Radioactivity Flashcards
Why are atomic nuclei unstable?
This is because of an imbalance in the forces within the nucleus, as forces exist between the particles in the nucleus
What is an isotope?
an atom that has the same number of protons but a different number of neutrons
Why are isotopes unstable?
because of their large size or because they have too many or too few neutrons
What do unstable nuclei emit to become more stable?
Radiation
What can radiation be in the form of?
a high energy particle or wave
What happens as the radiation moves away from the nucleus?
it takes some energy with it
This reduces the overall energy of the nucleus
This makes the nucleus more stable
What is the process of emitting radiation called?
Radioactive decay
What type of process is radioactive decay?
a random process
Why is radioactive decay a random process?
As it is not possible to know exactly when a particular nucleus will decay
What device is used to detect radiation?
A Geiger-Muller tube
What happens within the Geiger-Muller tube?
ions are created by radiation passing through it
Why is the Geiger-Muller tube connected to a Geiger counter?
The Geiger counter counts the ions created in the Geiger-Muller tube
What is count-rate?
Count-rate is the number of decays recorded each second by a detector
What are objects containing radioactive nuclei called?
Sources of radiation
What is activity?
The rate at which the unstable nuclei from a source of radiation decays
What is the equation for activity?
Activity (Bq) × Time period (s)
What is the equation for count rate?
Number of decays ÷ Time period (s) = … decays per second
What kind of radiation is emitted by an unstable nucleus?
nuclear radiation
Why is an alpha particle the same as a helium nucleus
This is because they consist of two neutrons and two protons
What charge do alpha particles have?
+2
What can alpha particles be affected by?
an electric field as they have a charge of +2
What are beta particles?
they are fast-moving electrons
Where are beta particles produced?
They are produced in nuclei when a neutron changes into a proton and an electron
What do beta particles have a charge of?
-1
What can beta particles be affected by?
an electric field as they have a charge of -1
What are gamma rays?
electromagnetic waves
that have no mass and no charge
How do gamma rays differ from other electromagnetic waves?
they have the highest energy
What do gamma rays not have?
a charge
Why are neutrons neutral?
they have no charge
What are the properties of alpha particles?
Range in air: few cm
Penetration: stopped by paper
Ionisation: high
What are the properties of beta particles?
Range in air: few 10s of cm
Penetration: Stopped by a few mm of Aluminium
Ionisation: medium
What are the properties of gamma rays?
Range in air: infinite
Penetration: reduced by a few mm of Lead
Ionisation: low
What is all nuclear radiation capable of?
ionising atoms that it hits
What happens when an atom is ionised?
the number of electrons it has changes
which gives it a non-zero charge
What are the uses of radiation?
For:
Producing electricity through nuclear fission
Medical procedures including diagnosis and treatment
Testing material
Determining the age of ancient artefacts
Checking the thickness of materials
Smoke detectors
What is nuclear fusion?
fusion of light nuclei to form heavier nuclei
release a lot of energy
happens in stars as it requires high temperatures and pressures
how all elements heavier than hydrogen were made
Why does nuclear fusion produce a lot of energy?
some of the mass of the original nuclei is converted into energy
What is nuclear fission?
When a fired neutron is absorbed by a large nucleus and splits a large unstable nucleus into 2 smaller nuclei and 2 or 3 neutrons
creates a chain reaction
smaller nuclei are called daughter nuclei
used in nuclear reactors
How can nuclear fission be controlled?
using control rods that are inserted into the reactor
and absorb neutrons
What is the energy released from nuclear reactors used for?
to heat water
and turn it into steam
which can turn turbines
to generate electricity in a electricity generator
What are the pros and cons of nuclear energy?
Pros:
uranium and plutonium are cheap (and provide a large amount of energy)
cleaner (doesn’t produce greenhouse gases)
Cons:
power plants are expensive to set up
nuclear waste is expensive to get rid off
chance of disasters
What is irradiation?
the process by which objects are exposed to radiation
What are the types of ionising radiations?
Alpha
Beta
Gamma
X-rays
What are the types of non-ionising radiation?
ultraviolet
microwaves
What is contamination?
