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A Level Physics > Radioactivity > Flashcards

Radioactivity Flashcards

1
Q

Ionisation

A

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

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2
Q

Ion

A

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

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3
Q

Irridation

A

The process by which an object is exposed to radiation

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4
Q

Contamination

A

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

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5
Q

Different types of radioactivity experiments

A

Ionisation chambers and pico-ammeters
Cloud chambers
Spark counter

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6
Q

Ionisation chamber radioactivity experiment

A
  • 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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7
Q

Results from ionisation chamber radioactivity experiment

A
  • 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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8
Q

Cloud chamber radioactivity experiment

A
  • 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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9
Q

Observations from cloud chamber radioactivity experiment

A
  • 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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10
Q

Geiger tube radioactivity experiment

A
  • 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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11
Q

Intensity / power / area equation

A 
Intensity = power/area
I = wm^-2
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12
Q

Intensity / radius equation

A 
I = k/r^2
I = P/4pi x r^2
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13
Q

Causes of background radiation

A 
Natural products (rocks, soil, food + drink)
Space
Human activity (medical uses, industry, nuclear fallout, nuclear power stations)
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14
Q

Radioactive decay equations (similar)

A 
N(t) = N. e^-(lambda * t)
C(t) = C. e^-(lambda * t)
A(t) = A. e^-(lambda * t)
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15
Q

Rate of decay / decay constant / Number of atoms

A

A = lambda * N

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16
Q

Half-life definition

A
  • 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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17
Q

Half life / constant / decay constant equation

A

Half life = (ln 2)/lambda

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18
Q

Decay constant definition

A

lambda = probability of one nuclei decaying

19
Q

Equation to find current number of/activity/count rate etc

A

original amount/(2^n) = current amount

n = number of half lives

20
Q

N-Z graph features

A
  • 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
21
Q

Metastable definition

A

Same radioisotopes stay in an excited state to be separated from the parent isotope

22
Q

Coulomb’s law definition

A

Attractive or repulsive force between 2 point charges

  • proportional to product of charges
  • inversely proportional to the square of separation
23
Q

Coulomb force equation

A

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

24
Q

De Broglie wavelength / planck’s constant / momentum equation

A

DBW = h/momentum

25
Q

Carbon dating

A

1/(2^n) * original amount = current amount
n = number of half lives

n * T(1/2) = age

26
Q

Why are electrons used to test scattering?

A

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

27
Q

Nucleon definition

A

Proton or neutron inside a nucleus

28
Q

Isotope definition

A

Same element but with different number of neutrons in nucleus

29
Q

Strong nuclear force definition

A

Force in the nucleus that overcomes the strong electrostatic repulsion of protons and neutrons, keeping them together

30
Q

Specific charge equation

A

Charge/mass

31
Q

Beta radiation (B-)

  • Where does it happen
  • What is emitted
A

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.

32
Q

Positron emission (B+)

  • Why does it happen
  • What is emitted
A

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

33
Q

Electron capture

A

When a proton turns into a neutron due to the interaction with an electron (WEAK INTERACTION)

34
Q

Annihalation

A

When a particle and its antiparticle meet, they destroy each other and become radiation.
Momentum is conserved when 2 photons are emitted

35
Q

Binding energy definition

A

Work done to separate a nucleus into its constituent neutrons and protons

36
Q

Binding energy equation(s)

A

Binding energy = mass defect * c^2

Binding energy in MeV = mass defect in u * 931.3

37
Q

Pair production

A

When a gamma PHOTON turns into a particle and antiparticle

38
Q

Mass defect definition

A

The difference in mass between the separated nucleons and the nucleus

39
Q

Different particle groups

A

Leptons
Hadrons (quarks), including
- Baryons
- Mesons

40
Q

Differences between leptons and hadrons

A

Leptons do NOT interact through the strong interaction
Hadrons interact through the four fundamental interactions
Hadrons: lepton number = 0

41
Q

Differences between baryons and mesons

A

Baryons decay into protons (directly/indirectly)
Baryons have B=1, mesons have B=0
Baryons: qqq
Mesons: qq’ ( ‘ = anti)

42
Q

Conservation rules

A

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

43
Q

Quark combination for mesons

A 
k0 ------- k+ 
       (ds')        (us')
       /                   \
 pi- ------- pi0 ------- pi+ 
(du') (dd or uu)  (ud')
      \                    /
        k- --------- k'0 
      (su')          (sd')

A Level Physics (8 decks)

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