John M. Flournoy

IRRADIATION YIELDS OF RADICALS IN GAMMA-IRRADIATED ICE AT 4.2 AND 77 K

The EPR spectra of both ice and deuterated ice which have been subjected to γ irradiation at 4.2°K are presented and discussed. Experimental radical irradiation yields at 4.2°K are reported for the H2O system as a function of sustained irradiation dosage. A comparison between the irradiation yields at 4.2° and 77°K is given and the resulting similarities discussed in terms of intra‐spur reactions. Finally, preliminary evidence is presented for the existence of an appreciable isotope effect for the irradiation yields in a mixture of H2O and D2O.

Observations of the Thermal Behavior of Radicals in Gamma‐Irradiated Ice

Ice was subjected to γ radiation at 77°K and the EPR spectra of the radicals produced were examined as a function of temperature. The spectrum consisted essentially of a doublet centered at g=2.008±0.002 and split by 40 gauss; the corresponding spectrum of irradiated D2O consisted of a triplet with approximately 6 gauss between adjacent lines. The doublet decayed rapidly above 100°K leaving a residual broad line which was thermally stable until approximately 145°K. The main spectrum has been attributed to the OH radical and the residual line assigned to the HO2 radical. The decay process of the OH radicals was shown to follow the rate law d(OH)/dt=—k(OH)32 where k=8.5×1012 exp—6000/RT (liter/mole)½ sec—1. The magnitude of the rate constant was shown to be a function of the total irradiation damage experienced by the ice sample.Stabilization of OH radicals at 77°K was studied as a function of total irradiation dosage; saturation is reached at an OH concentration of 1.8×10—3M or 0.003 mole %. The EPR spectr...

EPR STUDIES OF ELECTRON IRRADIATED ICE AND SOLID HYDROGEN

Electron paramagnetic resonance studies of ice and H/sub 2/ irradiated in a 40-Mev electron linear accelerator are describ/sup 6/ or ice at 77 deg K and dosages of 9 x 10/sup 6/ and 18 x 10/sup 6/ rad, a strong resonance at g = 2 consisting of a doublet and other unresolved lines was observed; no H atom splitting was observed. At 4.2 deg K and various dosages (cumulative) resonances 250 gauss each side of g = 2 appeared; the same unresolved structure in the g = 2 region was found. A maximum total H atom concentration of 8 x 10/sup 6/ moles was obtained at 16 x 10/sup 6/ rad. Higher doses produced no more H atoms. For solid H/sub 2/ at 4.2 deg K only H-atom lines were observed. Modulation frequency effects at high rf levels were studied. Dose saturation study indicated H-atom concentration saturation at 7.2 x lO/sup -6/ rad; the H-atom concentration was 1.5 x 10/sup -6/ mole/g. The saturation level may have been limited by beam heating effects. (T.R.H.)

Isotope Effects and the Mechanism of Atom Production in Gamma‐Irradiated Ice at 4.2°K

The relative intensities of the electron spin resonance (ESR) spectra of H and D atoms were determined for mixtures of H2O and D2O which were irradiated and observed at 4.2°K. A careful analysis of the results indicates that the yield of atoms per unit irradiation dosage exhibits no isotope effect, except for the system containing trace amounts of H2O in D2O. The presence of a large isotope effect for a system of D2O containing approximately 0.1% H2O is discussed in terms of energy transfer in the solid state.

Temperature Control Method for Use between 4.2° and 77°K

A simple system is described for maintaining controlled experimental temperatures between the normal boiling points of helium and nitrogen. No special apparatus is involved other than that normally required for the handling of liquid helium and the measurement of low temperatures. The technique has been used to control the temperature of a resonant cavity to within ±0.2°K, for T>20°K, using a copper‐Constantan thermocouple and a variable range recording potentiometer to measure temperature.