1. Use of Cosmic-Ray Neutron Data in Nuclear Threat Detection and Other Applications Neutron Monitor Community Workshop—Honolulu, Hawaii October 24-25, 2015 Physicist National Urban Security Technology Laboratory Science and Technology Directorate Paul Goldhagen

2. Paul Goldhagen Uses of cosmic-ray neutron data National Urban Security Technology Laboratory (formerly, Environmental Measurements Laboratory) 2  ~30 people  Established 1947, AEC- DOE - DHS  HASL - EML - NUSTL  Support to emergency responders  Long history of fallout and radiation measurements  35 years of neutron spectrometry  DHS Government lab in New York City Science and Technology Directorate

3. Paul Goldhagen Uses of cosmic-ray neutron data  Cosmic rays and cosmic-ray-induced (cosmogenic) neutrons  Variation of cosmic particle intensity in the atmosphere  Cosmic rays and cosmogenic neutrons on Earth affect:  Nuclear threat detection for homeland/national security  Measurements for nuclear treaty verification  Microelectronics reliability (single-event upsets)  Radiation dose to airplane crews/passengers (and everyone)  Hydrology measurements  Production of cosmogenic radionuclides – atmospheric tracers, geological dating, background for neutron activation  Calculations and measurements of cosmic-ray neutron spectra  Importance of neutron monitor data Overview 3

4. Paul Goldhagen Uses of cosmic-ray neutron data Cosmic rays in Earth’s atmosphere 4 electrons/positrons photons neutrons protons mesons muons

5. Paul Goldhagen Uses of cosmic-ray neutron data  Cosmic rays: energetic atomic nuclei from space  Protons (90%), He ions (9%), heavier ions (1%); No neutrons  Collision with atmosphere  cascades of all kinds of particles, including neutrons (and protons, mesons, muons, photons, electrons)  Two kinds / sources  Galactic (GCR) – continual, high energy, dominate effects  Solar – sporadic (~1 GLE/y), high rates for hours, lower energy, affect GCR  GCR-induced neutrons dominate radiation effects in the atmosphere from airplane altitudes to the ground  Rates depend on air pressure, magnetic latitude, solar activity, and nearby materials  Materials can scatter, absorb, moderate, regenerate neutrons  Effects depend on neutron energy distribution Cosmic-ray-induced neutrons in the atmosphere 5

6. Paul Goldhagen Uses of cosmic-ray neutron data  Altitude or air pressure - Shielding by air  Big effect, but calculable, measured, well known  Neutron rate at 10,000 ft. = 11  rate at sea level  Barometric pressure changes can change rate >50% at sea level  Latitude - Shielding by geomagnetic field  Calculable, measured  Effect increases with altitude  Rate at poles / equator  8 at 20 km, 3.3 at 9 km, 2 at sea level  Solar activity - magnetic field of solar wind  Not calculable, measured by neutron monitors  ~11-year sunspot cycle: Radiation min at sunspot max  Effect increases with geomagnetic latitude & altitude  Solar modulation >2 (polar) at 20 km, <30% at sea level GCR neutron rates in the atmosphere depend on 6

7. Paul Goldhagen Uses of cosmic-ray neutron data Neutron monitor count rate and barometric pressure during super-storm Sandy 7 Neutron count rate (counts/sec) Pressure (mm-Hg) 712 760 Newark neutron monitor 12 days in 2012 Pressure Raw count rate Pressure-corrected rate

8. Paul Goldhagen Uses of cosmic-ray neutron data Effect of air pressure (elevation) 8 Log scale (6,250 ft) Neutron flux decreases exponentially with increasing air pressure (11,300 ft)

9. Paul Goldhagen Uses of cosmic-ray neutron data Effect of geomagnetic field (latitude) 9 Measured Calculated

10. Paul Goldhagen Uses of cosmic-ray neutron data Solar activity changes 10

11. Paul Goldhagen Uses of cosmic-ray neutron data Sunspot number and GCR flux 11

12. Paul Goldhagen Uses of cosmic-ray neutron data Solar modulation of cosmic-ray neutron flux Daily neutron monitor rate in Delaware 12

13. Paul Goldhagen Uses of cosmic-ray neutron data Uses of cosmic-ray neutron data

14. Paul Goldhagen Uses of cosmic-ray neutron data  DHS, DOE, and DoD fund programs to improve detection of hidden nuclear devices and fissile materials  Primary method is radiation detection  Passive detection – detect gamma rays emitted by uranium and gammas and neutrons emitted by plutonium  Active interrogation: use pulsed incident radiation; detect neutrons and  rays from induced fission of HEU as well as Pu  To find hidden materials, detectors must be sensitive enough to detect / measure background radiation  Passive gamma detection: Low-E  rays easily shielded; variable background from common radioactive materials; nuisance alarms from medical treatments, commercial sources Radiation detection to find nuclear threats 14

