Preparation And Optical Properties Of Low - Scavenging Liquid Scintillator

Neutron diagnostics generated by Laser fusion through the time-of-flight (TOF) technique with a fast scintillation detector can provide valuable diagnostic information for the fusion experiments occurred in the capsule of ICF. However, it is difficult to detect primary neutrons generated by fast ignition experiment. Because the intense X-ray burst precedes the neutrons in TOF. In fast ignition experiments, a high intensity pulse coming from a petawatt laser produces the neutrons and high-energy electron current which generates X-rays. X-rays are more intense than the neutrons. Even using gating techniques of the phototube to restrain detection of the precedent radiation, the highly-intense X-ray still submerge the relatively weaker neutron signal especially when the slow decay component or the afterglow of the scintillator controls the TOF region where the neutron is expected. Therefore, a scintillator with a fast decay component or primary decay of a few nanoseconds, a very weak afterglow is essential for successful neutron diagnostics.In the neutron diagnostics, the liquid scintillators are filled in glass capillary bundles. While the incident neutron paralleled with the axle of glass capillary bundles go through the liquid scintillators, they mainly collide with the hydrogen nucleus of the organic liquid scintillators. Because the quality of carbon nucleus is larger than the neutron, collision is relative lower than the hydrogen. The recoil protons from the collision lose their energy in the movement to excite the solvent of the liquid scintillators. The spatial distribution of the scintillator light is dominated by transverse spread of the recoil hydrogen ions about the neutron scattering sites. This spread can be reduced by using a deuterated scintillator, since the range of a scattered deuteronis about half that of a proton with the same energy.A scintillator is always made up of an aromatic solvent and one or more fluors (primary fluor and wavelength-shifter). The solvent whose quality percentage is99%acts as a vehicle for energy transfer of solution and interact with neutron to produce scattering electrons. Therefore, the physical and chemical performances play important roles in a scintillator, good transparency in the wavelength-dependent fluorescence emission spectra, high refractive index, long-term stability and high flash-point is required for an optimal solvent. P-Xylene(PX) with stable chemical performance has long decay length and high flash-point. As for phenyl-o-xylylethan(PXE), it is low poisonous to widely apply to various fiels. Di-isopropylnaphthalene(DIN) with good delocalization is attracted by many researchers. According to our literature survey, PX, PXE and DIN are regarded as the candidate solvents in this paper, PPO (2,5-Diphenyloxazoze) and bis-MSB (p-bis(o-methylatyryl)-benzene) are the primary solute and the second solute. The absorption of PX, PXE and DIN were measured by an UV-Vis spectrometer to find out PX was with the longest attenuation length among the three solvents. The fluorescence emission spectra of PPO with different concentrations respectively dissolved in PX, PXE and DIN were tested using a FL spectrofluorimeter, the results showed that emission spectra of PPO in PX overlapped well with the absorption of bis-MSB. The decay time of liquid scintillator based on PX, PXE and DIN were performed employing the time-correlated single photon counting (TCSPC) technique featured in high dynamic range of several orders of magnitude in light intensity, PX with the fastest decay time and the highest percentage of the fast component was searched. According to the above three parameters including attenuation length, fluorescence emission spectra and decay time, the optimal solvent fit for the neutron diagnostics is PX. The light yields of the optimal solvent with different concentrations of PPO and bis-MSB were tested to confirm the optimal concentrations of PPO and bis-MSB are3.5g/L and30mg/L, respectively. Finally, the optimal formula liquid scintillators were deuterated. The deuterated percentage, absorption, fluorescence emission spectra and decay time of the deuterated liquid scintillator were performed. The results showed that the the optical properties were not related to deuterium.