Photon Production Efficiency Research Articles

Production and application of a novel energy-tunable X-ray source at the RPI LINAC

The 60-MeV electron linear accelerator at Rensselaer Polytechnic Institute (RPI) is used to produce parametric X-rays (PXR). PXR is an intense, quasi-monochromatic, energy-tunable, and polarized X-ray source derived from the interaction of relativistic electrons with the periodic structure of crystal materials. Experiments were performed using highly oriented pyrolytic graphite (HOPG), LiF, Si, Ge, Cu, and W target crystal radiators. Smooth X-ray energy tunability is achieved by rotating the crystal with respect to the electron beam direction. Measured energy linewidths consistently agreed with predicted values except in cases using lower quality HOPG. When the predicted energy linewidth was narrower than our Si X-ray detector resolution (350eV at 17.5KeV), a near-absorption edge transmission technique that takes advantage of the PXR energy tunabilty was used to measure the PXR energy linewidth for example, Si(400) FWHM of 134eV at 9.0keV (2%). Per electron, the photon production efficiency of PXR is comparable to synchrotron radiation sources. A theoretical model that considers electron multiple scattering, electron divergence, and crystal mosaicity was used to broaden the PXR photon distribution in order to calculate the predicted PXR photon yield. Comparing measurements and calculations resulted in a typical relative error below 50%. In some cases with LiF, the differences between predicted and measured values were as low as 2% for LiF(400). Finally, this work reports for the first-time PXR imaging. This was achieved using LiF(220) interacting with 56MeV electrons with electron beam currents up to 6μA. The LiF and graphite PXR target crystals were compared for use in soft tissue imaging, e.g. mammography using energies 17–20keV. Low Z materials like graphite and LiF were most suitable for PXR production because of their low Bremsstrahlung production, electron scattering, and photon absorption. Graphite was more efficient at producing PXR photons while the LiF energy line width was narrower.

Numerical study on microdischarges in plasma display panels with arbitrary cell geometry

In this study, a plasma display panel (PDP) cell is modeled in a two-dimensional cross-sectional region and plasma discharge characteristics are analyzed by numerical simulations based on the finite difference method developed here. An orthogonal curvilinear coordinate system is introduced to apply to the arbitrary PDP cell geometry for systematic computations. Wall voltage transfer curves derived through experiments and computation are compared in detail. They show good agreement. The effect of PDP cell geometry on the voltage margin and on ultraviolet (UV) photon production efficiency are also studied. Results show that the thickness of front dielectric layer has a marked effect on the voltage margin and UV photon production efficiency. Furthermore, the dielectric ribs prevent the crosstalk of discharge in two ways: they decrease a number of excited species leaking to adjacent PDP cells and decrease charge distribution on the dielectric surface near the cell boundaries.

Effects of neutron source selection on land-mine detection efficiency

One proposed method of land-mine detection is based on measurements of the 10.8 MeV photons from the 14N(n, γ) reaction. In this study, simulations of the photon production efficiencies for nitrogenous explosive material (TNT), buried in soil having variable moisture content, were completed for different published neutron spectra. Monte Carlo simulations were performed with MCNP with a cylindrical geometry of TNT considered as target material and with neutron energies ranging from thermal to 20 MeV. The numbers of 14N(n, γ) reactions in TNT were tallied to obtain response functions. To find the effectiveness of different neutron sources, response functions were folded with the neutron spectra. Response curves reveal that higher water content increases response for fast neutrons, and reduces response for slow neutrons. Lower energy neutron sources, i.e. D(d, n) or 252Cf, are more suitable than higher energy neutron sources such as 241Am–Be or T(d, n). Although its advantages disappear with increasing depth, the usage of moderating spheres of CH 2 increases the signal significantly when compared with a bare source, while also reducing neutron dose to workers.

Free Energy Control of Reaction Pathways in Electrogenerated Chemiluminescence

Electrogenerated chemiluminescence (ECL) from 9,10-diphenylanthracene (DPA) in acetonitrile has been examined following reaction of its radical ions with various donors and acceptors by using high speed potential pulses at a microelectrode. The reaction pathways were identified by examining the reaction orders of the limiting reagents and by comparison of the temporal emission pulses with simulated reaction schemes. For reactions with a free energy value more negative than that required to directly form the excited state singlet (3.06 eV), first-order behavior was observed for DPA radical ions indicating direct singlet formation (S-route). For the remaining systems the reaction order was second order in DPA radical ions, indicative of excited singlet formation via triplet−triplet annihilation (T-route). Despite evidence of triplet quenching by the unreacted radical ions, the efficiency of photon production at high concentrations of DPA by the T-route (0.012) approached that of the S-route, and is much hig...

