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

Robert Ajvazyan,Simon Zhamkochyan,Vanik Kakoyan,Rachel Montgomery,Amur Margaryan,Henrik Vardanyan,John Annand,Kenneth Livingston,Dimiter Balabanski,Branislav Vlahovic,Patrik Khachatryan,Vachik Khachatryan,Nersik Grigoryan

doi:10.3390/particles1010009

Robert Ajvazyan, Simon Zhamkochyan + Show 11 more

Open Access

https://doi.org/10.3390/particles1010009

Copy DOI

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 ((OCH3)2CH2), 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 16O 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 12C 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/cm2. 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 mm2 low-pressure MWPC units using an α-particle source. The possibility of measuring the 16O(γ, α)12C cross-section in the 8–10 MeV energy region by using a LCB γ-ray beam is also discussed. A measurement of the 16O(γ, α)12C cross-section will enable the reaction rate of 12C(α, γ)16O to be determined with significantly improved precision compared to previous experiments.

Highlights

Thermonuclear burning in stars is responsible for the synthesis of most chemical elements heavier than helium in the universe
We present a new active target for measuring the cross-section of the 16O(γ, α)12C reaction, using an Laser Compton Backscattered (LCB) γ-ray beam of energy Eγ = 8–10 MeV
The rejection factor for a single Multi Wire Proportional Chamber (MWPC) unit, i.e., the ratio of β-particle to α-particle detection efficiencies is about 10−4

Summary

Introduction

Thermonuclear burning in stars is responsible for the synthesis of most chemical elements heavier than helium in the universe. The 4He(αα, γ)12C and 12C(α, γ)16O reactions are two of the most important fusion processes in astrophysics [1] These reactions essentially govern the helium burning phase, and their rates determine the ratio of 12C:16O (C/O) in the “ashes” of the helium burning process. We present a new active target for measuring the cross-section of the 16O(γ, α)12C reaction, using an LCB γ-ray beam of energy Eγ = 8–10 MeV. It is a position- and time-sensitive detector system based on low-pressure Multi Wire Proportional Chamber (MWPC) technology.

Methods

Findings

Discussion