On the role of secondary pions in spallation targets

TL;DR

This paper demonstrates through simulations that secondary pions significantly influence neutron and photon production in thick spallation targets, with neutral pions responsible for most high-energy photons and charged pions contributing substantially to neutron yield, yet yields remain robust despite variations in pion multiplicity.

Contribution

It reveals the crucial role of secondary pions in hadronic cascades and their impact on neutron and photon yields in thick spallation targets, highlighting a robustness to pion multiplicity variations.

Findings

Neutral pions produce ~90% of high-energy photons.

Charged pions contribute ~40% to neutron yield.

Photon and neutron yields are insensitive to pion multiplicity changes.

Abstract

We use particle-transport simulations to show that secondary pions play a crucial role for the development of the hadronic cascade and therefore for the production of neutrons and photons from thick spallation targets. In particular, for the n_TOF lead spallation target, irradiated with 20 GeV/c protons, neutral pions are involved in the production of ~90% of the high-energy photons; charged pions participate in ~40% of the integral neutron yield. Nevertheless, photon and neutron yields are shown to be relatively insensitive to large changes of the average pion multiplicity in the individual spallation reactions. We characterize this robustness as a peculiar property of hadronic cascades in thick targets.