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