1. Project Structure
Advanced Neutron Spectrometer on the International Space Station (ANS-ISS)
Mark Christl
NASA/MSFC
Oct 23, 2015
Honolulu, HI 1 1

2. RadWorks (aka Radiation Sensors)
Advance Exploration System (AES) Sponsoring office
RadWorks: JSC Lead
JSC: HERA, BIRD charged particle sensors (ionizing radiation)
LaRC: Storm shelter and modeling
MSFC: ANS (neutron spectrum)
Phase I: Develop neutron spectrometer for exploration missions
Design, test and demonstrate instrument
Fabricate prototype unit
Compare with other techniques
Key performance parameters: 0.5 to 50 MeV, 2.3 kg, 4W
Phase II: ISS test flight demonstration
design, fabricate and qualify ANS-ISS version
deploy to ISS
operate and acquire data for analysis
Phase III: Operational Instrument for Manned Exploration

3. Space Radiation Environment
Radiation risk to crew includes charged and neutral particle
Estimate 25% of dose on ISS is due to neutrons
Sources of charged particles in LEO include: GCR, Trapped protons and SEP
Neutrons are generated through the interaction of these charged particles with matter : spacecraft/habitat, planetary surface or atmosphere
Mixed radiation field includes all of the above

4. Space Radiation Environment (cont’d)
Penetrating: no energy loss through direct ionization (tissue, shielding)
High radiation weighting factor

5. ANS Gate and Capture Technique
Thermal neutron

6. Gate and Capture Technique
Boron-10
loaded plastic scintillator
Lithium-6 doped glass scintillator

7. ANS Prototype (2014) Fiber array: 72×73 fibers 120 um dia.
1 mm spacing
15 cm length

8. ANS Prototype (2014)

9. ANS-ISS Engineering Model nPMT+nFEE

10. EM nPMT+nFEE signal separation
Noise peak
Neutron capture signal
Beta continuum
Alpha peak

11. Signal Response TRIUMF

12. AmBe Source Exposure Neutron Capture Signal Proton Recoil Signal
n-capture p-channel
Late signal p-channel

13. Comparison of 3 neutron source spectra

15. Gamma-ray Sensitivity (preliminary)
n & p rates over 2 days

16. p-recent dist for B10 and Li6May 15, 2013

17. Neutron Angular Production

18. Neutron Spectra @ 45o – p + Al reaction

19. ANS GEN-II Geant4 Simulations Figure 1 ANS GEN-II diagram

20. Figure B2 Fraction events versus energy deposited in the ANS GEN-II detector volume for an incident neutron energy of 0.5 MeV before neutron capture.

21. Figure B3 Fraction events versus energy deposited in the ANS GEN-II detector volume for an incident neutron energy of 10 MeV before neutron capture.

22. Figure B4 Fraction events versus energy deposited in the ANS GEN-II detector volume for an incident neutron energy of 20 MeV before neutron capture.

23. Figure B7 ANS GEN-II optical photon response distribution for 0
Figure B7 ANS GEN-II optical photon response distribution for 0.5 MeV neutrons before neutron capture.

24. Figure B8 ANS GEN-II optical photon response distribution for 10 MeV neutrons before neutron capture.

25. Figure B9 ANS GEN-II optical photon response distribution for 20 MeV neutrons before neutron capture.

26. Figure 11 Geant4 simulation of ANS GEN-II neutron response versus energy and PMT optical photon current.

27. ANS GEN-II response for high-rate 98 MeV protons at 950 V. The fit is 1.09x106E-1.16.

28. ANS GEN-II response for AmBe source 30 mV at 950 V.
The normalization is 7.11x107.

29. ANS-ISS Overview Deployment location: Internal
Attachment method: Velcro
Mission duration
Primary: 6 months
Secondary: ISS duration
Launch configuration: Soft-stow
Payload delivery : June/July2016
Mass: 11 lbs
Volume: 5”x9”x10”
Power: 7 W
Voltage: 28 VDC
Data Link: USB to ISS laptop
Data Rate: 100 kbits/sec
Memory: 4GBytes

30. Next Steps
Evaluate and test the response matrix with mono-energetic beams of neutrons ( PTB Dec 2015 ):
E = 0.024, 0.14, 0.25, 0.57, 1.2, 2.5, 5, 8 , 14, 19 MeV
Conduct flight test on ISS to evaluate trigger efficiency and background in a space environment ( Aug )
Compare measured spectrum with previous results (2016+ )
Next phase: Finalize design and qualify
Tech-demo → operational instrument
5 year mission duration
Validate data analysis approach
Further Instrument Developments :
Glass spheres replacing fibers
Single set of four 1” PMTs

31. Backup Material

32. Response to edge trig; 1”x1”x2”

33. Comparison with He-3 Monitor

34. SPE Peak and Average values

35. Relevance of the accelerator exposures

36. Rate comparison SPE intensity IUCF intensity Threshold > 10 MeV
Rate in protons/sec
1.4X1011
2.3X1010
2.6X109
6.0X108
IUCF intensity