Combining Counting Rates

Solid-state detectors based on silicon- or germanium-diodes possess better resolution than gas counters, particularly when cooled with liquid nitrogen, but they allow only very low count rates. PIN diodes have also recently become available and have been developed for the instruments used in the examination of Martian soils (Sects. 3.3 and 8.3). A very recent development is the so-called silicon-drift detector (SDD), which has very high energy resolution (up to ca. 130 eV) and large sensitive detection area (up to ca. 1 cm ). The SNR is improved by an order of magnitude compared to Si-PIN detectors. Silicon drift detectors may also be used in X-ray florescence spectroscopy, even in direct combination with Mossbauer spectroscopy (see Sects. 3.3 and 8.3). 

In wide field microscopy, spatial information of the entire image is acquired simultaneously thus providing comparatively short acquisition times compared with scanning microscopy implementations. Combining TCSPC with wide field microscopy is not straightforward. However, a four quadrant anode multichannel plate (MCP) has been used for time- and space-correlated SPC experiments [25, 26]. This detector has excellent timing properties that make it very suitable for FLIM. Unfortunately, it can be operated only at low count-rates ( 105-106 Hz) therefore, it requires comparatively long acquisition times (minutes). 

E represents the combined collection and detection efficiency of the system and F the intrinsic photon-economy of the technique. The factor 77 accounts for the subtractive noise, tA is the dead-time of the detector and Q the count rate of the system. 

The products were analyzed for chemically combined phenanthrene content by radio assay, based on the beta radiation emitted by the C atoms of the labeled phenanthrene. The radiation count rate of the labeled phenanthrene, measured under standard conditions, was used as a reference. The combined phenanthrene content of subsequent samples was calculated from a direct proportionality between the observed count rate of the samples and their labeled phenanthrene content. The beta radiation of the samples was counted with a thin-window (1.4 mg./sq. cm.) Geiger-Miiller tube and a scaler (Nuclear-Chicago Corp., Model No. 186.). 

While we think we have arrived at the right combination of sample introduction and system and ion counting parameters, it remains an empirical challenge to produce reliable isotope measurements using LA-TOF-ICP-MS. Adjusting for an appropriate instrumental count rate is key to approaching... 

The measured recovery of added 90Sr tracer in the QC sample is then taken to be the yield for all samples in a batch. If the 90Sr tracer is from a standard solution, then the QC sample measurements provide the combined yield and counting efficiency. (Note This is described in the alpha-particle spectral analysis in Experiment 15.) The 90Sr activity in each sample is its net count rate multiplied by the ratio of the QC sample activity (in Bq or pCi) to the average QC sample count rate. 

In the more than 30 years that have followed, radiocarbon studies have evolved through two generations of instrumental methods. Libby employed solid carbon counting (combined with an application of the anticoincidence principle to reduce background count rate) to establish the fundamental validity of the method (6). This goal was achieved in December 1949 with the publication of the famous Curve of Knowns, which demonstrated that the residual content of a series of samples was directly related to their age (7). 

To experimentally demonstrate that the gate works, we first verify that we obtain the desired CNOT (appropriately conditioned) for the input qubits in states HH, HV, VH and VV. In Fig. 4 we compare the count rates of all 16 possible combinations. Then, it was proven that the gate also works for a superposition of states. The special case where the control input is a 45° polarized photon and the target qubit is a H photon is very interesting we expect that the state H + V)ai H)a2 evolves into the maximally entangled state ( HH)b11,2 + VV)b1 b2)- We input the state I ) first we measure the count rates of the 4 combinations of the output polarization (HH,..., VV) and then after going to the +), —) linear polarization basis a Ou-Hong-Mandel interference measurement is possible this is shown in Fig. 5. 

The counting-rate meter, as its name implies, is a device which indicates the average counting rate directly without requiring, as in the scaler-timer combination, separate measurements of the number of counts and the time. It does this by a circuit which, in effect, smooths out the succession of randomly spaced pulses from the counter into a steady current, whose magnitude is proportional to the average rate of pulse production in the counter. 

An interesting development of the IPDA has recently been reported by Benjamin et al. (22). They use a high gain ( 10 ) MCP combination coupled with a rapid readout of the PDA to allow detection of individual photons. Centroiding of the photon pulse allows spatial resolutions less than the pixel width. Also, a P-46 phosphor is used for fast time response. This system may be quite useful for line profile measurements in the EUV, where low counting rates can be tolerated. 

The simplest technique for measuring the resolving time t of a nonparalyzable counting system uses a method of matched samples. Two samples of similar counting rates are counted separately and then together. The combined sources should give about 20% fractional dead time, obs t. From the difference between the measured count rate of the... 

A more accurate technique is based on the use of a short-lived radionuclide, e.g. ""Tc or "In. The count rate is then measured a number of times during at least one half-life with the source left untouched in position all the time. When the background count rate can be neglected (which is usually the case) combining (8.8a) with the equation for radioactive decay gives after some algebra... 

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