P6.1 - Radioactive Emissions Flashcards
What are isotopes?
Isotopes are atoms of the same element (same number of protons) containing a different number of neutrons.
Some isotopes of an element may be…?
Some isotopes of an element may be stable whilst others are unstable and decay, emitting alpha, beta or gamma radiation.
E.g. - Carbon-12 is completely stable whereas Carbon-14 is radioactive - Those extra 2 neutrons make the entire nucleus unstable. An unstable nucleus has too much energy and must get rid of it.
What does an unstable nucleus have to do?
An unstable nucleus has too much energy and must get rid of it.
What is nuclear radiation?
Nuclear radiation is just emitted energy by a nucleus of an unstable atom.
What are the properties of alpha radiation?
- Particles.
- A helium nucleus.
- Stopped by a few sheets of
paper/skin or cm of air. - Heavily ionising.
- Slow.
What are the properties of beta radiation?
- Particles.
- Fast moving electron.
- Stopped by a few mm of
aluminium. - Moderately ionising.
- Fast.
What are the properties of gamma radiation?
- Wave.
- High energy EM wave.
- MOST is stopped by a few cm
of lead or m of concrete. - Lightly ionising.
- Speed of light
What is ionisation?
Ionisation is the process of turning a neutral atom / particle into an ion.
Why is nuclear radiation bad?
- The three types of nuclear
radiation are dangerous
because they are ionising
radiation. - Ions are extremely reactive.
- The system/ions are in a higher energy state and need to lose energy - Incomplete outer shell so they react with neighbouring particles.
Explain why nuclear radiation is so dangerous to the human body?
- Nuclear radiation is ionising.
- If the ions are created
near/in the body, they will
react with the cells of the
body. - The cells become damaged.
- The damaged cells continue
to replicate as normal cells
do, giving rise to a tumour.
Which type of nuclear radiation is the least and most dangerous outside the body?
- Alpha radiation is the least dangerous because it can't penetrate the skin. - You get skin cancer at worst which you can just cut off.
- Gamma is the most dangerous because it can penetrate the skin - Although there is a lower change of ionisation than alpha radiation, any ions created will damage cells of vital organs.
Which type of nuclear radiation is the least and most dangerous inside the body?
- Alpha radiation is the most
dangerous because it is
heavily ionising. - Gamma radiation is the
least dangerous because it
can penetrate the body and
leave it.
Why does alpha radiation have a much smaller range than gamma radiation?
- You have to transfer energy
to an atom to ionise it.
- Alpha particles transfer more energy to the material they are travelling through than gamma rays because they are highly ionising.
- Therefore alpha radiation has
a much shorter range.
What does a heavier/unstable isotope mean?
Higher likelihood of it emitting all three types of radiation.
What happens when a beam of radiation is passed through an electric field between a positive and negative plate?
Alpha particles - Attracted towards the negatively charged plate because it has a positive charge.
Beta particles - Attracted towards positively charged plate because it has a negative charge - Deflection of beta is much greater owing to its much smaller mass.
Gamma radiation experiences no deflection because it has no charge.
What happens to the nucleus in alpha radiation and what is the equation?
- The number of protons and
neutrons decrease as the
nucleus lose two protons
and two neutrons. - Mass number decreases by
4. - Proton number decreases by
2 - New element.
What happens to the nucleus in beta radiation and what is the equation?
- A neutron decays to a
proton and an electron
which is emitted as a beta
particle. - Proton number increases by 1. - New element.
What happens to the nucleus in gamma radiation and what is the equation?
- Nucleus emits a high
frequency electromagnetic
wave. - No change to mass number
and atomic number.
What happens to the nucleus in neutron emission and what is the equation?
- Nucleus emits the neutron.
- Mass number decreases by 1 - Proton number stays the same. - Same element.
What type of process is radioactive decay?
- Radioactive decay is a
random process. - You cannot predict when a
single unstable nucleus will
decay and emit nuclear
radiation.
What is half life?
- The time taken for half the unstable nuclei in a radioactive substance to decay. - The time taken for the activity to half.
