Photon Ratio Research Articles

Feasibility of in vivo tissue characterisation by Compton scattering profile measurements

The authors investigate a technique for the characterisation of biological tissues, based on energy analysis of Compton scattered photons. The incident beam consists of 59.54 keV photons and a backscatter geometry is used. Compared to the technique based on the ratio of photons coherently scattered due to the Rayleigh effect and those incoherently scattered due to the Compton effect, the present technique provides similar results for mineral content evaluation, with an error lower than 1%. However it allows the determination of fat content in a soft tissue matrix - even in the cases in which the Rayleigh peaks is not measurable - although the error can rise up to 3%.

Abundances in the interstellar medium

Recent developments in the theory of element production and the chemical evolution of the galaxy are presented. Following this, observational data and their interpretation are given. A case by case analysis of results for D, He, Li and CNO isotope data in the disk and center of our galaxy is presented; previous results for element gradients are also summarized. The primordial abundances of D and He cannot be directly obtained from observations; corrections for stellar processing are discussed. From these data and the Li abundances, it appears that the abundance of the light elements is consistent with the standard big bang. In agreement with previous results, the range ofη, the baryon to photon ratio, is 5–8 10−10. If the amount of non-baryonic matter is small, these results indicate an open universe, in the standard big bang model. New data show a gradient in the (12C/13C) and (16O/18O) ratios with galactocentric distance, DGC. The presence of a gradient in the (14N/15N) ratio is less clear and there is no measurable gradient in the (32S/34S) ratio. In the interstellar medium near the sun, the carbon isotope ratio is −20 percent lower than the solar system ratio. This indicates that there has been only a moderate amount of enrichment of the nearby interstellar medium since the formation of the solar system. These results and previously determined galactic element gradients are interpreted in the framework of chemical evolution models. Delayed recycling of nucleosynthesis products is essential for the correct interpretation of the results. Comparisons of data with galactic evolution models are discussed.

The featureless continua and hydrogen lines of Seyfert 2 galaxies

We present optical and ultraviolet spectra taken in similar sized large apertures for 15 Seyfert 2 galaxies. Measurements of emission-line strengths of Lyα, Hα, and Hβ are used together with measurements of the ultraviolet slopes to estimate the ratio of recombination photons to ionizing photons. The photon ratios indicate that the ionizing continuum is being emitted anisotropically for at least six of the eight objects with UV slope measurements. The median value of the UV slope is α = - 1.35 (F<SUB>nu</SUB>_ is proportional to ν<SUP>alpha</SUP>^), which is indistinguishable from the UV slope of Seyfert 1 galaxies. This result suggests that in the occultation/reflection picture of Seyfert nuclei, the reflecting particles are free electrons and not dust. We verify previous observations of variability in Mrk 477 and show that this galaxy exhibits characteristics of both Seyfert 1-and Seyfert 2 galaxies.

Photocontrol of stem elongation in plant neighbourhoods: effects of photon fluence rate under natural conditions of radiation

Abstract.We investigated the effects of photon fluence rate on internode elongation in fully de‐etiolated plants growing under sunlight. Our goal was to find out whether perception by the stems of fluence rate changes related to canopy density may be involved in the modulation of internode growth in canopies formed by plants of similar stature (e.g. crop stands). UsingDatura feroxL. andSinapis albaL. seedlings growing under natural radiation, we found that internode elongation is promoted by localized shading. This effect was observed with internodes receiving light with a high (&gt;0.9) or a low (0.3) red (R) to far‐red (FR) photon ratio. Selective removal of the different wavebands from the light impinging on the internodes showed that part of the response to fluence rate is due to photons in the R + FR range. The blue (B) component, most likely acting through a specific photoreceptor, also inhibited elongation. However, changes in the fluence rate of B light did not have detectable effects on the response of the internodes to R:FR ratio. Fibre‐optic studies and measurements with integrating‐cylinder sensors in even‐aged populations of seedlings showed that both the quality and quantity of radiation received by the stems are profoundly influenced by changes in canopy density. When density is very low (leaf area index = LAI ≥ 1) only the R:FR ratio is reduced, due to FR reflected from nearby leaves. In the LAI range of 1 to 2, though a large proportion of the leaf area is still receiving full sunlight, the photon fluence rate at the stem level drops dramatically. These results suggest that in even‐aged populations of LAI &gt; 1 elongation growth is promoted by the low R:FR ratioandthe reduced fluence rate. Perception of these two factors at the stem level may elicit morphological adaptations in the canopy before the onset of severe competition among neighbours for the resource of light.

