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Neutron Detection Techniques

Outline. Neutrons ReviewCommon ReactionsCommon DetectorsCommercial Detector SystemsAssociated HardwareLaboratory Techniques

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Neutron Detection Techniques

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    1. Neutron Detection Techniques Geoff Gardner Physics 556 Professor Koltick

    2. Outline Neutrons Review Common Reactions Common Detectors Commercial Detector Systems Associated Hardware Laboratory Techniques “Secret Weapon”

    3. Why detect Neutrons? Applications involving neutrons Nuclear Power Plants Scanning Technologies Fundamental Physics What does it mean to detect a neutron? The detector needs to produce some sort of measurable signal Electrical? Audible?

    4. Why is detecting Neutrons so Difficult Neutrons have mass but NO CHARGE!!!! Can not directly produce ionization. Can not be directly detected. We must rely on some other mechanism or reaction to create the charged particle. There are many varieties of charged particle detectors

    5. Common Reactions 3He n + 3He ? 3H + 1H + 0.764 MeV BF3 n + 10B ? 7Li* + 4He (93%) ? 7Li + 4He + 0.48 MeV ? +2.3 MeV ( 7%) ? 7Li + 4He + 2.8 MeV Scintillation n + 6Li ? 4He + 3H + 4.79 MeV Cross sections only significant around thermal energies

    6. Neutron Review Energy ranges Thermal E ~ 0.025 eV Epithermal E ~ 1 eV Slow E ~ 1 keV Fast E ~ 100 – 10MeV Moderation of Neutrons A decrease of intensity “Slows” down or Decreases the Energy of the Neutron At Thermal Energies Capture Dominates (n,g) Resonance Structure in Cross Section Fast Often occurs by inelastic scattering event (ballistic collision) (n,p) (n,a), (n, 2n)

    7. Neutron Elastic Scattering Events

    8. Gas Proportional Counters

    9. Scintillators Saint Gobain Crystals is a leading Manufacture BC501 (data sheet) BC720 (data sheet) Properties of Scintillators Efficiency (measured in percent) ~ Density Photon Wavelength (measured in nm) Photons per Neutron Decay Time (good for liquids) Materials Li glass 7,000 photons/neutron ZnS(Ag) 160,000 photons/neutron Xylene ~ mineral oil

    10. Semiconductor Detectors Thin Film coated semiconductors Efficiency around 4% Diodes with neutron reactive coating (B,Li) Charged particles emitted, can attenuate in the film Research on Enhancements (Kansas State) Sandwiching layers of detectors Doubled Films Dimpled Surfaces

    11. Detection Efficiency

    12. Other Techniques

    13. Texas Nuclear Neutron Dosimeter Moderator (10” polyethylene) Scintillator (Li6I (Eu) crystal) PMT (RCA 6199) Preamplifier Discriminator Outputs (mrem/hr)

    14. Canberra Dineutron

    15. Laboratory Hardware Photomultiplier Tube (PMT) Vacuum tube Dynodes produce electron by “secondary emission” Very High gain mu mettal Base (voltage divider) Power Supplies (kV) Discriminators Constant Fraction Discriminator (CFD) Time to Amplitude Converter (TAC) Analog to Digital Converter (ADC) Multi-Channel Analyzer (MCA) Gate Generators Counters & Scalars

    16. Laboratory Techniques Pulse Shape Discrimination (PSD) Characterize radiation event by pulse shape

    17. Application

    18. Neutron Flux Calibration Tool Testing two different scintillators BC720 (hydrogenous plastic w/ ZnS phosphor) BC501A (mineral oil) Equipment Used XP2230 (2” 12 stage LF) Discriminator (lecroy 821) Gate Generator (lecroy 222) Visual Scaler (Joerger) Fan outs, = signal path Counts per 10/s

    19. Application

    20. References Radiation Detection and Measurement, Knoll Introductory Nuclear Physics, Krane High Efficiency Thin-Film Coated Semiconductor Neutron Detectors, D.S. McGregor, Kansas State University Neutron Detectors for Materials Research, T.E. Mason, ORNL www.saint-gobain.com Kenny Wakeland, 2K Corporation

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