Amplification and scintillation properties of oxygen-rich gas mixtures for optical-TPC applications

Abstract

We studied electron amplification and light emission from avalanches in oxygencontaining gas mixtures. The mixtures investigated in this work included, among others, CO 2 and N 2 O mixed with Triethylamine (TEA) or N 2 . Double-Step Parallel Gap (DSPG) multipliers and THick Gas Electron Multipliers (THGEM) were investigated. High light yields were measured from CO 2 +N 2 and CO 2 +TEA, though with different emission spectra. We observed the characteristic wave-length emission of N 2 and of TEA and used a polymer wave-length shifter to convert TEA UV-light into the visible spectrum. The results of these measurements indicate the applicability of optical recording of ionizing tracks in a TPC target-detector designed to study the cross-sections of the 16 O( γ ¡ , α ) 12 C reaction, a central problem in nuclear astrophysics.

An optical readout TPC (O-TPC) for studies in nuclear astrophysics with gamma-ray beams at HIγS1

“…The production rate of deuterium during Big Bang Nucleosynthesis is currently ill determined due to a substantial uncertainty in the measured values of the cross section. For this measurement research into the choice of gas is needed as we previously performed [16] for the case of 16 O with a smaller prototype Optical Readout TPC.…”

“…The Quantum Efficiency (QE) of its photocathode, shown in figure 4, was measured at the Physikalisch-Technische Bundesanstalt (PTB) at Braunschweig, Germany. A large QE (20%) was measured at 338 nm, the wavelength of the majority of the light emitted by nitrogen [16]. Note that 3.18 MeV alpha-particle tracks viewed by the 142 mm diameter lens yield approximately 1000 photo-electrons in the photo-cathode of the Hamamatsu demagnifier.…”

“…Note that an approximately 9.5 MeV gamma-ray beam yields an approximately 1.8 MeV alpha-particle and an approximately 0.6 MeV 12 C from the dissociation of 16 O. A "three alpha-particle event" from the dissociation of 12 C is shown in figure 13.…”

“…The ratio of carbon-to-oxygen at the end of helium burning has been identified three decades ago as one of the key open questions in Nuclear Astrophysics [1] and it remains so today. To solve this problem one must determine the p-wave [SE1(300)] and d-wave [SE2(300)] cross section S-factors, defined in Ref [1], of the 12 C(α, γ) 16 O reaction at the Gamow peak (300 keV) with an accuracy of approximately 10% or better [1].…”

“…Several new measurements of the 12 C(α, γ) 16 O reaction using gamma-ray detectors have been reported [2,3] with center of mass energies in the vicinity of 1.0 MeV. However, the astrophysical cross section S-factors were determined with very low accuracies (±40-80%) and, most importantly, one cannot rule out a low value (close to zero) of the extrapolated E1 S-factor [4,5].…”