Effects of light quality and quantity on growth of the clonal plant Eichhornia crassipes.

Plant canopy shade reduces photosynthetic photon flux density (PPFD) and ratio of red to far-red light (z). Both effects can cause plants to increase potential for light acquisition through vertical growth and leaf area expansion. Clonal plants such as Eichhornia crassipes might alternatively increase light interception via horizontal growth of stolons or rhizomes and placement of new ramets in less shaded microsites. Effect of simulated canopy shade and component effects of PPFD and z were tested by filtering or adding light uniformly, to a whole group of connected ramets, or locally, to individual ramets within a group. In uniform treatments, low PPFD reduced total growth but low z did not. Low PPFD and low z independently reduced stolon and ramet production and caused etiolation of petioles; effect of low PPFD plus low z on ramet production was greater than that of either factor alone. Lateral clonal growth thus did not seem to be a response to uniform shading; instead, uniformly low PPFD or low z increased partitioning to established ramets. Low z changed partitioning without changing total growth. In local treatments, reduction of growth of individual ramets due to low PPFD and inhibition of new ramet production attributable to spectral composition of light were mitigated when connected ramets were unshaded; plants may respond differently to patchy than to uniform shade.

Some spectral properties of several soil types: implications for photomorphogenesis*

Abstract. Light transmission through several sands, soils and size classes of glass beads was investigated. The glass beads served as a highly reflective model system for the sands. Light penetration was significantly better through sands than through either sandy or silty loams. For sandy soils, there was a shift in the spectrum leading to a change in the red‐to‐far‐red photon ratio with increase in depth: this ratio dropped by more than 30% in the first few millimetres, and in some cases increased again with further increases in depth. The depths at which these changes occurred in the soil profile were specific for a given soil type. Similar spectral changes were obtained when sample depth for a sandy soil was held constant, and particle (ped) size of that soil was decreased. No such changes, either with sample depth or ped size, were observed with loams. Per cent transmittance in the blue (442 nm) was more than three orders of magnitude lower than in the red (632.8 nm) for sandy soils. When dry sandy soils were water‐saturated, their transmittance increased by up to three orders of magnitude, and the red far‐red ratios in the transmitted light increased in all cases. By contrast, water‐saturated loams were essentially opaque. The possible significance of these spectral properties of soils in seed germination and seedling photomorphogenesis is discussed.

Urknall und Evolution des Kosmos

For the very early times (" Urblitz" < 10-6 s) cosmology requires knowledge about the fundamental particles and their interactions at very high energies. The Grand Unified Theories (GUTs) provide insight into the open problems of the cosmological standard model: The absence of antimatter, the number ratio of photons and baryons and the problem of the large-scale homogeneity and isotropy. The importance of an extremely high energy density of the "vacuum" is discussed for the inflationary expansion in the very early universe and the related origin of matter. Finally, ideas about the future evolution of the cosmos are considered.

X‐ray production in thin films by electrons with energies between 40 and 100 keV. 2—Characteristic cross‐sections and the overall x‐ray spectrum

AbstractTwo approximate theories are considered for the production of characteristic x‐rays when thin foil targets are bombarded with electrons with energies between 40 and 100 keV. One, due to Kolbenstvedt, is semi‐classical in nature whilst the other, due to Bethe, contains two parameters which are normally adjusted empirically. Data from six different target materials are presented, but because errors in experimentally derived absolute cross‐sections are large, a comparison is made between theoretical and observed ratios of characteristic Kα photons to bremsstrahlung photons in a 20 eV channel directly beneath the peak. By adjusting the Bethe parameters and using a modified Bethe‐Heitler theory to predict the bremsstrahlung, agreement between experiment and theory of typically 10% is recorded. Finally, a means of simplifying the equations used to enable rapid calculation of x‐ray spectra with a pocket calculator is indicated.