Electrogenerated chemiluminescence. XIV. Effect of supporting electrolyte concentration and magnetic field effects in the 9,10-dimethylanthracene-tri- p-tolylamine system in the tetrahydrofuran

A comparison of the efficiency of photon production in the chemiluminescence studies of Weller and Zachariasse and in ECL for the system involving reaction of 9,10-dimethylanthracene (DMA) radical union and tri- p-tolylamine (TPTA) radical cation in tetrahydrofuran (THF) solutions was undertaken. The luminescence intensity increased and the magnitude of the magnetic field effect decreased when the supporting electrolyte (TBAP) concentration was decreased from 0.2 M to 10 mM. The ECL efficiency, extrapolated to low TBAP concentrations, was in good agreement with that of the chemiluminescence studies.

Production of Photons in the Bactericidal Effect of Transient Electric Arcs in Aqueous Systems

The radiation in the visible and ultraviolet regions from submerged, transient electrical arcs was measured with a K(3)Fe(C(2)O(4))(3) chemical actinometer and was compared to the bactericidal effect obtained with the same electrical arrangements. Photon production and bactericidal effect were obtained at lower voltages with a smaller electrode separation than with a wider one. At higher voltages, both increased with wider electrode separations. The voltages at maximal photon production efficiency coincided with those of maximal bactericidal efficiency. However, the same photon radiation produced by different electrical arrangements did not always yield the same bactericidal effect in the small discharge vessel usually employed. In a larger discharge vessel, the bactericidal effect was closely correlated with the photon production. The efficiency of photon production by transient arcs was smaller than that of germicidal mercury lamps, particularly with respect to wavelengths of great bactericidal activity. The mechanisms of inactivation and their use for practical disinfection purposes are discussed.

Production of photons in the bactericidal effect of transient electric arcs in aqueous systems.

The radiation in the visible and ultraviolet regions from submerged, transient electrical arcs was measured with a K(3)Fe(C(2)O(4))(3) chemical actinometer and was compared to the bactericidal effect obtained with the same electrical arrangements. Photon production and bactericidal effect were obtained at lower voltages with a smaller electrode separation than with a wider one. At higher voltages, both increased with wider electrode separations. The voltages at maximal photon production efficiency coincided with those of maximal bactericidal efficiency. However, the same photon radiation produced by different electrical arrangements did not always yield the same bactericidal effect in the small discharge vessel usually employed. In a larger discharge vessel, the bactericidal effect was closely correlated with the photon production. The efficiency of photon production by transient arcs was smaller than that of germicidal mercury lamps, particularly with respect to wavelengths of great bactericidal activity. The mechanisms of inactivation and their use for practical disinfection purposes are discussed.

Study of Organic Scintillators

The scintillation counting behavior of a group of fifty-five pure crystalline organic compounds has been extensively studied. The data obtained have been analyzed with the goal of developing a better understanding of the scintillation process and of scintillator behavior. The materials were carefully purified, and massive crystals were grown. Relative scintillation average-pulse-height efficiencies at 30°C and —70°C for cobalt-60 gamma-ray excitation, gamma-ray excited scintillation decay times, and 2537 A ultraviolet-excited reflection and transmission photofluorescence spectra have been determined. A few solutions were also studied for comparison purposes. The purification and properties of the different materials are discussed in detail. The experimental data have been analyzed on the basis of Birks' photon cascade theory of the scintillation process. The ratio of the scintillation efficiency to the integrated photofluorescence intensity is shown to be a measure of Birks' primary photon production efficiency. The primary photon efficiencies vary over a relatively narrow range, so that there is a rough general correlation between the scintillation efficiencies and the integrated photofluorescence intensities. The best phosphors are those with rigid molecular and crystal bonding so that both the primary photon production and photofluorescence efficiencies are reasonably high. There is a tendency for the best scintillators to have the simplest and most sharply defined photofluorescence spectra. The scintillation efficiencies have been correlated with molecular structures and the mobility of the π electrons (or with the resonance interactions) within the molecules. In the simpler cases, consideration of singly charged quinoid structures permits the calculation of parameters which can be directly correlated with the scintillation efficiencies. In more complex cases, steric hindrance, hyperconjugation, ``unshared'' and ``nonbonding'' electron pairs, five-membered aromatic rings, heavy atom (triplet-state) effects, and quinoid (quenching) ground states must be considered. In all cases, the effects of thermal (vibrational) perturbations are present. ``Bond density'' and ``bound valence'' values have proved to be useful in correlating scintillation phenomena and molecular structure effects. Strongly colored compounds are usually poor scintillators. Earlier predictions of high scintillation efficiency for quinquephenyl and sexiphenyl are reaffirmed, and coronene, benzo[ghi]-perylene, and 1,2,5,6-dibenzanthracene are also predicted to be significantly better than the presently known organic scintillators. The further study of compounds containing five-membered aromatic rings appears promising. A generally good correlation has been found between the scintillation efficiencies and molecular diamagnetic anisotropy values. Some relationships between the scintillation decay times and the molecular structures can also be seen. The best crystalline organic scintillators are colorless substances of high melting point possessing molecules of simple structure and low atomic number in which there is extensive resonance conjugation of rings, ethylenic double bonds, and other groups to give extended, rigidly interlocked systems.