RADIOACTIVITY AND PARTICLES Flashcards
what is the nucleus?
- an atom made up of protons and neutrons
- the number of protons determines what element the nucleus is
what are isotopes?
- contain the same number of protons, but a different number of neutrons
- same atomic number, different mass number
what is the number of protons in the nucleus known as?
- atomic number or proton number
what is the number of protons plus neutrons known as?
- mass or nucleon number
what is the mass of the nucleus?
relative atomic mass
what are unstable nuclei?
- emit particles, or energy, in order to become stable again
- these unstable nuclei are called radioactive nuclei
what is the unit for radioactive activity?
becquerel (Bq)
one becquerel is one decay per second
three types of radioactive decay:
- alpha
- beta
- gamma
what are alpha particles?
made of two protons and two neutrons bound together
what speed are alpha particles emitted at?
10% the speed of light
what charge do alpha particles have?
+2
are alpha particles highly or lowly ionising?
highly ionising
what are alpha particles stopped by?
a few centimetres of air or a sheet of paper
what are beta particles?
an electron emitted when a neutron in the nucleus is turned into a proton
what speed are beta particles emitted at?
50% the speed of light
what charge do beta particles have?
-1
are beta particles weakly or highly ionising?
weakly ionising
what are beta particles stopped by?
a few millimetres of aluminium
what is a gamma ray?
high energy electromagnetic wave
what speed to gamma rays travel at?
the speed of light
are gamma rays highly or weakly ionising?
weakly ionising
what are gamma rays stopped by?
a few centimetres of lead
background sources of radioactivity:
- radon gas
- medical exposure
- rock
- cosmic rays
what happens to the atomic and mass number when you emit an Alpha particle?
atomic number lowers by two
mass number lowers by four
what happens in beta decay?
a neutron turns into a proton and emits an electron
what happens to the atomic and mass number when beta decay occurs?
atomic number increases by one
mass number does not change
what happens to the atomic and mass number when you emit a gamma ray?
has no mass
no effect
what is radioactive decay?
a random process
what is the half-life?
the time taken for one half of the nuclei to decay
what is ionisation?
the formation of an ion
how to find half-life:
- measure at least three half from your graph and calculate the average
dangers of alpha, beta and gamma:
- alpha sources are only dangerous if they get into the body
- gamma and beta sources can cause harm from outside the body
what happens when ionisation occurs in the DNA?
- strand can become damaged
- damage to DNA causes mutations when cells divide and reproduce
- mutations in DNA can lead to cancer
how to store nuclear waste:
burying it
what is nuclear fission?
- released fission neutrons trigger further fissions
- energy from fission-energy is released primarily as the kinetic energy of fission fragments
what are control rods?
in order to maintain a constant rate of reaction, control rods are used to absorb excess neutrons
control rod material?
boron and cobalt
what are moderators?
when the fast neutrons emitted by the neutron process are travelling too fast to cause further fissions, they must be slowed to ‘thermal’ speeds by a moderator
moderator materials:
graphite
light water
heavy water
what is shielding?
reactors are surrounded by thick sheilding (usually concrete or steel) which prevents workers from being exposed to radiation
what can be detectors of ionising radiation?
photographic film or a Geiger-Muller detector
what does the fission of U-235 produce?
- two radioactive daughter nuclei and a small number of neutrons
similarities between fission and fusion?
mass of the products is less than the mass of the reactants
this missing mass is converted into energy- E= mc^2
differences between fission and fusion:
- in fission, a heavier nucleus is split into two lighter, radioactive parts called fission fragments
- in fusion, two lighter nuclei are joined together to create a heavier nucleus
what is nuclear fusion?
when two lighter nuclei are fused together, the heavier nucleus that us created has lower mass than the two initial nuclei combined
what does fusion require?
very high temperatures and pressures, because the positively charged nuclei repel each other
what is the energy source for stars?
fusion
uses of radioactivity in medical contexts:
- lead lined syringes
- finding tumours
- gamma knife
