P7: Radioactivity Flashcards
What are the 3 subatomic constituents of an atom?
Proton
Neutron
Electron
Where is most the mass of an atom concentrated?
In the nucleus
Approximately what proportion of the total radius of an atom is the radius of the nucleus?
1/10,000
Describe the arrangement of protons, neutrons and electrons in an atom?
The proton and neutrons are found in the atom’s nucleus
The electrons are found in discrete energy levels around the nucleus
What type of charge does the nucleus of an atom have? Why?
Positive charge
The nucleus contains protons and neutrons
Protons have a positive charge
Neutrons have no charge
Give 2 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?
Electrons more further away from the nucleus
They move to a higher energy level
Explain how an atom’s electron arrangement changes when it emits EM radiation?
Electrons move closer to the nucleus
They move to a lower energy level
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 and electrons have equal and opposite charges, so charge cancels
What do all forms of the same element have in common?
They all have the same 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 the 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
How do atoms turn into positive ions?
They lose one or more of their outer electrons
Electrons are negatively charged, so the resultant charge of the atom is positive
What may lead to a scientific model being charged or replaced?
The discovery of new experimental evidence which dosen’t agree with the existing theory
How did the plum-pudding model describe the atom?
A ball of positive charge, with negatively charged electros distributed evenly throughout it
Prior to the discovery of the electron, what was believed about the atom?
The atom was believed to be invisible
What 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 nuclear model
State the conclusions of the Alpha-Scattering experiment?
Most of the mass of the atom is concentrated at the centre in the nucleus
The nucleus is positively charged
What reinforces a scientific theory?
When experimental results agree with the hypothesised theoretical calculations and theories
What did James Chadwick’s experiment on the atom prove?
The existence of neutrons
Why do unstable nuclei give out radiation?
Unstabel nuclei undergo decay to become more stable
As they released radiation their stability increases
What is the name of the process in which an unstable nucleus gives out radiation to become more stable?
Radioactive decay
Define the activity of an unstable uncleus?
Activity is the rate of decay of a source of unstable nuclei
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
State 4 types of nuclear radiation?
Alpha particles
Beta particles
Gamma rays
Neutrons
What are the constituents of an alpha particle?
Two protons and two neutrons
It is the same as a helium nucleus
What is the range of an alpha particle through air?
A few centimetres (normally 2-10cm)
What are the constituents of a beta particle?
Fast moving electron
What will stop beta radiation from passing through a point?
A thin sheet of aluminium
Several metres of air
What will stop gamma radiation from passing through a point?
Several centimetres of lead
A few metres of concrete
What type of radiation is most ionising?
Alpha radiation
What type of radiation is least ionising?
Gamma radiation
State any changes to mass or charge that occur due to the emission of a gamma ray?
Both mass and charge remain unchanged
Describe the nature of radioactive decay?
Random
Which nuclei decays and when is determined only by chance
It is impossible to predict which nuclei will decay and when
Describe the half-life of a radioactive isotope?
The time it takes for the number of unstable nuclei in a substance to halve
The time it takes for the count rate from a sample to fall to half its initial level
What is radioactive contamination?
The presence of unwnated radioactive nuclei on other materials
What is irradiation?
The process of exposing a material to nuclear radiation
The material does not become radioactive
Give 4 sources of background radiation?
Rocks
Cosmic rays from space
Nuclear weapon testing
Nuclear accidents
How should background radiation be dealt with in calculations?
The background count should be subtracted from any readings before calculations are attempted
What is the unit used to measure radiation dosage?
Sieverts (Sv)
How many millisieverts equal 1 sievert?
1000 millisieverts = 1 sievert
Why might the radiation that different people experience differ?
Some occupations involve working with radiation
Background radiation differes with location duento things such as the locality of nuclear power stations or radiation related testing
What factor determines how dangerous a particular radioactive isotope is?
The half-life of the isotope
Why are isotopes with long half-lives particularly harmful?
They remain radioactive for much longer periods of time
They must be stored in specific ways to avoid humans and the environment from being exposed to radiation for too long
State 2 uses of nuclear radiation in the field of medicine?
Examining of internal organs
Controlling and destroying unwanted tissue
How is radiation used in sterillisation?
Gamma emitters are used to kill bacteria/parasites on equipment
Explain the process of radiotherapy?
Gamma emitters direct gamma rays at the cancerous cells
The cancerous cells absorb the radiation and are killed
What is nuclear fission?
The splitting of large, unstable nuclei from smaller more stable nuclei
Give an example of a fissionable isotope?
Uranium - 235
What usually needs to happen to induce fission?
The unstable nuclei must absorb a neutron
Sponataneous fission
Alongside the smaller nuclei, what else is emitted in a fission reaction?
Two or three neutrons
Gamma rays
Energy
What form of energy do all fission products have?
Kinetic energy
What takes place during a chain reaction in a nuclae 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 the consequence of an uncontrolled chain reaction?
The rate of fission events becomes too high and results in the production of too much energy
This can lead to a nuclear explosion
What are the three main compounds of the core nuclaer reactor?
Fuel rods
Control rods
Moderator
What is the role of the moderatir in a nuclear reactor?
To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission
How is the chain reaction in a fission kept under control?
Control rods are positioned in between the fuel rods
The rate of fission is controlled by moving thses rods up and down
The lower the rods are inserted, the slower the rate of fission
What term is used to describe nuclei in which fission can be induced through the absorption of slow neutrons?
Fissile nuclei
What is nuclear fusion?
The joining of two light neclei to produce a heavier nuclei and release energy
Name 2 isotopes of hydrogen which are commonly used in nuclear fusion?
Deuterium and Tritium
Which releases more energy, fission or fusion?
Nuclear fusion
