Characteristics dependence of the silicon photoelectronic multipliers on temperature

The characteristics dependence on the ambient temperature for three types of silicon photoelectronic multipliers have been studied in this research. The prototypes of Si-photoelectronic multipliers with a p+–p–n+ structure produced by JSC Integral (Republic of Belarus), serially produced silicon photoelectronic multipliers KETEK РМ3325 and ON Semi FC 30035 have been used as objects of research. We present the setup diagram and research technique. Measurements of the photocurrent magnitude versus the illumination intensity, calculations of the critical and threshold intensities, and the dynamic range have been performed. We also present the photocurrent dependences on the illumination intensity at different ambient temperatures. As it was found, these dependences have a linear section, the length of which characterizes the critical intensity value, and the inclination angle of the linear section to the intensity axis characterizes the photodetector sensitivity to optical radiation. It has been determined that the temperature increase leads to an increase in the critical intensity value and to a decrease in the sensitivity value. We present the dependences of the threshold intensity on the overvoltage at different ambient temperatures. The dependence of the threshold intensity on overvoltage is most strongly pronounced when the supply voltage is below the breakdown voltage. It was found that the threshold intensity is increased with the temperature increase and the threshold intensity dependence on the temperature is the same for all investigated photodetectors. It was found that the dynamic range value is decreased with the temperature increase, which is caused by a more significant change in the threshold intensity as compared to the critical one. The results given in this article can be applied when developing and designing the tools and devices for recording optical radiation based on silicon photoelectronic multipliers.

Effect on Noise of Intensity-Axis Correction of Spectra Recorded with Charge-Coupled Device Detectors

We have examined the effect of intensity-axis correction on noise in white light spectra recorded with charge-coupled device (CCD) detectors. Measurements were made with five detectors in Raman spectrometers. Detectors were both liquid-nitrogen and thermoelectrically cooled devices and one room temperature device. Both random and pattern noise have been considered. We used cross-correlation of noise sets to provide an indicator of a fixed pattern in the spectra and an assessment of the efficacy of the correction procedure in removing this pattern. For four of the five detectors intensity-axis correction provided a significant improvement in signal-to-noise ratio. Correction was particularly important for measurements made with lower-cost CCD detectors of the kind proposed for process control instruments.

The transfer of signals from photoreceptor cells to large second-order neurones in the ocellar visual system of the locust Locusta migratoria

The operation of the first synapse in the ocellar pathway of the locust Locusta migratoria has been studied by making simultaneous intracellular recordings from photoreceptors and large, second-order L-neurones. 1. The transfer curve for the synapse, obtained by plotting the amplitudes of the initial peak responses by the two cells to pulses of light against each other, shows that L-neurones are extremely sensitive to changes in photoreceptor potential and that the connection is tonically active in darkness. 2. Postsynaptic current in an L-neurone, produced when pulses of light are delivered from a dark background, saturates at a slightly brighter light intensity than does the postsynaptic potential. 3. The signal-to-noise ratio improves with increases in light intensity in both cells, but the reduction in noise as signals are transmitted from photoreceptors to L-neurones is less than would be expected from the number of photoreceptors that probably converge on each L-neurone. 4. In both cells, in the presence of different intensities of background illumination, the slope of the intensity­response curve is maintained as the curve moves along the light intensity axis. Adaptation is relatively slow so that, at least for several minutes after an increase in background illumination, both cells maintain a sustained response and the responses to stimuli of increased illumination are reduced in amplitude. During sustained background illumination, the transfer curve for the synapse between a photoreceptor and an L-neurone shifts along both axes without a change in its maximum slope. 5. The slope of the synaptic transfer curve depends on the speed as well as the amplitude of changes in light. 6. In response to injection of depolarising pulses of current into a photoreceptor, an L-neurone generates brief, hyperpolarising responses. The amplitude of the responses depends on the strength and speed of the depolarising stimuli. After an initial response by an L-neurone, subsequent responses are reduced in amplitude for 200 ms. 7. The amplitude of L-neurone responses to electrical stimulation of a photoreceptor increases when the hyperpolarising constant current is injected into the photoreceptor.

A method for calculating the distribution of pH in tissues and a new source of pH error from the 31P-NMR spectrum

The true distribution of the pH in tissues can be determined from the in vivo 31P-nuclear magnetic resonance (NMR) spectrum by converting the parts per million (PPM) axis of the pH responsive resonance to pH using the Henderson-Hasselbalch equation. In addition, the intensity axis of the resonance must be divided by the derivative of the Henderson-Hasselbalch equation to correct for the nonlinear relationship between pH and PPM. This nonlinear relationship causes the apparent center of the resonance in PPM to be dependent not only on the center of the pH distribution but also on its width and distance from the pKa, where Ka is the association constant. Therefore, the pH determined from uncorrected spectra may be in significant error, particularly if the pH distribution is distant from the pKa and is broad. The method was applied to the isolated perfused Morris hepatoma 5123C to determine the distribution of intracellular pH (pHi) using resonances from two intracellular compounds. The two resonances did not report the same pHi unless the spectral data were properly corrected. The method should be of interest to anyone interested in pHi.