Beam pulsing

Due to the pulsed radiation output of the LINAC the detectors and the detector electronics have to handle very high counting rates in very short periods. Therefore the detectors have to work in a mode, where the detector output is integrated for one or several beam pulses. For that purpose the crystals are coupled to photo- diodes. Their currents are read out and analysed by the electronic board, which has been developed for this special application. 

On-demand beam pulsing has been shown to be effective for eliminating pulse pileup in the X-ray detection system, minimizing the energy dissipated in delicate specimens, yet maximizing the data throughput of the overall system. In essence. 

To evaporate the source material, various heating methods are used such as resistance heating, electron beam, pulsed excimer laser, or cathodic arc (where the source is the cathode). 

X = 0, CH2, CHCOOH, C(COOH)2, NH, NCH3 N(CH2CH=CH2), N(CHs)2 Cl Bobrowski and Das published a series of papers on the transients in the pulse radiolysis of retinyl polyenes31-37, due to their importance in a variety of biomolecular processes. They studied32 the kinetics and mechanisms of protonation reaction. The protons were released by pulse radiolysis, on a nanosecond time scale, of 2-propanol air-saturated solutions containing, in addition to the retinyl polyenes, also 0.5 M acetone and 0.2 M CCI4. Within less than 300 ns, the electron beam pulse results in formation of HC1. The protonated products of retinyl polyenes were found to absorb optically with Xmax at the range of 475-585 nm and were measured by this absorption. They found that the protonation rate constants of polyene s Schiff bases depend on the polyene chain... 

With respect to the practical considerations of gas flow and vacuum requirements, the PHPMS experiment might, upon cursory consideration, appear to be easily extended into the VHP region. That is, several MS-based analysis techniques routinely use ion source pressures of 1 atm. However, when an attempt to increase the pressure within a PHPMS ion source is made, the factors that do become problematic are those related to the subtle principles on which the method is based. Most importantly, the PHPMS method requires that the fundamental mode of diffusion be quickly established within the ion source after each e-beam pulse, so that all ions are transported to the walls in accordance with a simple first-order rate law while the IM reactions of interest are occurring. This ensures that a constant relationship exists between the ion density in the cell and the detected ion signal. The rates of the IM reactions can then be quantitatively determined from the observed time dependencies of the reactant ion signal because the contribution of diffusion to the time dependencies are well known and easily accounted for. 

Experimental details for the cross-section measurements were presented in the literature. Briefly, after the irradiation by electron beam pulse for a few nanoseconds, the time-dependent absorption for the atomic line transition Rg Rg -i-/zv was measured to observe the time-dependent population of the excited rare gas atoms Rg. The population of excited Rg was determined using an absorption law for the atomic lines, where the broadening of the absorption profile due to the thermal Doppler effect and due to the attractive interatomic potentials was reasonably taken into consideration. The time-dependent optical emission from energy transfer products, such as ... 

The choice of the method depends on the type of process. With electron beams the critical process parameters are beam energy, beam current, scanning factors and uniformity, beam pulse characteristics, and the configuration of the product being processed. 

Fig. 1 left FTIR spectrum (a) and 2D-IR spectrum (b) of the ground state for perpendicular polarization of pump and probe pulse. A broadband IR probe pulse measures the spectral change as a function of delay and frequency of a narrowband IR pump pulse (c). right time resolved absorption spectrum (d, magic angle polarization) and transient 2D-IR spectrum (e) recorded 20 ps after UV excitation. The T2D-IR spectrum was recorded with magic angle between UV-pump (500 fs, 5 iJ) and IR-pump polarizations and perpendicularly polarised IR-pump and probe beams, pulse sequence (f). 

A.E. Tselev, Cross-beam pulsed laser deposition as a method for preparation of thin films of metastable solid solutions. PhD Thesis, TU Dresden, Dresden (2000)... 

Very recently Kouchi et al. constructed an ion beam pulse radiolysis system and use it for the study of the LET effect in irradiated polystyrene thin films [106]. The nanosecond pulsed MeV ion beam with the variable repetition rate was obtained by chopping ion beams from a Van de Graaff. Time profiles of the excimer fluorescence from polystyrene thin films, excited by He+ impact, were... 

Basic Studies on Product Analysis and Ion Beam Pulse Radiolysis of Polymers. 102... 

The present chapter describes mainly the radiation effects of various ion beams on spin-coated polystyrene and PMMA films studied mainly by product analysis and by nanosecond ion beam pulse radiolysis. 

Direct measurement of short-lived reactive intermediates by time-resolved spectroscopic methods is very important for understanding the detailed mechanisms of radiation effects. Very recently a new ion beam pulse radiolysis system using optical multi-channel detection has been developed. Although the use of ion beam pulse radiolysis for studying the radiation effects of ion beams on polymers was first reported by us [3, 30], the new system is highly modified for investigating ion beam reactions. Electron beam pulse radiolysis was also carried out complementarily. 

The investigation of the ion beam interaction with polystyrene by means of ion beam pulse radiolysis has the advantage that the reactive intermediates can be directly detected. Time profiles of the excimer fluroescence from ion irradiated polystyrene were measured using the polystyrene thin films. Thus, the transient phenomenon excited by the ion with a definite kinetic energy was observed. 

In Fig. 5, the schematic diagram of the ion beam pulse radiolysis system with an optical emission spectroscope is also shown. The emission produced by the pulsed ion beam impact is detected through a monochromator by a fast photomultiplier tube (PMT) operated in a counting mode. The time profile of the emission is obtained by a coincident measurement between a photon and a... 

Fig. 5. The schematic diagram of the pulsing system and the ion beam pulse radiolysis system with an optical emission spectroscopy. PMT denotes photomultiplier tube HV, high voltage supply CFD, constant fraction discriminator TAC, time to amplitude converter and PH A, pulse height analyzer. From Ref. 36...

Fig. 10. Decay curves observed in electron beam, synchrotron radiation (SR), and ion beam pulse radiolysis of neat n-dodecane liquids...

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