Photoelectrochemical observations on chlorophyll- carotene interactions in a lipid bilayer film

Photoelectrochemical investigations were undertaken on energy transfer and other interactions between chlorophyll-a (Chl-a) and β-carotene (Car) in lipid monolayers. A heterobilayer composed of a Chl-a-lecithin monolayer and a Car- lecithin monolayer was prepared on an SnO 2 semiconductor electrode by Langmuir-Blodgett techniques. When the bilayer-coated electrode was irradiated in an aqueous electrolyte, anodic photocurrents due to the sensitizations by Chl-a and Car respectively were observed. The photocurrent efficiency (ratio of photons to electrons) was much for Car (about 10 -3) than for Chl-a (about 10 -1). This large difference permits a quantitative estimation of the energy transfer from Car to Chl-a, based on the concept that the energy transfer results in an increase in the Car- induced sensitized photocurrent. The effect of added Chl-a on the Car photocurrent was measured for heterobilayers with various Chl-a-to-Car molar ratios. The experimental results, as well as theoretical calculations, showed that the Car-to- Chl-a energy transfer is inefficient. The effect of Car on the Chl-a-sensitized photocurrent was also studied with the same bilayer system. The effect was shown to be complex depending on the Car content. A lowering of the Chl-a photocurrent occurred at high Car contents, which is considered to reflect the quenching of the Chl-a excited triplet by Car. The usefulness of the present photoelectrochemical approach for the study of energy transfer between the photosynthetic pigments is demonstrated.

Constraints on the density of baryons in the Universe

It is shown that not only does Big Bang nucleosynthesis provide an upper limit on the baryon density of the Universe, but if one takes into account arguments concerning the production of 3 He in stars, one can show that the 3 He plus deuterium abundance can also provide a lower limit on the baryon density of the Universe. The derived constraints are that the baryon: photon ratio, y, must be between 1.5 x 10- 10 and 7 x 10 -9 with a best fit between 3 and 6 x 10 -10 . This small range for y has implications for our limits on numbers of neutrino types, for Big Bang baryosynthesis, and for arguments about the nature of the dark matter in clusters of galaxies. With reference to the dark matter, the derived baryon density for Big Bang nucleosynthesis corresponds very closely with the implied density of matter in binaries and small groups of galaxies. This implies that non-baryonic matter is not dominant by a large factor on scales as large as binaries and small groups of galaxies. It is also shown that the constraints on the lower limit on the baryon density constrain the lower limit on the primordial 4He abundance. Consistency seems to be possible only if the primordial 4 He is between 23 and 25 % by mass if there are three or four species of neutrinos.

Thermal production of superheavy magnetic monopoles in the early universe

Starting with an initial abundance of zero, we calculate the thermal production of magnetic monopoles by using the monopole-antimonopole annihilation cross section and detailed balance. The final abundance of monopoles depends exponentially upon m/ T i ; m is the monopole mass ∼10 16 GeV and T i is the temperature when production commences. For m/ T i ≈35–55 the present monopole to photon ratio is nM/ n γ ≈10 −23−10 −38, less than the bound derived from the present mass density, but possibly large enough to be detected. This calculation provides a lower bound on the monopole abundance for a given m/ T i .

Coherent production of photons by neutrinos

The reaction ν+N→ ν+N+ γ, involving the coherent emission of a photon in a neutrino-nucleus collision, can produce “single shower” events that simulate the reaction ν+e→ ν+e. The ratio of coherent photons to electrons (for an 27Al target) is estimated to be 40% at E ν =20GeV and 10% at E ν =20 GeV. We examine the extent to which the “excess” of showers seen in the Aachen-Padova experiment could be understood by this mechanism.

Study of Strong Spin-Isospin Mode Analog States at 4.5 MeV inB12inC12(e, e′π+)B12

Strong spin-isospin mode, $T=1$, ${T}_{z}=1$ analog states at 4.5 MeV in $^{12}\mathrm{B}$ were studied by the reaction $^{12}\mathrm{C}(e, {e}^{\ensuremath{'}}{\ensuremath{\pi}}^{+})^{12}\mathrm{B}$ at the electron energy ${E}_{e}=200$ MeV. The photoproduction cross sections at seven angles ranging from 30\ifmmode^\circ\else\textdegree\fi{} to 150\ifmmode^\circ\else\textdegree\fi{} were obtained with use of virtualphoton theory and an experimentally determined real-to-virtual photon ratio. The results are compared with theoretical calculations and also with the available data on inelastic scattering from the 19.5-MeV $T=1$, ${T}_{z}=0$ analog complex in $^{12}\mathrm{C}$.

