Nuclear Physics Flashcards
Describe the structure of an atom.
a positively charged nucleus and negatively charged electrons in orbit around the nucleus
How can atoms form positive ions?
losing electrons
How can atoms form negative ions?
gaining electrons
What is an experiment to support the nuclear model of the atom?
scattering of alpha particles by a sheet of thin metal
What does Rutherford’s Alpha Particle Scattering experiment prove?
- there is a very small nucleus surrounded by mostly empty space
- nucleus contains most of atom’s mass
- positive nucleus
What is the nucleus composed of?
protons and neutrons
Relative charge of proton?
+1
Relative charge of neutron?
0
Relative charge of electron?
-1
What is the proton number?
number of protons found in the nucleus
What is the atomic number?
number of protons found in the nucleus
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The electron and proton numbers are equal in…
an atom (neutral)
The electron and proton numbers are unequal in…
ions (charged)
What is the nucleon number?
total number of protons and neutrons in the nucleus
What is the mass number?
total number of protons and neutrons in the nucleus
How can you calculate the number of neutrons in a nucleus?
nucleon number - proton number
What is the symbol A?
nucleon number
What is the symbol Z?
proton number
What is the symbol X?
element
What is the symbol for an element?
X
What is the symbol for nucleon number?
A
What is the symbol for proton number?
Z
What is an isotope?
atoms of the same element with the same number of protons and electrons, but different neutron numbers
What is an isotope, in terms of nucleon and proton numbers?
different nucleon number of the atoms, same proton number
Describe the process of nuclear fusion.
lighter nuclei collide with high energy and join to form a larger nucleus, releasing energy
What is the difference between nuclear fission and fusion?
nuclear fission - splitting of heavy nuclei
nuclear fusion - joining of 2 light nuclei
What is the nuclide equation for nuclear fusion?
- you add the nucleon and proton numbers
- total nucleon number is the same before and after
Describe the process of nuclear fission.
- heavy nuclei are often unstable, so they break apart
- either independently or if a neutron is fired into the large nucleus, triggering it to break apart
- energy is released
What is the nuclide equation for nuclear fission?
- total nucleon number is conserved
atom + neutron -> atom1 + atom2 + neutrons
Describe the mass and energy changes in nuclear fission and fusion.
they both release energy by decreasing mass slightly
How is energy released in nuclear fission/fusion?
decreasing mass slightly, typically around 0.1%
What is radioactivity?
the process by which an unstable nucleus becomes more stable
Which sources significantly contribute to background radiation?
- radon gas in air
- rocks and buildings
- food and drink
- cosmic rays
How can ionising nuclear radiation be measured?
using a detector connected to a counter
A detector is connected to a counter to…
measure ionising nuclear radiation
How is count rate measured?
counts/s or counts/minute
How is the emission of radiation from a nucleus?
spontaneous and random in direction
The _______ is spontaneous and random in direction.
emission of radiation from a nucleus
What is an alpha particle?
helium nucleus
What is an alpha particle’s ionising effects? Why?
highly ionising due to its large mass and charge
What is an alpha particle’s penetrating abilities?
- least penetrating
- travel about 5 cm through air, stopped by materials such as thin paper or skin
State the order of ionising effects of the three types of radiation.
- alpha
- beta
- gamma
What is a beta particle?
a high-energy electron
What is a beta particle’s ionising effects? Why?
- mildly ionising
- fast, large KE, although the mass is small
- charge of -1
- beta particles can still strip away electrons of other atoms they encounter
What is a beta particle’s penetrating abilities?
can travel through skin, stopped by a few millimetres of aluminium
What are gamma emissions?
high frequency electromagnetic waves
What is gamma’s ionising effects? Why?
- weakly ionising
- they have no charge and no mass
What is gamma’s penetrating abilities?
only stopped by several cm of lead (dense)
Effect of a magnetic field on gamma
none
Effect of a magnetic field INTO page on alpha
deflects slightly upwards
Effect of a magnetic field OUT OF page on alpha
deflects slightly downwards
Effect of a magnetic field INTO page on beta
deflects a lot downwards
Effect of a magnetic field OUT OF page on beta
deflects a lot upwards
Effect of an electric field on gamma
none
Effect of an electric field on alpha
deflects towards negative side (less than beta)
Effect of an electric field on beta
deflects towards positive side a lot
Why do alpha only deflect slightly?
large mass compared to its charge
Why do beta deflect a lot?
very small mass compared to its charge
If a beta particle deflects upwards in a magnetic field, the field is….
out of the page
If a beta particle deflects downwards in a magnetic field, the field is….
into the page
If an alpha particle deflects upwards in a magnetic field, the field is….
into the page
If an alpha particle deflects downwards in a magnetic field, the field is….
out of the page
What is radioactive decay?
a change in an unstable nucleus that can result in the emission of alpha or beta and/or gamma
What happens during alpha or beta decay?
the nucleus changes to that of a different element
In what types of decay does the nucleus change to a different element?
alpha or beta decay
Why may isotopes of an element be radioactive?
excess of neutrons in the nucleus/heavy nucleus
What is the effect of alpha/beta decay and gamma emissions on the nucleus?
- increased stability
- reduced number of excess neutrons
What happens in beta emission?
neutron -> proton + electron
- proton stays in the nucleus
- electron is the beta particle
What is the decay equation like for alpha decay?
forms helium nucleus, element loses 4 in nucleon number and 2 in atomic number
What is the decay equation like for beta decay?
an electron is ejected and the element gains 1 in atomic number
What is the decay equation like for gamma decay?
element stays the same in nucleon/proton number but becomes more stable
Define the half-life of a particular isotope.
time taken for half the nuclei of that isotope in any sample to decay
State some effects of ionising nuclear radiation on living things.
- cell death
- mutations
- cancer
State some safety precautions for all ionising radiation.
- reducing exposure time
- distance
- using shielding to absorb radiation
- do not point sources at people (anna precisa entender)
How should you store alpha?
- thin package as α-particles are weakly penetrating
- protective clothing must still be worn when handling
How should you store beta?
lead container
How should you store gamma?
bury. deep underground.
charge of alpha particles
+2
State and describe one use of alpha particles
Smoke detectors
particles ionise the air, allowing current to flow between positive and negative plates, with potential difference between them.
when smoke is present, alpha particles collide with and are absorbed by smoke particles, so less current flows, causing the alarm to sound
do gamma rays have mass and charge
nope nope nope
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state and describe a use of gamma rays
medical tracers - due to it being highly penetrating, it is easy to detect which areas of the body it has travelled. it is weakly ionising so it is not dangerous in small dose
What is half life
Time taken for the count rate of a radioactive source to decrease by half
safety precautions for all ionising
radiation
reducing exposure time,
increasing distance between source and living
tissue and using shielding to absorb radiation
effects of ionising nuclear radiations on living things
cell death, mutations and
cancer
