- 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%

Radioactivity Flashcards by Malachy Lush

Ionisation

Process by which an atom or molecule acquires a negative or positive charge by gaining or losing electrons, forming ions

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Ion

An atom/molecule with a net charge due to the loss or gain of one or more electrons

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Irridation

The process by which an object is exposed to radiation

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Contamination

When you get a radioactive substance on or inside your body (swallowing/breathing/flesh wound)
Contaminating materials then irridate you

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Different types of radioactivity experiments

Ionisation chambers and pico-ammeters
Cloud chambers
Spark counter

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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

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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

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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

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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

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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

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Intensity / power / area equation

Intensity = power/area
I = wm^-2

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Intensity / radius equation

I = k/r^2
I = P/4pi x r^2

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Causes of background radiation

Natural products (rocks, soil, food + drink)
Space
Human activity (medical uses, industry, nuclear fallout, nuclear power stations)

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Radioactive decay equations (similar)

N(t) = N. e^-(lambda * t)
C(t) = C. e^-(lambda * t)
A(t) = A. e^-(lambda * t)

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Rate of decay / decay constant / Number of atoms

A = lambda * N

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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%

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Half life / constant / decay constant equation

Half life = (ln 2)/lambda

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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') ```