Light Emission Curve Research Articles

Organic glass scintillator (OGS) property comparisons to Stilbene, EJ-276 and BC-404

A new fast organic glass scintillator (OGS), recently developed at Sandia National Laboratories, has been proposed as a lower cost alternative to stilbene for detecting fast neutrons in intense gamma-ray fields, where excellent pulse-shape analysis (PSA) is required. In this paper we evaluate this proposition by measuring OGS’s scintillation properties and comparing them to three well known materials: stilbene, EJ-276, and BC-404. The measured properties were single photon light emission curves, coincidence time resolution (CTR), luminosity (photons/MeV), and figure of merit (FOM) for neutron/gamma PSA. From the light emission curves, we found that OGS has an 0.82 ns 10–90 risetime, close to EJ-276’s value of 0.81 ns and 25% faster than BC-404 and stilbene’s values at 0.96 and 1.01 ns, respectively. CTR values were measured from 75 to 325 keV, with OGS approaching 200 ps at 325 keV, compared to 250, 325 and 325 ps for BC-404, stilbene, and EJ-276, respectively. OGS had the highest luminosity, at 15,821 photons/MeV, compared to stilbene (13,054), BC-404 (8410), and EJ-276 (5522). For PSA, we studied neutron and gamma-ray pulse shapes as a function of energy and investigated various PSA algorithms, finding a properly selected tail/peak ratio to be generally best. OGS PSA FOM values were found to be twice as large as for EJ-276 and almost as good as stilbene’s – reaching 2.9, 1.5, and 3.2 at 1 MeVee respectively. Since OGS can be produced by lower cost casting techniques, this work supports further OGS development efforts.

Comportamento da produção de espécies reativas de oxigênio em miocárdio de ratos submetidos a treinamento de baixa intensidade em diferentes temperaturas

INTRODUÇÃO: A prática de exercício físico proporciona aumento da produção de espécies reativas de oxigênio (ERO) resultantes do metabolismo aeróbio e, gera uma quantidade significativa de calor, em conseqüência da produção de energia, resultando em sobrecarga orgânica. A associação entre ERO e exercício, e entre exercício e variações da temperatura ambiente têm sido estudadas, contudo, há escassez de informações que considere a associação entre produção de radicais livres no miocárdio e atividade física em temperatura elevada. OBJETIVO: Comparar a produção de ERO em miocárdio de ratos submetidos ao treinamento de baixa intensidade em diferentes temperaturas. MÉTODOS: Foram utilizados 20 ratos Wistar, machos, jovens, peso (250 a 280g), divididos em quatro grupos: G1 (n = 5) expostos ao treinamento e calor (39º ± 1C); G2 (n = 5) expostos somente ao calor durante o mesmo período de G1, sem treinamento; G3 (n = 5) expostos ao treinamento em temperatura ambiente (22º ± 1C); G4 (n = 5) expostos à temperatura ambiente sem treinamento. O treinamento foi realizado em esteira rolante climatizada por cinco semanas, evoluindo 5 minutos a cada duas sessões finalizando em 60 minutos em baixa intensidade 8m/min. O ambiente foi controlado entre 39 ± 1ºC e 22 ± 1ºC e entre 40 e 60 % de umidade relativa. A lipoperoxidação foi avaliada por Quimiluminescência (QL). A análise dos dados foi realizada a partir do teste Two Way ANOVA para análise da QL e t de student para a Capacidade Antioxidante Total (TRAP). RESULTADOS: A análise da QL revelou uma curva de emissão de luz significantemente mais baixa para o grupo exposto ao exercício em normotermia comparado aos sedentários mantidos no calor. A análise da TRAP mostrou diminuição em todos os grupos experimentais em relação ao G4. CONCLUSÃO: Concluiu-se que houve níveis menores de produção de ERO nos grupos submetidos somente ao calor ou somente ao exercício.

Capillary underwater discharges in repetitive pulse regime

In this study a capillary underwater discharge, that is sustained with AC (50 Hz) voltages up to 7.5 kV, is investigated. In a capillary discharge scheme, the current is, at some point along its path between two submerged electrodes, flowing through a narrow elongated bore in a dielectric material. When the current density is sufficiently high, local boiling and subsequent vapour breakdown results in the formation of a plasma within this capillary. At the same time the capillary emits an intense jet of vapour bubbles. Time-dependent electrical current, voltage and light emission curves are recorded for discharges in solutions of NaCl in distilled water and reveal different discharge regimes, depending on the conductivity and the excitation voltage, ranging from repetitive microsecond discharge pulses to a quasi-continuous discharge with a glow-like voltage-current characteristic.