15. Paul Goldhagen Uses of cosmic-ray neutron data  Neutrons are a signature of fissile materials  Plutonium emits neutrons – spontaneous fission of 240 Pu  Common radioactive materials don’t  Passive neutron detection  Far fewer nuisance alarms for neutrons than for gamma rays  Neutrons are harder to shield than gamma rays  Active interrogation: use pulsed incident radiation; detect neutrons and  rays from induced fission of HEU as well as Pu  To find hidden materials, detectors must be sensitive enough to detect / measure background  The background for neutron detection is neutrons produced by cosmic rays Neutron detection for homeland/national security 15

16. Paul Goldhagen Uses of cosmic-ray neutron data Background rate in deployed detectors can and must be measured, but need to understand background in advance to:  Design new, better detection systems  Improve signal/background; reduce nuisance alarms  Test and compare developmental detection systems  Deal with rapidly varying position-dependent background  Mobile standoff detection in cities – varying shielding from buildings  Searching ships  For some applications, can’t measure background, must calculate it  For some applications, cosmogenic neutrons are the signal Need to understand background neutrons 16

17. Paul Goldhagen Uses of cosmic-ray neutron data  DHS DNDO TAR funded LANL, NUSTL, UD to calculate the cosmic-ray neutron background everywhere on Earth.  UD: Primary CR spectrum, directional geomagnetic cutoffs, atmosphere  LANL: coding, normalization, transport, solar modulation  NUSTL: Benchmark measurements of cosmogenic neutron energy spectra in airplane and on ground at various locations  MCNP6 calculations: cosmic source, method, results, version 2.0  n, p, ,  spectra on 2054 point global grid at ground and 10 altitudes  Directional n,  spectra on ground; altitude scaling to location of interest  Agreement with NUSTL measurements  Date (corresponding to NM data) is an input. To be valid in future, calculations require ongoing neutron monitor data Background radiation algorithm development 17 Supported by the US Department of Homeland Security, Domestic Nuclear Detection Office, under competitively awarded contract/IAA HSHQDC-12-X-00251.

18. Paul Goldhagen Uses of cosmic-ray neutron data MCNP6 cosmic source option  Built-in spectra  Historic (PRL / Lal, 1980)  Modern (UoD / Clem, 2006)  SDEF card  PAR keyword enhanced  New keyword DAT  New keyword LOC (Clem)  Benchmarking  NASA ER-2 flights  NUSTL Long Dwell / Goldhagen 18 Description of SDEF keywords. KeywordValuesDescription PAR [-]cr [-]ch [-]ca [-]c7014 [-]c14028 [-]c26056 All cosmic particles Cosmic protons only Cosmic alphas only Cosmic nitrogen only Cosmic silicon only Cosmic iron only DAT MDYMDY Month (1-12) Day (1-31) Year (4 digit) LOC LAT LNG ALT Latitude (-90 to 90; S to N) Longitude (-180 to 180; W to E) Altitude (km) Garrett McMath and Gregg McKinney LANL, Nuclear Engineering & Nonproliferation Division

19. Paul Goldhagen Uses of cosmic-ray neutron data Cosmic-ray neutron spectrum on the ground Livermore, CA - Nov 2006 19 with geomagnetic field in the atmosphere

20. Paul Goldhagen Uses of cosmic-ray neutron data 20 2 Ways to plot neutron spectra Same data Differential Flux, d  /dE (m -2 s -1 MeV -1 ). E · d  /dE (m -2 s -1 ). Flux proportional to area under curve

21. Paul Goldhagen Uses of cosmic-ray neutron data Cosmic-ray neutron spectrum 21 Thermal High energy Slowing-down region ~1/E Evaporation

22. Paul Goldhagen Uses of cosmic-ray neutron data  NUSTL has measured the energy spectrum of cosmic-ray neutrons on:  Airplanes  Ground  Ships NUSTL measurements 22 Components of NUSTL’s new neutron spectrometer

23. Paul Goldhagen Uses of cosmic-ray neutron data Measurement on the ground Livermore, CA - Nov 2006 23

24. Paul Goldhagen Uses of cosmic-ray neutron data 24 2 Ways to plot neutron spectra Same data Differential Flux, d  /dE (m -2 s -1 MeV -1 ). E · d  /dE (m -2 s -1 ). Flux proportional to area under curve