A measurement of direct photon production at large pT at the CERN ISR

We have measured direct photon production in pp collisions at the CERN intersecting storage rings for c.m. energies 31 < √ s < 63 GeV and transverse momenta up to 9GeV/ c, using segmented lead/liquid-argon calorimeters. The ratio of direct photon to π 0 production is significantly larger than zero, starting at p T ≈ 4 GeV/ c and increasing to values of about 0.4 at 9GeV/ c. No significant √s dependence is seen.

THE QUANTITATIVE EDS ANALYSIS OF THE CONSTITUENTS OF BINARY ALLOYS WITHOUT STANDARD SAMPLES

In general, the quantitative electron probe microanalysis is based on comparisons with standard samples. In this article, a method of the quantitative analysis of binary alloys without reference to standard samples is introduced. After simultaneous measurements of the ratios of the Ka photons of two elements in the binary alloys (Cu-Ga, GaAs) in SEM-EDS equipment, the constituents of the binary alloys are calculated from a simplified formula for the energy loss of the incident electrons, the X-ray excitation cross-section and the secondary fluorescence. When the overvol-tage of the incident electrons is kept in the range 2-3, the calculated results show good agreement with the actual constituents. The "instrument sensitivity" of the characteristic X-ray of the pure elements determined in the literature is calculated and discussed by using this simplified model.

Limits on the production of large transverse momentum direct photons deduced from the measurement of low-mass electron pairs

The hadronic production of electron pairs with masses between 200 and 500 MeV and large transverse momentum has been measured at the CERN Intersecting Storage Rings (ISR). The expected relation between low-mass electron pairs and real photons is used to determine the direct hadronic production of photons. Contrary to indications from some previous experiments, the observed spectrum is consistent with expectations from the decay of known mesons, and leads to a value for the ratio of direct photons to π 0 of γ/ π 0 = (0.55 ± 0.92)% for 2 < p T < 3 GeV and 〈√ s〉 = 55 GeV.

Fluorescence yields of metal halide vapors excited by photodissociation

We have measured the absolute quantum efficiency (photon ratio) of atomic and/or molecular fluorescence owing to excitation by photodissociation at 205 nm (FWHM=15 nm) in a number of metal halide vapors. The measurements were done at pressures of about 0.1 Torr. The results are TlI=0.42, InI=0.20, HgI2=0.09, HgBr2=0.26, ZnI2=0.14, and CdI2=0.09. We believe these to be the first measurements of fluorescence yields in the metal halide vapors.

Copious Direct Photon Production: A Possible Resolution of the Prompt-Lepton Puzzle

We propose that all direct leptons not due to vector meson decay can be attributed to the decay of virtual photons. At ${p}_{\ensuremath{\perp}}\ensuremath{\approx}3$ GeV/c, we expect $\frac{\ensuremath{\gamma}}{\ensuremath{\pi}}$, the ratio of direct photons to pions, to be about 10 to 20% for $\sqrt{s}\ensuremath{\approx}20\ensuremath{-}60$ GeV.

Theory of early universe explains particle production

If the early universe had a strongly time‐dependent gravitational field, the field would have created pairs of particles, according to Ya. B. Zel'dovich (Institute of Applied Mathematics, USSR Academy of Sciences). This mechanism might explain the existence of particles in the universe, and it offers the hope of understanding why the present ratio of photons to baryons in the universe is 108.

Methods for Improving the Signal-to-Noise Ratio of Photon- and Electron-Beam-Accessed Magnetic-Film Memory Systems

Methods are described for reducing shot-noise in magnetic-film memories which are to be read magneto-optically with the auxiliary aid of an electron beam. In such memories the principal source of shot noise is from the light which is used to illuminate the memory array. The following methods of reducing array shot noise are considered: (1) selective background, (2) magneto-optical balance, (3) temperature control of magneto-optical spectra in rare-earth iron garnets (REIG). It is concluded that the use of REIG spectra appears to offer not only the best, but also a satisfactory solution to the array shot-noise problem.