Use of firefly luciferase in atp-related assays of biomass, enzymes, and metabolites

The kinetics of ATP reagents not affected by product inhibition or other forms of inactivation of luciferase during the measurement time has been clarified. Under these conditions the decay rate of the light emission expressed as percentage per minute is a measure of luciferase activity and can be given as the rate constant k (min-1), directly reflecting the degradation of ATP in the luciferase reaction. Three types of reagents with different analytical characteristics and different application possibilities have been identified. Stable light-emitting reagents are suitable for measurements of ATP down to 1000 amol. This is the only type of reagent suitable for monitoring ATP-converting reactions, i.e., assays of enzymes or metabolites, assays of oxidative phosphorylation, photophosphorylation, and so on. A higher luciferase activity resulting in a slow decay of the light emission by approximately 10% per minute (k = 0.1 min-1) gives a reagent suitable for measurements down to 10-100 amol. The slow decay of light emission allows use of manual luminometers without reagent dispensers. A further increase of the luciferase activity resulting in a decay rate of approximately 235% per min (k = 2.35 min-1) and only 10% of the light emission remaining after 1 min is suitable for measurements down to 1 amol corresponding to half a bacterial cell. With this type of flash reagent the total light emission can be calculated from two measurements of the light intensity on the decay part of the light emission curve. This new measure is not affected by moderate variations in luciferase activity, but only by changes in quantum yield and self-absorption of the light in the sample. Flash-type reagents require the use of reagent dispensers. The stringent requirements for ATP-free cuvettes, pipette tips, and contamination-free laboratory techniques make it unlikely that flash reagents would be useful in nonlaboratory surroundings. A potential application for this type of reagent is sterility testing. In general, it is concluded that one should select the ideal ATP reagent carefully for each application. Obviously the reagents used in a particular application do not have to match the decay rates given earlier exactly. However, various applications of the ATP technology and the properties of manual and automatic luminometers fall quite nicely into categories corresponding to the properties of the three reagents described. The rapidly growing interest in ATP technology has already resulted in the development of a greater variety of luminometers, from hand-held instruments to high-throughput systems. The continuation of efforts in both reagent and instrument development will undoubtedly result in many new applications.

A mechanism for impact ionization of Si n-channel MOSFETs

Cross-gap excitation by the collision of a conduction electron and a valence electron in the drain junction of an Si n-channel MOSFET is discussed on the basis of substrate current characteristics and light emission spectra. The characteristic curve of the logarithm of substrate current relative to drain current vs drain voltage is represented by a “refracted” straight line. The refraction in the characteristic curve can be related to electron-hole pair creation by an indirect interband transition along the Δ-axis of the Brillouin zone. A broad peak is found around 2–2.5 eV in the light emission curve above the drain voltage of 5 V. This peak is due to radiative recombination along the Δ-axis, superimposed on a monotonic emission curve due to bremsstrahlung. The indirect interband transition along the Δ-axis plays a significant role in impact ionization in a high electric field.

Luminol chemiluminescence using xanthine and hypoxanthine as xanthine oxidase substrates

Luminol chemiluminescence induced by the xanthine or hypoxanthine-O 2-xanthine oxidase system is analyzed and compared. Characteristics of the light emission curves were examined considering the conventional reaction scheme for the oxidation of both substrates in the presence of xanthine oxidase. The ratio of the areas of the light intensity versus time curves for hypoxanthine compared with xanthine is greater than that expected from the rate of superoxide production during substrate oxidation to uric acid. The O 2 ⨪ to uric acid ratio for each substrate can account for differences in xanthine and hypoxanthine-supported light emission, since uric acid is a strong inhibitor of O 2 ⨪-dependent luminol chemiluminescence. These results are consistent with a free radical scavenging role for uric acid. A similar but weaker scavenging effect of xanthine may also contribute to the observed differences in chemiluminescent yields between both substrates.

Inference of the Hard X-Ray Source Dimensions in the 1972, August 7 White Light Flare

SummaryBroadband photographs and spectra of the white light flare of 1972, August 7 have been compared with hard X-ray spectra from the same event. There is a very close temporal correspondence between the hard X-ray and white light emission curves, and these emissions come from layers that are separated by a height of less than 2000 km. The flare shows at least two distinct particle acceleration phases: the first, occurring at a stationary source, gave very bluish continuum emission from 4 bright stationary knots while the X-ray (E > 60 keV) spectrum hardened and reached peak intensity. This phase occurred between 1520 and 1523 UT. In the second phase (1524–1537 UT) the bright knots dissolved and a faint wave moved out from the flare center at 40 km s–1. The spectrum of the wave was nearly flat in the range 4950–5900 Å and analysis of the spectrum indicates that the emission was probably due to heating and ionization by 20–100 keV electrons. The X-ray spectrum, as derived from Interkosmos 7 and ESRO TD-1A satellite data, becomes softer during the wave phase. The close correspondence between the X-ray and continuum emission events shows that, in effect, the hard X-ray source has been resolved. It consists of several changing patches approximately 3″ × 5″ in area, consistent with the upper limit of 1′ from balloon observations (Takakura et al., 1971).

