On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS

arXiv:2405.04836 · astro-ph.IM, physics.ao-ph · Submitted 2024-05-08 · Read on arXiv

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Introduction to the show: ident: Astrophysics. The day in astrophysics: observations, models and what the data forces.

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: We're looking at the paper: "On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS".

Jocelyn: Here's the gist of the paper. On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS provides validation and calibration tests for its performance.

Vera: The results from these tests were used to validate a simulation model of XGRE and TARANIS.

Jocelyn: Detector Composition and Design XGRE consisted of three sensors, each having one layer of LaBr3 crystals for X-ray/gamma-ray detections, and two layers of plastic scintillators for electron and charged-particle discrimination.

Vera: Each detection unit contained an 84×90×8.7 mm3 LaBr3 scintillation crystal (manufactured by Saint-Gobain) sandwiched between two 84×90×5 mm3 plastic scintillators.

Title and authors: Vera: This paper, "On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS", focuses on taking this XGRE detector and testing it in a controlled environment to get those solid numbers we need. Jocelyn It's interesting that they brought together a team from Osaka University, CEA Saclay, and the University of Paris for this calibration work.

Subrahmanyan: The authors are clearly spanning the necessary expertise here; you have the engineers building the hardware and the astrophysicists who understand what those measurements actually constrain in terms of cosmic structure formation. Vera Right, so they're essentially bridging that gap between a complex detector system and its performance on a satellite mission.

Jocelyn: They are testing XGRE by looking at its composition—three sensors with LaBr3 crystals and plastic scintillators—and then doing thermal cycle tests using flight models from April to May two thousand eighteen. Subrahmanyan The key thing they're looking for in those tests is how the gain of the detector changes with temperature, because that directly affects how well you measure energy.

Vera: They found a negative correlation on the high-temperature side, meaning as it got hotter, the detector's gain actually decreased. Jocelyn That tells us something important about the thermal stability we have to account for when we plan operations on orbit.

The paper's summary: Vera: The summary of this paper explains that they performed three steps for validation: with the detection units, with the sensors themselves, and then finally with the actual satellite. Jocelyn That stepwise approach is standard in space instrumentation; you check each component before putting it all together.

Subrahmanyan: They detailed how they determined the energy range of those LaBr3 crystals for XGRE1, XGRE2, and XGRE3, finding ranges like zero point zero four to eleven point six MeV for the first sensor and so on. Vera And they gave us specific energy resolution numbers too, such as twenty point five percent, twenty-five point nine percent, and twenty-eight point six percent at zero point six six two MeV for each sensor respectively; those are concrete performance metrics we need to keep in mind when interpreting data later on.

Jocelyn: They also derived an energy calibration function, like E equals zero point plus a factor times the channel number in MeV, which is how they correct the raw counts to get real energy values. Subrahmanyan This calibration function is what allows us to reconstruct the actual X-ray or gamma-ray energy from what the detector actually measured.

Vera: The paper also used Monte Carlo simulations with Geant4 version four point one zero.three hundred thirty and CADMesh version one point one.thirty-three to compare their measurements against the simulation results obtained during the satellite calibration test for XGRE, which helps confirm their model accuracy <ref:2405.04836#pg1>.

The paper's improvements: Jocelyn: Now let's talk about what they suggest improving in the way they use these tests, because that’s where it gets really useful for future work. Vera They propose several key improvements, starting with better event classification for electrons and gamma rays. Subrahmanyan Specifically, they suggest using pulse duration to distinguish between terrestrial gamma-ray flashes and terrestrial electron beams; events longer than one millisecond are interpreted as electron beams rather than TGFs, based on data from BATSE/CGRO <ref:2405.04836#pg1>.

Vera: That’s a significant distinction because it helps us separate the physics of lightning discharges into two different categories. Jocelyn They also suggest using the difference in count rates between the XGRE sensors due to their varying mounting angles to estimate where a TGF is actually originating from, which helps with source localization.

Subrahmanyan: That spatial estimation based on angle differences sounds like a useful way to map out where the high-energy radiation is coming from in a lightning discharge event, which feeds into our models of atmospheric physics. Vera They also offer an improved method for reconstructing energy spectra by applying those derived calibration functions directly to the raw detector counts.

