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The modelling of background noise in astronomical gamma ray telescopes

The modelling of background noise in astronomical gamma ray telescopes
The modelling of background noise in astronomical gamma ray telescopes
Gamma ray photons interact with matter through a wide variety of complex physical mechanisms, which can be readily imitated by other particle processes. Unfortunately since γ-ray telescopes are obliged to function in a hostile radiation environment above the earth's atmosphere the net result is low signal to noise observations and a corresponding loss in sensitivity.
Consequently, understanding the generation of the systematic background noise is crucial if the full performance of a γ-ray instrument is to be realised. In the past it was not possible to reliably estimate the background levels in a fully quantitative manner; semi-empirical methods were employed. Although the basic underlying sources of the background noise were reasonably well understood, and the spectral intensities of the associated particles were reasonably well known, it was not possible to associate resultant noise components with the input source of that noise with any real degree of accuracy.
The advent of sophisticated and accurate computer programmes capable of dependably representing the requisite particle physics processes and interactions coupled with the advances made in the context of high power/low cost computers has revolutionised the situation. The so-called 'mass modelling' technique is a truly physics-based approach, which takes the input particle spectra of the local radiation environment together with a computer representation of the mechanical structure and chemical composition of the instrumentation and associated spacecraft to trace the trajectories and interactions of all the incident particles throughout the system. All energy deposits from the various interactions and likewise those from the prompt and delayed secondary products are also accurately recorded.
Subsequent energy discriminators and time coincidences can be applied to the event arrays with additional software to simulate on-board electronics systems. Internal spectral counting rates may be readily derived and analysed in terms of a wide variety of desired purposes. The impact of an accurate physics-based mass modelling technique has been to expand application of the procedure to effectively all the main aspects of a space γ-ray astronomy mission: instrument design; internal counting rates and spectral sensitivity estimates; optimisation of the design of the on-board processing electronics; operational planning and mission optimisation; estimation of radiation damage and its limitation; calibration planning and interpretation; the production of accurate instrumental response matrices; data analysis software; normalisation of astronomical results across instrument and instrumental degradation boundaries; and data archiving.
0038-6308
285-376
Dean, A.J.
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Bird, A.J.
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Diallo, N.
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Ferguson, C.
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Lockley, J.J.
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Shaw, S.E.
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Westmore, M.J.
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Willis, D.J.
ca62ae58-e59a-4a0f-8f00-e0aafdf23452
Dean, A.J.
2f9093f2-855c-4769-b1aa-6dd621b5dcf1
Bird, A.J.
045ee141-4720-46fd-a412-5aa848a91b32
Diallo, N.
3b6e09f0-bf9d-4cff-a305-03a637dbcfb8
Ferguson, C.
9513d2e3-7541-43e5-8efa-d55c9b217c0a
Lockley, J.J.
aad4b4b4-38c4-4c4d-93d2-6fed1a9c3bb8
Shaw, S.E.
65776027-991a-45ae-8338-e1c73909ce64
Westmore, M.J.
5d6b3349-70ae-4a47-85ba-f353116fa50d
Willis, D.J.
ca62ae58-e59a-4a0f-8f00-e0aafdf23452

Dean, A.J., Bird, A.J., Diallo, N., Ferguson, C., Lockley, J.J., Shaw, S.E., Westmore, M.J. and Willis, D.J. (2003) The modelling of background noise in astronomical gamma ray telescopes. Space Science Reviews, 105 (1-2), 285-376. (doi:10.1023/A:1023995803108).

Record type: Article

Abstract

Gamma ray photons interact with matter through a wide variety of complex physical mechanisms, which can be readily imitated by other particle processes. Unfortunately since γ-ray telescopes are obliged to function in a hostile radiation environment above the earth's atmosphere the net result is low signal to noise observations and a corresponding loss in sensitivity.
Consequently, understanding the generation of the systematic background noise is crucial if the full performance of a γ-ray instrument is to be realised. In the past it was not possible to reliably estimate the background levels in a fully quantitative manner; semi-empirical methods were employed. Although the basic underlying sources of the background noise were reasonably well understood, and the spectral intensities of the associated particles were reasonably well known, it was not possible to associate resultant noise components with the input source of that noise with any real degree of accuracy.
The advent of sophisticated and accurate computer programmes capable of dependably representing the requisite particle physics processes and interactions coupled with the advances made in the context of high power/low cost computers has revolutionised the situation. The so-called 'mass modelling' technique is a truly physics-based approach, which takes the input particle spectra of the local radiation environment together with a computer representation of the mechanical structure and chemical composition of the instrumentation and associated spacecraft to trace the trajectories and interactions of all the incident particles throughout the system. All energy deposits from the various interactions and likewise those from the prompt and delayed secondary products are also accurately recorded.
Subsequent energy discriminators and time coincidences can be applied to the event arrays with additional software to simulate on-board electronics systems. Internal spectral counting rates may be readily derived and analysed in terms of a wide variety of desired purposes. The impact of an accurate physics-based mass modelling technique has been to expand application of the procedure to effectively all the main aspects of a space γ-ray astronomy mission: instrument design; internal counting rates and spectral sensitivity estimates; optimisation of the design of the on-board processing electronics; operational planning and mission optimisation; estimation of radiation damage and its limitation; calibration planning and interpretation; the production of accurate instrumental response matrices; data analysis software; normalisation of astronomical results across instrument and instrumental degradation boundaries; and data archiving.

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Published date: 2003

Identifiers

Local EPrints ID: 37735
URI: https://eprints.soton.ac.uk/id/eprint/37735
ISSN: 0038-6308
PURE UUID: e59f552e-684e-4209-ae1e-d07085309bc7
ORCID for A.J. Bird: ORCID iD orcid.org/0000-0002-6888-8937

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Date deposited: 26 May 2006
Last modified: 06 Jun 2018 13:10

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Contributors

Author: A.J. Dean
Author: A.J. Bird ORCID iD
Author: N. Diallo
Author: C. Ferguson
Author: J.J. Lockley
Author: S.E. Shaw
Author: M.J. Westmore
Author: D.J. Willis

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