Pulsed electron accelerators

The radiation effect produced by heavy ions can be simulated with electrons if the ions have high velocities. It is in this case that the spatial distribution of active particles in the track is close to the one in tracks of fast electrons. At small velocities of heavy ions the tracks of delta electrons overlap each other to a considerable extent, which results in the concentration of charged particles in a microvolume of the ion s track being very high. With development of powerful pulsed electron accelerators it became possible to create high concentrations of active particles in a medium. According to Ref. 372, with such accelerators one is able to reproduce and study the processes occurring in tracks of heavy ions. 

It is difficult to span the intervening energy gap between photo- and radiation chemistry, however, high powered pulsed lasers, utilising multiphoton absorption by the medium, do much to remedy this situation. For the most part, the work described falls into two categories, data with steady state irradiation i.e. light sources and Co-y rays, and pulsed experiments as with lasers and pulsed electron accelerators such as Van de Graaffs and Linacs. 

Flash X-ray generators or pulsed electron accelerators with peak energy of 500 keV or greater. 

Pulsed Electron Accelerator. The very high intensity pulsed electron accelerator used was a 705 Febetron (Field Emission Corporation, McMinnville, Oregon, U.S.A.). This is nominally a 2 Mev. accelerator. Its mode of operation has been described previously (16). 

Pulse radiolysis requires access to an electron accelerator or similar device. This requirement usually restricts work to specialized laboratories. Thorough descriptions of the experimental apparatus and protocols have been given.23,24... 

More common in the liquid phase is pulse radiolysis6. In this technique, electron accelerators which can deliver intense pulses of electrons lasting a very short time (ns up to /is) are used. Each single pulse can produce concentrations of intermediates which are high enough to be studied by methods such as light absorption spectroscopy or electrical conductivity. 

The electron itself is frequently used as a primary source of radiation, various kinds of accelerators being available for that purpose. Particularly important are pulsed electron sources, such as the nanosecond and picosecond pulse radiolysis machines, which allow very fast radiation-induced reactions to be studied (Tabata et al, 1991). Note that secondary electron radiation always constitutes a significant part of energy transferred by heavy charged particles. For these reasons, the electron occupies a central role in radiation chemistry. 

High Field Photonics in Laser Plasmas Propagation Studies, Electron Acceleration, and Nuclear Activation With Ultrashort Intense Laser Pulses... 

Although this work is restricted to electron acceleration, it has to be mentioned here for completeness that an increasing amount of work is currently devoted (often in the same laboratories) to the study of proton and light ion acceleration with laser pulses, also in view of future medical applications. Among a number of recent works on this subject, see for example [9] and [10]. 

Recently, an interesting correlation between the laser pulse polarization and the ellipticity of the electron beam profile has been observed [71]. However, no major influence of laser polarization on the efficiency of the electron acceleration processes has been observed so far, nor this influence has been predicted by theory and simulations, differently from the proton acceleration. For proton acceleration, a great improvement on bunch charge and quality are expected by using circularly polarized laser pulses focused on thin foils at ultra-high intensities [72-74]. 

A rapid reaction kinetic technique (time scale = 10-1000 ps) that typically uses a Van de Graff accelerator or a microwave linear electron accelerator to promptly generate a pulse of electrons at sufficient power levels for excitation and ionization of target substances by electron impact. The technique is the direct radiation chemical analog of flash photolysis and the ensuing kinetic measurements are accomplished optically by IR/visible/UV adsorption spectroscopy or by fluorescence spectroscopy. 

That the hydrated electron is a separate chemical entity has been demonstrated by the technique of pulse radi l sis This consists of subjecting a sample of pure water to a very short pulse of accelerated electrons. The energetic electrons have the same effect upon water as a beam of y-ray photons. Shortly after the pulse of electrons has interacted with the water, a short flash of radiation (ultraviolet and visible radiation from a discharge tube) is passed through the irradiated water sample at an angle of 90° to the direction of the pulse to detect the absorption spectra... 

In pulse radiolysis experiments these radicals are formed by a short pulse, 10-12-10-6 s depending on the experimental set up, in concentrations enabling their physical observation. The linear electron accelerator of the Hebrew University of Jerusalem, which is used, forms up to... 

Pulsed-electron irradiation expts are usually conducted with accelerators charged from 0.1 to 6.0 MeV and pulse durations ranging from 3—60 nsecs. The expls are pressed pellets with thicknesses of about 0.2 of the electron range. Calorimeters are used to measure the fluences. 

Irradiation Source. One to two rad electron or x-ray pulses are required to produce 6 to 12 nAf e aq. We use 1 Msec, pulses of 16 m.e.v. tungsten x-rays generated with an ARCO electron accelerator. The pulse must, however, be introduced in a time short compared to the measured half-lives. Any similarly pulsed x-ray beam of 150 to 200 k.e.v. would serve equally well since there is no rigid requirement of uniform irradia-... 

Much of the work in the early development of the preceding techniques incorporated pulsed electron-impact ionization sources or any of several types of laser ionization techniques. In almost all of these cases the ions were created in a pulsed fashion in vacuum and formed in or sent into the acceleration region of the mass spectrometer, where a static acceleration field present there injected them into the mass spectrometer. Such ion sources use the TOF-MS very efficiently because the repetition rate of the spectrometer is limited by the frequency of the ionization event itself. This arrangement allows the TOF-MS to mass analyze of all of the ions formed completely. However, many of the most popular ionization techniques being used in inorganic analysis today are continuous in nature. 

The positrons that arrive at the formation foil share the time structure of the electron accelerator, giving 2 ps long pulses of about 104 slow positrons at 600 Hz. Since a 7-ray detector would be saturated, the coincidence technique cannot be used, giving an order of magnitude worse signal-to-noise ratio than that in the previous experiments (due to 7 scintillations in the Lyman-a photo-multiplier), but the higher data rate more than compensates for this in total time to reach a given precision. 

Work is currently underway to re-measure the 1S-2S energy level splitting. An electron accelerator beam dump at AT T Bell Laboratories has been shown to produce 4 x 104 slow positrons/pulse at 30 Hz, and further improvements are expected.[ll] We anticipate a 10 increase in the number of available thermal Ps. In collaboration with M. Fee and K. Danzmann at Stanford, we are also working... 

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