Jocelyn: And they suggest an AI approach to calculate the effective area of XGRE across different elevation and azimuth angles using verified Monte Carlo simulations, which gives us a tool to estimate detection efficiency from various directions. Subrahmanyan This calculation is vital because the effective area itself changes depending on where the incoming radiation is coming from, so knowing that helps us plan our observations better.

Conclusion: Vera: So to wrap up, this paper on "On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS" confirms that the hardware works as expected under thermal cycling and provides specific energy ranges for each sensor. Jocelyn The improvements they propose are all about getting more precise information out of the data, specifically better ways to classify particle events and estimate their source location on the ground.

Subrahmanyan: From a cosmological viewpoint, being able to accurately characterize these high-energy atmospheric signals helps us refine our models of how energy is deposited and how those particles interact with the Earth's magnetic field. Vera And that means when we look at the TARANIS data later, we can trust the energy spectra and spatial information more than ever before.

Jocelyn: It sets a clear path for future missions by showing exactly what kind of calibration tests are necessary to get reliable results from instruments designed to study lightning phenomena. Subrahmanyan And those specific calibration procedures will be key when we try to link these atmospheric events back to the larger picture of cosmic particle acceleration.

Vera: We've seen how they've validated the simulation model using Geant4 and comparing it against the actual measurements from the satellite test, which gives a strong foundation for trusting their derived effective areas. Jocelyn So, this paper is about making sure that when we look at TGFs and TEBs, we have the best possible tools to understand what's happening in the atmosphere.

Subrahmanyan: That's it for this paper on "On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS".

Division of Electrical, Electronic, and Infocommunications Engineering, Graduate School of Engineering, Osaka University · Service d’Astrophysique, IRFU/DRF · Laboratoire Astroparticule et Cosmologie, Universite de Paris/CNRS · Institut de Recherche d’Astrophysique et Planetologie · Birkeland Centre for Space Science, University of Bergen · Kobayashi-Maskawa Institute for the Origin of Particles and the Universe

astro-ph.IM, physics.ao-ph

Submitted: 2024-05-08

Updated: 2026-10-28

Journal ref: Journal of Astronomical Telescopes, Instruments, and Systems 10(2), 026005 (7 May 2024)

DOI: 10.1117/1.JATIS.10.2.026005

License: http://creativecommons.org/licenses/by-nc-nd/4.0/

Importance score: 79/100

The gist: On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS provides validation and calibration tests for its performance.

Key concepts

XGRE Detector Composition: XGRE consists of three detection units. Each unit has one LaBr3 crystal for X-ray/gamma-ray detection and two plastic scintillators for electron discrimination. Different combinations of these crystals allow researchers to identify whether a detected event is an X-ray, gamma ray, or an electron.
Thermal Cycle Test: The detector units underwent thermal cycling between 35°C (high) and -25°C (low) using flight models. Tracking the gain variation during this cycle revealed a negative correlation: as the temperature increased on the high side, the detector's sensitivity decreased.
Effective Area Calculation: Using Monte Carlo simulations with verified models, researchers calculated how much of space each sensor can effectively detect. This calculation showed that for X-rays and gamma rays, the area varied significantly based on the incident angle and elevation.
Electron Energy Estimation: For detected electrons, their kinetic energy is estimated by comparing how much energy they deposit in the upper plastic scintillator versus the LaBr3 crystal. This ratio helps determine if an electron has a lower or higher incident kinetic energy.

Terminology

Calibration — 66× in this paper · explained in 9 episodes
Accuracy — 7× in this paper · explained in 1 episode
Verification — 6× in this paper · explained in 2 episodes
Composition — 5× in this paper · explained in 2 episodes
Gamma-ray Burst Monitor — 5× in this paper
Compton Scattering — 2× in this paper · explained in 2 episodes
Hysteresis — 2× in this paper · explained in 3 episodes
Pair Production — 2× in this paper · explained in 2 episodes
Preconditioning — 2× in this paper · explained in 2 episodes
Burst and Transient Source Experiment — 1× in this paper
Compton Gamma-Ray Observatory — 1× in this paper
Core — 1× in this paper · explained in 2 episodes
Localization — 1× in this paper · explained in 2 episodes
Polarization — 1× in this paper · explained in 2 episodes

Summary

On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS provides validation and calibration tests for its performance. The results from these tests were used to validate a simulation model of XGRE and TARANIS.

