Stemming from the discovery and isolation of radioactive elements by the Curies came observations of chemical and physical changes produced by ‘emanations’. From ~1900 AD, observations were sporadic and spread across a range of chemical systems. Several conflicting results from irradiated water were reported – one recording no decomposition, whereas another study observed hydrogen and hydrogen peroxide formation. The field progressed slowly while the only practical source of radiation was X-rays. After the mid-1940s, the isotope output from nuclear reactors gave chemists high-activity radiation sources with which to conduct experiments. Particle accelerators were utilized and led to the pulsed radiolysis technique, which unlocked the door to the study of ultrafast solution reactions of free radicals and excited states. The radiation chemistry of water is now a qualitative and quantitative basis for the initiation and study of a wide range of chemical and physical processes. Polymeric systems, solid-state dosimeters, and gaseous plasmas are active areas of research. The radiological use of radiation has an active radiobiology field developing new biochemical processes involving DNA stability.

Optical emission spectra in the 300–700 nm range were collected from four perovskite-structured materials (CaTiO3, SrTiO3, BaTiO3 and CaZrO3), a pyrochlore-structured material (La2Zr2O7) and zirconolite (CaZrTi2O7), using either a Febetron 706 variable energy pulsed-electron-beam generator (pulse duration 3 ns) or a Vickers pulsed-electron LINAC (pulse duration 0.5 μs). The long-lived emissions (up to microseconds after the electron pulse) consist of broad (halfwidths ∼100 nm) bands centred around ∼400 nm. For the CaZrO3, La2Zr2O7 and CaZrTi2O7 samples, the emission intensity per unit dose was also measured as a function of electron beam energy over the range 0.2–0.6 MeV. The data for all three samples suggest a single stage dependence on electron beam energy. CaZrO3, La2Zr2O7, and CaZrTi2O7 have emission thresholds of 0.28±0.03, 0.27±0.03, and 0.26±0.03 MeV respectively, which give oxygen displacement values of 49±5, 47±5, and 45±5 eV respectively. Data collected in this study are discussed in the context of previously measured and calculated oxygen displacement values.

Optical emission spectra in the 300–700 nm range were collected from single crystal CaTiO3, SrTiO3 and BaTiO3, and polycrystalline CaTiO3 samples, that were irradiated at room temperature using a Febetron 706 variable energy pulsed-electron-beam generator. The long-lived emissions (up to microseconds after the electron pulse) consist of broad (halfwidths ∼100 nm) bands centred around 380, 425, and 445 nm for CaTiO3, SrTiO3 and BaTiO3, respectively. These emission bands are similar to cathodoluminescence emissions from 25 keV electron irradiation attributed by others to direct conduction-valence band transitions in unreduced samples and oxygen vacancies in reduced samples. CaTiO3, SrTiO3 and BaTiO3 all have emission thresholds of 0.26±0.02 MeV. This corresponds to a threshold displacement energy for oxygen, Ed of 45±4 eV.

An overview of the fundamental early processes discussed in this section is summarized schematically in Figure 10. From this time onwards, thermal processes proceed.

Optical emission spectra in the 300-700 nm range were collected from zirconolite and rutile specimens irradiated with a 3 μs pulsed electron beam using a Febetron 706 variable energy pulsed electronbeam generator. The long-lived emissions (up to microseconds after the electron pulse) consist of broad (halfwidths ~ 100 nm) bands centred around ~400 nm. Over the range 0.2 MeV to 0.6 MeV, the emission intensity per unit dose versus electron beam energy data from the rutile sample showed a single stage dependence on electron beam energy, whereas the zirconolite data suggested a two stage dependence. Rutile has a threshold of 0.23 ½ 0.02 MeV, which gives an Ed value of 39 ½ 4 eV for oxygen. Zirconolite has a threshold of 0.26 ½ 0.02 MeV, which gives an Ed value of 45 ½4 eV for oxygen. These data are discussed in the context of previously measured and calculated Ed values for other oxides.

The kinetics of luminescence decay in electron-irradiated sapphire single crystals have been investigated using time-resolved luminescence spectroscopy. The data, observed over timescales from tens of nanoseconds to tens of milliseconds, characteristically feature a rapid decay of intensity punctuated by discrete plateau regions. Simple theoretical models, invoking such theories as first- or second-order mechanisms, rate laws or power-law dependences, are unable to explain these features. A theoretical model comprising bimolecular electron - hole recombination, together with unimolecular electron detrapping from two discrete traps, qualitatively accounts for these features.

