WAVELENGTH OF SCINTILLATION LIGHT FROM XENON-DOPED LIQUID ARGON AND ITS APPLICATION TO PHOTOIONIZATION DETECTORS

α粒子在液体氩中10kV/cm的电离率约为初始电荷的10%。这是由于离子和电子在电离密度大的α轨道中重新组合。将光电离分子掺入液体氩中，使其在复合过程中被闪烁光子电离，使其电离率提高。丙烯和三甲胺的光离量子效率分别为60%和20%。在液态Xe中也有类似的效果。在液态Xe中，三甲胺和三乙胺的量子效率为80%。为了研究液体Ar和液体Xe中量子效率差异的原因，我们考虑了闪烁光的波长与掺杂在液体中的分子的电离势之间的关系，特别是多余的能量。在液态Ar中，沉淀光子的波长为130nm，在液态Xe中，沉淀光子的波长为175nm。当Xe掺杂在液氩中时，当Xe浓度为10 ~ 200ppm时，波长从130nm位移到175nm。基于这一事实，我们测量了光电离的量子效率，并研究了它与闪烁光子波长的关系。结果表明，掺Xe液体Ar中三甲胺的量子效率随着Xe浓度的增加而降低，即随着多余能量的减少而降低。因此，液态Ar和液态Xe中量子效率的差异不能用多余能量来解释。相反，笼子效应是最可靠的解释。

Ionization yield for alpha particles in liquid Ar at 10kV/cm is about 10% of the initially prodeced charge. This is due to recombination of ions and electrons in alpha tracks where ionization density is large. If photoionization molecules are doped in liquid Ar, they will be ionized by scintillation photon from recombination and the ionization yield will increase. The quantum efficiencies of photoionization are 60% for allene and 20% for trimethylamine. The similar effect is seen in liquid Xe. The quantum efficiencies of trimethylamine and triethyl-amine are 80% in liquid Xe. To investigate the reason for this difference in the quantum efficiencies in liquid Ar and liquid Xe, we have considered the relation between the wavelength of scintillation light and the ionization potential of molecules doped in the liquids, especially the excess energy.The wavelength of sintillation photon in liquid Ar is 130nm and that in liquid Xe is 175nm. When Xe is doped in liquid argon, the wavelength shifts form 130nm to 175nm for the Xe concentration of 10 to 200ppm. Based on this fact, we have measured the quantum efficiencies of the photoionization and studied the relation to the wavelength of the scintillation photon. As a result, the quantum efficiency of trimethylamine in Xe-doped liquid Ar decreases with increase of the Xe concentration, that is, with decrease of the excess energy. Therefore, the difference in quantum efficiencies in liquid Ar and that in liquid Xe cannot be explained by the excess energy. Instead, the cage effect is the most reliable candidate for the reason.