14-1

Radiochemistry Techniques in Research

• Unique Aspects of Radiochemistry Research• Availability of Radioactive Material• Targetry• Measuring Beam Intensity and Fluxes• Recoils• Radiochemical Separation and Measurement

14-2

Aspects of Radiochemistry

• Chemical study of radioactive substances nuclear analytical methods application of radionuclides chemistry of the radioelements physics and chemistry of high activity level matter radiotracer studies

• Features of radioisotope research Large activity range

pCi to MCi Chemical ionization at high concentrations

* Oxidation in solution* Redox change of radionuclides

Range of concentrations Molar to atom-at-a-time

* 2nd order kinetics impacted * Sorption to surfaces ignored in normal chemistry

Nuclear Transmutation

14-3

Reaction with water

• Radicals are formed by the interaction of radiation with water Radicals drive

reactionsSolvated

electrons, peroxide

14-4

Radicals

• G values moles of molecules or species formed or decomposed

per Joule of energy absorbed

14-5

Hot Atom Chemistry

• Chemical reactions produced by nuclear transformation Neutron irradiation of ethyl iodide

Iodine extracted into aqueous phase* 127I(n,)128I

Possible to produce specific isotope• Conditions needed

Bond of produced atom must be broken Should not recombine with fragments Should not exchange with target molecule

Slow kinetics Separation of new species

• Bonds are broken due to reaction energy Bond energies on the order of eV In neutron capture the emitted photon provides recoil

• Halogens produced in this method

14-6

Hot Atom Chemistry

• Beta reactions TeO3

2-IO3- + e-

Recoil is not quantized* Kinetic energy shared* E is maximum beta energy (MeV)

Rmax(eV)=573E(E+1.02)/M 0.5 MeV in 100 amu is about 4 MeV

* Energy is distributed Translational, rotational, vibrational

* Bond usually not broken Internal conversion set atom in excited state

Rearrangement of electrons

14-7

Hot Atom Chemistry

• Conservation of momentum imparts recoil Solve based on momentum For M in amu and E photon

energy in MeVEr(eV)=537E2/M

Photon on the order of 7 MeV

14-8

Availability of radionuclides

• Source Natural or

synthesized Reactions

with neutrons or charged particles

14-9

Targetry

• Targets for nuclear reactions Stable during reaction

Heat transfer Limitation of other products

Limit interactions with neutrons* Boron containing samples

Ease of production Evaporation Electrospray Electroplating

* the direct deposit of a metal on a cathodic surface by reduction

* precipitation of a cationic species in an insoluble form on an electrode

Vacuum deposition Limited contaminants

14-10

Electroplating

14-11

ElectroplatingVacuum Deposition

14-12

Target thickness• Thickness of targets can be measured using a variety of

techniques Weighing

Mass of known area of target material and computes its density.

-particle thickness gauges collimated beam of low energy -particles passes

through the foil whose thickness is to be measured X-ray fluorescence or neutron activation Radiochemical methods if target is active or tracer

added Mono-energetic ions through material

14-13

Beam Intensity • Measurement of charged particle

beam intensities performed with physical methods measure the intensity of a

charged particle beam with a Faraday cup

beam is stopped in electrically isolated section of beam pipe

collected charge is measured with an electrometer beam intensity is just the

current divided by the charge on each ion

• Faraday cup is long cylinder to inhibit electron escape geometrically

• magnetic field applied to the cup along with a suppressing voltage to prevent electron escape

• Also can use secondary ionization chamber or foil Foil can monitor reactions and

determine beam from products and cross section

14-14

Separation methods

• Ion Exchange• Chromatographic Methods

paper chromatography thin-layer chromatography electrochromatography extraction chromatography

• Solvent Extraction• Volatilization

exploitation of differences in vapor pressure for radiochemical separations

removal of radioactive rare gases from aqueous solutions or melts by sweeping with inert gas

often gives clean separations• Electrochemical Methods