Simulations of Galactic Cosmic Ray Impacts on the Herschel/PACS bolometer Arrays with Geant4 Code

TL;DR

This study uses Geant4 simulations to analyze how Galactic cosmic ray impacts affect Herschel/PACS bolometer arrays, revealing the dominant role of external spacecraft components in secondary events and their effects on detector performance.

Contribution

It provides the first detailed simulation of cosmic ray impacts on Herschel/PACS bolometers, highlighting the significance of spacecraft shielding and secondary particle effects.

Findings

External components cause most secondary events affecting detectors

25% of cosmic ray hits impact adjacent pixels

Energy depositions increase bolometer temperature by 1-6%

Abstract

The effects of the in-flight behaviour of the bolometer arrays of the Herschel/PACS instrument under impacts of Galactic cosmic rays are explored. This instrument is part of the ESA-Herschel payload, which will be launched at the end of 2008 and will operate at the Lagrangian L2 point of the Sun-Earth system. We find that the components external to the detectors (the spacecraft, the cryostat, the PACS box, collectively referred to as the `shield') are the major source of secondary events affecting the detector behaviour. The impacts deposit energy on the bolometer chips and influence the behaviour of nearby pixels. 25% of hits affect the adjacent pixels. The energy deposited raises the bolometer temperature by a factor ranging from 1 to 6 percent of the nominal value. We discuss the effects on the observations and compare simulations with laboratory tests.