Dimethyl POPOP

Walker, D., and Waugh, T. D. J. Heterocyclic Chem., 1964,1,72. Dimethyl-POPOP is still on the market, 40 years after its invention. 

The formulations are taken from the literature and some predate the secondary scintillators dimethyl-POPOP and bis-MSB. These secondary scintillators may be used in any of the formulations given and are especially recommended for quenched solutions, in which an increased amount of secondary scintillator is desired. 

Both should be given adequate time to dissolve completely, preferably overnight. The best general purpose secondary scintillator is bis-MSB (p-Z /s-(( -methylstyryl)-benzene). 5/j-MSB is readily soluble in solvents and has a fast rate of dissolution. Bis-MSB is used at 0.5 to 1.5 g/1 and does not react chemically with most liquid scintillation samples, while Dimethyl POPOP can react with acids to produce a yellow to greenish colour. 

A suitable mixture for toluene-soluble materials is toluene containing 5 g PPO/1 or 7 g butyl-PBD/1 0.1 g POPOP or dimethyl-POPOP/1. This mixture cannot be used for measuring the radioactivity in aqueous samples since water is immiscible with toluene. A further solvent (secondary solvent) miscible with both water and primary solvent must be added to this mixture to enable water to be incorporated. This amount of aqueous solution which can be incorporated in a particular mixture without phase separation depends on the identity of the secondary solvent, the relative proportions of primary and secondary solvents and the temperature. 

Toluene-based PPO, POPOP (or dimethyl POPOP) in toluene. 

POPOP (l,4-di[2-(5-phenyloxazolyl)]-benzene) and Dimethyl-POPOP serve as secondary scintillators. 

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