What is the activity?
- The number of nuclei that
decay every second. - The total number of
emissions per second.
- Can be measured by a Geiger counter - Each click is a tiny current produced when the radiation ionises atoms of the gas inside the tube.
- Units = becquerels (Bq).
What is the position of electrons in an atom?
- Electrons in atoms, don’t actually “orbit” around
the nucleus. - Instead, electrons occupy (discrete) energy levels.
Explain the idea of energy levels?
- Different energy levels are at different
distances from the nucleus. - The lowest energy level is closest to the nucleus.
- Different atoms have different values for energy
levels.
What can happen to electrons in low energy levels and how?
- Electrons in low energy levels, can move up to a
higher energy level by gaining energy - the
electrons are excited to higher energy levels. - The electrons in atoms can be excited by
absorbing EM radiation.
What does the EM radiation for the excitation of the electrons have to have?
- Only incident EM radiation of an exact, certain
frequency can excite electrons in a particular
energy levels. - This is a very strange fact that cannot be
explained by considering EM radiation to be a
wave. - Instead, Physicists consider EM radiation to
consist of “particles of light” known as photons.
Explain how an electron excites.
- A single photon is absorbed entirely by a single electron.
- The energy of the photon is proportional by the frequency of the EM radiation.
- If the energy of the photon exactly matches the
difference in energy between the two levels, the
electron will excite to a higher energy level.
Why does an electron have to de-excite?
- Only a certain number of electrons are allowed to
exist at any given energy level. - Thus, electrons that have excited to higher energy
levels, will de-excite and return to their original
energy level.
Explain how an electron that has excited more than one energy level de-excites.
- An excited electron will de-excite and return to
its original energy level and emit radiation. - The electron will de-excite in steps.
- Each time it de-excites, it emits energy in the
form of a photon of a given frequency. - The emitted photons are of lower energy (and
therefore frequency and longer wavelengths) than the original photon
that was absorbed and caused excitation.
What is one way to excite electrons?
One way to excite electrons in the atoms of a gas is to pass electric current through it.
What is an emission spectrum?
An emission spectrum shows a set of frequencies of radiation emitted by an atom when excited electrons move to lower energy levels.
What does the frequency of radiation emitted when electrons de-excite depend on?
The frequency of radiation emitted depends on the difference in energy of the energy levels.
What happens as UV photons excite electrons.
Lower frequency, visible light photons emitted as electrons de-excite.
What is an absorption spectrum?
An absorption spectrum shows a set of frequencies of radiation absorbed by an atom when excited electrons move to higher energy levels.
Give an example of how a star’s absorption spectra looks.
- Light emitted from stars contain all frequencies of
EM radiation. - As light passes through stars, certain frequencies of
photons get absorbed by hydrogen and helium
atoms. - The frequencies that match in energy to the energy
difference between the energy levels appear as
black lines in the star’s spectra.
Describe the difference between an ‘excited’ atom and an ‘ionised’ atom?
- In an excited atom, orbital electrons are in a higher
energy state/level. - In an ionised atom, orbital electrons have left the
energy levels of the atom.
Describe in terms of the electrons what happens when:
A) Photons are absorbed
B) Photons are emitted
A) Electrons excite to a higher energy level.
B) Electrons de-excite to a lower energy level.
Suggest and explain why hydrogen cannot emit X-ray photons.
- The energy of emitted photons is equivalent to the
energy difference between energy levels in an atom. - Hydrogen energy levels must not have a difference
large enough to give rise to high energy X-ray
photons.
Explain why some atoms can absorb ultraviolet radiation, but emit visible light (and so glow in the dark).
- Some atoms absorb UV radiation, as there exists
an energy difference between their energy level,
that exactly matches the energy of the UV
photons. - After absorbing a UV photon, an orbital electron
will excite to a higher energy level. - The excited electron will then de-excite to its
original energy level, in steps, emitting photons of
energy equivalent to the energy different between
the levels. - The energy difference between the levels
matches the energy of visible light photons.
