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Physics A-level > 26 Radioactivity > Flashcards

26 Radioactivity Flashcards

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1
Q

Rutherford (1911)

A

-knew that atoms of certain elements are unstable and emit radiation

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2
Q

Rutherford experiment

results

A
  • alpha particles directed at a thin piece of metal.
  • most alpha particles passed through with little deflection( 1 in 2000 were deflected)
  • a small percentage of alpha particles were deflected through angles more than 90 degrees ( 1 in 10000)
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3
Q

Rutherford Experiment

explanation

A
  • most of the concentration in the small region (nucleus)

- The nucleus is positively charged because it repels the alpha particle

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4
Q

size of the nucleus

A

-d² =D/10000n

d=nucleus diameter
D=atom diameter
n= number of atoms

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5
Q

radiation and radioactive

A

The source is radioactive not the radiation

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6
Q

Radiation

A
  • ionised air so it can conduct electricity

- three different types of radiation

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7
Q

radiation and magnetic field

A

alpha and beta radiation are deflected in opposite ways and has no effect on gamma radiation

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8
Q

ionisation experiment

A
  • can be investigated using an ionising chamber and a picammeter
  • air at atmospheric pressure
  • ions in the chamber are attracted to the oppositely charged electrode where they are discharged
  • electrons pass through the picammeter as a result of ionisation in the chamber
  • the current is proportional to the number of ions per second
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9
Q

ionisation of alpha

A

strong ionisation but a short range in air (cm)

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10
Q

ionisation of beta

A

weaker than alpha but bigger range than alpha (meters)

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11
Q

ionisation of gamma

A

weaker than alpha and beta but has an infinite range in air

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12
Q

cloud chamber

A

contains saturated air with vapour at a low temperature. alpha and beta radiation leave visible tracks of condensation of water droplets.

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13
Q

Cloud chamber alpha

A

produce straight tracks from the source

all the racks are the same showing that alpha particles have the same range

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14
Q

Cloud chamber beta

A

produce wispy tracks that are easy to deflect. The tracks are less easy to see because beta isn’t as ionising

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15
Q

absorption tests

A

uses a Geiger tube and counter to investigate absorption of different materials. Each particle is one count.

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16
Q

count rate

A

The number of counts per unit time detected by a Geiger Muller tube. Count rates should always be corrected by measuring and subtracting the background count rate

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17
Q

Geiger tube

A

a sealed metal tube that argon gas at low pressure.
ionizing radiation enters the tube, the particle ionising the gas. negative ions are attracted to the rod and the positive ions to the wall. ions accelerate and collide with gas atoms producing more ions. a pulse of charge passes around the circuit through a resistor causing a voltage pulse across the resistor.

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18
Q

radiation range in air

A

alpha - 100mm
beta- 1m
gamma - inserverse square law

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19
Q

radiation absorption

A

alpha - stopped by paper and thin foil
beta - 5mm of aluminium
gamma - several cm of lead

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20
Q

radiation ionisation

A

alpha - produce 104 ions per mm in air at strandard pressure

beta - produces about 100 ions per mm

gamma - very weak ionising effect

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21
Q

alpha ( experiment)

A

alpha particles are collected as a gas in a glass tube fitted with two electrodes. When a voltage was applied to the electrode, the gas conducted electricity and emitted light. using a spectrometer, he proved that the spectrum of light from the tube was the same as from a tube filled with helium gas

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22
Q

beta radiation

A

measuring the deflection of a beam of beta particles using electric and magnetic fields. The measurement was used to work out the specific charge of the particles (specific charge of the electron).

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23
Q

beta negative

A

an electron is created and emitted from a nucleus with too many neutrons as a result of a neutron changing to a proton

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24
Q

beta positive (positron)

A

a nucleus with too many protons, a proton changes to a neutron

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25
Q

inverse square law (intensity)

A

The intensity of gamma radiation from a point source varies with the square of the distance from the source

intensity = radiation energy per second/total area. 
I = nhf/4π²
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26
Q

hazards of ionising radiation

A

damages living cells
(destroy cell membranes causing cells to die)
(damage vital molecules such as DNA)
Also as a result of exposure to ionising radiation, living cells die or grow uncontrollably or mutate

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27
Q

radiation monitoring

A

film badge- a strip of photographic film in the light proof wrapper. different areas of the film are covered by absorbers of different materials and different thicknesses. When the film is developed the amount of exposure to each form of ionising radiation can be estimated from the blackening film.

28
Q

background radiation

A

radiation due to naturally occurring radioactive substances in the environment

29
Q

Radioactive materials

A 
air
medical
ground and buildings
food and drink
cosmic rays
nuclear rays
air travel
nuclear power
30
Q

Half-life

A

The time is taken for the mass of a radioactive isotope to decrease to half the initial mass or for its activity to halve. this is the same as the time taken for the number of nuclei of the isotope to decrease to half the initial number.

