Equivalent Photon Research Articles

Measurement of energy dependence for XRCT radiochromic film

Gafchromic XRCT, radiochromic film is assessed over a broad energy range, from kilovoltage to megavoltage x rays for variations in reflected optical density to dose response. A large energy dependence was found with reflected optical density output for the same delivered dose varying from 7.8 +/- 0.35 at 25.5 keV (50 kVp) peaking at 12.1 +/- 0.5 at 54 keV (125 kVp) to 0.975 +/- 0.03 at 2300 keV (10 MV) when normalized to 1 at 1400 keV (6 MV) energy. The response is constant (within 3%) in the 36-69 keV equivalent photon energy range, which corresponds to x-ray tube generating potentials of approximately 100-150 kVp. This matches well with beam qualities for diagnostic computed topography applications.

Beam normal spin asymmetry in the quasireal Compton scattering approximation

he two-photon exchange contribution to the single spin asymmetries with the spin orientation normal to the reaction plane is discussed for elastic electron-proton scattering in the equivalent photon approximation. In this case, the hadronic part of the two-photon exchange amplitude describes real Compton scattering (RCS). We show that in the case of the beam normal spin asymmetry this approximation selects only the photon helicity flip amplitudes of RCS. At low energies, we make use of unitarity and estimate the contribution of the piN multipoles to the photon helicity flip amplitudes. In the Regge regime, the quasi-RCS (QRCS) approximation allows for a contribution from two-pion exchange, and we provide an estimate of such contributions.

Vector meson production in ultraperipheral heavy ion collisions

Ultraperipheral heavy ion collisions (UPCs) are an important alternative for studying QCD dynamics until the next generation of e+e−/ep/eA colliders becomes a reality. Due to the coherent action of all the protons in the nucleus, the electromagnetic field is very strong and the resulting flux of equivalent photons is large, which allows us to study two-photon as well as photonuclear interactions at high energies. In this paper we present a brief review of the vector meson production in UPCs at high energies using the QCD colour dipole approach to describe their photonuclear production and the perturbative QCD Pomeron (BFKL dynamics) to describe the double meson production in photon–photon processes. Predictions for rates and integrated cross sections are presented for energies of RHIC and LHC.

Lepton-pair production from deep inelastic scatteringin peripheral relativistic heavy ion collisions

We calculate the inelastic electron- and muon-pair production in peripheral relativistic heavy ion collisions in the region of large Q 2 of one of the photons. This offers a possibility to study the quark distribution functions in ions in "ultraperipheral heavy ion collisions". The calculations are compared with those making use of the equivalent photon and the equivalent lepton approximation. We compare the results for Pb-Pb and Pb-p collisions at RHIC (γ ≈ 100) and LHC (γ ≈ 3000) energies. Furthermore we include nuclear modifications to the parton distribution functions in our calculations to study their effect on the cross sections.

High-power light-emitting diode based facility for plant cultivation

Based on perspectives of the development of semiconductor materials systems for high-power light-emitting diodes (LEDs), an illumination facility for greenhouse plant cultivation was designed with the dominating 640 nm photosynthetically active component delivered by AlGaInP LEDs and supplementary components from AlGaN (photothropic action, 455 nm) and AlGaAs (photosynthetic 660 nm and photomorphogenetic 735 nm) LEDs. Photosynthesis intensity, photosynthetic productivity and growth morphology as well as chlorophyll and phytohormone concentrations were investigated in radish and lettuce grown in phytotron chambers under the LED-based illuminators and under high-pressure sodium (HPS) lamps with an equivalent photon flux density. Advantages of the high-power LED-based illuminators over conventional HPS lamps, applicability of AlGaInP LEDs for photosynthesis and control of plant growth by circadian manipulation of a relatively weak far-red component were demonstrated.

Recoverin Improves Rod-Mediated Vision by Enhancing Signal Transmission in the Mouse Retina

Vision in dim light requires that photons absorbed by rod photoreceptors evoke signals that reliably propagate through the retina. We investigated how a perturbation in rod physiology affects propagation of those signals in the retina and ultimately visual sensitivity. Recoverin is a protein in rods that prolongs phototransduction and enhances visual sensitivity. It is not present in neurons postsynaptic to rods, yet we found that light-evoked responses of rod bipolar and ganglion cells were shortened when measured in recoverin-deficient retinas. Unexpectedly, the effect of recoverin on postsynaptic signals could not be explained by its effect on phototransduction. Instead, it is an effect of recoverin downstream of phototransduction in rods that prolongs signal transmission and enhances visual sensitivity. An important implication of our findings is that the recovery phase of the rod photoresponse does not contribute significantly to visual sensitivity near absolute threshold.

