Topic 6 - radioactivity Flashcards
What is the radius of an atom?
1x10^-10 metres
What are the stree subatomic constituents of an atom?
Proton
Neutron
Electron
Where is most of the mass of an atom concentrated?
In the nucleus
What proportion of the total radius of an atom is the radius of the nucleus?
1/10,000
Where are protons found?
In the nucleus
Where are electrons found?
In discrete energy levels (shells) around the nucleus
Where are neutrons found?
In the nucleus
What charge does the nucleus of an atom have? Why?
A positive charge
It contains protons and neutrons
Protons are positive
Neutrons have no charge
Give two ways that an atom’s electron arrangement can be changed
Absorbing electromagnetic radiation
Emitting electromagnetic radiation
Explain how an atom’s electron arrangement changes when it absorbs EM radiation
The electrons move to higher energy levels (away from the nucleus)
Explain how an atom’s electron arrangement changes when it emits EM radiation
Electrons move to a lower energy level (towards the nucleus)
How does the ratio of electrons to protons in an atom result in the atom having no overall charge?
The number of protons is equal to the number of electrons
Protons are positive and electrons are negative so it evens out
What do all forms of the same element have in common?
The number of protons
What is the name given to the number of protons in an atom?
Atomic number
What is an atom’s mass number?
The total number of protons and neutrons in an atom
What is an isotope of an atom?
An atom of an element that has a different number of neutrons, but the same number of protons
What property differs between isotopes of an atom?
The mass of the atom
How do atoms turn into positive ions?
The lose one or more of their outer electrons
Electrons are negatively charged, so the resultant charge of the atom is positive
What are the relative masses of a proton, neutron and electron?
Proton = 1 Neutron = 1 Electron = 1/1850
What is the relative charge of a proton?
+1
What is the relative charge of an electron?
-1
State four types of nuclear radiation
Alpha particles
Beta particles
Gamma rays
Neutrons
What is background radiation?
Radiation that is always present
Give four sources of background radiation
Rocks
Cosmic rays
Nuclear accidents
Nuclear weapon testing
How do you measure and detect background radiation?
Photographic film
Geiger-Müller counter
How is photographic film used to measure radiation?
It turns dark when it absorbs radiation
How are Geiger muller tubes used to measure radiation?
When it absorbs radiation it produces a pulse, which a machine uses to count the amount of radiation. The frequency of the pulse depends of how much radiation is present. A high frequency would mean the tube is absorbing a large amount of radiation
What constitutes an alpha particle?
Two protons and two neutrons
Same as a helium nucleus
What is the range of an alpha particle through air?
A few centimetres
What will block beta radiation?
A thin sheet of aluminium
Several metres of air
What will block gamma radiation?
Several centimetres of lead
A few metres of concrete
Which type of radiation is most ionising?
Alpha radiation
Which type of radiation is least ion ionising?
Gamma radiation
How does gamma emission affect mass/charge of an atom?
Both mass and charge remain unchanged
Describe the plum-pudding model of the atom
A sphere of positive charge, with the negatively charged electrons distributed evenly throughout it
Prior to the discovery of the electron what was believed about the atom?
That is was indivisible
Which experiment led to the plum-pudding model being discarded?
Rutherford’s alpha scattering experiment
What is the name given to the currently accepted model of the atom?
The Bohr model
Describe Rutherford’s experiment
Alpha particles were fired at a thin sheet of gold foil
Most particles went straight through
Some particles were deflected by small angles
A few particles were deflected by large angles
What are the conclusions of rutherfors’s experiment?
Most of an atom is empty space
The nucleus has a positive charge
Most of the mass is concentrated in the nucleus
What happens in the process of beta plus decay?
A proton turns into a neutron and a positron
What is the process called when a neutron changes into a proton and an electron?
Beta minus decay
When alpha decay occurs, what happens to the atomic number and the mass number of the atom?
The atomic number decreases by 2
The mass number decreases by 4pa new element is made since the atomic number has changed
What effect does beta minus decay have on the mass number and atomic number of an atom?