Pulse radiolysis and emission spectroscopy techniques have been used to examine the production of the 2p1 state of Ar and the 4p 2P1/2 and 4p 2D5/2 states of Ar+ at gas pressures below 1 Torr. The rate of formation of these states has been compared with the results from calculations using the time-dependent Spencer–Fano theory of high-energy electron degradation. It is found that the theory successfully predicts the time scale of events in pulse-irradiated argon gas.

We have designed and are building a subpicosecond electron injector. The injector is based on an 8 MeV photoinjector, used previously at Los Alamos in the APEX experiment. The nominal design includes magnetically compressing a 20 ps long, 3 nC bunch to a FWHM bunch length of 2/3 ps (peak current in excess of 3 kA) using a four dipole chicane buncher. The geometrical averaged transverse normalized transverse emittance after compression is about 15 /spl pi/ mm mrad.

A Febetron 706 was used to irradiate a cadmium sulphide crystal at room temperature with 3 ns pulses of electrons with energy up 0.60 MeV. Time resolved emission spectroscopy was used to measure the irradiation induced luminescence spectrum at wavelengths between 200 and 600 nm. A prominent emission band with a maximum at 520 nm was observed. The irradiation electron energy was varied between 0.50 and 0.60 MeV and the emission intensity was recorded at 520 nm. A threshold for the onset of luminescence was observed at an electron energy of approximately 0.51 MeV. The threshold is attributed to sulphide ion displacement resulting in the production of F+ type centres. The sulphide ion displacement energy was calculated to be 53 +/- 1 eV.

A Febetron 706 was used to irradiate a cadmium sulphide crystal at room temperature with 3 ns pulses of electrons with energy up 0.60 MeV. Time resolved emission spectroscopy was used to measure the irradiation induced luminescence spectrum at wavelengths between 200 and 600 nm. A prominent emission band with a maximum at 520 nm was observed. The irradiation electron energy was varied between 0.50 and 0.60 MeV and the emission intensity was recorded at 520 nm. A threshold for the onset of luminescence was observed at an electron energy of ∼0.51 MeV. The threshold is attributed to sulphide ion displacement resulting in the production of F+ type centres. The sulphide ion displacement energy was calculated to be 53 ± 1 eV.

Point defects have been produced in CaO, MgO, and α‐Al 2 O 3 single crystals by electron irradiation, and thresholds for atomic displacement have been measured using timeresolved luminescence spectroscopy. Oxygen displacement energies of approximately 50 eV have been determined; however, a temperature‐dependent threshold observed for an emission band in MgO may arise from a magnesium displacement. A 300‐nm emission in α‐Al 2 O 3 may be due to an F‐center transition. Studies of radiative recombination kinetics are consistent with an electron‐detrapping model.

The formation and decay of the ``2p'' electronic excited states of the rare gases neon, argon, krypton, and xenon in a buffer gas of either helium or neon has been studied by pulse radiolysis techniques. The formation rate constants for these states are all greater than \ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, precluding atom-atom collisional processes and supporting a subexcitation electron mechanism. The rate constants generally show a trend ${\mathit{k}}_{\mathrm{Xe}}$>${\mathit{k}}_{\mathrm{Kr}}$>${\mathit{k}}_{\mathrm{Ar}}$>${\mathit{k}}_{\mathrm{Ne}}$. Quenching rate constants for the deactivation of some of the 2p levels are also reported.

The techniques of electron pulse radiolysis and emission spectroscopy have been used to determine the ionic recombination rate constants, Xe2+ + X- + Xe --> alpha XeX* + 2Xe in the formation of the XeBr* and XeI* exciplexes. These values show the typical pressure dependence of an increase to a maximum value of a approximately 3 X 10(15) M-1 s-1 (alpha approximately 4 X 10(-6) cm3 s-1) before the onset of diffusion controlled reaction. The comparison of the Xe2+/Br- data to the predictions of the Langevin-Harper diffusion controlled and Bates termolecular theories show that the experimental values are far larger and peak at much lower pressures than calculated, indicating that an additional mode of recombination is occurring. This is attributed to the electrostatic tidal pathway, observed previously in Xe2+/Cl- and Kr2+/Cl-recombination. In contrast the Xe2+/I- measured peak is in excellent agreement with the Bates prediction and at high pressures has rate constants even larger in magnitude than the Langevin-Harper diffusion controlled values. The application and extension of these theories to this system are discussed.