Dose rate dependence of the relative biological effectiveness of 103Pd for continuous low dose rate irradiation of BA1112 rhabdomyosarcoma cells in vitro relative to acute exposures

Purpose: To measure the relative biological effectiveness (RBE) of continuous low dose rate irradiation (CLDRI) using 103Pd sources relative to acute high dose rate irradiations (AHDRI) from a 250 kVp x-ray beam and an x-ray beam having an equivalent mono-energetic photon energy equal to the average energy of the 103Pd source for BA1112 rhabdomyosarcoma cells.Materials and methods: A customized 103Pd irradiator was built to provide CLDRI using 103Pd at different dose rates relevant to clinical interstitial brachytherapy to BA1112 rhabdomyosarcoma cells growing in exponential phase in culture. A special x-ray beam that simulates the photon energies emitted by the 103Pd source was also developed to provide acute high dose rate irradiation at those energies. Cell survival curves from different irradiation conditions were measured. The RBE with respect to AHDRI using standard 250 kVp x-rays was determined from the doses required to achieve a cell surviving faction of 0.01.Results: For acute irradiation, the RBE of the x-rays simulating 103Pd was 1.24 relative to 250 kVp x-rays. A profound dose rate effect was observed at low dose rates in the range of 6.8 – 14.4 cGy/h that are typical of permanent interstitial brachytherapy. At cell-surviving fraction of 0.01, the RBE of CLDRI at 6.8 and 14.4 cGy/h using 103Pd sources was reduced by a factor of 3 and 2, respectively, relative to the acute exposure. This observation is in good agreement with recent in vivo tumor cure studies performed on BA1112 tumor.Conclusion: The relative biological effectiveness of the photons emitted by 103Pd depends on both the linear energy transfer (LET) of the low energy photons and the dose rate of the irradiation. The higher LET of 103Pd photons is biologically more effective in killing BA1112 tumor cells compared to conventional 250 kVp x-rays when both are delivered at the same dose rate. But the gain in RBE that results from the higher LET can be quickly negated by the reduced dose rate of the irradiation.

Structural properties and quality of the photoexcited state in Cu(In 1− xGa x)Se 2 solar cell absorbers with lateral submicron resolution

We analyze the quality of the photoexcited state in Cu(In,Ga)Se 2 absorbers prepared under conditions similar to module pilot line production with different Ga-admixtures in terms of the splitting of the quasi-Fermi levels by confocal microscopic photoluminescence (PL) with submicron lateral resolution. The lateral luminescence patterns exhibit structures in the length scale of some micrometers (3–10 μm) which by far exceed the geometrical sizes of individual grains with diameters of 1 μm or below, detected simultaneously by optical reflection, and by scans of atomic force microscopy (AFM). The luminescence yields recorded at (83–250) K and at about (10 4–10 2) air mass 1.5 (AM1.5)-equivalent photon fluxes show lateral alterations by factors (2–20) depending on Ga-content, excitation level, and temperature. From temperature and excitation regimes, we are able to extrapolate the lateral variations towards 300 K and AM1.5-equivalent fluxes, and we translate PL-yields into lateral alterations of the splitting of quasi-Fermi-levels Δ( E Fn− E Fp) and of corresponding variations in maximum hypothetic open circuit voltages V oc.

YAP scintillators for resonant detection of epithermal neutrons at pulsed neutron sources

Recent studies indicate the resonance detector (RD) technique as an interesting approach for neutron spectroscopy in the electron volt energy region. This work summarizes the results of a series of experiments where RD consisting of YAlO3 (YAP) scintillators were used to detect scattered neutrons with energy in the range 1–200 eV. The response of YAP scintillators to radiative capture γ emission from a U238 analyzer foil was characterized in a series of experiments performed on the VESUVIO spectrometer at the ISIS pulsed neutron source. In these experiments a biparametric data acquisition allowed the simultaneous measurements of both neutron time-of-flight and γ pulse height (energy) spectra. The analysis of the γ pulse height and neutron time of flight spectra permitted to identify and distinguish the signal and background components. These measurements showed that a significant improvement in the signal-to-background ratio can be achieved by setting a lower level discrimination on the pulse height at about 600 keV equivalent photon energy. Present results strongly indicate YAP scintillators as the ideal candidate for neutron scattering studies with epithermal neutrons at both very low (<5°) and intermediate scattering angles.