Detector Composition and Design

XGRE consisted of three sensors, each having one layer of LaBr3 crystals for X-ray/gamma-ray detections, and two layers of plastic scintillators for electron and charged-particle discrimination. Each detection unit contained an 84×90×8.7 mm3 LaBr3 scintillation crystal (manufactured by Saint-Gobain) sandwiched between two 84×90×5 mm3 plastic scintillators. Particle discrimination can be performed by taking coincidence counting of the LaBr3 crystal and the plastic scintillators; X-rays or gamma rays when each crystal is hit alone; electrons within the measurable energy range when the LaBr3 and one of the three crystals are hit simultaneously; and high-energy electrons, positrons, and other charged particles exceeding their measurable energy range when three crystals are hit simultaneously.

Thermal and Operational Verification

The on-ground validation and calibration tests were performed in three steps: with the detection units, with the sensors, and with the satellite. A thermal-cycle test using flight models was conducted from April to May 2018 at LESIA. The maximum and minimum temperature during the test was 35◦C and −25◦C, respectively. The gain variation was tracked by fitting the total absorption peak of 88Y at 898-keV with a Gaussian function for the energy spectra acquired every 30 min. In the cycle on the high-temperature side, a negative correlation was observed, in which the gain decreased as the temperature increased.

Calibration and Energy Range Determination

The energy range of the LaBr3 crystals sensitive to X-rays and gamma rays was determined to be 0.04–11.6 MeV, 0.08–11.0 MeV, and 0.08–11.3 MeV for XGRE1, 2, and 3, respectively. The energy resolution at 0.662 MeV (full width at half maximum) was to be 20.5%, 25.9%, and 28.6%, respectively. An energy calibration function was calculated for each sensor, such as E = 0.0729 + 2.52 × 10−3 × ch [MeV] (2). The energy range of each sensor was 0.04–11.6 MeV, 0.08–11.0 MeV, and 0.08–11.3 MeV for XGRE1–3, respectively.

Simulation Validation and Effective Area Calculation

Monte Carlo simulations were performed with Geant4 version 4.10.330–32 and CADMesh version 1.1.33 to validate the simulation results by comparing them with the measurement results obtained in the satellite calibration test. The effective area of XGRE, derived from a Monte Carlo simulation with the verified model, reached the maximum at 0.1 MeV, 838 cm2, and the minimum at 3.5 MeV, 191 cm2, in total for the three sensors. The effective area below 0.3 MeV was sensitive to the elevation and azimuth angle of incident X-rays and gamma rays.

Angular Resolution Analysis

The direction of arrival of gamma rays can be measured by utilizing the characteristic that the effective area changes with elevation and azimuth angles of incident particles on the low-energy side. The estimation accuracy of azimuth angle at an elevation angle of 45◦ is about ±30◦ near azimuth 0◦, and about ±50◦ near azimuth 180◦. The amount of changes increases as the elevation angle decreases.

Electron Detection Capability

When electrons are detected, their kinetic energy is deposited in the upper plastic and LaBr3 scintillators, and the amounts of deposits depend on the energy of the incident electrons. The average energy deposit in the plastic scintillators is around 1 MeV for the entire range of incident electron energies. For electrons above 3 MeV, the incident energy of electrons can be estimated from the energy deposit at LaBr3. The effective areas at an elevation angle of 90◦ were 155 cm2 for electrons with an incident energy of 2 MeV, but it monotonically increases with the incident electron energy, and It is 664 cm2 for electrons with an incident energy of 10 MeV. The change in effective area with azimuth angle is observed in the entire energy range of 1–10 MeV, and the amount of changes by an incident angle is higher than that of photons.

Conclusion

XGRE was the key instrument of TARANIS for high-energy atmospheric phenomena such as TGFs and TEBs. The assembly of the flight model started in February 2018, and validation tests of the sensors were performed in Paris, before its delivery to CNES Toulouse in November 2018. The knowledge obtained during the development of XGRE will be valuable for a future mission of high-energy atmospheric physics and high-energy astrophysics.

