Radioactivity Flashcards
Ionisation
Process by which an atom or molecule acquires a negative or positive charge by gaining or losing electrons, forming ions
Ion
An atom/molecule with a net charge due to the loss or gain of one or more electrons
Irridation
The process by which an object is exposed to radiation
Contamination
When you get a radioactive substance on or inside your body (swallowing/breathing/flesh wound)
Contaminating materials then irridate you
Different types of radioactivity experiments
Ionisation chambers and pico-ammeters
Cloud chambers
Spark counter
Ionisation chamber radioactivity experiment
- Chamber contains air at atmospheric pressure
- Ions are created in the chamber
- Ions are attracted to the oppositely charged electrode where they are ‘discharged’
- Electrons pass through the picometer as a result of the ionisation in the chamber
- Current is proportional to the number of ions per second created in the chamber
Results from ionisation chamber radioactivity experiment
- Alpha radiation causes strong ionisation, but only has a range of a few cm
- Beta radiation has a much weaker ionising effect than alpha radiation, therefore producing fewer ions per mm than alpha
Gamma radiation has virtually no ionising effect because photons have 0 charge
Cloud chamber radioactivity experiment
- Contains air saturated with a vapour OR at a very low temperature
- Alpha and Beta particles passing through the cloud chamber leave a visible track of condensed water droplets as the air is supersaturated
- The ions produced trigger the formation of water droplets
Observations from cloud chamber radioactivity experiment
- Alpha particles produce straight tracks that radiate from the source + are easily visible
- Tracks given from an isotope are all of the same length as alpha particles have the same range
- Alpha particles from a source all have the same range in air as each other as they all are emitted with the same energy
- This is because each alpha particle and the nucleus that emits it move apart with equal and opposite momentum amounts - Beta particles produce wispy tracks, easily deflected (collisions with air)
- Tracks hard to see as they are less ionising
- Since Beta particle are admitted with a (anti) neutrino, energy is admitted in various proportions
Geiger tube radioactivity experiment
- Sealed metal tube containing argon gas at low pressure
- Metal rod down the middle of the tube is at a positive potential
- Tube wall connected to negative + earthed
- Ionising particle ionises the gas atoms along the track
- Positive ions to wall, negative to rod
- Ions accelerate and collide with atoms, creating more ions
Intensity / power / area equation
Intensity = power/area I = wm^-2
Intensity / radius equation
I = k/r^2 I = P/4pi x r^2
Causes of background radiation
Natural products (rocks, soil, food + drink) Space Human activity (medical uses, industry, nuclear fallout, nuclear power stations)
Radioactive decay equations (similar)
N(t) = N. e^-(lambda * t) C(t) = C. e^-(lambda * t) A(t) = A. e^-(lambda * t)
Rate of decay / decay constant / Number of atoms
A = lambda * N
Half-life definition
- Time taken by a sample of radioactive nuclei to decrease by 50%
- The time it takes the count rate of activity from a radioisotope to decrease by 50%
Half life / constant / decay constant equation
Half life = (ln 2)/lambda
Decay constant definition
lambda = probability of one nuclei decaying
Equation to find current number of/activity/count rate etc
original amount/(2^n) = current amount
n = number of half lives
N-Z graph features
- N=Z up to z~20, then increasingly N>Z to be stable
- Alpha emitters located beyond Z=60
- Nucleus has too many:
- Neutrons = neutron to a proton and emit a B- particle
- Protons = proton to a neutron and m=emit a B+ particle
- Protons when Z>60 = alpha particle emitted (does NOT change N to Z ratio, ratio required for stability is smaller
Metastable definition
Same radioisotopes stay in an excited state to be separated from the parent isotope
Coulomb’s law definition
Attractive or repulsive force between 2 point charges
- proportional to product of charges
- inversely proportional to the square of separation
Coulomb force equation
F = (k * Q1 * Q2)/r^2
Q1 Q2 = charges of the 2 points
r = distance between the 2 points
k = 1/(4 * pi * epsilon0)
epsilon0 = permittivity of vacuum: in data booklet
De Broglie wavelength / planck’s constant / momentum equation
DBW = h/momentum
Carbon dating
1/(2^n) * original amount = current amount
n = number of half lives
n * T(1/2) = age
Why are electrons used to test scattering?
More accurate method (diffraction)
Nuclei in a thin sample acts as a diffraction grating for the electron
- When De Broglie wavelength of electrons is of electrons is of a similar magnitude to diameter of nuclei
De Broglie wavelength is large for an electron
- Can probe smaller objects
Nucleon definition
Proton or neutron inside a nucleus
Isotope definition
Same element but with different number of neutrons in nucleus
Strong nuclear force definition
Force in the nucleus that overcomes the strong electrostatic repulsion of protons and neutrons, keeping them together
Specific charge equation
Charge/mass
Beta radiation (B-)
- Where does it happen
- What is emitted
Beta radiation consists of fast-moving electrons
Occurs in an unstable nucleus when a neutron turns into a proton
Beta particle created immediately and is emitted
ANTINEUTRINO with no charge also emitted.
Positron emission (B+)
- Why does it happen
- What is emitted
Takes place when a proton changes into a neutron in an unstable nucleus with too many protons.
Antiparticle of electron, carries +ve charge
NEUTRINO is emitted
Electron capture
When a proton turns into a neutron due to the interaction with an electron (WEAK INTERACTION)
Annihalation
When a particle and its antiparticle meet, they destroy each other and become radiation.
Momentum is conserved when 2 photons are emitted
Binding energy definition
Work done to separate a nucleus into its constituent neutrons and protons
Binding energy equation(s)
Binding energy = mass defect * c^2
Binding energy in MeV = mass defect in u * 931.3
Pair production
When a gamma PHOTON turns into a particle and antiparticle
Mass defect definition
The difference in mass between the separated nucleons and the nucleus
Different particle groups
Leptons
Hadrons (quarks), including
- Baryons
- Mesons
Differences between leptons and hadrons
Leptons do NOT interact through the strong interaction
Hadrons interact through the four fundamental interactions
Hadrons: lepton number = 0
Differences between baryons and mesons
Baryons decay into protons (directly/indirectly)
Baryons have B=1, mesons have B=0
Baryons: qqq
Mesons: qq’ ( ‘ = anti)
Conservation rules
Conservation of charge:
Charge before = charge after
Conservation of energy:
Total energy of particles + antiparticles before the collision = rest energy + kinetic energy
Total energy of particles + antiparticles after the collision = rest energy + kinetic energy
Rest energy of products = total energy before - kinetic energy of products
Conservation of lepton numbers:
Total lepton number for any branch = total lepton number for that branch after the change
Baryon number before = baryon number after
Quark combination for mesons
k0 ------- k+
(ds') (us')
/ \
pi- ------- pi0 ------- pi+
(du') (dd or uu) (ud')
\ /
k- --------- k'0
(su') (sd')
