P4 - Atomic Structure And Radiation Flashcards
Define radioactive decay
Define activity
Activity is the rate at which a source of unstable nuclei decays
What is activity measured in?
Activity is measured in becquerel (Bq)
Define count-rate
Count-rate is the number of decays recorded each second by a detector such as a Geiger-Muller tube
What types of nuclear radiation may be emitted?
An alpha particle
A beta particle
A gamma ray
A neutron
What is an alpha particle composed of?
Two neutrons and two protons; same as a helium nucleus
What does a beta particle consist of?
A high speed electron ejected from the nucleus as a neutron turns into a proton
An unstable nucleus becomes more stable by…
Emitting an alpha or beta particle, or a gamma ray
What is a gamma ray composed of?
Electromagnetic radiation from the nucleus
Students should be able to apply their knowledge to the uses of radiation and evaluate the best sources for given situations
Explain why the emission of a gamma ray is different to an alpha and beta particle
Gamma ray is uncharged and has no mass
So its emission does not change the number of protons or neutrons in a nucleus
So the mass and the charge of the nucleus are unchanged
Compare the changes in the nucleus and particles emitted in alpha and beta decay
In alpha decay, the nucleus loses 2 protons and 2 neutrons, whereas in beta decay, a neutron in the nucleus changes into a proton
In alpha decay, 2 protons and 2 neutrons are emitted as an alpha particle, whereas in beta decay, an electron is created in the nucleus and instantly emitted
Alpha decay causes ____ the mass and charge of the nucleus to ____
Both
Decrease
Beta decay does not cause the mass of the nucleus to ___ but does cause the charge of the nucleus to ___
Change
Increase
Describe, in quantitative terms, what happens when an unstable nucleus emits an alpha and beta particle
Alpha: atomic number decreases by 2 and mass number decreases by 4
Beta: atomic number increases by 1 and mass number is unchanged (because a neutron changes into a proton)
Describe a method for to determine background radiation and specific radiation emitted by a radioactive source
Measure the count rate without the radioactive source present. This is the background count rate
Measure the count rate with the source in place
Subtract both of these measurements to get the count rate from the source alone
Describe a method to test the range that each type of radiation travels in air
Move the Geiger tube away from the source in a sealed container
When the tube is far enough away from the source so that it’s no longer detecting any radiation, the count rate from the source will fall to 0
Describe a method to test the absorption of each type of radiation
Place different materials between a Geiger tube and a radioactive source in a sealed container
Add more layers of material until the count rate from the source is 0. This is when the radiation from the source has been stopped by the absorber material
Compare the penetrating power, range in air and ionising power of each radiation source
Alpha particles has a range of 5cm, beta particles have a range of 1m and gamma rays have unlimited range in air because they spread out without being absorbed
Alpha particles are absorbed by a thin sheet of paper, beta by an aluminium or lead sheet and gamma by thick lead sheet or concrete
Alpha particles have the greatest ionising power and gamma rays have the weakest
Define radioactive contamination
Contamination is the unwanted presence of materials containing radioactive atoms on other materials . The hazard is due to the decay of the contaminating atoms and this depends on the type of radiation emitted (higher ionisation emissions are more hazardous)
Define irradiation (compare with radioactive contamination)
Irradiation is the process of exposing an object to nuclear, ionising radiation such as x-rays or gamma rays. The irritated object does not become radioactive
Compare the hazards associated with contamination and irritation
Describe the process of ionisation
The radiation from a radioactive substance can knock electrons out of atoms. The atoms become charged because they lose electrons.
Suggest suitable precautions that should be taken to protect against any hazard that the radioactive source used in the process of irradiation may present
Keeping as far away as possible from the source of radiation by using special handling tools with long handles
Spending little time in high risk areas
Shielding themselves by staying behind thick concrete barriers or using thick lead plates
Why is peer review important?
It is important that the findings of studies into the effects of radiation on humans are published and shared with other scientists so that they can be checked by peer review
Why is ionisation damaging?
What is the half life of a radioactive isotope?
Time it takes for the number of nuclei of the isotope to halve
OR
Time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level
Students should be able to explain the concept of half life and how it is related to the random nature of radioactive decay
What is the formula to calculate the net decline, expressed as a ratio, in a radioactive emission after a given number of half lives?
The count rate after n half-lives = initial count rate / 2^n
A Geiger counter clicks even without a radioactive source near it. Suggest why this is
Background radiation
Define background radiation
The constant low-level ionising radiation present in the environment.
The level and radiation dose may be affected by occupation and location
Where does background radiation come from?
Natural sources such as rocks and cosmic rays in space due to radon gas
Man-made sources such as the fallout from nuclear weapons testing and nuclear accidents
What is radiation dose measured in?
Sieverts (Sv)
1 sievert = ?
1 Sv = 1000 mSv
Isotopes with the shortest half-lives have the most _______ _______, so they emit a lot of radiation in a ____ time
Unstable nuclei
Short
What does the effect of radiation on living cells depend on?
Type and amount of radiation received (dose)
Whether the source is inside or outside the body
How long the cells are exposed to the radiation
Smaller doses pose less risk, but the risk is never 0 due to background radiation
As the activity of a radioactive source _____, the rate it gives out radiation decreases. This means hazards decrease with time according to the half-lives of their isotopes
Decreases
Compare the use of alpha radiation inside and outside of the body
Inside: dangerous as affects all surrounding tissue. High ionisation can damage cells and cause mutations in DNA. They also can stay in the body for a long time, irradiating cells and increasing cancer development
Outside: some danger as they are absorbed by skin and this can cause localised radiation burns and damage retinal cells. However, they have low penetrating power. Still, they can be inhaled and the effects are described above.
Why is gamma and beta radiation not commonly used inside and outside of the body?
Very dangerous in both cases because:
- High penetration power and range, so they can penetrate tissues and organs, however with less ionising intensity compared to alpha radiation
What are nuclear radiations used for in medicine?
Exploration of internal organs
Control or destruction of unwanted tissue
How are radioactive tracers used in medicine?
Why is radioactive iodine used to test if a patient’s kidney is blocked?
Traces the flow of a substance through the organ. It contains a radioactive isotope that emits gamma radiation as it can be detected outside the system
Half life of 8 days, so it lasts enough for the test to be done. It can be detected outside of the body and it decays into a stable product
How are gamma cameras used in medicine?
Why is a gamma emitter used only?
Used to take images of internal body organs. Before an image is taken, a patient is injected with a solution that contains a gamma-emitting radioactive isotope. The solution is then absorbed by the organ and nearby gamma cameras detects the radiation emitted
It must have a half life long enough to give a useful image, but short enough to decay into a stable product after the image is taken
How is gamma radiation in a narrow beam used?
Used to destroy cancerous tumours. Gamma is used because it can penetrate deeper into the body
How are radioactive implants used in medicine?
Destroy cancer cells in some tumours. Permanent implants use isotopes with half lives long enough to irradiate the tumour over a given time, but short enough so that most of the unstable nuclei will decay soon afterwards