25. Paul Goldhagen Uses of cosmic-ray neutron data Measurements on these container ships 25 SS Lurline 826 ft 22,221 Tons MV Mahimahi and MV Manoa 860 ft 30,167 Tons

26. Paul Goldhagen Uses of cosmic-ray neutron data Neutron spectra from cosmic rays on ships and from simulated threat 26

27. Paths of AIR ER-2 flights Altitude profiles of 3 flights Have analyzed data from boxed portions of flights NASA ER-2 Paul Goldhagen Atmospheric Neutrons 27 June 1997

28. Paul Goldhagen Uses of cosmic-ray neutron data High-altitude cosmic-ray neutron spectra 28 (preliminary)

29. Paul Goldhagen Uses of cosmic-ray neutron data  Multisphere neutron spectrometer (Bonner spheres)  Set of spherical moderators of different sizes surrounding detectors ( 3 He counters) that respond to slow (thermal-energy) neutrons  Big moderators slow down higher-energy neutrons than small moderators (up to ~30 MeV)  To detect high-energy neutrons, add heavy-metal shells (Pb, Fe) to some spheres  High-energy neutron hits large nucleus  hadron spray with readily detectable fission-energy “evaporation” neutrons  Covers whole energy range of cosmic-ray neutrons: 10 -8 - 10 4 MeV  Calculate energy response of detector assemblies using MCNPX/6  Low resolution; need spectral unfolding: MAXED code Extended-range multisphere neutron spectrometers 29

30. Paul Goldhagen Uses of cosmic-ray neutron data NUSTL multisphere neutron spectrometer 30

31. Paul Goldhagen Uses of cosmic-ray neutron data High-energy neutron detector 31 15-inch diameter polyethylene ball Steel shell 3 He gas proportional counter

32. Paul Goldhagen Uses of cosmic-ray neutron data NUSTL multisphere neutron spectrometer 32 “Ship effect”

33. Paul Goldhagen Uses of cosmic-ray neutron data Multisphere neutron spectrometer in container 33

34. Paul Goldhagen Uses of cosmic-ray neutron data Measurements on the ground in Hawaii elevations from sea level to 12,800 feet 34

35. Paul Goldhagen Uses of cosmic-ray neutron data Other applications – national security

36. Paul Goldhagen Uses of cosmic-ray neutron data  For INF and START treaties, radiation detection equipment (RDE) used to verify number of missile warheads  RDE: array of moderated 3 He counters used to measure fission neutron rate (subtracting cosmogenic background neutrons)  Proper operation verified in field using Am-Li neutron source  Russia proposed using background neutrons instead of transporting neutron source – less hassle  Can we trust that proper operation of RDE is verified using just background neutrons?  Need calculated cosmic-ray neutron count rate at each site / time  Real-time neutron rate needs real-time neutron monitor data Nuclear arms treaty verification 36

37. Paul Goldhagen Uses of cosmic-ray neutron data  Argon-37 (T ½ = 35 days) is produced by nuclear explosions  Proposed for use in CTBT inspections to detect underground nuclear tests  Cosmic-ray neutrons produce background 37 Ar in the ground  DTRA-funded researchers at Univ. of Texas use MCNP6 to calculate cosmic-ray neutron spectrum / intensity incident on the ground and 37 Ar background production rate  Rate depends on soil composition, location, solar modulation  Requires neutron monitor data for most recent 2 months Test ban treaty nuclear forensics 37

38. Paul Goldhagen Uses of cosmic-ray neutron data Single-event upsets in microelectronics (Mike Gordon, IBM) 38 A few nucleons cause Most nucleons pass  particles, heavy ions Neutrons & protons (ionization by each particle) (via recoils from nuclear reaction)  Flip bits, corrupt data (JEDEC Standard JESD89A)  Occur if enough charge is deposited in the sensitive volume.

39. Paul Goldhagen Uses of cosmic-ray neutron data  Aircrews occupationally exposed to radiation from cosmic rays  High-energy mixed radiation field  Effective dose can’t be measured using personal dosimeters  40% - 60% of biologically effective dose from neutrons  Continual exposure of large group  ~160,000 civilian aircrew members in U.S.  Civil aircrew working hours aloft ~ 500-1000 h / year  Annual effective dose 1 to 6 mSv (U.S. radiation workers average 2.2)  Air crews are one of the most exposed groups of radiation workers Radiation protection for airplane crews (Kyle Copeland, FAA) 39

