Radioanalytical Chemistry

1
Radioanalytical Chemistry

• Part of
• Intermediate Analytical Physical Chemistry

2
What is ionising radiation?

• Causes ionising events on interaction with matter
• Production of highly reactive species
• In water H, OH, H2O2, O2, H2
• In an inert gas X and e-
• Virtually all mass of atom in nucleus

3
Decay Reactions

• Isotopes with ngtp are radioactive
• Stable np ratio 1-1.5

4
Alpha particle decay

• Heavy elements eject helium nucleus
• May decay further
• Generally Edaughterlt Eparent
• Poor penetrating power, high energy, very
  ionising
• Little external hazard, great internal hazard

5
Negatron emission

• High np ratio convert n to p and emit electron
• Low mass, penetrating, low energy, low ionisation
• External hazard, easily shielded

6
Positron emission

• Low np ration converts p to n and emits a
  positron (positive electron!)
• Positron collides with electron and liberated as
  2 identical ? rays of 0.511 MeV

7
Electron capture

• Low np ratio adjusted by capture of low lying K
  shell electron.
• Combines with proton to give neutron.
• Vacancy filled ,emission of X-rays.

8
Gamma emission

• Always accompanies other types of decay
• Daughter isotopes in excited states emit ?
• No mass, very penetrating, difficult to shield
• Great health hazard
• Wide range of characteristic energies

9
Radioactive decay laws

• Kinetic problem, not affected by T, p, allotropic
  form, compound
• Each nuclei has same probability of decay
• Fundamental decay eqn dN/dt -?N
• N N0exp-?t
• A A0exp-?t
• A activity in disintigrations per sec

10
(No Transcript)
11
(No Transcript)
12
Half-life and units

• T0.5 time taken for activity to decay to half
  initial value
• SI unit Becquerel (Bq)
• 1 Bq 1 disintegration s-1
• Curie (Ci) disintegrations s-1 from 1 g 226Ra
• 1 Ci 3.7 x 1010 Bq

13
Ionisation Detectors

• Gas filled chamber
• Ionisation produces cations and electrons
• Collection at cathode and anode produces current
• 3 types
• Ionisation chamber (?)
• Proportional counter (?)
• Geiger-Muller counter (high energy ?, low energy
  ?)

14
Scintillation Detectors

• Radiation causes phosphor, Tl(I)I, to emit light
• Light converted electric current by
  photomultiplier tube
• Solid scintillators (? and high energy ?)
• Liquid scintillators (low energy ?)

15
Solid State Detectors

• Semiconductor Ge(Li) (?)
• Radiation causes ionisation
• Electrons collected
• High resolution

16
?-ray Spectrometry

• Energy ? pulse height
• Complicated by
• Energy loss on contact with detector
• Additive rays
• ?- or ? produce electromagnetic radiation
• scattering
• Calibration necessary

17
(No Transcript)
18
Radioanalytical Methods

• Direct determination
• Isotope dilution analysis
• Radioimmunoassay
• Activation analysis

19
Isotope dilution analysis

• Radioactive X added to system containing X
• Pure X isolated
• Activity will be diluted
• Need
• radioactive form of X
• Separation method for X
• Counting method
• Problem - weighing small amounts
• Sub-stoichiometric IDA
• isolate equal but sub-stoichiometric amount of
  sample and standard

20
Radioimmunoassay

• Derivative IDA, clinical assays
• Sensitive, specific, easy, small sample
• binder (antibody) ligand (antigen)
  tracer (labelled antigen) complex
• Separate complex (bound phase) from free phase
  (unbound tracer)
• Amount of antigen related to distribution of
  tracer between bound/free phases

21
Activation analysis

• Irradiate inactive sample, count induced
  activity, relate to standard
• Induced activity prop to time, half life, delay,
  flux, capture X section, abundance, atomic mass,
  NA

22
Applications

• Medicine
• Cystic finbrosis, Na in nail tissue
• F in tooth enamel
• Criminology
• Gunshot residues, Sb, palm, bullet entry
• Hair analysis, eg As
• Authentication of art work, non-destructive
• Environmental
• Hg, mirrors environmental contamination
• Cd, smelting and fertiliser plants
• V, burning fossil fuels
• As, near Hg/Cu/Pb smelting

23
What to do now.

• Go to www.hull.ac.uk/chemistry
• Select lecture notes for year 2
• You will find
• This presentation
• An introduction to the course
• The full course notes with exercises and typical
  exam questions
• Worked answers to exercises

24
How to use the resources

• The course has been designed for independent
  study.
• You can use the allocated lecture slots to work
  through the materials
• There are no formal lectures
• There will be seminar sessions in LTA at 12.15 in
  weeks 10 and 11 to deal with any problems you are
  having. USE THESE SESSIONS

25
(No Transcript)