Wavelength Shifter in Water Cherenkov Detectors

• E. Heiberg and J. Marshall, Rev. Sci. Instrum. 27 (1956) 618 Early work at the University of Chicago. A water-filled cylindrical lucite chamber, a bit like micro-K but with only one 5-inch tube, is used to detect Cherenkov light from cosmic ray muons. The device is operated with the PMT at the bottom and at the top... with the PMT at the bottom, the pulse-height from muons is about an order of magnitude higher than with the PMT at the top, for pure water, due to the directionality of Cherenkov radiation. Then five different compounds are added, to the water, two of which enhance light output by a modest factor of 1.2-1.3. These two also reduce the directionality of the light output, so in the end the pulse-height with the PMT at the top grows to about 2/3 of that seen with the PMT at the bottom.

• Bezaguet et al., Nucl. Instrum. Meth. 158 (1979) 303 Work at CERN. Now the radiator is water in a box that is painted white, and so directionality from the Cherenkov radiation is lost even for pure water. They see a factor of 3.8 increase in pulseheight when on of the waveshifters from Heiberg and Marshall is added! Perhaps this improvement is a consequence of the change from a lucite/TIR box to a white light integration box.

• G. Van Ginkel, Int. J. Appl. Radiat. Isot. 31 (1980) 307 Work at Utrecht. Cherenkov light from phosphorus-32 beta decay betas in small vials of water + waveshifter is measured, and characterized in terms of an overall efficiency for phosphorus-32. Some new waveshifters, beta methyl umbelliferon and esculin are evaluated.

• Badino et al., Nucl. Instrum. Meth. 185 (1981) 587 Work by a Italian/Brazilian Group. The idea was to add one wave-shifter explored by Heiberg and Marshall, amino-G, to water and see how the the directionality of Cherenkov radiation was influenced. The test detector was painted very black and emphasized directionality, so a pulse-height increase of 1.2 was found. Probably if a white-painted light integration box were used, a pulseheight increase of a factor of 3-4 would have been seen.

• Bem et al., J. Radioanalytical Chem. (1983) 69 Polish work trying out more waveshifters in non-water matrices. Betas from phosphorus-32 and chlorine-36 are used, and salicylic acid is studied as a waveshifter.

• Gebicki et al., Int. J. Appl. Radiat. Isot. 31 (1984) 1133 Polish work. Cherenkov light from chlorine-36 beta decay betas in small vials of various matrices (including water) + waveshifter is measured, and characterized in terms of an overall efficiency for chlorine-36. Salicylamide is highlighted.

• Dai et al., Nucl. Instrum. Meth. in Phys. Res. A (2008) 290 Very recent work at Carleton in Canada. New wave-shifters were evaluated for addition to SNO, and as much as a factor of 4 pulse-height increase was deduced in a little muon setup. Their favorite wave-shifter is Carbostyril 124, which they used at a relatively high concentration of 15.4 ppm. They calculated that a concentration of only 0.5 ppm would have been sufficient, however. They also suggested the use of Alexa Fluor 350, although they did not test it.