Separate Physics - P4 Atomic Structure Flashcards
Approximately how big is the radius of an atom?
Very small – a radius of about 1x10-10 m
How much smaller is the radius of a nucleus compared with the radius of an atom?
The radius of the nucleus is approximately 1/10,000th the radius of an atom
What happens when electrons fall to a lower energy level (closer to the nucleus)?
They release electromagnetic radiation
What does contamination mean in terms of radioactivity?
If a substance is contaminated, it’s covered in radioactive material.
What two subatomic particles are in the nucleus of an atom?
Protons and Neutrons
What happens if the electrons in an atom absorb electromagnetic radiation?
They move to a higher energy level (further from the nucleus).
What is the overall electrical charge of an atom?
No overall charge – electron and proton numbers are equal
What does irradiation mean?
Exposing an object to nuclear radiation (the object itself does not become radioactive)
What is the mass number of an atom?
The number of protons and neutrons in an atom
What is an isotope?
Atoms of the same element with different numbers of neutrons.
Before the discovery of the electron, what were atoms thought to be (as suggested by Dalton)?
Tiny spheres that could not be divided
What did Rutherford’s scattering experiment reveal about the atom?
- The mass of the atom was concentrated in the centre (nucleus).
- The nucleus was small.
- The nucleus was positively charged.
What precautions should be taken around hazardous radioactive materials?
- Wearing gloves / using tongs
- Protective suits
- Breathing apparatus
- Limiting exposure time
What happens to an atom if it loses one or more outer electron(s)?
It becomes a positive ion.
What was the Plum Pudding model?
The atom was suggested to be a ball of positive charge with negative electrons embedded in it.
How did Bohr adapt the nuclear model of the atom?
Bohr suggested electrons orbit the nucleus at specific distances (energy levels).
List alpha, beta and gamma radiation from most to least ionising.
Alpha (most ionising)
Beta (moderately ionising)
Gamma (least ionising)
Name the three types of radiation that can be emitted by unstable nuclei.
- Alpha radiation
- Beta radiation
- Gamma radiation
What is nuclear ‘activity’ measured in?
Becquerels (Bq) where 1 Bq is 1 decay per second
List alpha, beta and gamma radiation in terms of their range in air (from shortest to longest).
Alpha (shortest range in air, few cm)
Beta (moderate range in air, few m)
Gamma (longest range in air)
What sub-atomic particle was discovered by James Chadwick?
Neutron
List alpha, beta and gamma radiation from most penetrating to least penetrating.
Gamma (most penetrating)
Beta (moderately penetrating)
Alpha (least penetrating)
Name the equipment used to measure radioactivity.
Geiger-Muller Tube
What is alpha (α) radiation?
A helium nucleus (2 neutrons and 2 protons)
What is beta radiation?
A fast-moving electron
What is gamma radiation?
An electromagnetic wave
As well as alpha, beta and gamma radiation what else can radiative substances release from their nuclei?
neutrons
How is an alpha particle represented in a nuclear equation?
Inside the body what radioactive source is most dangerous?
Alpha
Name the material that stops:
a) Alpha radiation
b) Beta radiation
c) Gamma radiation
a) Paper stops alpha radiation
b) A fem mm of aluminium stops beta radiation
c) Thick sheets of lead or metres of concrete stops gamma radiation
How is a beta particle represented in a nuclear equation?
Complete the nuclear equation for the alpha decay of Radon219.
Complete the nuclear equation for the beta decay of Carbon-14.
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 the radioactivity of a source over time?
It decreases
What is the half-life of the following sample?
2 days
Outside of the body what radioactive sources are most dangerous?
Beta and Gamma
How can the process of radioactivity be described?
Random
What is half-life?
The time taken for the number of nuclei of a radioactive isotope to halve (or the count rate to halve)
Higher Q. How can net decline in radioactivity be calculated?
- Find the activity after each half-life
- Divide the final activity by the initial
- Multiply by 100 to make a percentage
Separate Q. Give two uses of radiation in medicine.
- Exploring internal organs (e.g. medical tracers)
- Control or destruction of unwanted tissue
Separate Q. Give two sources of natural background radiation.
- Rocks
- Cosmic rays from space
Separate Q. Give two things that would affect the amount of background radiation you would experience.
- Occupation (e.g. pilots experience higher levels than office workers)
- Location (some areas will have a higher count of background radiation due to the rock type in that area)
Separate Q. How many millisieverts are in one sievert?
1000
Separate Q. What two things should be considered when choosing a type of radioactive isotope for a medical tracer?
- The half-life of the isotope (needs to be short so it doesn’t stay in the body for a long time).
- The radiation type should be beta or gamma so it can pass out of the body (alpha would not be able to penetrate the skin and so would stay in the body, causing damage)
Separate Q. Give two sources of man-made background radiation
- Fallout from nuclear weapon testing
- Nuclear accidents
Separate Q. What is a radiation dose measured in?
Sieverts (Sv)
Separate Q. Describe how radioactive isotopes are used as medical tracers.
- Gamma or beta emitting radioactive isotopes are injected / swallowed.
- The isotope emits radiation as it goes round the body.
- The radiation is detected outside of the body (e.g. using a G-M Tube) and the path of the radiation through the body is monitored.
Separate Q. How would you complete the diagram to show a chain reaction?
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
Separate Q. What is nuclear fission?
The splitting of a large unstable nucleus (such as uranium or plutonium)
Separate Q. For fission to occur, what must the unstable nucleus absorb?
A slow-moving neutron
Separate Q. What is nuclear fusion?
The joining of two light nuclei to form a heavier nucleus
Separate Q. Describe how radiotherapy is used to kill cancer cells.
- High doses of ionising radiation can kill cancerous cells.
- Beams of gamma rays are directed at specific targets (e.g. tumours). This direct targeting reduces the number of healthy cells that are killed.
- Radiation-emitting implants can also be used. These are implanted next to the tumour.
Separate Q. How do nuclear reactors generate electricity?
- Nuclear fission releases energy (carried by gamma rays and in the kinetic energy stores of the decay products).
- This energy is used to heat water.
- The water turns into steam and the steam turns a turbine, which turns a generator, to produce electricity.
Separate Q. What are the products of nuclear fission?
- Two smaller nuclei (roughly equal in size)
- Two or three neutrons
- Gamma rays
Separate Q. What type of energy do all the products of nuclear fission have?
Kinetic energy
Separate Q. How are chain reactions controlled inside a nuclear reactor?
Control rods are lowered into the nuclear reactor to absorb neutrons.
Separate Q. Why are scientists not currently using nuclear fusion to generate electricity?
- Nuclear fusion requires such high temperature and pressures.
- This makes a nuclear fusion reactor very difficult and expensive to build.
Separate Q. What happens to the neutrons released by nuclear fission?
They are absorbed by other unstable nuclei and start a chain reaction.
Separate Q. How are uncontrolled chain reactions utilised?
Nuclear weapons
