Radiation pulsed

For an understandmg of pulsed excitation of spin ensembles it is of fiindamental importance to realize that radiation pulses actually contain ranges of frequencies A burst of monocln-omatic microwaves at frequency... 

The most direct and easy way consists in focusing the laser pulse onto a solid target and to collect the radiation emitted by the produced plasma. The wide emitted spectrum extends from infrared to X-rays and it is produced by different physical mechanisms Bremsstrahlung, recombination, resonant lines, K-shell emission from neutral (or partially ionized) atoms. In particular, this latter mechanism has been recognized, since a decade, as a way of producing ultrashort monochromatic radiation pulses at energy up to several keV. 

Usually, the average concentration of a reactive species such as OH or H is not directly observed in pulse radiolysis experiments, partly because the timescale of spur reactions is so short (< 10 ns) that most spur reactions have occurred during the radiation pulse which produces these species and partly because these species are very difficult to monitor on such a timescale. Instead, solutes are often added to water prior to radiolysis and the quantity of products formed by reaction of the solute... 

The electronic instrumentation necessary for the operation of the proportional counter is shown in Figure 18.6. Pulses from the detector pass through a preamplifier and amplifier, where they are shaped and amplified. Emerging from the amplifier, the pulses go to a discriminator. The discriminator is set so as not to trip on noise pulses but rather to trip on radiation pulses of any larger size. The number of discriminator pulses produced is recorded by the scaler. 

The organic1 secondary expls were sealed in quartz containers and exposed to a single radiation pulse. None of the expls detonated and subsequent examination of the samples revealed negligible damage... 

Figure 4. Ionization yield as a function of laser intensity for a radiation pulse with a linear tum-on of 1007 //. The field frequency is an = 10 a.u.. These yields are computed at t = 11007 //. The line represents the results for the time-dapendent Schrodinger equation treatment while the dots are the results of the Klein-Gordon equation treatment,...

Figure. 5. Two-color photoelectron spectrum for a radiation pulse containing two fre-...

THz spectroscopy was born from research efforts to produce and detect ultra-short electrical currents as they traveled down a transmission line.26 In 1988-1989, it was discovered that electromagnetic radiation pulses produced by time-varying current could be propagated through free space and picked up by a detector.27 By placing a sample between a THz source and detector, one could measure the differences in radiation pulses due to scattering or absorption by the sample to understand its chemical properties. 

But what causes the radiation pulses asks Miss Muxdroozol as she stares into the glowing flower. 

The mass spectrometry analysis was performed by the matrix assisted laser desorption/ionisation time-of-flight (S8-MALDI) technique using a Voyager-DE PRO Biospectrometry Workstation (Applied Biosystems, USA). Radiation pulses of 0.5 ns and 3 Hz frequency from N2 laser operating at 337 nm were used to desorb the species and negative/positive ions formed were detected in reflectron mode. Sulfur used as a matrix material was also dissolved in toluene and mixed with the samples solution prior to deposition onto a target. 

A number of simplifying assumptions allow for a mathematical model for this method The radiation pulse is uniformly distributed across the front face of the specimen and is ab-... 

An essential requirement is that the characteristic time, T2, for the decay of the macroscopic polarisation must be much longer than the time taken for the polarising radiation pulse to dissipate. This requirement is readily satisfied the pin-diode S2 is held closed until the pulsed radiation has dissipated, and is then opened to capture the coherent radiation emitted by the polarised gas, due to one or more rotational transitions producing spontaneous emission. If all is well, the emission is detected against a near-zero radiation background. 

The conversion of an oscillating electric field E(t), the so-called time domain spectrum, into a frequency domain spectrum is known as a Fourier transformation. A simple but neat description of this transformation is given by Hollas [16]. The oscillating electric field arising from a molecular emission line following the radiation pulse is converted into an oscillating voltage f(t) with a frequency v, which we may write... 

Fig. 11. —Ignition of a-Cellulose Containing Carbon Black, by Radiation Pulse. [(O Total radiant energy per unit surface (p) density of the sheet (c) heat capacity (L) thickness (a) thermal difFusivity (t) time of irradiation.]...

Consider a molecule in its ground state tj/g, an exact eigenstate of the molecular Hamiltonian, subjected to the very short external perturbation M S (Z) (such as caused by a very short radiation pulse, in which case M is proportional to the dipole moment operator). From Eq. (2.74) truncated at the level of first-order perturbation theory... 

The basic principle is to observe the change in absorbance after an intense radiation pulse has created a significant population of short-lived reactive intermediates. Early experiments used xenon flash lamps as excitation sources and were able to detect intermediates with lifetimes >10 second. Modern experiments use pulsed lasers as excitation sources. The monochromatic output of a laser allows selective excitation the narrow pulse width allows detection of species with lifetimes as low as 10 second. A complementary experiment uses a pulse of electrons from a linear accelerator to generate the reactive species. More experimental detail is available in many reviews [139]. 

An electronic or vibrational excited state has a finite global lifetime and its de-excitation, when it is not metastable, is very fast compared to the standard measurement time conditions. Dedicated lifetime measurements are a part of spectroscopy known as time domain spectroscopy. One of the methods is based on the existence of pulsed lasers that can deliver radiation beams of very short duration and adjustable repetition rates. The frequency of the radiation pulse of these lasers, tuned to the frequency of a discrete transition, as in a free-electron laser (FEL), can be used to determine the lifetime of the excited state of the transition in a pump-probe experiment. In this method, a pump energy pulse produces a transient transmission dip of the sample at the transition frequency due to saturation. The evolution of this dip with time is probed by a low-intensity pulse at the same frequency, as a function of the delay between the pump and probe pulses.1 When the decay is exponential, the slope of the decay of the transmission dip as a function of the delay, plotted in a log-linear scale, provides a value of the lifetime of the excited state. 

The small-angle data were gathered on a Kratky small-angle "camera" equipped with a Nal(Tl) scintillation counter and a Ni filter for CuKa radiation. Pulse-height-analysis was set to accept 90% of the CuKa radiation symmetrically, and the x-ray source was a special short (7mm) line focus tube (Siemens) so that there was no vignetting of the source by the x-ray tube window. After subtraction of instrumental background, all the scans were normalized to the intensity expected from a sample of optimum thickness (Itransmitted/l - 1/e). 

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