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 àpCi to MCi àChemical ionization at high concentrations *Oxidation in solution *Redox change of radionuclides §Range of concentrations àMolar to atom-at-a-time *2 nd 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 reactions àSolvated 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 àIodine extracted into aqueous phase * 127 I(n,  ) 128 I ËPossible to produce specific isotope Conditions needed §Bond of produced atom must be broken §Should not recombine with fragments §Should not exchange with target molecule àSlow 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 §TeO 3 2-  IO e - àRecoil is not quantized *Kinetic energy shared *E is maximum beta energy (MeV) ËR max (eV)=573E(E+1.02)/M Ë0.5 MeV in 100 amu is about 4 MeV *Energy is distributed ËTranslational, rotational, vibrational *Bond usually not broken §Internal conversion set atom in excited state àRearrangement 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 MeV àE r (eV)=537E 2 /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 àHeat transfer §Limitation of other products àLimit interactions with neutrons *Boron containing samples §Ease of production àEvaporation àElectrospray àElectroplating *the direct deposit of a metal on a cathodic surface by reduction *precipitation of a cationic species in an insoluble form on an electrode àVacuum deposition §Limited contaminants

14-10 Electroplating

14-11 Electroplating Vacuum Deposition

14-12 Target thickness Thickness of targets can be measured using a variety of techniques §Weighing àMass 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 àbeam 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