Apple, Jeffrey A.

Christl, Mark

Gibson, Brian F.

Kuznetsov, Evgeny

Watts, John W.

NASA Technical Reports Server

Project Structure
1
Mark Christl
NASA/MSFC
Oct 23, 2015
Advanced Neutron Spectrometer on the 
International Space Station (ANS-ISS) 
https://ntrs.nasa.gov/search.jsp?R=20150022206 2019-08-31T05:33:34+00:00Z
Deep Space Radiation Environment
• Radiation risk to crew includes charged and neutral 
particle
• Sources of charged particles in LEO include: GCR, 
SEP, Trapped Belts
• Secondary neutrons are generated through the 
interaction of these charged particles with matter : 
spacecraft/habitats and planetary surface or 
atmosphere (e.g. albedo from Earth’s atmosphere)
• Mixed Radiation Field includes all of the above
Properties of neutrons
• Isolated neutrons have a half life of 13 minutes, 
so no primary neutrons sources
• Penetrating: no energy loss through direct 
ionization (tissue, shielding)
• Estimated 25% of dose on ISS is due to neutrons
• Neutrons have high Q values
ANS Technique: Gate and Capture
Thermal 
neutron
B10 technique
Li6 technique
ANS GEN-II 
Instrument (2014)
ANS GEN-II 
Instrument (2014)
Waveforms for EM_Ver1 
nPMT+nFEE
9
Response to edge trig; 1”x1”x2”
EM_Ver1 nPMT+nFEE signal 
separation
11
Neutron capture 
signal
Beta continuum
Alpha 
peak
Noise peak
Signal Response TRIUMF
AmBe Source Exposure
Neutron Capture Signal
Proton Recoil Signal
n-capture p-channel
Late signal p-channel
Comparison of 3 measured neutron source 
spectra
Gamma ray rejection
Gamma-ray Sensitivity (preliminary)
n & p rates over 2 days
Comparison to Boron loaded detector
p-recent dist for B10 and Li6May 15, 2013
Comparison to NMS
Neutron Spectrum
Simulations
Neutron Angular Production
10
-6
10
-5
10
-4
10
-3
10
-2
0 50 100 150 200
95
85
75
65
55
45
35
25
15
5MeV
500keV
50keV
5keV
500eV
50eV
5eV5x5x5 cm
Angle (deg)
N
e
u
tr
o
n
 F
lu
x
 (
m
m
-2
)
200MeV p + Al  n + X
Neutron Spectra @ 45o – p + Al reaction
Figure 1 ANS GEN-II diagram
ANS GEN-II Geant4 Simulations
Figure B1 Fraction events versus energy deposited in the ANS GEN-II detector 
volume for an incident neutron energy of 10 eV before neutron capture.
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.
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.
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.
Figure B7 ANS GEN-II optical photon response distribution for 0.5 MeV neutrons before 
neutron capture.
Figure B8 ANS GEN-II optical photon response distribution for 10 MeV neutrons before neutron 
capture.
Figure B9 ANS GEN-II optical photon response distribution for 20 MeV neutrons before neutron 
capture.
0
10.5
23.44930077
74.55190277
237.0220032
753.559021
2395.780029
7616.859863
24216.09961
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1E-05
1.100000024
3
18
65
140
Optical Photon Current
Fr
eq
u
en
ct
Neutron Energy (MeV)
1.E-01-1.E+00
1.E-02-1.E-01
1.E-03-1.E-02
1.E-04-1.E-03
1.E-05-1.E-04
1.E-06-1.E-05
1.E-07-1.E-06
1.E-08-1.E-07
Figure 11 Geant4 simulation of ANS GEN-II neutron response versus energy and PMT optical 
photon current.
Figure 17 ANS GEN-II response for high-rate 98 MeV protons at 950 V. The fit is 1.09x106E-1.16.
Figure 22 ANS GEN-II response for AmBe source 30 mV at 950 V. The normalization is 7.11x107.
Current Status
• NASA has not yet selected a neutron spectrometer for 
manned exploration
• Current state-of-the-art is based on boron loaded 
scintillator (cf. Lithium-6)
• ANS is a competing technique: advantages: positive 
neutron identification, better background rejection 
and cleaner spectral measurements in mixed 
radiation fields; disadvantage: lower neutron cross 
section, no commercial detector available 
• ISS will provide the space flight environment to test 
ANS-ISS and mature the technique and design
ANS-ISS Summary
Objectives
• The ISS provides a relevant spaceflight 
environment for testing hardware
• Mature the ANS measurement 
technique and design
• Deploy to ISS for 6 month mission
• Transmit data to ground for analysis
• Analyze data to determine the fast 
neutron spectrum on the ISS
• Compare with FND (soon)
• Evaluate environment background 
ANS-ISS Allocation
• Mass: 5 kgs
• Volume: 5”x9”x10”
• Power: 7.5 W
• Voltage: 28 VDC
• Data Link: USB to ISS laptop
• Data Rate: 100 kbits/sec
• Attachment location: Internal 
• Attachment method: Velcro 
• Mission
• Primary: 6 months
• Secondary: ISS duratiuon
• Launch configuration: Soft stow
• Payload readiness date: 
June/July2016
Next Steps
• Evaluate and test the response matrix with mono-energetic 
beams of neutrons:
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 
susceptibility in a real space environment
• Compare derived spectrum with historical results and Boron 
loaded detector
• Finalize design and qualify: 
Tech-demo → Operational instrument
5 year mission duration
Verify de-convolution approach
Potential alterations: 
single set of 4 PMTs
spheres replacing fibers
Backup Material
Space Exposure
SPE Peak  and Average values
Relevance of the accelerator 
exposures
Example calculation of the proton intensity for a deep space exposure to neutrons produced by to 
solar energetic protons interacting on a spacecraft/habitat sized shhelter: 
 
Assumptions: 
Area of spacecraft/habitat right circular cylinder: 5m x5m   = 118 m
2
 (=1.18x10
6
 cm
2
) 
Wall thickness: 10 g/cm
2
 (based on ISS and including more than such the spacecraft wall)
 
 
Incident flux: 1cps/cm
2
-sr (particle event threshold is 10 Hz/cm
2
-sr at >10 MeV)  
Total incident proton intensity (p+Al=> X) = 1.2x10
6
 p/s-sr  
 
For an average daily fluence of 10
4
 /cm
2
-sr => 10
4
x1.2x10
6
/(24x3600)=1.3x10
5
 p/s  
 (peak flux probably is several factors higher than daily average) 
 
 
For frustum 5x3.3=> 62.5 m
2
 surface area; mass 9000kgs => 14.4 g/cm
2
 
Incident flux: 1cps/cm
2
-sr  
Total incident proton intensity (p+Al=> X) = 0.625x10
6
 p/s-sr 
 
For an average daily fluence of 10
4
/cm
2
  => 10
4
x1.25x10
6
/(24x3600)= 0.7x10
5
 p/s  
 (peak flux probably is several factors higher than daily average) 
 
Rate comparison
Threshold > 10 MeV >30 MeV >60 MeV >100 MeV
Rate in protons/sec 1.4X1011 2.3X1010 2.6X109 6.0X108
SPE intensity
IUCF intensity


Advanced Neutron Spectrometer on the International Space Station (ANS-ISS)

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