31
Q

nucleus

A

the relativity small part of the atom where all the positive charge is concentrated

32
Q

atomic number

A

of an atom of an element is the number of protons in the nucleus of the atom. it is also the order number of the element in the periodic table

33
Q

photon

A

electromagnetic radiation consists of photons. each photon is a wave packet of electromagnetic radiation.
E=hf

34
Q

ionising radiation

A

radiation that produces ions in the substances it passes through. it destroys cell membranes and damages vital molecules such as DNA directly or indirectly by creating ‘free radicals’ ions which react with vital molecules

35
Q

proton

A

particle that has equal and opposite charge to an electron

36
Q

neutron

A

uncharged particle that has a rest mass of 1.674 x10-27

37
Q

intensity of radiation

A

at a surface is the radiation energy per second per unit area of normal incidence to the surface

38
Q

x-ray

A

electromagnetic radiation of wavelength less than 1nm. X-ray are emitted from a X-ray tube as a result of fast-moving electrons from a heated filament as the cathode being stopped on impact with the metal anode. think lead plates are needed to absorb a beam of x-rays

39
Q

dose equivalent

A

a comparative measure of the effect of each type of ionising radiation, defined as the energy that would need to be absorbed per unit mass of matter from 250 k of x-radaiation to have the same effect as a certain ‘dose’ of the ionising radiation. the unit of dose equivalent is the sievert (Sv)

40
Q

background radiation

A

radiation due to naturally occurring radioactive substances in the environment . also can be caused by cosmic radiation

41
Q

decay curve

A

an exponential decrease curve showing how the mass or activity of a radioactive isotope decrease with time

42
Q

activity

A

of a radioactive isotope, the number of nuclei of the isotope that disintegrate per second. Bq

A = λN

43
Q

decay constant

A

the probability of an individual nucleus decaying per second

44
Q

excited state

A

an atom which is not in its ground state

45
Q

de Broglie wavelength

A

a particle of matter has a wake-like nature which means that is can behave as a wave.
λ = h/p = h/mv

46
Q

energy transfer per second from a radioactive source

A

AE

47
Q

decay constant

A

ΔN/ Δt = -λN

48
Q

decay of an isotope

A

A = Are^-λt

49
Q

half-life T 1/2

A

T 1/2 = In(2) / λ

50
Q

carbon dating

A

radioactive isotope of carbon-14
n + N — C +p
formed in the atmosphere as a result of cosmic rays knocking out neutrons from the nuclei

51
Q

Argon dating

A

ancient rock contains trapped Argon gas as a result of the decay of the radioactive isotope of potassium to argon.

the age of the rock can be calculated by measuring the proportion of argon of argon-40 to potassium-40

52
Q

radioactive tracers

A

radioactive tracer is used to follow the path of a substance through a system.
have a half-life which is stable enough for the necessary measurements to be made and short enough to decay quickly after use
emit B radiation or y radiation so it can be detected outside the flow path

53
Q

detecting underground pipe leaks

A

radioactive tracer injected into the flow. a pipeline is used to detect leakage
B- emitter or gamma emitter

54
Q

modelling oil reservoirs mathematically to improve oil recovery

A

water contains a radioactive tracer is injected into a oil reservoir at high pressure, forcing some of the oil out.
tritiated water HO, B emitter with a half-life for 12 years

55
Q

investigating the uptake of fertilisers by plants

A

plants watered with a solution containing a fertiliser. by measuring the radioactivity of the leaves, the amount of fertile reaching them can be determined
fertiliser = phosphorous

56
Q

monitoring the uptake of iodine by the thyroid gland

A

patient is given a solution donating sodium iodine which contains a small quantity of radioactive iodine
solution of sodium iodide contains iodine
B emitter of 8 days

57
Q

thickness monitoring

A

metal foil is manufactured by using rollers to squeeze plate metal on a continuous production line. a sector measures the amount of radiation passing through the foil. if the foil is too thick, the detector reading drops. a signal is sent if the reading drops which brings the roller together

58
Q

power forces for remote devices

A

satellites, weather sensors and other remote devices can be powered using radioactive isotopes in thermally insulated sealed container which absorbs all the radiation emitted by the isotope.

59
Q

N-Z graph

light isotopes

A

stable nuclei flow the straight line N =Z

the nuclei have equal numbers of proton and neutrons

60
Q

N-Z graph

as Z increases beyond 20

A

stable nuclei have more neutrons than protons. the neutron / proton ratio increases. the extra neutrons help ti blind the nucleons together without introducing repulsive electrostatic forces as more protons would do

61
Q

N-Z graph

α emitter

A

beyond Z= 60, most of them with more than 80 protons and 120 neutrons. these nuclei have more neutrons than protons but they are too large to be stable. this is because the strong nuclear force of repulsion between the protons

62
Q

B- emitters

A

occur to the left of the stability belt where the isotopes are neutron rich compared to stable isotopes.

63
Q

B+ emitters

A

occur to the right of the stability belt where the isotopes are proton-rich compared to stable isotopes

64
Q

technetium generator

A

used in hospitals to produce a source which emits gamma radiation only. some radioactive isotopes such as the technetium isotope Tc form in the excited state long enough to be separated from the parent state
contains an ion exchange column containing ammonium molybdenite exposed to neutron radiation several days to make lots of unstable nuclei. when a solution of sodium chloride is passed through the column, some of the chlorine ions exchange with pertechnate ions but not with molybdenite ion so the solution that emerges contains Tc nuclei

65
Q

diagnostic use of Tc

A

monitoring blood flow

gamma camera= image internal organs and bones

66
Q

nuclear density

A

V = 4/3 π ro^3 A

67
Q

inverse square law

A

I = k / X^2

Physics A-level (13 decks)

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