40. Paul Goldhagen Uses of cosmic-ray neutron data  Measure soil water, snow, biomass using cosmogenic neutrons  Previously elusive scale, tens of hectares, 10 – 60 cm deep  Same principal as Am-Be soil moisture gauges: water moderates / thermalizes evaporation (MeV) neutrons  Use moderated (and bare) neutron detectors to measure rates of 1 – 1000 eV slowing-down neutrons (and thermals)  Over 200 probes in use  COSMOS network in U.S. (NSF); networks in other countries  Thermal-neutron rate depends on soil composition  Normalize using neutron monitor rate; best if nearby (U.S.) Hydrology Zreda, Desilets, et al., Univ. of Arizona, Sandia Natl. Lab. 40

41. Paul Goldhagen Uses of cosmic-ray neutron data  Cosmic-ray neutrons create cosmogenic radionuclides in the air and ground  Atmospheric tracers ( 7 Be)  Geological dating ( 10 Be, 14 C, 36 Cl, …)  Background for neutron activation measurements  Source terms require knowledge of cosmic-ray neutron spectrum and intensity  For shorter half-life nuclides, intensity requires neutron monitor data  DS2002 resolution of Hiroshima neutron dosimetry discrepancy  Measurements of neutron activation nuclides in Hiroshima samples ( 36 Cl, 60 Co, 63 Ni, 152 Eu) seemed high at large distances. Actually caused by cosmic-ray neutron background. Production of cosmogenic radionuclides 41

42. Paul Goldhagen Uses of cosmic-ray neutron data  Cosmic particle intensity in the atmosphere varies with  Altitude/pressure – big, but calculable, measured, well known  Geomagnetic latitude / cutoff rigidity – calculable, measured  Solar activity – measured by neutron monitors, not predictable  Cosmic rays and cosmogenic neutrons on Earth affect:  Nuclear threat detection for homeland security  Measurements for nuclear treaty verification, nuclear forensics  Radiation dose to airplane crews/passengers and everyone  Microelectronics reliability (single-event upsets)  Hydrology measurements  Production of cosmogenic radionuclides – atmospheric tracers, geological dating, background for neutron activation  These applications need ongoing neutron monitor data Summary 42

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44. Paul Goldhagen Uses of cosmic-ray neutron data Additional / background information 44 Slides following this one contain additional and background information that is not part of the planned oral presentation. These slides may be useful for answering questions. paul.goldhagen@hq.dhs.gov

45. Paul Goldhagen Uses of cosmic-ray neutron data Neutron flux on a logarithmic energy scale 45

46. Paul Goldhagen Uses of cosmic-ray neutron data Cosmic rays during high solar activity 46 A: First coronal mass ejection (CME) at Sun. B: First CME arrives at Earth. GCR decrease suddenly — a “Forbush decrease.” C: 2 nd CME at Sun. This one accelerates high-energy particles that reach Earth minutes later. The sudden increase recorded by the neutron monitors is a “ground level enhancement.” D: 2 nd CME arrives at Earth. GCR decrease again. This CME produces largest geomagnetic storm in 10 years. Cosmic ray variations recorded at 7 different neutron monitor stations On average, solar activity reduces cosmic ray intensity on Earth

47. Paul Goldhagen Uses of cosmic-ray neutron data Largest solar particle event ground level enhancement in 50 years 47 07:00 Time 08:00 Neutron Rate (counts/second) Jan 20, 2005 US East coast  2.5 South Pole  50

48. Paul Goldhagen Uses of cosmic-ray neutron data Cosmic-ray neutron spectrum on the ground Livermore, CA, Nov 2006 48 (preliminary) without geomagnetic field in the atmosphere

49. Paul Goldhagen Uses of cosmic-ray neutron data Radiation exposure of U.S. population NCRP 160 49 Percent of all sources (6.2 mSv) Percent of background (3.2 mSv) Space 5% Space 11%

50. Paul Goldhagen Uses of cosmic-ray neutron data  Neutrons, unlike charged particles, pass through the electron clouds of atoms without slowing down  When neutrons hit atomic nuclei, they usually bounce off (scatter), though sometimes they get absorbed  If the target nucleus is heavy, the neutrons barely slow, like a golf ball bouncing off a bowling ball  If the target nucleus is light, it recoils, and the neutron slows down a lot, like a golf ball bouncing off another golf ball  Hydrogen is the element with the lightest nucleus, so materials with a lot of hydrogen (plastic, oil, water) slow neutrons best  After a few tens of scatters, neutrons get as slow as the thermal motion of the hydrogen atoms and don’t slow more  These thermal neutrons are the easiest to detect or absorb Neutron moderation (slowing) & thermalization 50

