Emission count rate

First, the excitation-power dependence of the emission count rate of single DMPBI nanocrystals was examined (Figure 12.9). The emission count rate of the single... 

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,...

In research environments where the configuration and activity level of a sample can be made to conform to the desires of the experimenter, it is now possible to measure the energies of many y-rays to 0.01 keV and their emission rates to an uncertainty of about 0.5%. As the measurement conditions vary from the optimum, the uncertainty of the measured value increases. In most cases where the counting rate is high enough to allow collection of sufficient counts in the spectmm, the y-ray energies can stih be deterrnined to about 0.5 keV. If the configuration of the sample is not one for which the detector efficiency has been direcdy measured, however, the uncertainty in the y-ray emission rate may increase to 5 or 10%. 

The majority of crystallites observed were 3 or 4 nm In size. In Figure 3, a bar graph Illustrates the size range distribution and a comparison of mass variation for the 3 and 4 nm crystallite sizes. Although only thirty analyses were oiade, overall visual analysis confirmed the presence of hundreds of 3 to 4 nm platinum crystals with negligible numbers less or greater than these dimensions. It appears that slight variations In crystallite diameter and thickness have resulted In a fairly uniform number of platinum atoms per crystallite for the majority of the crystallites analyzed. In order to normalize count rates, the decrease In the field emission Intensity was taken Into account. 

A common cause of inaccuracy in SPC-based time domain detection is pulse-pileup, that is, the arrival of photons during the dead-time of the detection system. Because the higher probability of emission (and detection) in the earlier part of the decay, pulse-pileup is more probable in this part of the decay. Consequently, the decay will be distorted and the lifetime will be biased towards higher values. Moreover, pulse-pileup will also result in a reduction of the detection efficiency (see Fig. 3.7 and Eq. (3.4)). Therefore, care should be taken to avoid excitation rates too close to the efficacy count rate (i.e., the inverse of the dead-time) in order to minimize these effects. 

Detectors are designed to either measure the total number of emissions (scalers) or the number of pulses per minute (count-rate meters). 

Spectroscopic techniques require calibration with standards of known analyte concentration. Atomic spectrometry is sufficiently specific for a simple solution of a salt of the analyte in dilute acid to be used, although it is a wise precaution to buffer the standards with any salt which occurs in large concentration in the sample solution, e.g. 500 pg ml-i or above. Calibration curves can be obtained by plotting absorbance (for AAS), emission signal (for AES), fluorescence signal (for AFS) or ion count rate (for MS) as the dependent variable against concentration as the independent variable. Often the calibration curve will bend towards the concentration axis at higher concentrations, as shown in Fig. 

Radioactive decay with emission of particles is a random process. It is impossible to predict with certainty when a radioactive event will occur. Therefore, a series of measurements made on a radioactive sample will result in a series of different count rates, but they will be centered around an average or mean value of counts per minute. Table 1.1 contains such a series of count rates obtained with a scintillation counter on a single radioactive sample. A similar table could be prepared for other biochemical measurements, including the rate of an enzyme-catalyzed reaction or the protein concentration of a solution as determined by the Bradford method. The arithmetic average or mean of the numbers is calculated by totaling all the experimental values observed for a sample (the counting rates, the velocity of the reaction, or protein concentration) and dividing the total by the number of times the measurement was made. The mean is defined by Equation 1.1. 

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... 

Within the radiation emission tracking techniques, there are two main variants positron emission, in which the tracer position is determined by triangulation as described in Section 2, and the "proximity" techniques, in which a gamma emitter is placed within the system of interest and its position found by measuring the relative count rates in an array of detectors. An example of the latter is computer-automated radioactive... 

A with a max at 3800A The absorption overlap of the nitrocompds is plainly evident. The position and slope of each curve in Fig 1 can be qualitatively correlated with the absorption range and % transmittance at the peak for each compd. Nitromethane, which absorbs more at shorter wave lengths and exhibits the least overlap of the toluene—PPO emission spectrum, accordingly has the least effect on the count rate of the pure scintillator... 

There is a deficit of sources below the visibility line. These sources could be already detected as dim X-ray sources by ROSAT but were not identified as isolated NSs. The limit for the number of isolated NSs from the BSC (Bright Source Catalogue) is about 100 sources at ROSAT count rate >0.05 cts s-1 (see Rutledge et al. 2003). However we do not expect to see so many young isolated NSs due to their thermal emission. An expected number of coolers observable by ROSAT is about 40 objects with ages < 1 Myr inside II < 0.5-1 kpc (see the visibility line in the fig.2 in comparison with the line for 20 sources, for example). As it was shown by Popov et al. (2003) most of... 

---