Point defects have been produced by electron irradiation in single-crystal alpha-Al2O3 from two different sources. Time-resolved luminescence spectroscopy has been used to study emission spectra and atomic-displacement thresholds for the defects. An emission band at 3.8 eV is present in only one of the crystals while a band at 4.2 eV is observed in both crystals. The former is probably due to F+-center emission and the latter possibly arises from an F-center transition. Emission kinetics are consistent with detrapping of electrons from two shallow traps.

Using pulse radiolysis techniques, rates of recombination of Ar2+ ions with electrons in bulk argon were measured over a wide pressure range (150 to 1065 torr) at bulk gas temperatures of 295, 335, and 375 K. No pressure dependence for the total recombination rate constant was observed at any temperature studied. This observation is consistent with the model, whereby the encounter pair is stabilized by electron energy loss while in the Coulomb field of the cation. The presence of a Ramsauer minimum in the electron/argon atom momentum-transfer cross section versus energy profile means that, at low energies, energy loss is very slow. The neutral-assisted three-body recombination mechanism in argon does not significantly enhance the total rate of recombination above the two-body rate.

The techniques of pulse radiolysis and emission spectroscopy have been used to measure ionic recombination rate constants for Kr2+/Cl- ions in irradiated Kr/CFCl3 gas mixtures. The measured values are seen to have the typical pressure dependence, showing an increase with pressure to a maximum value of approximately 3 x 10(15) M-1 s-1 (approximately 5 x 10(-6) cm3 s-1) at approximately 250 Torr, before the onset of diffusion-controlled reaction. However, the experimental values at low/medium gas pressures are seen to be far larger, and to peak at a much lower pressure, than predicted by Bates three-body recombination theory. At high gas pressures, the data are parallel to, but lower than the values predicted by Langevin-Harper diffusion-controlled reaction. This behavior is identical to that observed in the previously studied Xe2+/Cl-/Xe recombination system, and thus the discrepancies in the Kr2+/Cl-/Kr system are likewise attributed to two-body electrostatic tidal action mechanisms significantly contributing to ionic recombination. Based on a qualitative investigation of the major emitting potential energy curves for both these systems, a criterion is proposed for the prediction of this additional reaction occurring in other exciplex systems.

Using pulse radiolysis techniques, rates of recombination of electrons with He+2 ions in the presence of helium over a wide pressure range (40–900 Torr) and at temperatures of 200, 235, 275, and 295 K were measured. Two- and three-body recombination processes were resolved, and a temperature dependence for the three-body recombination rate constant of T(−2.9±1.2)gas observed. This result agrees well with theoretical predictions of a temperature exponent of −2.5 by Bates and Khare and Pitaevskii, and remarkably well with recent work by Cao and Johnsen which gave a temperature exponent of −2.9 for the rate constant for three-body recombination of electrons with simple molecular ions in the presence of helium.

The techniques of electron pulse radiolysis and emission spectroscopy have been used to determine the ionic recombination rate constants, Xe 2 + +X - +Xe→XeX * +2Xe in the formation of the XeBr * and XeI * exciplexes. These values show the typical pressure dependence of an increase to a maximum value of a α∼3×10 15 M -1 s -1 (α∼4×10 -6 cm 3 s -1 ) before the onset of diffusion controlled reaction. The comparison the Xe 2 + /Br - data to the predictions of the Langevin-Harper diffusion controlled and Bates termolecular theories show that the experimental values are far larger and peak at much lower pressures than calculated, indicating that an additional mode of recombination is occurring

The emission spectroscopy/pulse radiolysis method of determining three-body ionic recombination rate constants in rare-gas-halogen source gas mixtures has been extended to systems where the emission is produced by both ionic and nonionic pathways. This has enabled recombination coefficient measurements to be done over a large pressure range for irradiated Kr/SF6 and Xe/CFCl3 gas mixtures. The rate constants measured for both these systems show the typical pressure dependence of an increase to a maximum value of approximately 2.5 x 10(15) M-1 s-1 (approximately 4 x 10(-6) cm3 s-1), before the onset of the diffusion-controlled reaction. These values have been compared to the predictions of the Langevin-Harper diffusion-controlled and the Bates termolecular recombination models. The large discrepancies between theory and experiment have shown that other recombination processes dominate the ionic recombination.