Low-energy Response Research Articles

Low-energy x-ray response of photographic films I Mathematical models

Relatively simple mathematical models are developed to determine the optical density as a function of the x-ray intensity, its angle of incidence, and its photon energy in the 100–10,000-eV region for monolayer and emulsion types of photographic films. Semiempirical relations are applied to characterize a monolayer film (Kodak 101-07) and an emulsion-type film (Kodak RAR 2497); these relations fit calibration data at nine photon energies well within typical experimental error.

Low-energy x-ray response of photographic films II Experimental characterization

Optical density versus exposure data have been obtained at nine photon energies in the 100–2000-eV x-ray region for five spectroscopic films (Kodak films 101-07, SB-392, RAR 2492, RAR 2495, and RAR 2497). These data were determined operationally by a direct comparison of the peak absolute intensities of spectral lines, which were measured with a calibrated proportional counter, with the microdensitometer tracings of the corresponding photographically recorded spectral lines. Film-resolution limits were deduced from an analysis of contact microradiograms of linear zone plates constructed of gold bars. The relationship between the specular densities as measured here and the diffuse densities have been experimentally determined for the five films. Finally, experimental measurements of the optical density versus the angle of incidence of exposing radiation of constant intensity were obtained. These data, relating density to the x-ray intensity, its photon energy, and its angle of incidence, are shown to be fitted satisfactorily in the 100–10 000-eV region by the semiempirical mathematical model relations that were derived in Part I of this research [ J. Opt. Soc. Am. B1, 818– 827 ( 1984)].

The Sea-Breeze-Induced Coastal Calm Zone as Revealed by Satellite Data and Simulated by a Numerical Model

Abstract Meteorological satellite scanning radiometer data from a visual sensor during daylight hours are characteristically influenced by sunglint from the ocean surface as the sensor scans in the direction toward the sun (between the satellite subpoint and solar subpoint). When seas are calm in the region near the primary specular point (PSP), the sun's rays are either reflected directly into the spacecraft sensor yielding a high energy (bright) response, or away from the sensor yielding a low energy (dark) response. The particular effect depends on the proximity of the calm area to the PSP. This paper shows examples of bright and dark linear patterns adjacent to and tending to parallel coastlines. The patterns are interpreted to be sea-breeze-induced calm zones originating during periods of offshore flow when the pressure gradient causing the sea breeze is exactly counterbalanced by the larger-wale synoptic gradient. A two-dimensional planetary boundary layer (PBL) numerical model successfully simulate...

INDEPENDENT EFFECTS OF PHYTOCHROME AND NITRATE ON NITRATE REDUCTASE AND NITRITE REDUCTASE ACTIVITIES IN MAIZE

Abstract— Involvement of phytochrome in the regulation of nitrate reductase (NR) and nitrite reductase (NIR) activities in excised, etiolated leaves of Zea mays (L.) variety ‘Ganga‐5’ is demonstrated using low energy and high irradiance responses of phytochrome action. Photoreversibility by far‐red light of red light stimulated increases in NR and NIR activities was lost by 2 h. Red light given to the leaves, when induction by NO‐3, was saturated, further increased both enzyme activities. Even if red light was given 4–8 h before NO‐3, it still increased both NR and NIR activities.

Coping with Plastic Scintillators in Nuclear Safeguards

Plastic scintillators offer several advantages for nuclear safeguards research and technology to those who design, assemble, encapsulate, and calibrate detectors from raw materials that are commercially available. These large, inexpensive detectors have good spatial uniformity and good high-energy gamma-ray response. Uniform light collection is obtained with a light pipe attached to a polished scintillator wrapped with aluminum foil. Best low-energy response is obtained by applying a variance analyzer to select the low-energy bias level.

Neutron dosimetry studies using CR-39 plastic

ABSTRACT The response of CR-39 plastic to monoenergetic neutrons when irradiated behind several different radiators has been studied using conventional pre-etching, followed by electrochemical etching, to reveal tracks as enlarged spots. The effects of varying the electrochemical-etching voltage and pre-etching time were also investigated. It was found that to produce a low-energy neutron response the electrochemical-etching voltage (at 5 kHz) must be greater than about 30 kV cm−1 (r.m.s.). A short pre-etching time was found to give the lowest background. The influence of the radiators can be qualitatively understood in terms of contributions from elastic H(n,n)p collisions and (n,p) and (n,α) reactions in the radiator materials.

Effects of red and far-red light on cell division in the shoot apex ofSilene coeli-rosa L.

28-day-old plant ofSilene coeli-rosa were exposed at 1,700 hours to 5 or 10 minutes red light, 5 or 10 minutes far-red light, red followed by far-red, far-red followed by red or maintained in darkness. Measurements of the proportions of cells with the 2 C and 4 C amounts of DNA in the shoot apex of the plants, sampled at 2,000 hours, showed that far-red light promoted an increase in the G2 proportion whereas red light resulted in an increase in the G1 proportion of the cell cycle, relative to the dark controls. Moreover these changes were red, far-red reversible. All light treatments resulted in increases in the mitotic index in the apex compared with the dark controls, suggesting increases in the growth rate. The data implicate phytochrome in a low energy response and suggest that, in the shoot apex, G1 is shortened markedly following exposure to farred light, whilst G2 is shortened the most following exposure to red light. The results are discussed in relation to flower-initiation.