The mass number stays the same as the total number of neutrons and protons hasn’t changed
The atomic number increases since there is one more proton
Define the activity of an unstable nucleus
Activity is the rate at chich a source of unstable nuclei decays
What is the unit of radioactive activity?
Becquerel (Bq)
What is count rate?
The number of radioactive decays per second for a radioactive source
Give an example of a detector that may be used to measure count rate
Geiger muller tube
Give example uses of radioactivity
Household fire alarms Irradiating food Sterilisation of equipment Tracing and gauging thicknesses of materials Diagnosis and treatment of cancer
How do smoke alarms work?
A radioactive substance is in the alarm which emits alpha radiation
The emitted alpha particle ionised the air in the detector and causes a current to flow between the plates
When smoke interferes with the radiation the air is no longer ionised so no current can flow.
This reduction in current flow triggers the alarm
State two uses of nuclear radiation in the field of medicine
Examining of internal organs
Radiotherapy in the treatment of cancer
What is the role of beta radiation in tracers?
The tracer is inserted in your body, and targets a specific part of the body
The radioactive substance in the tracer releases beta radiation which can be detected by external machines
How is beta radiation used to determine thickness?
A beta source is placed above the material and a detector is placed below it
If there is an increase in radiation detected by the detector, too much radiation is passing through the material and so it is too thin
If a decrease in radiation is detected then the material blocks too much radiation so it too thick
Why is ionising radiation dangerous?
It can cause cell mutations
It can damage tissue and kill cells
What is a consequence of cell mutation?
Cancer
What precautions should people tale when using ionising radiation?
Avoid handling the source directly
Wear radiation protective clothing
Keep the radiation in lead containers to reduce the amount of radiation that can escape
Keep exposure time to a minimum
What precautions are takenTo reduce harm for doctors and patients using ionising radiation?
Only a small does is given
It has a short half life
They wear protective clothing
What is radioactive contamination?
The presence of unwanted radioactive nuclei on other materials
What is irradiation?
The process of exposing a material to nuclear radiation
The material does not become radioactive
How is a radioactive tracer used in medicine?
It placed inside the body
It releases gamma radiation which is detected by a detector which moves around the body
Can then be used to produce a picture of the patient’s body
How does a PET scanner work?
It uses a tracer
The scanner selects the gamma rays which are released by the tracer
Multiple images are taken and this Is used to form a 3C image of the patient’s body
Isotopes are used I. PET scanners. What is important about where they are produced and why?
They must be produced near the hospital because they have a short half life so must be used soon after production
What are the advantages of nuclear power for generating electricity?
Doesn’t produce carbon dioxide
Fuel is readily available
Less nuclear fuel used to produce the same amount of energy
Does not contribute to global warming
What are the disadvantages of using nuclear power to generate electricity?
Unpopular
Security risks
Expensive to commission and decommission the stations
Radioactive waste can be hard to dispose of
Risk of nuclear accidents
Hat is nuclear fission?
The splitting of large, unstable nuclei to form smaller, more stable nuclei
What usually needs to happen to induce fission?
The unstable nuclei must absorb a neutron
What is emitted in a fission reaction?
Gamma rays
Energy
2 or three neutrons
2 smaller nuclei
Name a common fissile nuclei
Uranium - 235
What are the three main components of the core of a nuclear reactor?
Fuel rods
Control rods
Moderator
What takes place during a chain reaction in a nuclear reactor?
An unstable nucleus absorbs a neutron
The nucleus undergoes fission and releases 2 or 3 further neutrons
These induce more fission, which results in a chain reaction
What is the consequence of an uncontrolled chain reaction?
The rate of fission events becomes to high and results in the production of too much energy
This can lead to a nuclear explosion
How is the chain reaction in a fission reactor kept under control?
Control rods are positioned in between the fuel rods
The rate of fission is controlled by moving these rods up and down
The lower the rods are inserted, the slower the rate of fission
What is the role of the moderator in a nuclear reactor?
To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by simile nuclei and cause fission
How is electricity produced in a nuclear power station?
The reactions release thermal energy which is used to boil water and produce steam which turns a turbine, starting the generator
