High-Resolution Gamma-Ray and Neutron Detectors For Nuclear Spectroscopy

Transcription

1 High-Resolution Gamma-Ray and Neutron Detectors For Nuclear Spectroscopy Thomas Niedermayr, I. D. Hau, S. Terracol, T. Miyazaki, S. E. Labov and S. Friedrich Former colleagues: M. F. Cunningham, J. N. Ullom, CA, U.S.A. A. Burger Fisk University, TN, U.S.A. Z. W. Bell, V. E. Lamberti Y-12 Security Complex, TN, U.S.A.

2 Composite Microcalorimeter Spectrometer 1 mm Mo Wiring Layer Sn or 10 B, 6 Li compounds 0.25 mm Mo Wiring Layer Si Substrate 0.5 µm SiN Mo/Cu multilayer TES Si Substrate 0.4 Normal Resistance [Ω] High sensitivity dr/dt Superconducting Temperature [K] 2 stage ADR 6-8 hours operation below T c

3 Frequency-Domain Multiplexing L FB ω 1 L S1 L S L S R FB R S C 1 L K1 Summing Loop V OUT A1 ( ω) = ( ω ω ) τ 1 A ( ω ω ) τ 2 ω 2 L S2 L S L SQ 10 6 R S C L K2 T < 1 K 10 4 With pulses 1000 Carrier only Sum signals from 2 sensors with summing loop Readout 2 sensors with one SQUID amplifier Demodulate output with lock-in amplifiers Scalable to n! Frequency [khz] Cunningham et al, Appl. Phys. Lett. 81, 159 (2002)

4 DC and AC Comparison Current Pulse (Time) Current Pulse (Frequency) 10 5 Current (µa) Time (msec) AC Bias DC Bias 15 Device Current Noise (pa/hz 1/2 ) AC Bias DC Bias Frequency (Hz) DC and demodulated AC pulse shapes are identical LC resonant circuit acts as a filter for AC Biased Data Demonstrated E FWHM = 60 ev at 60 kev for 2 multiplexed detectors, same as DC case

5 γ-ray Spectrum of a Mixed Pu Isotope Source Determination of Pu Isotopes Abundances Multiplexed microcalorimeters Ge spectrometer (Fano limit) 57 Co-Sn K β1 escape U K α2 Pu K α2 238 Pu 241 Am 57 Co-Sn Kα1 escape 57 Co-Sn Kα2 escape U K α1 Np K α1 241 Am Np K α2 239 Pu Pu K α1 241 Pu 240 Pu Energy [kev] E FWHM ~ 90 ev at 100 kev

6 Fast-Neutron Spectrometer Intrinsic Detection Efficiency (%) Ideal Detector TES based Calorimeter (1+ MeV) Organic scintillator (8 MeV) MeV Time of Flight (2.5 MeV) 1-15 MeV Diamond semiconductor (14 MeV) 8-20 MeV Recoil prop. counter (1 MeV) MeV 3He gridded ionization chamber (1 MeV) MeV Capture Gated (5 MeV) 1-20 MeV 3He semiconductor sandwich (1 MeV) MeV Recoil proton telescope (60 MeV) MeV Energy Resolution (%) data from F.D. Brooks, H. Klein / NIM A 476 (2002) 1 11

7 Neutron Transmission Spectroscopy MCNP simulation of the neutron emission spectrum from Pu and PuO 2 Pu Neutron Flux PuO 2 σ elastic for 16 O 16 O Elastic Cross-Section) Energy (MeV) Active or passive interrogation for elemental composition analysis Advantages: large penetration depth and nondestructive

8 Neutron Detection Principle Choose absorber material with high (n,α) cross section After neutron capture: Heavy charged particles are created and stopped in the absorber E deposited = Q reaction + E neutron Q reaction + E neutron Counts Q reaction γ-rays Pulse Height Photons with E γ < Q reaction can be discriminated against neutrons

9 Neutron detection materials 10 B n + 10 B " α + 11 Li Q = 2.79 MeV (GS) " α + 11 Li * Q = 2.31 MeV (ES) Counts Low energy γ-rays 94% 6% Energy (MeV) 6 Li n + 6 Li " α + 3 H Q = 4.78 MeV Counts Low energy γ-rays 100% 4.78 Energy (MeV) Expected spectrum for thermal neutrons

10 First neutron spectrum TiB 2 absorber for neutron detection: large heat capacity per unit mass (metal) C absorber = 10 nj/k m abs = 4 mg Thermal neutrons spectrum 1 mm TiB mm 300 Counts Counts Energy (MeV) MeV: 10.5 kev # 0.5 % 2.79 MeV: 5.5 kev # 0.2 % Energy (MeV)

11 Large absorber design Al or Au wires TES Neutron Absorber V ~ several cm 3 C abs ~ several nj/k Low thermal conductivity suspension (sapphire balls) Resolving power at 1 MeV Volume (mm 3 ) Efficiency (%) Size will be adjusted for particular application: Max. count rate capability limits maximum size of each individual pixel Source strength sets number of pixels to multiplex

12 Summary High resolution γ spectroscopy with multiplexed detectors "0.1% FWHM energy resolution at 100 kev High resolution neutron spectroscopy "0.2% FWHM energy resolution at 2.79 MeV