unit 5 Flashcards
the structure of an atom
a positively charged nucleus with negatively charged electrons around it
how does the scattering of alpha particles by a sheet of thin metal of the atom prove the nuclear model of atom
the majority of them go straight through because the atom is mainly empty space
some are deflected through small angles because positive alpha particles are repelled by positive nucleus which contains most of the mass
a very small number of atoms are deflected straight back because the nucleus is extremely small
how can positive ions be formed
when atoms lose electrons
how can negative ions be formed
when atoms gain electrons
what is an ion
an electrically charged atom formed by the loss or gain of electrons
why do atoms gain or lose electrons
to become more stable
how to know whether an atom is stable
there is the same number of protons and electrons
how to know whether the ion is postive
more protons than electrons
how to know whether the ion is negative
more electrons than protons
what is the proton number
also know as atomic number
the number of protons in an atom
what is the nucleon number
also known as the mass number
the total number of particles in the nucleus of the atom
how can the number of neutrons be found
nucleon number - proton number -
what is the charge of a proton
+1
what is the charge of a neutron
0
what is the charge of an electron
-1
what are isotopoes
they are atoms of the same element that have an equal number of protons but a different number of neutrons
they tend to be more unstable due to the imbalance and are more likely to decay
can elements have more than 1 isotope
yes
what is nuclear fission
the splitting of a large, unstable nucleus into two smaller nuclei
what happens during fission
the nucleus splits into two smaller nuclei as well as two or 3 neutrons
gamma rays are also emitted
the energy stored within the nucleus of atom
what is the energy transfer in fission
energy transferred from nuclear potential to kinetic
why does the mass change during fission
the mass of the products is less than the mass of the original nucleus
this is because the remaining mass has been converted into energy which is released during the fission process
what is nuclear fusion
when two light nuclei join to form a heavier nucleus
what is the problem with trying to replicate nuclear fusion
it requires extremely high temperatures to maintain
where does the energy for nuclear fusion come from
the energy produced comes from a very small amount of the particles mass being converted into energy
what is background radiation
the radiation that exists around us all the time
what are the sources that contribute to background radiation
radon gas(in the air)
rocks and buildings
food and drink
cosmic rays
how can ionising nuclear radiation be measured
using a detector connected to a counter
what is count rate
the count rate is the number of decays per second
measured in count/s or count/min
the happens when the source is further away from the detector
the count rate decreases because the radiation becomes more spread out the further away it is
what is a corrected count rate
count rate - background radiation
describe the emission of radiation from a nucleus
spontaneous and random in direction
when do nuclei emit radiation
when they need to become more stable.
it reduces the overall energy of the nucleus
what is the process of emitting radiation known as
radioactive decay
because radioactive decay is a random process, it means that:
equal probability of any nucleus decaying
rate of decay is unaffected by surrounding conditions
it is only possible to estimate the probability of a nuclei decaying in a given time period
what are the different types of radioactive decay
alpha particles
beta particles
gamma radiation
what does an alpha particle consist of
2 neutrons and 2 protons
same as a helium nucleus
what is the charge of an alpha particle
+2
what are beta particles
they are fast moving electrons
have a charge of -1
what are gamma rays
they are electromagnetic waves and have the highest energy
they have no charge
what is the penetrating power of alpha particles
stopped by paper
what is the penetrating power of beta particles
stopped by a few mm of aluminum
passes through paper
what is the penetrating power of gamma rays
very high, can only be stopped by lead
what is ionisation
the process of which an atom becomes negative or positive by gaining or losing electrons
all nuclear radiation is capable of ionising atoms
what happens when an atom is ionised
the number of electrons is has changes
how ionising are alpha particles
they are the most ionising form of radiation because they leave a dense trail of ions behind them, affecting all atoms
how ionising are beta particles
they are moderately ionising
leave a less dense trail then alpha but are usually more dangerous
how ionising are gamma rays
least ionising form of radiation
but still can be dangerous
what factors does the ionising effect depend on
the greater the charge of the radiation, the more ionising it is
the higher the kinetic energy of the radiation, the more ionising it is (alpha is highest because highest mass)
what are the ranges of the types of radiation from shortest to longest
alpha (shortest)
beta
gamma rays (infinite)
when are particles deflected in an electrical field
if it has charge
when are particles deflected in a magnetic field
if it has charge and is moving perpendicular to it
what particles are deflected by electric and magnetic fields
alpha and beta
gamma has no charge so no deflection
in an electric field, which way are alpha particles deflected towards
towards the negative plate
in an electric field, which way are beta particles deflected towards
the positive plate
how does gamma radiation move in an electric field
not deflected so passes straight through between the plates
what happens during alpha or beta particle decay
the nucleus changes to that of a different element
why may isotopes be radioactive
because there is an excess of neutrons or the nucleus is too heavy
what is half life
the time taken for half the nuclei of that isotope in any sample to decay
how is radiation useful in smoke detectors
the alpha radiation will ionise the air within the detector, creating a current
when theres smoke, the alpha emitter is blocked
the alarm is triggered due to no current
how can radiation be used to measure the thickness of materials
beta particles are used and depending on the thickness, the amount of particles being absorbed will be more or less.
this can be used to regulate the thickness of materials
how are gamma rays used in the diagnosis and treatment of cancer
gamma rays penetrate the body and kill the bacteria or cancer cells
how can radiation be used to sterilise food and medical equipment
gamma rays are used because objects can be sterilized without the packaging being removed
it kills any microorganisms
what are the effects of ionising nuclear radiations on living things
cell death
mutations
cancer
how are radioactive sources stored safely
storing them in lead lined boxes and keeping distance
minimising the amount of time the source is handled
how is radioactive waste disposed of
by burying them underground to prevent it from being released into the environment
