Receiving slit selection

Figure 3.40. Examples of proper (ScS) and improper (ScS ) selection of scatter slit aperture. DS - divergence slits, RS - receiving slits.

The radiation source for the twin calorimeter of figure 10.2 is a 100 W tungsten lamp. The wavelength is selected by a monochromator, and the light is split in two parts and led into the radiation-absorbing cells of each unit by three light cables. With a 2 mm slit, the band pass is about 13 nm, and for radiation with A = 436 nm the power delivered to each cell is about 60 p,W. The reference cells are simply steel rods and receive no light. 

To measure a fluorescence excitation spectrum, a band of fluorescence from a solute in C was selected by the monochromator M2 and was received by the photomultiplier After amplification the outputs of Pi and P2 were passed to the ratio recorder, R. The frequency drum on Mi was motor-driven and as the frequency was varied the slits were adjusted so as to maintain the output of P2 approximately constant. If the contents of F were so chosen as to make the output of P2 proportional to the quantum output of Mj at all frequencies, then since Pi was proportional to ht (see eq. 2) and P2 was proportional to I0, the recorded ratio was proportional to t, i.e., the true excitation spectrum was recorded. 

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