When radioactive particles get onto other objects
What is the problem with contamination?
Radioactive particles are likely to decay and irradiate you
What determines how harmful radiation is?
what type of radiation it is
location (inside, outside or on the body)
Dosage (how long you have been exposed, how far away from the source you are, how radioactive the substance is)
When does the emission of a neutron occur?
When an unstable nucleus (has too many neutrons) loses a neutron in order to become stable
Why is ionising radiation more harmful?
It can enter living cells and interact with molecules inside
it can ionise our DNA - causing mutations
which could lead to cells diving uncontrollably - causing cancer
What are the safety measures to protect against radiation?
wear gloves and overalls
hold with tongs
place substance in a lead-lined box
What are the symptoms of radiation sickness?
hair loss
vomiting
tiredness
What are the methods of radiotherapy?
Externally:
gamma rays fired at the tumour (so it receives the highest dose)
Internally:
a radioactive source is either placed inside cancer cells or next to cancer cells
which fires beta radiation
What is radiotherapy used for?
to treat cancer
What are medical tracers used for?
to track the movement of isotopes around the body
(by tracking the radiation they emit)
which can be used to check if organs are working properly
How are medical tracers inserted into the body?
by injecting or swallowing it
What isotopes are used for medical tracers?
isotopes with a short half-life
as they emit radiation for a short period
which stops them from being harmful
What are the benefits and risks of radiation?
Medical tracer:
can identify and diagnose diseases
but requires low doses and a short half-life
Radiotherapy:
can save a life so worth the side-effects
may only prolong a person’s life
1 Bq (Becquerels) =
1 decay per second
What is half life?
The time taken for the number of radioactive nuclei in a sample to halve
which causes the number of decays/activity to also halve (decrease)
Alpha decay equation
e.g.
226 4
Ra —> x + He
88 2
Beta decay equation
e.g.
14 14 0
C —-> N + e
6 7 -1
Gamma equation
… —> …. + y (gamma symbol)
What is the relative atomic mass of an electron?
1/2000 (very small)
What happens when the shells increase?
their energy levels increase
What is ionisation?
when electrons absorb enough energy to leave their atom
which leaves behind a positive ion - more protons than electrons
What is ionisation?
when electrons absorb enough energy to leave their atom
which leaves behind a positive ion - more protons than electrons
What did John Dalton describe atoms as?
solid spheres
different types of spheres make up different elements
What did J.J Thompson describe the atom as?
A plum pudding
the atom is a ball of positive charge that consists of negatively charged electrons
What was Rutherford’s experiment?
Rutherford shot a beam of positively charged particles (alpha particles) at a thin sheet of gold foil
What were the expected results in Rutherford’s experiment?
He expected the particles to pass through the foil because the positive charge of the nucleus was thought to be evenly spread out.
What does the nuclear model describe the atom as?
Nearly all of the mass of the atom is concentrated in the centre of the atom (in the nucleus)
The nucleus is positively charged
Negatively charged electrons orbit the nucleus at a distance
What did Niels Bohr suggest?
Electrons orbit the nucleus in fixed shells at set distances from the nucleus
What prevents the atom from collapsing?
the orbiting of the electrons
What did James Chadwick discover?
the neutron
which have no charge and the same mass as a proton
What happens when atoms absorb electromagnetic radiation?
electrons move to a higher energy level further away from the nucleus
What happens when atoms emit electromagnetic radiation
electrons drop to a lower energy level closer to the nucleus
How does photographic film detect radiation?
a bright spot appears where ionising radiation hits the film
How does a smoke detector work?
A radioactive material fires alpha particles at a smoke detector.
If there is smoke between the radioactive material and the smoke detector, then fewer alpha particles will reach the detector.
This will set off the smoke alarm.
How is radiation used in paper production?
We can fire beta particles through paper in a factory to make sure that the paper being produced is the right thickness.
If the thickness of the paper changes, greater or fewer beta particles will reach the detector. Production can then be stopped.
What is background radiation?
the radiation that we are exposed to all around us everyday
