Count rate saturated

Ion intensities up to a count rate of 2 x 10 are measured using a secondary electron multiplier (SEM). When it becomes saturated above that value, it is necessary to switch to a Faraday cup. Its ion-current amplification must be adjusted to fit to the electron multiplier response. 

To determine the ftq, value of Hg a solid sample is used, in which some of the iodine is present as radioactive 1-131. The count rate of the sample is 5.0 X 1011 counts per minute per mole of L An excess amount of Hg2I2(s) is placed in some water, and the solid is allowed to come to equilibrium with its respective ions. A 150.0-mL sample of the saturated solution is withdrawn and the radioactivity measured at 33 counts per minute. From this information, calculate the ft, value for Hg2l2. 

Figure 12.9 The excitation-power dependence of the emission count rate of single DMPBI nanocrystals (dots), and a saturation curve calculated from a two-level model (solid line). One count rate value to one laser power was calculated as an average of 30 nanocrystals. S. Masuo, A. Masuhara, T. Akashi, M. Muranushi,...

D Position Sensitive Detectors are multi-wire electrical-field detectors. The principal limitation of the total counting rate reduces the applicability at a synchrotron beamline in particular for 2D detectors. But even strong, narrow peaks pose a problem, because the whole image is distorted as soon as local saturation occurs. The detector response is changing, because the wires are worn out by use. 

The determination of Pn values is based on the beta saturation counting rate (cP ), the neutron saturation counting rate (C11 ), the beta-neutron coincidence saturation counting rate (dP ), the beta counting efficiency (eg), and the neutron counting efficiency (en). The usual relation for the delayed neutron emission probability is... 

The laser-induced X-ray count rate data, normalized to laser power and beam current, were fitted with a Lorentzian using a least-squares technique to obtain the resonance centroid in the laboratory frame. The average resonance width, corrected to the rest frame of the ions, was 8.5 0.4 cm-1, compared to the natural width of 8.0 cm-1. This is consistent with some saturation in the transition probability and also in the detection sensitivity of the proportional counter at increased count rate. The wavenumber of the resonance centroid, in the rest frame of the moving ion, is obtained using the relativistic Doppler formula,... 

A mercury atom that was ionized by a weak electron beam was captured in a miniature Paul (radio frequency) trap that has internal dimensions of rQ s 466 pm and zQ s 330 pm. The rf trapping frequency was 21.07 MHz with a peak voltage amplitude of about 730 V. The ion was laser cooled by a few microwatts of cw laser radiation that was frequency tuned below the 6s Si -6p Pi electric dipole transition near 194 nm. When the Hg+ ion was cold and the 194 nm radiation had sufficient intensity to saturate the strongly allowed S-P transition, 2 x 10 photons/s were scattered. With our collection efficiency, this corresponded to an observed peak count rate of about 10 s-1 against a background of less than 50 s— -. 

Although the overall count rate limitation with negligible deadtime correction losses is about 10 counts s , experimental expefience shows that it is rather easy to saturate the system, especially for highly localized scattering events (e.g. strong Bragg reflections). This shows the interest in the development of new detection systems. 

Although the local count rate is limited by the space charge effect, as we have seen before, it is the read-out system which will be the limiting component of the system as a whole. Certainly with synchrotron radiation as a source, but already with a rotating anode X-ray generator, area detector systems will be saturated quickly. In addition, the demands concerning the data acquisition system become even more stringent. 

Moreover, the studies on nanoaperture-enhanced fluorescence point out that for a properly tailored aperture, count rates per molecule greater than a few hundred thousands photons per second were readily obtained, whereas for a single molecule in open solution, fluorescence saturation prevents the count rate from exceeding a few tens of kilocounts per second. This allows for fast and reliable screening for single molecules. 

The basic pXRF measurement is a spot analysis where the beam is positioned on the area of interest and a fluorescence spectrum is accumulated. Efforts must be made to optimize the detector configuration for a particular measurement. In particular, with a synchrotron excitation source, it is common for a solid-state detector to be easily saturated by fluorescence from major elements in the sample as well as from scattered radiation. Consequently, the count rate in the detector needs to be optimized by varying one or more of the following incident beam intensity, detector collection solid angle... 

Tf = 5 ns, and a detection system of 5% effieieney the eount rate would be lO s. This count rate is unrealistically high. Practically achieved count rates are between a few 10 s and about 10 s Higher excitation power yields higher count rates, but increases the excited volume by saturation [101]. Moreover, photobleaching within the diffusion time results in an apparent reduction of the correlation time [49, 140, 539]. For comparable emission rates photobleaching is faster for two-photon-excitation than for one-photon excitation [140]. 

Data sheets of TCSPC devices sometimes specify a maximum count rate" that is simply the reciprocal signal processing time. This definition is misleading because for random input pulses it can be reached only for an infinite detector count rate. The term saturated count rate" should better be used instead of maximum count rate". 

Dead-time corrections have become necessary with the introduction of solid state detectors which suffer from count rate overload associated with the electronics. Dead-time losses can result in serious nonlinear distortions in the XAS data. Typically, one measures the number of photons before (ICR = n) and after (m) processing by the associated electronics, and the saturation curve is plotted. The curve is fit to an equation for dead-time derived from either the paralizable [m = /8n(l - nr)] or nonparalizable model [m = /3n expf-nr)], where t is the dead-time and /8n gives the true count rate. The dead-time t and the constant /8 are determined for each channel, and the correction is then applied to each data point to obtain the true count rate. 

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