Calorimeter Facilities

The aim of this talk is to provide an introduction to calorimetry on which the following more specialized presentations can build. I shall be selective in the choice of Calorimeter Facilities; strictly speaking there are only two in existence at storage rings, MARK-J at PETRA and MAC at PEP, each having the distinction of including hadron calorimetry. The examples chosen will all be taken from the storage ring environment, where the conditions are quite different from those which prevail at fixed target facilities. The apparatus sits in the centre of mass, consequently the average energy of the particles is lower and they enter the calorimeters at large angles to the normal. Each example will be used to illustrate the basic principle of a method of calorimetry or readout.The outline of the talk is as follows:(1) What is a calorimeter?(2) Facilities MARK-J.JADE-lead glass.TASSO-liquid argon.MAC-proportional chamber readout.AFS (R807)-uranium and BBQ readout.UA2-BBQ readout.(3) UA1 (a) energy calibration,(b) low energy response,(c) the problems associated with attempts to cover 4π solid angle.(4) LEP physics and calorimetry.(5) Summary and conclusions.

The Effects of Low Temperature Magnetic Cycling on the Properties of Ferromagnetic Materials

The interaction of dislocations with magnetic domain walls and the low energy response of dislocations at cryogenic temperatures have been investigated as a means of improving the structure sensitive properties of steel. Both cutting tools and carburized surfaces have shown an improvement when subjected to a cyclic magnetic field in the temperature range of 77 K to room temperature (RT). An annealing effect of the treatment suggests it may be a low energy substitution for conventional thermal tempering in specific applications.

The Connection between High Energy and Low Energy Responses to Red and Far‐Red Light of Hypocotyl Elongation in Red Cabbage Seedlings (Brassica oleracea var. capitata‘Marner Septemberrot’)

AbstractGrowth responses of hypocotyls of Brassica oleracea L. var. capitata caused by diurnal irradiation of various duration (0.5 h/d up to continuous irradiation) and various irradiance (0.3–1.5 W m−2) with red and far‐red light from sources characterized below can be described by the equation: image (W= relative effect, I= irradiance, t1= irradiation time per day, Ws= constant dependent on material and wavelength, α, B and ts, = constants dependent on wavelength.)On the basis of that equation a possible connection between longtime and short‐time irradiation responses is discussed.

Evaluation of Well-Type Ge(Li) Detectors for Low-Level Radiochemical Analysis

Well-type Ge(Li) detectors have been evaluated for low-level gamma-ray spectrometry and radiochemical analyses. The detectors were found to have good resolution, high peak-to-Compton ratios and low backgrounds. The use of an anticoincidence shield further improves the detector performance. The detector efficiencies and backgrounds are compared with those obtained with other Ge(Li) detector systems. The well detectors were found to have better detection efficiencies and as low backgrounds as either large coaxial detectors or opposed detector systems. Sum-coincidence effects are more pronounced in the well detector and use of this feature is discussed. Applications which utilize the low-energy response of the detector are described. Minimum detectable activity levels were determined for several nuclides.

The active form of phytochrome: A new hypothesis based on phytochrome pelletability studies

Difficulties arising from the current dogma that the far-red absorbing form of phytochrome ( P fr ) is the only active form are discussed. A new hypothesis is proposed in which phytochrome is held to be the photoreceptor for both low energy (pulse) and high energy (HIR) responses. There is a common basic mechanism of action involving interaction between phytochrome and a binding site within the cell. The phytochrome involvement in low energy responses exhibits an action spectrum for binding that matches the P r absorption spectrum and reversibility by far-red irradiation. Upon prolonged irradiation the phytochrome-binding site interaction acquires different characteristics that are reminiscent of those displayed in HIR, e.g. dependence on sustained irradiation for continual binding, dependence of the degree of binding on irradiance and the similarity of the action spectrum with that of HIR action spectra, e.g. that for inhibition of lettuce hypocotyl lengthening. As expected on the basis of the new hypothesis the particulate fraction of phytochrome contains both P r and P fr . Arguments are advanced that the presence of P r in pellets of particulate phytochrome cannot be accounted for by (i) the “induced fit” hypothesis, (ii) the “pigment cycling” hypothesis, and (iii) the “open phytochrome-receptor model”. We conclude that phytochrome molecules, after being sufficiently energized can interact with their intracellular binding sites irrespective of their chromophoric configuration.

