PHY-101: Ultimate Atom-to-Energy Physics
Compendium
State the relative charges of the particles that make up atoms - Each protons has an electrical
charge of +1
Each neutron has zero electrical charge
Each electron has an electrical charge of -1
State the relative masses of the particles that make up atoms - Each proton has a mass of 1
Each neutron has a mass of 1
Each electron has a mass of 0.0005
How big is an atom? - 10⁻¹⁰ m
How big is the nucleus of an atom - About 10,000 times smaller than an atom, i.e. 10⁻¹⁴
m
What about an atom determines what element it is? - The number of protons, also called the
*atomic number*. E.g. if an atom has 26 protons, it must be Iron (Fe)
Describe what is meant by an isotope - An isotope is an atom that has a different number of
neutrons to what the atom usually has
Explain why a material is radioactive - An isotope will be unstable if it has too many or too few
neutrons. In order to become stable, the isotope emits radiation
State the definition of activity, and the unit it is measured in - The activity of a radioactive
material is the number of isotopes that decay per second. It is measured in Bq.
State what happens to activity over time - Activity decreases over time
Describe what is meant by half-life - One half-life is the time it takes for the activity of a
radioactive material to halve.
After one half-life, half of the isotopes will have decayed
State the three types of ionising radiation and describe what they are made of - Alpha: two
neutrons and two protons
Beta: an electron
,Gamma: a high energy electromagnetic wave
Recall the nuclear representation for alpha, beta, and gamma radiation -
State what occurs in the process of beta emission - Beta decay occurs when there are too many
neutrons in the nucleus. A neutron turns into a proton and electron! The proton stays in the
nucleus, and the electron is emitted as radiation.
What is the electrical charge of alpha, beta, and gamma radiation - Alpha has an electrical
charge of +2
Beta has an electrical charge of -1
Gamma has zero electrical charge
State the range in air of alpha, beta, and gamma radiation - Alpha: a few centimeters
Beta: a few meters
Gamma: many kilometers
State the ionisation strength and therefore the penetration strength of the three types of
ionising radiation - Alpha: strongly ionising, stopped by paper
Beta: moderately ionising: stopped by aluminium foil
Gamma: weakly ionising: stopped by thick lead or concrete
State what it means to say that alpha, beta, and gamma are *ionising* radiation - As the
radiation passes through a material, it knocks electrons out of their atoms, thus creating
ions.
State three sources of background radiation - Radon gas (the most common), rocks and soil,
cosmic rays, human activity (nuclear power stations, nuclear medicine), food
Background radiation is not exactly the same in all parts of the UK/ the world. Explain why. -
There are variations in what the rocks underground are made of. E.g. granite has more uranium
in it than other types of rock. Some rocks end up releasing more radon gas than
others
Describe a use of alpha radiation - Smoke detectors. Alpha particles ionise the air, creating ions
and free electrons, which then make an electrical current. If smoke enters the detector, it blocks
the current. The drop in current sounds an alarm.
, Describe how radiation can be used to measure the thickness of metal in a factory - Fire
radiation at material sheet. If lots/few get through, material is too thin/thick.
Alpha would all be absorbed, gamma would nearly all get through, so *beta* is used because
the absorbed amount would *depend* on thickness
Describe how radiation can be used for medical imaging - Scanners detect the beta or gamma
radiation given off by a substance (tracer) injected.
By analysing the areas where the tracer does and doesn't build up, it's possible to work out how
well certain body functions are working and identify any abnormalities.
Describe how radiation can treat cancer - Gamma radiation can destroy cancerous cells by
ionising their DNA. So that healthy tissue is not also damaged (too much), the beams of gamma
radiation are focused from all different directions so that the radiation is only concentrated
where it is needed
Describe a non-medical use for gamma radiation - Gamma radiation is used for sterilisation.
