Electron linear accelerator, pulsed

Production X-ray tube Synchrotron Nuclear reactor Electron linear accelerator pulsed source Proton spallation pulsed source... 

Fig. 1. Block diagram of the nanosecond pulse radiolysis system using the Hokkaido University 45 MeV electron linear accelerator...

So far the microwave electron linear accelerator is the most suitable for this purpose. In this accelerator electrons are injected into an evacuated cylindrical waveguide in which pulsed radiofrequency of several megawatts from a klystron oscillator travels. Electrons enter the radiofrequency field at the correct phase are accelerated to a velocity close to that of light. By means of gun control, electrons are injected only during the radiofrequency pulse, and thus the electron pulses of several nanosecond duration, useful for conventional nanosecond or microsecond pulse radiolysis, are produced. 

Pulse radiolysis systems capable of picosecond time resolution use the fine structure of the output from the electron linear accelerator. Electrons in the accelerating tube respond to positive or negative electric field of the radiofrequency, and they are eventually bunched at the correct phase of the radiofrequency. Thus the electron pulse contains a train of bunches or fine structures with their repetition rate being dependent on the frequency of the radiofrequency (350 ps for the S-band and 770 ps for the L-band). 

At the Institute for the Organic Synthesis and Photoreactivity (ISOF) is operating a 12 MeV (maximum energy with no load) Vickers L-band (1.3 GHz) traveling wave electron linear accelerator. The LINAC was put in operation mainly to be used as energy source for pulse radiolysis studies. 

The first experiments with the TOF method were accomplished on stationary reactors, obtaining a pulsed neutron beam by mechanical choppers. The real potential of the method was realized after the building of pulsed neutron sources, such as pulsed reactors, electron linear accelerators and proton synchrotrons - spallation sources. In electron linear accelerators (LINAC) and proton synchrotrons, targets from 239 j heavy atoms are used. Slowing-... 

The maximum neutron flux from research reactors Is limited by heat dissipation in the moderator. The optimum performance of a moderator assembly can therefore be Improved by pulsed neutron methods. The first phase in the development of pulsed neutron sources was based on electron linear accelerators which produce fast neutrons in a heavy metal target by (Y,n) and (y>f) processes C3 ] The problems of heat dissipation again limit the flux but the use of an incident proton beam overcomes this difficulty. The Spallation Neutron Source (SNS) C35] Is based on a 800 MeV proton... 

Fig. 6. Apparatus for Doppler-free two-photon spectroscopy of positronium, produced with a pulsed electron linear accelerator.

Pulse radiolysis was performed using e from a linear accelerator at Osaka University [42 8]. The e has an energy of 28 MeV, single-pulse width of 8 nsec, dose of 0.7 kGy, and a diameter of 0.4 cm. The probe beam for the transient absorption measurement was obtained from a 450-W Xe lamp, sent into the sample solution with a perpendicular intersection of the electron beam, and focused to a monochromator. The output of the monochromator was monitored by a photomultiplier tube (PMT). The signal from the PMT was recorded on a transient digitizer. The temperature of the sample solution was controlled by circulating thermostated aqueous ethanol around the quartz sample cell. Sample solution of M (5 x 10 -10 M) was prepared in a 1 x 1 cm rectangular Suprasil cell. 

The hydrated electron may well find use in analytical chemistry laboratories. Not only have we shown that e aq is a valuable species for measuring submicromolar concentrations of its scavengers, but we have also demonstrated that satisfactory results may be obtained by very feeble x-ray pulses. While we irradiated our samples with 16 m.e.v. electrons or x-rays from a linear accelerator, an inexpensive pulsed x-ray unit of 150-200 k.e.v., capable of delivering 1 to 2 r/pulse, should serve equally well. Furthermore only minimal shielding is required under these conditions, thereby greatly facilitating manipulations needed for carrying out routine analyses. 

Another aspect of pulse radiolysis which has been improved is the pulse duration. For most experiments of interest to the physical organic chemist the common machines with pulse durations of 10 7-10-5 s are quite satisfactory, though for certain reactions, such as those involving protonation, examination on a shorter time scale can be of value. Several accelerators which supply nanosecond pulses are currently in use, but they are employed mostly with microsecond detection systems. Work in the 10-12-10-1° s region has recently become possible by the stroboscopic technique utilizing the fine structure pulses from a linear accelerator (Bronskill et al., 1970). More recently, a system which produces a single pulse of 40 picoseconds has been constructed (Ramler et al., 1975) and utilized for the observation of hydrated electrons at very short times (Jonah et al., 1973). 

A pulse of 2-10 Mev electrons from a linear accelerator, passed through aqueous solutions of pyridinium ions leads rapidly to substantial concentrations of pyridinyl radicals , including those derived from the coenzyme, nicotinamide adenine dinucleotide . The pyridinyl radicals disproportionate, are protonated or dimerize. The reducing agent is a solvated electron or the COj" radical anion (Eq. 4) . 

Samples were irradiated by a 10 ps single or 2 ns electron pulse from a 35 MeV linear accelerator for pulse radiolysis studies (17). The fast response optical detection systems of the pulse radiolysis system for absorption spectroscopy (18) is composed of a very fast response photodiode (R1328U, HTV.), a transient digitizer (R7912, Tektronix), a computer (PDP-11/34) and a display unit. The time resolution is about 70 ps which is determined by the rise time of the transient digitizer. 

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