AQA Combined Physics 6.4 Flashcards
Revision for Paper 1
What does a short half-life mean?
The activity falls quickly due to rapid decay
What is half-life?
The time taken for the number of nuclei of a radioactive isotope to halve
Why is radioactive contamination so dangerous?
Radioactive particles could get inside the body
What is the hazard of radioactive contamination?
The hazard is due to the decay of the contaminating atoms
How can net decline be calculated?
1) Find the activity after each half-life
2) Divide the final activity by the inital
3) Multiply by 100 to make a percentage
How can the process of radioactivity be described?
Random
What would be the nuclear equation for the decay of Uranium-238
238 U - 234 Th + 4 He
92 90 2
How many protons does an atom of the same element have?
The same number
How can electron arrangements change?
- Absorption of electromagnetic radiation (higher energy level)
- Emission of electromagnetic radiation (lower energy level)
Describe the basic structure of an atom
A positively charged nucleus orbited by negatively charged electrons
How did Bohr adapt the nuclear model as suggested by Rutherford?
Bohr suggested electron orbit the nucleus at specific distances (energy levels)
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
Before the discovery of the electron, what were atoms thought to be (as suggested by Dalton)?
Tiny spheres that could not be divided
Describe alpha 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)
- Are absorbed by a piece of paper
- They are strongly ionising
What can a Geiger-Muller tube record?
The count-rate (number of radiation decays reaching the device per second)
What is ‘activity’ in terms of nuclear radiation?
The rate at which a source of unstable nuclei decays
20 years after the nucleus became scientifically accepted, what did James Chadwick identify?
Neutrons
What can nuclear radiation emission change in a nucleus?
The mass or the charge
What happens to the radioactivity of a source over time?
It decreases
How can an alpha particle be represented?
4
He
2
How is nuclear ‘activity’ measured?
In becquerels (Bq) where 1 Bq is 1 decay per second
What happens to Rn^219^ when it experiences alpha decay?
219 215 4
radon —– polonium + He
86 84 2
*Mass and charge both decreased
How can a beta particle be represented?
0
e
-1
What can nuclear equations represent?
Radioactive decay
Describe gamma radiation (structure, penetration, absorption and ionising strength)
- Waves of electromagnetic radiation
- Penetrate far into materials
- Absorbed by thick sheets of lead or metres of concrete
- Weakly ionising
As well as alpha, beta and gamma radiation what else can radioactive substances release?
Radioactive substances can release neutrons (as they rebalance their atomic and mass numbers)
Some atomic nuclei are unstable - what can the nucleus emit (and in doing so become more stable)?
Radiation - a random process of radioactivity decay or the unstable nuclei
What is radioactive contamination?
The unwanted presence of materials containing radioactive atoms on other materials
What happens to the mass or charge of a nucleus when it experiences gamma emission?
The mass and charge remain the same
What happens to C^14^ when it experiences beta decay?
14 14 0
carbon —- nitrogen + e
6 7 -1
*Mass remains but charge increased
Describe beta radiation (structure, penetration, absorption and ionising strength)
- A fast moving electron (virtually no mass)
- Penetrate a few metres in air
- Are absorbed by a 5mm sheet of aluminium
- Moderatley ionising
Approximately how big is the radius of an atom?
Very small - a radius of about 1x10^-10^m
What does a long half-life mean?
The activity falls slowly due to slow decay?
Inside the body what radioactivity source is most dangerous?
Alpha
What is the overall electrical charge of an atom?
No overall charge - electron and proton numbers are equal
What is the atomic number?
The number of protons in an atom
How much smaller is the radius of a nucleus compared with the radius of an atom?
1/10,000th the radius of an atom (but contains most of the mass)
How are electron arranged around the nucleus of an atom?
Electrons are arranged at different distances from the nucleus
What happens to an atom if it loses one or more outer electron(s)
It becomes a positive ion
What is an isotope?
Atoms of the same element with different numbers of neutrons
What types of ionising nuclear radiation are there?
1) Alpha
2) Beta
3) Gamma
What is irradiation?
Exposing an object to nuclear radiation (the object itself does not become radioactive)
Outside of the body what radioactive sources are most dangerous?
Beta and Gamma
What can the positive charge of a nucleus be subdivided into?
Protons
What is the mass number?
The number of protons and neutrons in an atom
What precautions should be taken around hazardous radioactive materials?
- Wearing gloves / using tongs
- Protective suits
- Breathing apparatus
- Limiting exposure time
