1. HE instrument and in-orbit performance
Yifei. Zhang
On behalf of HE Group in HXMT,
IHEP,

2. Main contents Outline HE Instrument and in-orbit performance
High Energy Detector
Anti-Coincident Detector
Automatic Gain Control System
Particle Monitor

3. Outline High Energy X-ray Telescope (HE)
Consisting of High Energy Detector (HED), Particle Monitor (PM), Automatic Gain Control System (AGC), Anti-Coincident Detector (ACD), Collimator, and electronic system.
Main characteristics
Total detection area ~5000 cm^2
Covering keV X/γ
Field of view
15：1.1×5.7 deg^2
2：5.7×5.7 deg^2
1：Covered with Tantalum
Energy resolution
High Energy X-ray Telescope is the main payload.
(Side)

4. Outline X/γ ray Detection and charged particle rejection X/γ
X/γ rays in FOV will be absorbed by NaI(Tl) crystal and treated as effective events.
X/γ rays coming from the back will be absorbed by CsI(Na) crystal. Those events can be rejected by PSD method in off-line processing.
Charged particles can be rejected by ACD.
X/γ
X/γ
e, p, …
X/γ
e, p, …

5. HE Instrument and in-orbit performance
High Energy Detector (HED)
NaI(Tl)/CsI(Na) phoswich detector
Detecting keV X/γ rays
keV
Be made up of
Beryllium, 1.5mm thick
NaI(Tl), φ190 mm×3.5 mm
CsI(Na), φ190 mm×40 mm
Quartz glass
PMT R877, gain ~1.0×10^5
Shock absorber
Magnetic shield
Charge sensitive amplifier, output a voltage pulse with a width less than 3 μs.
Array with 18 HEDs, total ~ 5000 cm^2
Shock absorber

6. HED In-orbit performance Light curve Energy spectrum
Pulse width spectrum
Time interval spectrum
CsI(Na)
NaI(Tl)
2μs
6μs

7. HED Redistribution Matrix Function (RMF)
Get the in-orbit RMF on the base of background calibration
Use Crab source to check and improve it.
More details in upper report ‘Insight-HXMT calibration’

8. HE Instrument and in-orbit performance
Anti-Coincident Detector (ACD)
Including 6 top-ACDs and 12 side-ACDs, plastic detector
Detecting charged particle and giving a mark for rejection.
Mainly made up of
Plastic wrapped with reflector
PMT followed by divider
Absorber and shield
Charge sensitive amplifier
Absorber,
EM shield
ACD (Side)
ACD (Top)

9. ACD Anti-Coincident Detector (ACD)
Plastic in top-ACD responding to HED field of view is designed to be 3.4 mm thick to enhance the transmission of X/γ rays. Other area is 6.4 mm thick as well as in side-ACD.
Plastic: 3.4 mm thick
Top-ACD
Side-ACD
Plastic: 6.4 mm thick

10. ACD
Veto efficiency
Average ~ 22% in all channel

11. HE Instrument and in-orbit performance
Automatic Gain Control System (AGC)
To reduce the effect caused by the change of temperature and magnetic field to keep HED working steady.
Located at the bottom of Collimator and near to the beryllium of HED.
MPPC, size 3×3 mm
Am-241, ~ 200 Bq
Readout electronics
AGC
MPPC
AGC
MPPC
PCB
PMT
Collimator
NaI(Tl)/CsI(Na)
Tagged alpha source

12. AGC Automatic Gain Control logic
Increase the PMT voltage of 312 mV when pulse height of a gamma ray coming from Am-241 tagged in AGC is lower than 50 channel. If not decrease 312 mV.
Reference Channel P0
Measured P
Left window
Right window

13. HE Instrument and in-orbit performance
Particle Monitor (PM)
Plastic detector
Monitoring the intensity of in-orbit charged particles
Warning to shut down other detectors’ power
Be made up of
Plastic, φ1cm × 1cm
PMT, R647-1
Shock absorber
Magnetic shield
Divider
Charge sensitive amplifier
Threshold
Electron, ≥1MeV
Proton, ≥ 20MeV PM
outline
Plastic
PMT
absorber
shield
divider
Amplifier

14. PM
Particle distribution in HXMT orbit
SAA

15. Summary Parameters Design Value In orbit performance Detection area
~5000 cm^2
5100 cm^2
Energy range
keV
~ normal mode by NaI(Tl)
~ GRB mode by CsI(Na) *
Resolution
59.5keV
~ 59.5keV (estimated)
Spatial resolution
1.1 deg ×5.7 deg,
5.7 deg ×5.7 deg
Time resolution
≤ 25 μs
2 μs
Dead time
~ 6 μs (without big signals contribution)
*: GRB mode is an expanded working mode by using the CsI(Na) crystal with a lower PMT supply voltage.

16. Thanks !