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35 Yuuki Wada is an assistant professor at the Graduate School of Engineering, Osaka University. He received his PhD in physics from the University of Tokyo in 2020

36 Philippe Laurent is employed at the CEA Astrophysical Department in Saclay and Astroparticle and Cosmology (APC) laboratory in Paris, France. He specializes in high-energy astrophysics and got his PhD in 1992, studying high-energy emission from black holes X-ray binaries

37 Ion Cojocarib was an instrumentation engineer at the Astroparticle and Cosmology (APC) laboratory, having participated in the integration, testing, and calibration of the XGRE instrument

38 Stephane Colonges ´ is an expert in reliability engineering at the APC laboratory of CNRS. He was involved in the TARANIS mission as a product assurance engineer

39 David Sarria is a researcher at the Birkeland Centre for Space Science, the University of Bergen in Norway. He received his PhD from the Institut de recherche en astrophysique et planetologie at the ´ University of Toulouse in 2015 and is a post-doctoral researcher at the Astroparticle and Cosmology (APC) laboratory at the University of Paris Diderot on the TARANIS spacecraft, particularly on Monte-Carlo modeling of the XGRE instrument

40 Kazuhiro Nakazawa is an associate professor at Nagoya University, focusing on X-ray and MeV gamma-ray astronomy in both observational and detector development aspects, including on-ground thundercloud gamma-ray observations.

Improvements for AI systems

Improved high-energy event classification capability: The system can distinguish between terrestrial gamma-ray flashes (TGFs) and terrestrial electron beams (TEBs) by analyzing pulse duration; for example, events with durations longer than 1 ms are interpreted as TEBs rather than TGFs, based on the analysis of BATSE/CGRO data.
Enhanced source localization for atmospheric phenomena: The AI can estimate the source location of TGFs by using the difference in count rates between XGRE sensors due to their varying mounting angles, allowing it to determine where high-energy radiation is originating from in a lightning discharge event.
Accurate energy spectrum reconstruction with calibration correction: The system can reconstruct the energy spectra of X-rays and gamma rays by applying derived calibration functions, such as E = 0.0058 + 2.82 x 10-3 x ch [MeV] for XGRE1, to raw detector counts.
Precise effective area calculation under varying conditions: The AI can calculate the effective area of the XGRE detector for X-rays and gamma rays across different elevation and azimuth angles by using verified Monte Carlo simulations, providing a tool to estimate detection efficiency from various directions.
Electron energy estimation from deposition patterns: For detected electrons, the system can estimate their incident kinetic energy by analyzing the ratio of energy deposits in the LaBr3 crystal versus the upper plastic scintillator, as the amount of deposits depend on the energy of the incident electrons.
Angular resolution determination for particle tracking: The AI can determine gamma-ray arrival direction by analyzing a two-dimensional plot showing the ratio of XGRE1 and 2 divided by XGRE3, which forms an oval orbit as the azimuth changes, allowing for unique angle determination if sufficient statistics are available.

Abstract

We developed the X-ray, Gamma-ray and Relativistic Electron detector (XGRE) onboard the TARANIS satellite, to investigate high-energy phenomena associated with lightning discharges such as terrestrial gamma-ray flashes and terrestrial electron beams. XGRE consisted of three sensors. Each sensor has one layer of LaBr 3 crystals for X-ray/gamma-ray detections, and two layers of plastic scintillators for electron and charged-particle discrimination. Since 2018, the flight model of XGRE was developed, and validation and calibration tests, such as a thermal cycle test and a calibration test with the sensors onboard the satellite were performed before the launch of TARANIS on 17 November 2020. The energy range of the LaBr 3 crystals sensitive to X-rays and gamma rays was determined to be 0.04-11.6 MeV, 0.08-11.0 MeV, and 0.08-11.3 MeV for XGRE1, 2, and 3, respectively. The energy resolution at 0.662 MeV (full width at half maximum) was to be 20.5%, 25.9%, and 28.6%, respectively. Results from the calibration test were then used to validate a simulation model of XGRE and TARANIS. By performing Monte Carlo simulations with the verified model, we calculated effective areas of XGRE to X-rays, gamma rays, electrons, and detector responses to incident photons and electrons coming from various elevation and azimuth angles.