Abstract
IN liquid scintillation counting the passage of β-particles through the phosphor solution results in a complex series of events, the useful ones culminating in the emission of photoelectrons at the photocathode of the photomultiplier. A number of parasitic events occur concomitantly that lead to a lowering of the yield, or total loss of the photoelectrons, that is, quenching. Possible sequences for these events, which occur during a time-interval of approximately 10−9 sec, have been outlined by several authors1–3. The addition of naphthalene to some liquid phosphors improves their counting characteristics. The enhancement in counting efficiency has been ascribed by Fust and Kallmann4 to the ability of the naphthalene to act as an intermediate solvent that is capable of transmitting the energy from the primary solvent to the scintillators, thereby by-passing the quenching agent. If this is true the series of events leading to photoelectron production could be outlined as follows: (A) emission of β-particle; (B) excitation of primary solvent molecules (toluene); (C) excitation of secondary solvent molecules (naphthalene); (D) excitation of primary solute molecules (PPO); (E) excitation of secondary solute molecules (POPOP); (F) production of photons.
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References
Hayes, F. N., J. App. Rad. and Isot., 1, 46 (1956).
Birks, J. B., Proc. Inst. Rad. Eng. Seventh Scintillation Counter Symp., Washington, 1 (1960)
Funt, B. L., and Hetherington, A., J. App. Rad. and Isot., 13, 215 (1962).
Fust, M., and Kallmann, H., Phys. Rev., 97, 583 (1955).
Dobbs, H. E., U.K.A.E.A. Publ. AERE M1075 (1962).
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DOBBS, H. Effect of Naphthalene on the Quenching of Liquid Scintillation Solutions. Nature 197, 788 (1963). https://doi.org/10.1038/197788a0
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DOI: https://doi.org/10.1038/197788a0
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