Testing the equivalent photon approximation of the proton in the process $ep \rightarrow \nu W X$

The accuracy of the equivalent photon approximation (EPA) of the proton in describing the inelastic process $ep\to \nu W X$ is investigated. In particular, the scale dependence of the corresponding inelastic photon distribution is discussed. Furthermore, an estimate of the total number of events, including the ones coming from the elastic and quasi-elastic channels of the reaction, is given for the HERA collider.

Production ofe+e−pairs accompanied by nuclear dissociation in ultraperipheral heavy-ion collisions

We present data on e+e− pair production accompanied by nuclear breakup in ultraperipheral gold-gold collisions at a center of mass energy of 200GeV per nucleon pair. The nuclear breakup requirement selects events at small impact parameters, where higher-order diagrams for pair production should be enhanced. We compare the data with two calculations: one based on the equivalent photon approximation, and the other using lowest-order quantum electrodynamics (QED). The data distributions agree with both calculations, except that the pair transverse momentum spectrum disagrees with the equivalent photon approach. We set limits on higher-order contributions to the cross section.Received 7 April 2004DOI:https://doi.org/10.1103/PhysRevC.70.031902©2004 American Physical Society

Use of lithium niobate detector for measuring X-ray intensity in mammographic range

A detector system that can measure X-ray intensity in the mammographic range of 22 to 36 kVp (equivalent photon energies of the beam between 11 and 15 keV) is presented. It consists of a lithium niobate detector and a high-sensitivity current-to-voltage converter.

Accessing the longitudinally polarized photon content of the proton

We investigate the QED Compton process in longitudinally polarized lepton-proton scattering both in the elastic and inelastic channels and show that the cross section can be expressed in terms of the polarized equivalent photon distribution of the proton. We provide the necessary kinematical constraints to extract the polarized photon content of the proton using this process at HERMES, COMPASS, and eRHIC. We also discuss the suppression of the major background process coming from virtual Compton scattering. We point out that such an experiment can give valuable information on ${g}_{1}{(x}_{B}{,Q}^{2})$ in the small ${x}_{B},$ broad ${Q}^{2}$ region at the future polarized collider eRHIC and especially in the lower ${Q}^{2},$ medium ${x}_{B}$ region in fixed target experiments.

Semiclassical electroweak Weizsäcker-Williams method. II. Boson masses and minimum impact parameter

A semiclassical electroweak generalization of the Weizs\"acker-Williams method was formulated in a previous paper, with equivalent boson masses and the minimum impact parameter left as free parameters. These two quantities are derived and examined in great detail here. The mass of an equivalent boson is found to be determined by the mass and the electroweak charges of the parent fermion. It is shown that equivalent photons are massless, and the W and Z equivalent bosons have roughly the same mass. Formulas for the minimum impact parameter are also derived for various cases of interest. Using these results, the generalized number spectrum functions for point particles and nuclei are compared to similar functions found in other theories. Excellent agreement is found in all applications of the method.

Charge-changing interactions of ultrarelativisticPbnuclei

Experimental data and theoretical results on charge loss $\ensuremath{-}27\ensuremath{\leqslant}\ensuremath{\Delta}Z\ensuremath{\leqslant}\ensuremath{-}1$, charge pickup $\ensuremath{\Delta}Z=+1$, and total charge-changing cross sections for $158A\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$ $_{82}^{208}\mathrm{Pb}$ ions on ${\mathrm{CH}}_{2}$, $\mathrm{C}$, $\mathrm{Al}$, $\mathrm{Cu}$, $\mathrm{Sn}$, and $\mathrm{Au}$ targets are presented. Calculations based on the revisited abrasion-ablation model for hadronic interaction and the relativistic electromagnetic dissociation (RELDIS) model for electromagnetic interaction describe the data. The decay of excited nuclear systems created in both types of interaction is described by the statistical multifragmentation model (SMM), which includes evaporation, fission, and multifragmentation channels. We show that at very high projectile energy the excitation energy of residual nuclei may be described on average as $\ensuremath{\sim}40\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ per removed nucleon, with some increase in this value compared to fragmentation of intermediate energy heavy ions at $\ensuremath{\sim}1A\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$. The importance of the electromagnetic interaction in production of $_{80}\mathrm{Hg}$, $_{81}\mathrm{Tl}$, and $_{83}\mathrm{Bi}$ projectile fragments on heavy targets is shown. A strong increase of nuclear-charge pickup cross sections, forming $_{83}\mathrm{Bi}$, is observed in comparison to similar measurements at $10.6A\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$. This process is attributed to the electromagnetic production of a negative pion by an equivalent photon, which is quantitatively described by the RELDIS model.

