Rutherford’s scattering experiment show?
The mass of the atom was concentrated in the centre (nucleus) and it was charged
How did Bohr adapt the nuclear model as suggested by Rutherford?
Bohr suggested electron orbit the nucleus at specific distances (energy levels)
What can the positive charge of a nucleus be subdivided into?
Protons
20 years after the nucleus became scientifically accepted, what did James Chadwick identify?
Neutrons (explaining the imbalance between atomic number and atomic mass)
Some atomic nuclei are unstable – what can the nucleus emit (and in doing so become more stable)?
Radiation – a random process of radioactive decay of the unstable nuclei
What is ‘activity’ in terms of nuclear radiation?
The rate at which a source of unstable nuclei decays
How is nuclear ‘activity’ measured?
In becquerels (Bq) where 1 Bq is 1 decay per second
What can a Geiger-Muller tube record?
The count-rate (the number of radiation decays reaching the device per second)
What types of ionising nuclear radiation are there?
- Alpha
- Beta
- Gama
Describe alpha (α) radiation (structure, penetration, absorption and ionising strength)
- 2 neutrons and 2 protons (like a helium nucleus)
- They don’t penetrate very far (a few cm in air) and are absorbed by a piece of paper
- They are strongly ionising
Describe beta (β) radiation
(structure, penetration, absorption and ionising strength)
- A fast moving electron (virtually no mass)
- Penetrate a few metres in air and are absorbed by a 5mm sheet of aluminium
- Moderately ionising
Describe gamma (γ) radiation
(structure, penetration, absorption and ionising strength)
- Waves of electromagnetic radiation
- Penetrate far into materials and are absorbed by thick sheets of lead or metres of concrete
- Weakly ionising
As well as alpha, beta and gamma radiation what else can radiative substances release?
Radioactive substances can release neutrons (as they rebalance their atomic and mass numbers)
What can nuclear equations represent?
Radioactive decay
How can an alpha particle be represented?
How can a beta particle be represented?
What can nuclear radiation emission change in a nucleus?
The mass or the charge
What happens to Rn219 when it experiences alpha decay?
*Mass and charge both decreased
What happens to C14 when it experiences beta decay?
*Mass remains but charge increased
What would be the nuclear equation for the decay of
Uranium-238?
What happens to the mass or charge of a nucleus when it experiences gamma emission?
The mass and charge remain the same
How can the process of radioactivity be described?
Random
What happens to the radioactivity of a source over time?
It decreases
What is half-life?
The time taken for the number of nuclei of a radioactive isotope to halve (or the count rate to halve)
What is the half-life of the following sample?
2 days
What does a short half-life mean?
The activity falls quickly due to rapid decay?
What does a long half-life mean?
The activity falls slowly due to slow decay?
Higher Q. How can net decline be calculated?
- Find the activity after each half-life
- Divide the final activity by the initial
- Multiply by 100 to make a percentage
What is radioactive contamination?
The unwanted presence of materials containing radioactive atoms on other materials
What is the hazard of radioactive contamination?
The hazard is due to the decay of the contaminating atoms
What is irradiation?
Exposing an object to nuclear radiation (the object itself does not become radioactive)
Why is radioactive contamination so dangerous?
Radioactive particles could get inside the body
Outside of the body what radioactive sources are most dangerous?
Beta and Gamma
Inside the body what radioactive source is most dangerous?
Alpha
What precautions should be taken around hazardous radioactive materials?
- Wearing gloves / using tongs
- Protective suits
- Breathing apparatus
- Limiting exposure time
Separate Q. What two sources of background ration are there?
Natural sources and man-made sources
Separate Q. List examples of natural background radiation
- Food
- Rocks
- Cosmic rays from space
Separate Q. List examples of man-made background radiation
- Fallout from nuclear weapons
- Nuclear accidents
Separate Q. What can affect the level of background radiation?
Occupation / location (e.g. pilots experience higher levels than office workers)
Separate Q. What is a radiation dose measured in?
Sieverts (Sv)
Separate Q. How many millisieverts are in one sievert?
1000
Separate Q. What risks are there when using radiation?
Radiation can enter living cells and ionise atoms leading to tissue damage
Separate Q. What risks are involved with lower doses of radiation?
Minor damage to cells can lead to mutations (and cancers)
Separate Q. What risks are involved with high doses of radiation?
Higher doses kill cells completely causing radiation sickness
Separate Q. What are medical tracers?
Gamma isotopes are injected / swallowed and detected which can show problems (e.g. iodine-123)
Separate Q. What is radiotherapy
High doses of ionising radiation can kill cancerous cells (directing gamma rays to specific points)
Separate Q. What is nuclear fission?
The splitting of a large unstable nucleus (such as uranium or plutonium)
Separate Q. How can the likelihood of ‘spontaneous fission’ be described?
Rare
Separate Q. For fission to occur, what must the unstable nucleus absorb?
A neutron
Separate Q. What happens to a nucleus undergoing fission?
It splits into two smaller nuclei (roughly the same size) and emits two or three neutrons, gamma rays and energy
Separate Q. What do all fission products have?
Kinetic energy
Separate Q. What might the neutrons of a fission reaction cause?
A chain reaction
Separate Q. How are controlled chain reactions utilised?
Nuclear reactors
Separate Q. How are uncontrolled chain reactions utilised?
Nuclear weapons
Separate Q. What is nuclear fusion?
The joining of two light nuclei (forming a heavier nucleus)
Separate Q. What can happen to some of the mass of two light nuclei during nuclear fusion?
It can be converted into the energy of radiation
