Neutron Detection Spring 2002

Size: px

Start display at page:

Download "Neutron Detection Spring 2002"

Hugh Park
5 years ago
Views:

1 Neutron Detection Spring 2002

2 Neutrons vs. X-rays

3 Ideal Large Detector Pulse Height

4 Neutron Interactions

5 Total Cross section for Moderators

6 Neutron Slowing Down

7 Neutron Histories in Moderated Detector

8 Inelastic Neutron Scattering

9 Elastic Scattering Kinematics

10 Elastic Scattering Kinematics

11 Recoil Proton Energy for Monenergetic Neutrons

12 Neutron Moderator Energy Distributions

13 Pulse Height vs. Energy in Plastic

14 Recoil Spectrum Distortion in Plastic

15 Fission Cross section for Slow Neutrons

16 Fission Cross section for Fast Neutrons

17 Fission Fragments

18 Cross section for Neutron Detector Reactions

19 Some Reactions for Neutron Detectors n+ 3 He p+ 3 H kev n B á Li MeV (94%) á Li MeV (6%) n+ 6 Li 3 H + á + ~ 4.8 MeV

20 He-3 and Li-6 Cross sections

21 He-3 Detector Spectrum

22 BF-3 Pulse Heights

23 Wall Effects

24 Degradation of BF3 Counters

25 Neutron Scintillator Choices Thermal ( < 0.5 ev) load scintillator with materials with high capture crosssection such as Li. B, Gd Epithermal (0.5 ev - 50 kev) Moderate neutrons and then use thermal techniques Fast neutrons (> 50 kev) detect through (n,p) or (n,d) elastic scatters hydrogen rich materials such as plastic scintillators

26 Neutron Scintillators

27 Li Scintillators - Glass and Phosphors Neutron Energy Glass Type Glass Thickness ev All types mm Thermal GS mm 10 ev KeV GS mm 100 ev - 1 MeV GS mm KeV KG2, GS mm 1-6 Mev GS20 25 mm 6 3 n+ Li H + α + ~ 4.8 MeV

28 Li Glass Pulse Height Response

29 Applications of Neutron Detection Reactors

30 PWR Out of Core Instruments

31 PWR Ranges

32 Instrument Requirements Start-up gamma Flux dominates require discrimination against gammas pulse mode possible Intermediate gamma still important switch to current mode reject gammas» CIC» MSV Full Power gammas not important simplicity for safety ion chambers

33 Compensated Ion Chamber

34 Mean Square Value Counter

35 BWR Ranges

36 BWR In-Core Fission Counter

37 Memory Effects

38 Operating Voltages

39 Self powered Neutron Detector

40 Applications of Neutron Detection Radiography

41 707 Body Panel

42 Fast Neutron Radiograph

43 C, O, and N Cross-sections

44 Nitrogen Cross-section

Early Experiment at NAC Cross section: barns 18 16 14 12 10 8 6 4 2 Total Neutron Cross Section H1 C12 N14 O16 0 0.2 0.3 0.4 0.5 0.6 0.7 0.

45 Early Experiment at NAC Cross section: barns Total Neutron Cross Section H1 C12 N14 O En: MeV Detecting explosives by taking difference of two radiographic images. The contrast comes from nitrogen and oxygen.

46 High Resolution Neutron Images

47 Resonant Images of Carbon

48 Neutron Resonance Radiography 9 Figure 1. Total Neutron Cross Section 8 7 H1 C12 N14 O16 Cross Section: barns N off N on C off O on C on O off En: Mev

Resonance Radiography Drug simulant 50 100

5g C:16.3g N:0.9g O:5.2g H:1.0g C:7.1g N:7.

49 Resonance Radiography Drug simulant Explosive simulant En=2.37MeV H:1.5g C:16.3g N:0.9g O:5.2g H:1.0g C:7.1g N:7.1g O:12.3g C:10.6g H:1.8g C:10.6g N:24.9g O-At-Valley/O-On-Res. Graphite Melamine 200 N-Off-Res./N-On-Res C-Off-Res./C-On-Res

50 Composite Picture

51 D-D Kinematics 10 8 Outgoing Neturon Energy (MeV) Incoming Deuteron Energy (MeV)

52 Using a D-D Neutron Source Ed = 2.3MeV Ed=0.8MeV (thick target) Different energies are obtained by rotating object-detector assembly around the source D-D Neutron Energy at Different Angles Deuteron Target 0 o En: MeV o 25 o Ed: MeV 115 o 100 o 90 o 80 o 70 o 50 o 60 o Object Detector

53 A terrorist overnight bag Simulation of NRR Bag size: 40 X 30 X 10 cm. Contents of interest: a bag of sugar (105g), a stash of cocaine- HCl (105g), a paperback book, a block of plastic explosive (270 g). Heavily loaded with various of items and has an average density of around 0.5g/cm 3. Source-Object: ~150cm; Object-Detector: ~50cm.

Neutron and X-Ray Images Neutron Image(0 degree) X-Ray Image(140kev) 50 50 100 100 150 150 200 50 100 150 200 200 50 100 150 200

54 Neutron and X-Ray Images Neutron Image(0 degree) X-Ray Image(140kev) Simulations were run on Blue Pacific supercomputer at Lawrence Livermore National Laboratory, with 5x10 8 source particles for each image.

55 Elemental Mapping

All Element Mapping Other Elements Mapping 0.3 All Elements Mapping 0.6 0.25 0.5 50 0.2 50 0.4 100 0.15 0.1 100 0.3 0.2 150 0.05 150 0.

56 All Element Mapping Other Elements Mapping 0.3 All Elements Mapping Elements other than H, C, N, O are reported as one component All-elements mapping is the total projected content. (atoms/cm 2)

57 Detecting Mines

Neutrons. ρ σ. where. Neutrons act like photons in the sense that they are attenuated as. Unlike photons, neutrons interact via the strong interaction

Neutrons. ρ σ. where. Neutrons act like photons in the sense that they are attenuated as. Unlike photons, neutrons interact via the strong interaction Neutrons Neutrons act like photons in the sense that they are attenuated as I = I 0 e μx where Unlike photons, neutrons interact via the strong interaction μ = The cross sections are much smaller than