51. Paul Goldhagen Uses of cosmic-ray neutron data  “Ship effect”: increase in the neutron background generated by cosmic rays near large masses of metal, such as ships High-energy cosmic-ray neutrons hit iron nuclei and excite them, releasing many fission-energy neutrons (spallation/evaporation)  Cold war study of standoff ship effect – classified  On ships, increased neutron background can cause nuisance alarms that interfere with detection and identification of hidden nuclear materials.  Background neutrons at fission energies are increased on ships by up to a factor of 2 to 4.  Varies with size/type of ship, location on ship, cargo  Neutron energy spectrum similar to shielded fission The neutron “ship effect” 51

52. Paul Goldhagen Uses of cosmic-ray neutron data  If terrorists hide a nuclear device or material in cargo on a container ship to U.S., how can we detect it before it arrives?  For a nuclear device, detection after arrival is too late  >10 million containers per year arrive in U.S.  Difficult to screen all containers in all foreign ports  Proposed solution: radiation detection in transit – detectors on every container or every container ship Days or weeks for detection (long dwell) instead of seconds  Very difficult and expensive in practice  Can it work – even theoretically? (No.)  If not, don’t fund pilot deployment; save tens of $millions  Long-Dwell In-Transit (LDIT) study, mostly for gamma detection; NUSTL did neutron background measurements DNDO Long-Dwell In-Transit Study 52

53. Paul Goldhagen Uses of cosmic-ray neutron data Cosmic-ray background neutron spectra measured on container ships and land 53

54. Paul Goldhagen Uses of cosmic-ray neutron data Neutron spectra from cosmic rays on ships and from simulated threat 54

55. Paul Goldhagen Uses of cosmic-ray neutron data Ground measurements outdoors, 2002-2003 55

56. Paul Goldhagen Uses of cosmic-ray neutron data Cosmic-ray neutron spectra measured on the ground at 5 locations with different elevations 56

57. Paul Goldhagen Uses of cosmic-ray neutron data Effect of air pressure (elevation) 57 Log scale (6,250 ft) Neutron flux decreases exponentially with increasing air pressure (11,300 ft)

58. Paul Goldhagen Uses of cosmic-ray neutron data Measured cosmic-ray neutron spectra scaled to sea level, NYC, mean solar activity 58

59. Paul Goldhagen Uses of cosmic-ray neutron data A nalytic model of neutron flux cutoff dependence 59 From: Belov, A., A. Struminsky, and V. Yanke, "Neutron Monitor Response Functions for Galactic and Solar Cosmic Rays", 1999 ISSI Workshop on Cosmic Rays and Earth, poster presentation. Described in: Clem, J. and L. Dorman, "Neutron monitor response functions," Space Sci. Rev., 93: 335-363 (2000).

60. Paul Goldhagen Uses of cosmic-ray neutron data  Results used to define terrestrial neutron flux in Annex A, “Determination of terrestrial neutron flux” in JESD89A Measurement and Reporting of Alpha Particle and Terrestrial Cosmic Ray-Induced Soft Errors in Semiconductor Devices http://www.jedec.org http://www.jedec.org  “Standard” neutron spectrum from NUSTL-IBM measurement  Scaling factor for any altitude/pressure, geographic location, solar activity from BSYD model  Also at http://www.seutest.com/cgi-bin/FluxCalculator.cgihttp://www.seutest.com/cgi-bin/FluxCalculator.cgi  Must manually enter solar modulation from neutron monitor data  Uncertainty ~20%; thermals may vary by factor of 2  Systematically high towards equator Measured ground-level cosmic-ray neutron spectrum and scaling factor 60

61. Paul Goldhagen Uses of cosmic-ray neutron data GCR-induced particles in the atmosphere Effective dose rate vs. altitude 61

62. Paul Goldhagen Uses of cosmic-ray neutron data  Radiation doses to aircrews are calculated  FAA: Air crews are occupationally exposed  No regulations, recommendation to inform, training materials  Civil Aerospace Medical Institute Radiobiology Research Team – Copeland  CARI-6 route-dose computer code – requires neutron monitor data  European Community: Air crews true radiation workers  Doses assessed, records to be kept  Funded program to calculate and measure doses  Several route-dose computer codes (all require neutron monitor data)  Some airlines ground pregnant aircrew  ISO standard under development to validate air route-dose codes What has been done - commercial aviation 62

63. Paul Goldhagen Uses of cosmic-ray neutron data High-altitude cosmic-ray neutron spectra 63 (preliminary) (preliminary: before atmospheric B field and heavy ions ) (preliminary )