Effect of conditions of crystallization on molecular relaxation in polypropylene

It was shown that annealing “Moplen” isotactic polypropylene (PP) granules at temperature of 433–443°K and remelting reduced T g. Samples slowly cooled from melt have lower T g than quenched samples. By the crystallization of PP from 1% tetrachloroethylene solution samples were obtained with a ‘shish-kebab’ structure, which are characterized by a very low intensity β-maximum of radiothermoluminescence. Annealing ‘shish-kebab’ specimens at 433–453°K produces an intense β-maximum near 210°K. After heating these specimens to 455°K or higher temperatures spherulitic PP samples are obtained for which the shape of light emission curve agrees with that of the light emission curve of initial PP granules heated under the same conditions. It was shown that storing annealed PP speciments with a spherulitic structure at room temperatures is accompanied by a gradual increase of T g. It was assumed that the main cause of variation of T g of PP during heat treatment and storate is the formation of micropores and stressed sections in the amorphous phase of PP.

Light emission from the Scenedesmus obliquus wild type, mutant 8, and mutant 11 strains, measured under steady-state conditions between 4 nanoseconds and 10 seconds

1. The entire time course of the delayed light emission, from 4 ns to several seconds, was measured from the wild type D 3 strain, from the mutant 8 strain, and from the mutant 11 strain of Scenedesmus obliquus algae. The algae were illuminated by 488 nm, 12 mW/cm 2 laser light which was modulated on and off by either a rotating slotted disc or by an electro-optic laser light modulator. The kinetics of the light emission from the algae were measured through a 690-nm interference filter during the time intervals between the stimulus laser light flashes. 2. The D 3 wild type strain and mutant 8 produced delayed light emission of an intensity which could be measured by our apparatus, while any emission present from mutant 11 was not intense enough to be recorded. This indicated that most, if not all, of the delayed light emission originated from photosystem II. 3. The delayed light emission curve for the wild type and mutant 8 strains decayed in a complex fashion, i.e. the delayed light emission decay curves could not be described analytically by a single exponential term. 4. The initial microsecond section of the delayed light emission curve intersected the prompt fluorescence decay curve at virtually a right angle for both the wild type and the mutant 8. The lack of a transition zone between the two curves indicated that the prompt fluorescence was not a fast component of delayed light emission. Also, the lack of a transition zone between the two curves is evidence that delayed light emission occurred concurrently with prompt fluorescence during the periods the algae were exposed to the laser light. Following the instant the stimulus laser light was extinguished, the prompt fluorescence intensity fell to zero and the presence of the less intense delayed light emission was revealed. 5. The intensity of light emission from an algal sample could be measured (a) a few microseconds before the stimulus light was extinguished, and (b) in the first microsecond after the stimulus light was extinguished. Since the delayed light emission decay curve was rather flat throughout the first microsecond following stimulus light extinction, the ratio of prompt fluorescence intensity to delayed light emission intensity could be closely approximated as the ratio of (a)/(b). This ratio was found to be 165:1 for the wild type algae and 165:0.3 for the mutant 8. The algal samples were always preilluminated by the modulated laser light for 20 min prior to the ratio measurements.

Occultation of Beta Scorpii by Jupiter on May 13, 1971

PHOTOELECTRIC observations of the occultation of the star β Scorpii by Jupiter were carried out at our field station at Kavalur on the night of May 13–14, 1971, at the cassegrain focus of the 38 cm reflecting telescope. Our photometric record was made by photographing a CRO trace in order to record the true light emission curve during the immersion and emersion phases of the occultation. The record was calibrated by photographing seconds pulses from a quartz clock simultaneously. A thin glass plate behind the focal plane diaphragm allowed continuous visual monitoring of the Jovian limb and the occultation phenomenon.

Fluorescence of Solutions Bombarded with High Energy Radiation (Energy Transport in Liquids) Part II

In organic solutions containing fluorescent molecules a considerable part of the high energy radiation absorbed in the bulk material is transformed into light emitted by the fluorescent molecules. There is a transfer of excitation energy from the bulk material to these molecules which reaches its maximum at concentrations of approximately 1 g/l and higher. Experiments with mixed solvents are described where relatively small concentrations (several mole percent) especially of naphthalene and $o$-diphenylbenzene act in some way as a second solvent. The excitation energy can be localized by investigating the fluorescence of these mixed solvents when different fluorescent solutes are added. It is found that the energy migrates from the original solvent to the second solvent and then to the fluorescent molecule. This intermediate energy transfer can change the light emission curve completely. From this change the dependence of the light emission on internal and self-quenching could be determined. Besides this internal energy transfer, an energy transfer via radiation occurs which is described in detail by studying the absorption of the fluorescent light inside the solution by adding small amounts of a second solute of the order of 0.1 g/l. Such small amounts change the light intensity considerably and shift the spectrum to the spectrum of the second solute. Photographs and data of the spectral distribution of such solutions are presented, which show that such drifts already occur with very small amounts of the second solute.