CP6 Flashcards
What are the three types of radiation?
- Alpha
- Beta
- Gamma
What is half-life?
The average time taken for half of the radioactive nuclei in a sample of radioactive material to have decayed.
Who discovered that atoms contained subatomic particles and when?
J.J Thomson discovered this in 1897 by carrying out various experiments.
What is the plum pudding model?
This is a model for atoms that explains the evidence of subatomic particles. The model had pudding with plums scattered throughout it. The pudding represented the positively charged material, with the plums representing negatively charged electrons throughout it.
What was the gold foil experiment?
Rutherford got a piece of gold foil and shined a laser of alpha particles at the gold foil. Rutherford observed that most alpha particles (rays) went straight through the foil however some alpha particles (rays) deflected off into different directions and some even bounced back. From this, Rutherford was able to conclude that an atom had mostly empty space, however the mass of all of the atom was in the center (nucleus) of the atom.
What is the radius of a nucleus?
1 x 10⁻¹⁵
What is the radius of an atom?
1 x 10⁻¹⁰
Where is most of the mass of an atom concentrated?
Most of the mass of an atom is concentrated in its nucleus.
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
0
What is the relative charge of an electron?
-1
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
1/1835
How are the number of protons and number of electrons linked?
The number of protons is equal to the number of electrons.
What does the atomic mass represent in terms of subatomic particles?
The atomic mass represents the number of protons and neutrons added together.
What does the atomic number represent in terms of subatomic particles?
The atomic number represents the number of protons only.
What are isotopes?
Atoms that have the same atomic number, but different atomic mass. This means that they have the same amount of protons as the normal element has however it has a different number of neutrons.
What is the emission spectrum?
A set of wavelengths of light or electromagnetic radiation showing which wavelengths have been given out (emitted) by a substance.
What is the absorption spectrum?
A spectrum of light (or electromagnetic radiation) that includes black lines. These are caused by some wavelengths being absorbed by the materials that the light (or radiation) passes through.
What is ionising radiation?
It is radiation that cause charged particles (ions) to be formed. It can cause tissue damage and DNA mutations.
What are some sources of background radiation?
The main source of background radiation is radon gas. Other sources include: Hospital treatments (such as x-rays), cosmic rays etc.
How is radon gas produced?
Radon gas is produced by rocks that contain small amounts of uranium. Radon diffuses into the air from rocks and soil and can build up in houses, especially where there is poor ventilation.
What does the amount of radon gas depend on?
The amount of radon in the air depends on the type of rock and its uranium content. Rock type and building stone vary around the country and so does the amount of radon.
What are cosmic rays?
Charged particles with a high energy that come from stars.
How can the radioactivity of a source be measured?
By using a Geiger-Müller (GM) tube.
What is a Geiger-Müller (GM) tube and how does it work?
It is a device that can detect ionising radiation and is used to measure the activity of a radioactive source. The GM tube is connected to a counter, and this counter clicks every time radiation is detected. The count rate you get from the GM machine is the amount of clicks per second or minute.
What happens to a substance when its nucleus starts to decay?
When decay occurs, radiation is emitted which causes the nucleus to lose energy and become more stable.
Can you predict when a nucleus starts to decay?
You cannot predict when a nucleus will decay - it is a random process.
What is radioactive decay?
It is when an unstable nucleus changes by giving out ionising radiation to become more stable.
What particles get emitted from an unstable nucleus during radioactive decay?
Alpha particles, Beta particles, Positrons, Gamma rays, Neutrons.
Describe the penetrating properties of alpha particles?
Alpha particles: will travel a few centimeters in the air, they are very ionising, they can be stopped by a sheet of paper.
Describe the penetrating properties of beta particles?
Beta particles: will travel a few metres in the air, they are moderately ionising, they can be stopped by 3mm thick aluminium
Describe the penetrating properties of gamma rays?
Gamma rays: will travel a few kilometers in the air, they are weakly ionising, they need thick lead or several metres of concrete to stop them
What happens when an unstable nucleus changes and emits particles?
When an unstable nucleus changes and emits particles, the atomic number can change. This makes the atom become a different element.
What happens during beta particle decay (β⁻)?
During β⁻ decay, a neutron changes into a proton and an electron. The electron is ejected from the atom. The atomic number is increased by 1 but there is no change to the mass number.
What happens during positron decay (β⁺)?
In β⁺ decay, a proton becomes a neutron and a positron. The atomic number goes down by one but the mass number does not change.
What happens to the mass number and atomic number of an atom when a neutron is ejected?
If a neutron is ejected from a nucleus, the mass number goes down by 1 but the atomic number doesn’t change.
When may nuclei lose energy?
Nuclei may also lose energy as gamma radiation when the subatomic particles in the nucleus are rearranged. This helps to make them more stable.
What is a nuclear equation?
It is an equation representing a change in atomic nucleus due to radioactive decay. The total mass number must be the same on each side and the total charges must be the same (e.g. Radium 226 emits an alpha particle: ²²⁶Ra₈₈ –> ⁴He₂ + ²²²Ra₈₆)
How can you do nuclear equation questions?
DO NUCLEAR EQUATION QUESTIONS
What can a small amount of ionising radiation over long periods of time do?
This can damage the DNA inside a cell, causing a mutation to occur.
How can you handle highly radioactive sources?
The intensity of radiation decreases with distance from the source, so:
1. sources are always handled with tongs. 2. The risk can be reduced by not pointing sources at people
3. The risk can be reduced by storing radioactive material in lead-lining containers
When is a person irradiated from radiation?
Someone is irradiated when they are exposed to alpha, beta or gamma radiation from nearby radioactive materials. Once the person moves away, the irradiation stops.
When is a person contaminated from radiation?
Someone becomes contaminated if they get particles if radioactive materials under their skin or inside their body. They will be exposed to radiation as the unstable isotopes in the material decay and this will continue until all of the material has decayed or until the source of contamination is removed (which is not always possible). Water and soil can also be contaminated, so contamination can also spread into the food chain.
