Total count rate

The Mossbauer spectrometer will typically divide the velocity scale into 256 channels. For a 0.93 GBq source (25 mCi), the total count rate of photons arriving at the detector and having the proper pulse-height is usually about C = 20,000 counts s Only about 85% of these will be 14.4 keV radiation the others are... 

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 dependence of the correction factor on the total count rate in the spectrum in the measurements with the p-type detector is presented in Figs. 3 and 4. Figure 3 shows a comparison of the dependences measured with the 241Am source for measurements with the base-line restorer threshold set to AUTO and VAR. Figure 4 presents the dependencies of the correction factors when 60Co was used as the second source. In Fig. 5 the dependence of the correction factor on the total count rate measured with the Ge(Li) detector is presented. The dependencies of the correction factors on the total count rate measured on the spectrometer with the Ortec 573 amplifier are presented in Figs. 6 and 7, with Fig. 6 pre-... 

Fig. 3 Correction factor for the 662 keV peak as a function of the total count rate measured on a p-type detector with an 241 Am source with the base-line restorer threshold set to AUTO (full circles) and with the base-line restorer threshold set to VAR (open...

Fig. 7 Correction factors for the x-ray peak at 32 keV (a) and the correction factors for the 662 keV peak (b) as functions of the total count rate measured on a low-energy p-type detector with a 60Co source...

The pulser peak method gives better estimates of the effective counting time than the methods implemented in the ADC converter which estimate the time when the gate of the ADC is closed electronically, since in the former the influence of the pile-up effect on the peak areas is taken into account. However, an automatic analysing procedure evaluating the pulser peak area introduces systematic effects which are caused by the distortion of the shape of the pulser peak. These systematic effects are reflected in the dependence of the count rate from a source located at a fixed position on the total count rate in the spectrum. The effects arise only partially from the difference between the calculation of the pulser peak area and the areas of other peaks in the spectrum. The other sources of systematic effects originate in the difference between the pulser peak shape and the shapes of other peaks in the spectrum and in the relatively low background near the pulser peak. 

The deviation of the correction factor from unity measured with spectrometers with PGT 386 amplifiers is comparable with the deviations measured in [5], There the authors reported a deviation of the peak count rate of approximately 2% at 1400 keV and 0.5% at 122 keV at a total count rate of 9000 s1. The measurement with the Ortec 573 amplifier yielded superior results. At the accuracy achieved, the deviation was not measurable up to 10000 s1 with this amplifier. The difference in the performance of the measurements with different amplifiers originates, most probably, in the fact that the Ortec amplifier is of newer design. 

The deviations of the correction factor from unity as a function of the total count rate requires the introduction of a rate- and spectrum-shape- dependent correction factor to be applied to the effective acquisition time measured on the spectrometers with PGT 386 amplifiers. Since the dependence of the factor on the spectrum... 

Figure 16.9. Annual modulation of the total counting rate (background plus possible dark matter signal) in seven years of data with the DAMA-Nal detector. A constant counting rate has been subtracted to give the residuals. The significance of the modulation is 6cr and its period is 1 year. The interpretation of the yearly modulation as due to a WIMP signal is controversial. (Figure from Bernabei et al.(2003).)...

Both the foil and the metal film containing the catalyst are thin enough to allow p-radiation from the solution, and from the adsorbate to reach the detector at acceptable p-radiation attenuation. Therefore, the components of the total count rate are the count rate from the bulk solution and from the electrode... 

The total count rate of Nal(Tl), height of flight and navigation data are recorded once each second. The count rate information is used for location of lost sources and small radioactive spots. Spectral information is recorded periodically. Time of spectra acquisition depends upon sensitivity of HPGe and one was chosen upon 10-20 seconds for condition of intensity of radiation in Chernobyl region. This period allows measurement of a minimum activity of the ground contamination of Cs 0.5 Ci/km ... 

Based on latitude survey data of Aleksanyan et al. (1985), Dorman et al. (2000) the polar normalized coupling functions for total counting rate and different multiplicities m can be approximated by special normalized... 

The expected variation in total counting rate or in multiplicity m will be... 

Instead of exciting the sample by the general radiation from the x-ray tube, one can use the almost monochromatic fluorescent radiation from a secondary fluorescer, as in Fig, 15-11. Proper selection of the secondary fluorescer can then restrict the number of fluorescing elements in the sample, because only those with Z less than that of the secondary fluorescer are excited. Thus an Fe secondary fluorescer will excite Cr in a stainless steel sample but not Fe or Ni. As a result, the sensitivity for Cr detection is increased, because selective excitation has decreased the load (total count rate) on the detector/analyzer system. 

Note that counting rates for each component are calculated by dividing the respective counts by time of acquisition to give total count rate Rt, true count rate / Tme, random count rate Rr, and scatter count rate Rs. 

For Lu-based scanners, there is an intrinsic activity as well as possible intrinsic random events due to176Lu, which need to be subtracted from the total count rate. These can be measured with the plastic tubing in place in the scanner but without any activity in it. Both prompt and delayed acquisitions are made of the tubing as described in section on Scatter Fraction, from which intrinsic prompt rate and intrinsic random rate are calculated. The true intrinsic count rate Rmt is obtained by subtracting the random rate from the prompt rate in all sinograms. Thus, for Lu-based scanners, true count rate Rtme is given as... 

Since directly measured from the total count rate, only two parameters, f(A) and t, must be obtained from the experimental time-correlation function points. This is an advantage over the analog homodyne method in which, in the corresponding case, the measured h(t) is fit to the form ... 

For a particular radioactive sample, the total counting rate (sample plus background) was 450 cpm, and this value was obtained over a l5.()-min counting period. The background was counted for 2.0 min and gave 7 cpm. listtmate... 

What total number of counts should be collected if the total counting rate is (a) 70 cpm and (b) 400 cpm ... 

Of course, the multidetector technique does not increase the maximum throughput rate of a TCSPC system. In any TCSPC device there is a small but noticeable loss of photons due to the dead time" of the processing electronics. The dead time of advanced TCSPC devices is of the order of 100 ns, and for count rates above 1 MHz the counting loss becomes noticeable (see Sect 7.9, page 332). The counting loss for a multidetector TCSPC system is the same as for a single detector system operated at the total count rate of the detectors of a multidetector system. 

To calculate the lens efficiency at 511 keV, the total counting rate of the source-lens-detector system was measured. To eliminate transmission of the non-diffracted beam through the lens and into the detector, the center of the lens was blocked. After background subtraction, we found = 153 c s (count rate in the peak) with the lens tuned. Next, the lens was removed from the system, and the measurement was repeated. The count rate without the lens was Nj = 77 c s (in the peak). 

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