Gamma waves are high enough energy that they can damage DNA of bacteria and kill
them
State what contamination is - Contamination is when radioactive material (e.g. uranium) gets on
or in you
State what irradiation is - Irradiation is the process of something being hit by ionising radiation
(alpha, beta, or gamma)
Why is irradiation a hazard? - Irradiation can be dangerous because alpha, beta, or gamma can
ionise atoms in your body. If DNA is ionised, it could be damaged. It could then mis-repair itself
and cause cancer
What is contamination a hazard? - The danger from contamination is that you will be continually
irradiated until contact with the radioactive material has been removed
Before the electron was discovered what did scientists think atoms were like? - Indivisible hard
spheres
What did the Plum Pudding Model say that an atom was like? - An atom is a positive ball of
charge with negative electrons embedded in it like plums in a pudding
Compendium
State the relative charges of the particles that make up atoms - Each protons has an electrical
charge of +1
Each neutron has zero electrical charge
Each electron has an electrical charge of -1
State the relative masses of the particles that make up atoms - Each proton has a mass of 1
Each neutron has a mass of 1
Each electron has a mass of 0.0005
How big is an atom? - 10⁻¹⁰ m
How big is the nucleus of an atom - About 10,000 times smaller than an atom, i.e. 10⁻¹⁴
m
What about an atom determines what element it is? - The number of protons, also called the
*atomic number*. E.g. if an atom has 26 protons, it must be Iron (Fe)
Describe what is meant by an isotope - An isotope is an atom that has a different number of
neutrons to what the atom usually has
Explain why a material is radioactive - An isotope will be unstable if it has too many or too few
neutrons. In order to become stable, the isotope emits radiation
State the definition of activity, and the unit it is measured in - The activity of a radioactive
material is the number of isotopes that decay per second. It is measured in Bq.
State what happens to activity over time - Activity decreases over time
Describe what is meant by half-life - One half-life is the time it takes for the activity of a
radioactive material to halve.
After one half-life, half of the isotopes will have decayed
State the three types of ionising radiation and describe what they are made of - Alpha: two
neutrons and two protons
Beta: an electron
,Gamma: a high energy electromagnetic wave
Recall the nuclear representation for alpha, beta, and gamma radiation -
State what occurs in the process of beta emission - Beta decay occurs when there are too many
neutrons in the nucleus. A neutron turns into a proton and electron! The proton stays in the
nucleus, and the electron is emitted as radiation.
What is the electrical charge of alpha, beta, and gamma radiation - Alpha has an electrical
charge of +2
Beta has an electrical charge of -1
Gamma has zero electrical charge
State the range in air of alpha, beta, and gamma radiation - Alpha: a few centimeters
Beta: a few meters
Gamma: many kilometers
State the ionisation strength and therefore the penetration strength of the three types of
ionising radiation - Alpha: strongly ionising, stopped by paper
Beta: moderately ionising: stopped by aluminium foil
Gamma: weakly ionising: stopped by thick lead or concrete
State what it means to say that alpha, beta, and gamma are *ionising* radiation - As the
radiation passes through a material, it knocks electrons out of their atoms, thus creating
ions.
State three sources of background radiation - Radon gas (the most common), rocks and soil,
cosmic rays, human activity (nuclear power stations, nuclear medicine), food
Background radiation is not exactly the same in all parts of the UK/ the world. Explain why. -
There are variations in what the rocks underground are made of. E.g. granite has more uranium
in it than other types of rock. Some rocks end up releasing more radon gas than
others
Describe a use of alpha radiation - Smoke detectors. Alpha particles ionise the air, creating ions
and free electrons, which then make an electrical current. If smoke enters the detector, it blocks
the current. The drop in current sounds an alarm.
, Describe how radiation can be used to measure the thickness of metal in a factory - Fire
radiation at material sheet. If lots/few get through, material is too thin/thick.
Alpha would all be absorbed, gamma would nearly all get through, so *beta* is used because
the absorbed amount would *depend* on thickness
Describe how radiation can be used for medical imaging - Scanners detect the beta or gamma
radiation given off by a substance (tracer) injected.
By analysing the areas where the tracer does and doesn't build up, it's possible to work out how
well certain body functions are working and identify any abnormalities.
Describe how radiation can treat cancer - Gamma radiation can destroy cancerous cells by
ionising their DNA. So that healthy tissue is not also damaged (too much), the beams of gamma
radiation are focused from all different directions so that the radiation is only concentrated
where it is needed
Describe a non-medical use for gamma radiation - Gamma radiation is used for sterilisation.
Gamma waves are high enough energy that they can damage DNA of bacteria and kill
them
State what contamination is - Contamination is when radioactive material (e.g. uranium) gets on
or in you
State what irradiation is - Irradiation is the process of something being hit by ionising radiation
(alpha, beta, or gamma)
Why is irradiation a hazard? - Irradiation can be dangerous because alpha, beta, or gamma can
ionise atoms in your body. If DNA is ionised, it could be damaged. It could then mis-repair itself
and cause cancer
What is contamination a hazard? - The danger from contamination is that you will be continually
irradiated until contact with the radioactive material has been removed
Before the electron was discovered what did scientists think atoms were like? - Indivisible hard
spheres
What did the Plum Pudding Model say that an atom was like? - An atom is a positive ball of
charge with negative electrons embedded in it like plums in a pudding
