Study of the ³⁷Cl(a,n)⁴⁰K reaction to constrain the reaction rate of destruction of ⁴⁰K in stars.

⁴⁰K is thought to be one of the main isotopes responsible for the radiogenic heating of the mantle in an Earth-like exoplanet. The radiogenic heat keeps the mantle and the outer core, that mainly consists of molten iron and nickel, in a state of turbulent convection. This motion is generating magnetic field, which is essential for developing a habitable environment [1]. In addition, it contributes to the formation of plate tectonics, which play a key role in the volcanic activity and eventually the carbon cycle of a planet. The abundance of ⁴⁰K in these planets depends on the composition of the interstellar medium from which they were formed. Thus, nuclear reactions that determine the amount of ⁴⁰K during stellar evolution are crucial. 

 

In this study, we constrain the reaction rate of ⁴⁰K(n,a)³⁷Cl, one of the two major destruction paths of ⁴⁰K in stellar nucleosynthesis by measuring the reverse reaction ³⁷Cl(a,n)⁴⁰K and applying the principle of detailed balance to the reaction rate as it has been done in the past for the other reaction responsible for the destruction of ⁴⁰K (40K(n,p)⁴⁰Ar reaction) [2]. We performed differential cross-section measurements on the ³⁷Cl(a,n₁γ)⁴⁰K, ³⁷Cl (a,n₂ γ) ⁴⁰K and ³⁷Cl (a,n₃ γ) 40K reactions, for six different center of mass energies in the range between 5.1 and 5.4 MeV. The experiment took place at the Edwards Accelerator Laboratory at Ohio University. The gamma rays from the reactions mentioned above were detected by two LaBr3 scintillators. Using the swinger facility to change the angle of the beam on target with respect to the detection system, we were able to obtain the differential cross-section for six different angles between 20 and 120° in the lab system. Here, we present some preliminary results of this ongoing analysis.