A model-based efficiency calibration of a Si(Li) detector in the energy region from 3 to 140 keV

The full-energy peak efficiency in a particular geometry of a collimated 3 mm × mm 2 Si(Li) detector with 0.5 mil thick beryllium and Mylar windows was determined over the energy range 3.3–136 keV by measuring the absolute intensities of X- and low-energy γ-rays from the decays of intensity-calibrated sources of 241Am, 57Co, 137Cs and 65Zn. The measured efficiencies were fitted to a simple analytic function of photon energy, with the fit showing good agreement with the data over the entire range of energies. The physical basis of the model as well as the meaningfulness of its parameters is discussed. A discrepancy between the fit and the measured efficiency of the 17.75 keV L β + L η X-rays from 241Am decay required a re-evaluation of the intensity per decay for these transitions. Some peculiarities of the low-energy efficiency response are discussed and are attributed to source self-absorption effects. The extension of the calibration to lower energies would be possible if more low-energy photon sources with known X-ray intensities were available. The use of L X-rays and L/K intensity ratios calculated from published data for medium- Z elements is discussed and is considered to be feasible for this extension purpose. Some radio-nuclides that are likely to be useful in the low-energy region are suggested.

The influence of red light on the geotropic responses of Avena coleoptiles

Summary Two low-energy responses to red irradiation in Avena -coleoptiles are reported. One of them leads to a stepwise enhancement of the geotropic curvature, the other to a reduction of the curving zone. The sensitivity to red light and thus the Pfr requirement of the second enhancement of the curvature and of the reduction of the curving zone are the same. Yet only the effect on the length of the curving zone is antagonized by far-red light.

Response to a suddenly switched localized spin perturbation

The long time (low energy) response of extended systems to a suddenly switched localized spin perturbation is studied in three special situations: the Kondo problem, the X-Y model and the ferromagnet.

A high speed pulse shape discriminator

A high speed pulse shape discriminator utilizing the true zero crossover technique is described. Tunnel diodes are used in leading edge “anti-walk” timing and for zero crossover detection. The circuit has been used for n-γ discrimination applications with liquid scintillators and is demonstrated at rates above 8×10 4 cps. The circuit's performance in a typical application is shown in results from a neutron time-of-flight experiment using a pulsed beam of neutrons from the 7Li(p, n) 7Be reaction and where the peak to background ratio of the neutron time-of-flight spectrum is improved by a factor of more than 40. The circuit is also applied to low energy n-γ discrimination in a measurement of the low energy response for the NE213 liquid organic scintillator. Results are presented which relate gamma ray energies to neutron energies of equivalent pulse heights in the range 100 keV to 2.0 MeV neutrons.

Regulation of Senescence in Bean Leaf Discs by Light and Chemical Growth Regulators

The senescence of excised discs of primary leaves of Phaseolus vulgaris, L., var. Red Kidney was followed by measuring the net breakdown of protein and chlorophyll. The chemical growth regulators indoleacetic acid, 2,4-dichlorophenoxy-acetic acid, gibberellic acid, kinetin, and 6-benzylaminopurine were relatively ineffective in retarding senescence in this tissue. White light, on the other hand, was very effective in senescence retardation. The response to light did not have the characteristics of a low energy (phytochrome) response and was blocked by concentrations of 3-(3,4-dichlorophenyl)-1, 1-dimethylurea which inhibited photosynthesis in the leaf discs. The light-induced retardation of senescence was concluded to be dependent on photosynthesis.

The hydrogen-chlorine system in the mm pressure range. (II) The vibrational ground state studied by self-absorption: (Canada)J R Airey et al, Can J Chem, 42 (10), Oct 1964, 2193–2200

The full-energy peak efficiency in a particular geometry of a collimated 3 mm × mm2 Si(Li) detector with 0.5 mil thick beryllium and Mylar windows was determined over the energy range 3.3–136 keV by measuring the absolute intensities of X- and low-energy γ-rays from the decays of intensity-calibrated sources of 241Am, 57Co, 137Cs and 65Zn. The measured efficiencies were fitted to a simple analytic function of photon energy, with the fit showing good agreement with the data over the entire range of energies. The physical basis of the model as well as the meaningfulness of its parameters is discussed. A discrepancy between the fit and the measured efficiency of the 17.75 keV Lβ + Lη X-rays from 241Am decay required a re-evaluation of the intensity per decay for these transitions. Some peculiarities of the low-energy efficiency response are discussed and are attributed to source self-absorption effects. The extension of the calibration to lower energies would be possible if more low-energy photon sources with known X-ray intensities were available. The use of L X-rays and L/K intensity ratios calculated from published data for medium-Z elements is discussed and is considered to be feasible for this extension purpose. Some radio-nuclides that are likely to be useful in the low-energy region are suggested.

The Solid - State Ionization Chamber

Shallow diffused silicon p-n junction detectors have been used as room-temperature particle spectrometers for protons, alpha particles, heavy ions, and fission fragments. By the use of high base resistivity devices operated at high reverse biases (> 200 volts), the width of the sensitive volume has been extended beyond 0.5 mm, permitting linear response to protons up to 9 mev. Improved diffusion techniques have resulted in more shallow diffusion depths so that the window effect is reduced, extending the low energy response to below 200 kev for alpha particles. Use of low-noise amplifiers has permitted observation of half-widths of the pulse height-distribution equivalent to 18 kev.