Multichannel analysers

Figure C3.5.3. Schematic diagram of apparatus used for (a) IR pump-probe or vibrational echo spectroscopy by Payer and co-workers [50] and (b) IR-Raman spectroscopy by Dlott and co-workers [39]. Key OPA = optical parametric amplifier PEL = free-electron laser MOD = high speed optical modulator PMT = photomultiplier OMA = optical multichannel analyser.

Por IR-Raman experiments, a mid-IR pump pulse from an OPA and a visible Raman probe pulse are used. The Raman probe is generated either by frequency doubling a solid-state laser which pumps the OPA [16], or by a two-colour OPA [39]. Transient anti-Stokes emission is detected with a monocliromator and photomultiplier [39], or a spectrograph and optical multichannel analyser [40]. 

An alternative type of spectrometer is the energy dispersive spectrometer which dispenses with a crystal dispersion element. Instead, a type of detector is used which receives the undispersed X-ray fluorescence and outputs a series of pulses of different voltages that correspond to the different wavelengths (energies) that it has received. These energies are then separated with a multichannel analyser. 

If the energy difference AE is chosen to be the energy width 8E of a single channel in the multichannel analyser, then each channel corresponds to a thickness 8z ... 

In connection with our field measurements, samples of geological materials were collected for analyses in the laboratory. Activity concentrations were measured by standard gamma spectrocqpy with a 90-cm3 Ge (Li) detector and a Canberra Model 8100 multichannel analyser. Details on calibration and procedure were published earlier (Stranden, 1985). Rn-222 exhalation measurements were also performed... 

To eliminate the need for recalibration during a measurement and to obtain additional information, the Royco instrument was supplemented with a Nuclear Data ND-60 Multichannel Analyser (MCA). The amplified signal of the Royco 225 (which is proportional to the cimount of light scattered from each particle) was connected to the input of the MCA which cem count and classify pulsed input signals into as many as 2048 channels and display the results on a cathode ray tube (CRT). This number of cells is of course much more than required to determine the PSD. The data were therefore grouped into eleven cells whose limits were consistent with those used earlier (5), emd the counts in these cells were then printed on a Texas Instruments 743 KSR Data Terminal interfaced with the MCA. 

Figure 7.34 Principle of kinetic single-photon counting. L, pulsed light source S, sample P, photodiode F, interference filter or monochromator D, photomultiplier R, voltage ramp generator (1 to start the ramp, 0 to stop it). The voltage V is fed into a multichannel analyser M. Inset voltage ramp V(t)...

A multichannel analyser is a type of digital x—y recorder in which x is the channel number (in this case the time after the excitation pulse) and y is the number of events which occur for the relevant channel (in this case the detection of a photon). For each excitation pulse the first emitted photon only is counted, but as the experiment is repeated many times with excitation pulse trains of thousands per second the whole kinetics of luminescence is reconstructed. 

Fig. 1.5. Schematic of a gamma-ray energy spectrometer for Doppler broadening studies. The signal from the detector pre-amp is processed by spectroscopy and biassed amplifiers (SA and BA respectively) before being recorded in the multichannel analyser (MCA).

Coleman, P.G., Griffith, T.C. and Heyland, G.R. (1974). The analysis of data obtained with time to amplitude converter and multichannel analyser systems. Appl. Phys. 5 223-230. 

Figure 1. Experimental system used in the time resolved absorption measurements. (EL=excimer laser, KrF, 248nm DG=delay generator OMA=optical multichannel analyser MC=monochromator and gated diode array detector C=cell X=xenon flash lamp L=lenses )...

AT/T measurements over the entire pulse bandwidth are performed using an optical multichannel analyser. In all measurements, the maximum signal is a few percent and linearity is verified to avoid saturation effects. 

Energy dispersive spectrometer (EDS), in which a multichannel analyser gives the photon energy spectrum. 

An aliquot of 5 mL of rainwater was placed into an acid washed polyethylene vial and transported via a 1 rabbit1 carrier to the reactor core which has a nominal neutron flux of 5 x lO- n cm 2 sec l. The samples were irradiated for five minutes. The irradiated vials were then transferred to inert vials which were placed at the snout of a 22% efficient APTEC detector coupled to a Caneberra Series 90 multichannel analyser and a pile up rejector unit. The resolution of the system was 2.1 KeV at the 1332 KeV cobalt peak. Typical dead times were 10% or less. The samples had an average delay time of 100 seconds and were counted for a period of 10 minutes. 

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