Abstract
When βray of 14C radiated the scintillator (toluene 1l+PPO 4 g +POPOP 0.1 g), liquid scintillation was observed with the apparatus of short resolving time for measurement of light pulses. Overall high voltage ( -2170 V) was supplied to the cathode of photomultiplier 56AVP/03. Signal pulses were led to the sampling oscilloscope SAS500.
Output of the hold circuit of the oscilloscope was led to X-Y recorder and the signal pulse curves of the scintillation were recorded.
The scintillator was poured in the cell (2 ×25 × 30mm) of sheet glass with toluene-14C. This cell was made "Optical coupling" with the photocathode ofphotomultiplier by silicone oil TSF451 (500, 000cs).
About 75% of β rays of 14C were observed, and average energy of these β rays was about 72.1 keV.The recorded pulse curve was the average pulse curve of many scintillations. The peak height maximum of the obtained pulse curve was about 810 mV high (R=25 Ω). From the area below the curve, total anode pulse current was calculated. It was about 2.67 × 10-10 coulomb. Then the number of ejected photoelectrons from the photocathode was about 53.8.
Corrected fluorescent spectra and absorption spectra of liquid scintillator, and absolute quantum efficiency curve of photomultiplier were obtained. Averageenergy of fluorescent photons was 2.85 eV. The product of these three spectra give the conversion efficiency from fluorescent photons to ejected photoelectrons.
When pathlength of absorbance were 1 cm, 5 mm, 2.5 mm, and 1.25 mm, conversion efficiency were 0.155, 0.160, 0.163, and 0.165 respectively.
Because the effective pathlength was estimated about 23 mm, conversion efficiency was about 0.163.
The refractive indexes of liquid scintillator and silicone oil were measured by Pulfrich refractometer.Geometrical collection efficiency was calculated with these indexes by the Fresnel equations for refraction.Photons of liquid scintillation, which were radiated from the cell to the opposite side, were reflected at the boundary face of sheet glass and air, and went to the photocathode, were large enough not to be disregarded.When this reflected light was involved, geometrical collection efficiency was about 0.50.
Number of total radiated photons was calculated with these data and was about 670 ± 50. Then the fluorescent efficiency of liquid scintillation was about 2.6 ± 0.3%. The fluorescent efficiencies of the fast component and the slow component were 2.1 % and 0.47% respectively.
