Boxcar Integrator

At this point it is important to mention that the experimental setup used for luminescence decay-time measurements is similar to that of Figure 1.8, although the light source must be pulsed (alternatively, a pulsed laser can be used) and the detector must be connected to a time-sensitive system, such as an oscilloscope, a multichannel analyzer, or a boxcar integrator (see Chapter 2). 

In some experimental arrangements, boxcar integrators are used instead of digital oscilloscopes. The basic operational scheme of a boxcar integrator is shown in Figure 3.26. 

Fig. 24. The RT emission spectra of the core-shell of Eu Y203/Al203 by site-selective excitation at Xexc = (a) 355, (b) 533.55, (c) 525.97, (d) 526.41 nm. The emission was detected using a boxcar integrator that averaged the signal from a cooled PMT with 15 ps gate and 0.3 ms delay from the pump laser pulse (redraw after (Chen, X.Y. et al.,...

In some instances, the design of the data acquisition system may be driven by the requirements of a specific application. In ICP-MS, for example, the masses of the elemental isotopes are well known, so only those masses need to be investigated. In such a situation, an attractive technique is the use of a number of single-channel devices, such as boxcar integrators [38], each of which is responsible for continually monitoring a specific mass of interest. At the expense of complete mass spectral coverage, a simple, inexpensive system that generates relatively small amounts of data with real-time temporal resolution can be utilized. 

The boxcar integrator is a device which is able to recover the waveform of a repetitive signal or measure the amplitude of a repetitive pulse buried in noise. The major advantage of using a boxcar integrator to measure lifetimes is the relatively low initial cost of the system. The boxcar is basically a sample-and-hold system with two modes of operation, single point and scan, which are used respectively for pulse measurement and waveform retrieval. The time of sampling is determined by a reference pulse that is... 

There are a number of potential pitfalls in the operation of a boxcar integrator and therefore a brief discussion of some of the operating principles is appropriate. A commonly used boxcar is the PARC Model 162 which, together with its associated plug-in modules, will be used as an example in the following discussion. 

Fig. 11. Block diagram showing the system and method for measuring fluorescence lifetimes with a boxcar integrator.

With aperture times available from lOOps to 550 ps, the boxcar integrator can be applied to the measurement of a wide range of lifetimes. However, there can be problems associated with the use of a boxcar to measure lifetimes. Some of these, together with some solutions, are discussed below. 

Fig. 12. Typical decay curves, measured with a boxcar integrator, following excitation of B1BrF, 6 0, P21, B—X for different quenching conditions, (a) [Br2 ] = 1-23 X 101S molecules cm 3, r = 4.18/Js (b) [Br2 ] = 6.0 X 1013 molecules cm 3, r = 24.2JJS.

Fig. 13. Diagram to show the effect of a rising baseline during the recovery of a fluorescence waveform with a boxcar integrator, (a) shows the results with a single scanning aperture and (b) how a second fixed aperture can be used to sample the baseline. The output curve is the difference between the signal in the scanning aperture and that sampling the baseline.

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