Active Oxygen Target for Studies in Nuclear Astrophysics with Laser Compton Backscattered γ-ray Beams

Abstract

An active target is being developed to be used in low-energy nuclear astrophysics experiments. It is a position-and time-sensitive detector system based on the low-pressure Multi Wire Proportional Chamber (MWPC) technique. Methylal ((OCH 3 ) 2 CH 2 ), at a pressure of a few Torr, serves as the working gas for MWPC operation, and in addition, the oxygen atoms of the methylal molecules serve as an experimental target. The main advantage of this new target detector system is that it has high sensitivity to the low-energy, highly-ionizing particles produced after photodisintegration of 16 O and insensitivity to γ-rays and minimum ionizing particles. This allows users to detect only the products of the nuclear reaction of interest. The threshold energies for detection of α particles and 12 C nuclei are about 50 keV and 100 keV, respectively. The main disadvantage of this detector is the small target thickness, which is around a few tens of µg/cm 2 . However, reasonable luminosity can be achieved by using a multimodule detector system and an intense, Laser Compton Backscattered (LCB) γ-ray beam. This paper summarizes the architecture of the active target and reports test results of the prototype detector. The tests investigated the timing and position resolutions of 30 × 30 mm 2 low-pressure MWPC units using an α-particle source. The possibility of measuring the 16 O(γ, α) 12 C cross-section in the 8-10 MeV energy region by using a LCB γ-ray beam is also discussed. A measurement of the 16 O(γ, α) 12 C cross-section will enable the reaction rate of 12 C(α, γ) 16 O to be determined with significantly improved precision compared to previous experiments.

Editorial for the Special Issue “The Modern Physics of Compact Stars and Relativistic Gravity 2017”

“…The only experimental work in our collection is the report by R. Ajvazyan et al [13] on the current state of the development of a specific target for low-energy nuclear astrophysics experiments. As such, it provides an update of a specific task in a large-scale experimental effort to measure astrophysics-relevant processes in the laboratory.…”