A test is made of the recombination model proposed by Thomas \et [Phys. Rev. A 38 (1988) 5793] for the energy resolution, of which the experimental value is far worse than that estimated by the Fano theory, in liquefied rare gas detectors. The energy resolution and the charge collection based on the recombination model are calculated for electrons or gamma rays in the liquid chamber doped with photoionizing molecules. The calculated energy resolution does not agree with that obtained by the recent experiments, although the agreement is good for the charge collection. It is suggested that the recombination is not a main cause of the energy resolution. Possible causes of poor energy resolution are discussed.
The scintillation yield for recoil Ar ions of 5 to 250 keV energy in liquid argon have been evaluated for direct dark matter searches. Lindhard theory is taken for estimating nuclear quenching. A theoretical model based on a biexcitonic diffusion-reaction mechanism is performed for electronic (scintillation) quenching. The electronic LET (linear energy transfer) is evaluated and used to obtain the initial track structure due to recoil Ar ions. The results are compared with experimental values reported for nuclear recoils from neutrons. The behavior of scintillation and ionization on the field are discussed. with notes on radiation physics and chemistry for dark matter searches.
The stopping powers of Ni, Ag, Au, and Pb for \ensuremath{\sim}7-MeV/N (where $N$ means nucleon) C ions and $\ensuremath{\alpha}$ particles have been measured. For the 7.00-MeV/N C ion, the stopping powers of Ni, Ag, Au, and Pb are found to be 1.353\ifmmode\pm\else\textpm\fi{}0.016, 1.080\ifmmode\pm\else\textpm\fi{}0.010, 0.832\ifmmode\pm\else\textpm\fi{}0.006, and 0.825\ifmmode\pm\else\textpm\fi{}0.006 MeV / mg ${\mathrm{cm}}^{2}$, respectively. From these results, the ${Z}_{1}^{3}$ deviation from the Bethe-Bloch formula is evaluated comparing with our experimental stopping power for $\ensuremath{\alpha}$ particles. In the course of analysis we employed appropriate effective-charge corrections. Pierce and Blann's effective-charge correction, e.g., gives a reasonable value (1.38) of the $b$ which appears in the Ritchie-Brandt theory, if a $\ensuremath{\chi}$ value of 1.29 in their theory is assumed.
An increase in scintillation of up to 17% has been observed in liquid argon with the application of low electric fields (<6 kV/cm) for /sup 1/H, /sup 4/He, /sup 18/O and /sup 36/Ar ions of energy 1-35 MeV/u. This increase occurs at a field much lower than that required for the proportional region (10/sup 6/ V/cm). The observed phenomenon is attributed to the recovery of quenching in the high excitation density region of the particle track by the external field.
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