Determination of the stellar (n,gamma) cross section of 40Ca with accelerator mass spectrometry

TL;DR

This paper measures the neutron capture cross section of 40Ca at stellar energies using a novel combination of activation and accelerator mass spectrometry, providing an independent and precise value relevant for astrophysical models.

Contribution

It introduces a new method combining activation and AMS to determine the 40Ca(n,gamma) cross section, offering an alternative to time-of-flight techniques.

Findings

Measured Maxwellian-averaged cross section at 30 keV: 5.73+/-0.34 mb

Provides an independent cross section value for astrophysical modeling

Highlights the role of 40Ca in stellar nucleosynthesis processes

Abstract

The stellar (n,gamma) cross section of 40Ca at kT=25 keV has been measured with a combination of the activation technique and accelerator mass spectrometry (AMS). This combination is required when direct off-line counting of the produced activity is compromised by the long half-life and/or missing gamma-ray transitions. The neutron activations were performed at the Karlsruhe Van de Graaff accelerator using the quasistellar neutron spectrum of kT=25 keV produced by the 7Li(p,n)7Be reaction. The subsequent AMS measurements were carried out at the Vienna Environmental Research Accelerator (VERA) with a 3 MV tandem accelerator. The doubly magic 40Ca is a bottle-neck isotope in incomplete silicon burning, and its neutron capture cross section determines the amount of leakage, thus impacting on the eventual production of iron group elements. Because of its high abundance, 40Ca can also play a secondary role as "neutron poison" for the s-process. Previous determinations of this value at stellar energies were based on time-of-flight measurements. Our method uses an independent approach, and yields for the Maxwellian-averaged cross section at kT=30 keV a value of <sigma>30 keV= 5.73+/-0.34 mb.