Neutron Background Detection for a Hard X-ray Balloon-borne Polarimeter

5 Jun 2014, 12:00
20m
Administratiezaal (Beurs van Berlage)

Administratiezaal

Beurs van Berlage

Oral Experiments: 2b) Astrophysics and Space Instrumentation II.b Astro & Space

Speaker

Mr Merlin Kole (KTH - Royal Institute of Technology)

Description

PoGOLite is a balloon-borne hard X-ray polarimeter. It determines polarisation by measuring the azimuthal angular distribution of Compton scattered photons in a plastic scintillator array. The use of an all plastic target yields a relatively large but low mass detection area. The dominant source of background for the polarisation measurements has been shown through Geant4 simulations to originate from high energy (MeV range) atmospheric neutrons. Neutrons can pass the instrument's Bismuth Germanium Oxide (BGO) anticoincidence shield undetected and subsequently scatter between plastic scintillator elements to produce a polarisation signature. A passive 15 cm thick polyethylene shield surrounding the polarimeter reduces the neutron induced background by an order of magnitude. The background level remains however significant, prompting the need for active monitoring of the continuously changing neutron flux. For this purpose PoGOLite makes use of a neutron sensitive phoswich scintillator cell. The phoswich cell consists of a 5 mm thick Lithium Calcium Aluminium Fluoride (LiCAF) scintillator, used for neutron detection. The LiCAF is surrounded by a BGO anticoincidence system. This small light weight detector can therefore be used to measure the neutron flux even in high radiation environments. This type of neutron detector was tested on a separate dedicated stratospheric balloon mission, called PoGOLino, prior to the PoGOLite flight which took place in July 2013. Results from both flights will be presented and implications on the polarisation measurements of PoGOLite from 2013 will be discussed.

Primary author

Mr Merlin Kole (KTH - Royal Institute of Technology)

Co-authors

Dr Elena Moretti (KTH - Royal Institute of Technology) Dr Hiromitsu Takahashi (Hiroshima University) Dr Kentaro fukuda (Tokuyama Corporation) Prof. Mark Pearce (KTH - Royal Institute of Technology) Dr Maxime Chauvin (KTH - Royal Institute of Technology) Mr Mikhalev Victor (KTH - Royal Institute of Technology) Dr Miranda Jackson (KTH - Royal Institute of Technology) Dr Mozsi Kiss (KTH - Royal Institute of Technology) Dr Noriaki Kawaguchi (Tokuyama Corporation) Mr Stefan Rydstrom (KTH - Royal Institute of Technology) Mr Sumito Ishizu (Tokuyama Corporation) Mr Takafumi Kawano (Hiroshima University) Dr Takayuki Yanagida (Kyushu Institute of Technology) Prof. Yasushi Fukazawa (Hiroshima University)

Presentation Materials

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