Suppressing the background process to QED Compton scatteringfor delineating the photon content of the proton

We investigate the QED Compton process (QEDCS) in $e p \rightarrow e \gamma p$ and $e p \rightarrow e \gamma X$ , together with the major background coming from virtual Compton scattering (VCS), where the photon is emitted from the hadronic vertex. We suggest new kinematical constraints which suppress the VCS background and are furthermore suitable for the extraction of the equivalent photon content of the proton at the HERA collider. We show that the cross section, commonly expressed in terms of the proton structure functions, is reasonably well described by the equivalent photon approximation of the proton, also in the inelastic channel in the proposed kinematical region.

Energy dependence of Cronin momentum in saturation model for p + A and A + A collisions

We investigate the QED Compton process (QEDCS) in $e p \to e \gamma p$ and $e p \to e \gamma X$, together with the major background coming from the virtual Compton scattering (VCS), where the photon is emitted from the hadronic vertex. We suggest new kinematical constraints which suppress the VCS background and are furthermore suitable for the extraction of the equivalent photon content of the proton at the HERA collider. We show that the cross section, commonly expressed in terms of the proton structure functions, is reasonably well described by the equivalent photon approximation of the proton, also in the inelastic channel in the proposed kinematical region.

Neutrino magnetic moments and photo-disintegration of deuterium

Neutrinos with non-zero magnetic moments can dissociate deuterium nuclei by a photon exchange, in addition to the weak neutral current process. We calculate the neutrino magnetic moment induced photo-dissociation cross section of deuterium using the equivalent photon method. This process would contribute extra events to the neutral current reaction which is observed with high precision in the salt-phase of SNO experiment. Using the SNO data and the recent laboratory measurements of the 7 Be( p , γ ) 8 B reaction which give a more precise value of the solar 8 B flux we find that the neutrino effective magnetic moment is μ eff 2 =(−2.76±1.46)×10 −16 μ B 2 which can be interpreted as an upper bound | μ eff |<3.71×10 −9 μ B (at 95% C.L.) on the neutrino magnetic moments.

Neutrino magnetic moments and photo-disintegration of deuterium

Neutrinos with non-zero magnetic moments can dissociate deuterium nuclei by a photon exchange, in addition to the weak neutral current process. We calculate the neutrino magnetic moment induced photo-dissociation cross section of deuterium using the equivalent photon method. This process would contribute extra events to the neutral current reaction which is observed with high precision in the salt-phase of SNO experiment. Using the SNO data and the recent laboratory measurements of the 7Be(p,γ)8B reaction which give a more precise value of the solar 8B flux we find that the neutrino effective magnetic moment is μeff2=(−2.76±1.46)×10−16μB2 which can be interpreted as an upper bound |μeff|<3.71×10−9μB (at 95% C.L.) on the neutrino magnetic moments.

Estimation of X-ray beam quality by electron paramagnetic resonance (EPR) spectroscopy

A novel dosimetry-based technique using EPR spectroscopy to determine X-ray beam quality is proposed. The radiation-sensitive material is made of a mixture of two polycrystalline substances with different X-ray absorption properties. The composite samples, consisting of polycrystalline lithium formate monohydrate and calcium formate, were prepared as pellets, X-irradiated, and analyzed with EPR spectroscopy. The ratio of the EPR signal amplitudes of the two constituents can serve as a measure of the X-ray beam quality given by the equivalent photon energy. The calculation of the signal amplitude ratio involves a reconstruction of the composite EPR spectrum. The logarithm of the signal amplitude ratio appears to be linearly correlated with the logarithm of the equivalent photon energy. The linear relationship can be used as a calibration for estimating the equivalent photon energy from the composite EPR spectrum. The composite material was used to investigate the changes in the equivalent photon energy in a Perspex phantom with increasing depth. When a 220 kV X-ray beam with an equivalent photon energy of about 100 keV was used, changes in the EPR signal amplitude ratio revealed a buildup of scattered photons with increasing depth in the phantom. This change could be related to the equivalent photon energy using the logarithmic calibration curve. It was found that the equivalent photon energy at the depth of 13 cm in the phantom was 25% lower than on its surface. The proposed method can be used for estimating equivalent photon energy in both standardized and non-standardized situations, the latter corresponding to beam setups where use of filters and ionization chambers is difficult or impossible. Also, the system can provide a means for measuring photon energy in X-irradiated phantoms.