Detectors pulse rise time

When a model for a CUORICINO detector (see Section 15.3.2) was formulated and the pulses simulated by the model were compared with those detected by the front-end electronics, it was evident that a large difference of about a factor 3 in the pulse rise time existed. This discrepancy was mainly attributed to the uncertainty in the values of carrier-phonon decoupling parameter. For the thermistor heat capacity, a linear dependence on temperature was assumed down to the lowest temperatures. As we shall see, this assumption was wrong. 

The y-detector of a Mossbauer spectrometer converts the incident y-photons into electric output pulses of defined charge (see Sect. 3.1.6). The detector signals are electronically amplified and shaped by an amplifier network to obtain strong needle pulses with well-defined rise time, so that the pulse height is proportional to the energy of the incident photon. The amplifiers are usually adjusted to obtain... 

In this beam-sweeping scheme the effective spatial distribution of the ions sampled is defined by the characteristics of the sweeping action and the detector slit parameters [20]. Maintaining the fast rise time of the deflection pulse is critical in maintaining spatially small ion packets at the detector surface, and thus adequate resolution. The overall resolution for the differential impulse-sweeping mode in Fig. 12.3 can be estimated with the following equation developed by Bakker [20] ... 

The rise time T, of the pulse generated by a semiconductor detector can be measured at the output of a charge-sensitive preamplifier. If the preamplifier is sufficiency fast, T, is determined by the following factors ... 

Figure 2.16 Schematic illustration of a one-dimensional position-sensitive detector. The gas-filled detector operates as a proportional counter, and the position information is encoded in the difference in the rise time between the pulses coming out of the two ends of the anode wire.

Fig. 37. The decay of the hydrated electron concentration (normalised to an electron yield of 1.07 after 140 ns) following radiolysis with 3MeV protons of pulse duration 1 ns. Significant decay of the hydrated electron optical absorption occurred during the proton pulse and the rise time of the photomultiplier detector.----, H2O -...

To evaluate the performance of the detector, 15000 events were collected in the CsI(Tl)-PD detector while it was simultaneously illuminated with Am and Na sources giving lines at 60, 511 and 1275 keV. At the same time a reference spectrum was collected with a standard Nal(Tl)-photomultiplier system. The pulse-shape spectrum for the raw events is shown in Figure 2. Two clear peaks are seen, easily distinguishing the fast events from the silicon and the slower scintillation events. The rise-time spectrum for the Si events is distorted as the readout system was too slow to accurately determine the rise-times of the fastest events. 

Using this pulse-shape spectrum, the cross-over point between the two detectors was set at a rise-time of 3/ s, shown by the dotted line in the figure. Events with faster rise-times were analysed as coming from the photodiode and were essentially all due to 60 keV events all others were assumed to come from the caesium iodide scintillator. The two types of event were analysed individually in order to obtain raw energy spectra from each detector (also shown in Figure 2). The peaks in the energy spectra were then used to calibrate the energy scales for the two systems. 

The time resolution of the point-by-point and step-scan FTIR approaches is limited by the rise time of the fast IR detector used in the experiment (ca. 10 ns). However, many photochemical and photophysical events take place on the subnanosecond timescale, which require a faster technique. Ultrafast IR spectroscopy is a variant of the pump-probe technique, where time resolution is achieved by spatially delaying the probe pulse with respect to the pump pulse (Figure 5). 

During recent years the development of fast photodetectors has made impressive progress. For example, PIN photodiodes (Vol. 1, Sect. 4.5) are available with a rise time of 20 ps [760]. The easiest and cheapest way to achieve measurements of pulses with AT > 10 s is through detection by photodiodes, CCD detectors or photomultipliers, as discussed in Vol. 1, Sect. 4.5. However, until now the only detector... 

Another advantage of these detectors is the fact that the detector output pulses rise rapidly, and hence they are well suited for fast ( 1 ns) timing with coincidence circuitry in time-to-pulse-height converters. The efficiency of the active volume of these detectors is essentially 100%, and AE/AC is linear over a rather broad range. Compared to scintillation counters, gas proportional counters or ionization... 

---