New instruments for real-time neutron spectrometry from thermal to GeV

1. New instruments for real-time neutron spectrometry from thermal to GeV R. Bedogni1, J.M. Gomez-Ros1,2, D. Bortot1,3, A. Pola3, M.V. Introini3, A. Esposito1, A. Gentile1, G. Mazzitelli1, B. Buonomo1 1 INFN – LNF Frascati (Italy) 2 CIEMAT Madrid (Spain) 3 Politecnico di Milano (Italy)

2. Introduction

3. Introduction Broad energy interval neutron spectrometry at beam-lines No single-device instrument exists to perform a complete energy range spectrometry (eV - GeV). To date, the only spectrometric technique able to provide all energy component is the Extended Range Bonner Sphere spectrometer Limitations: - time consuming irradiation sessions - poor energy resolution (partially compensated with a-priori information taken from MC simulations)

4. Introduction ERBSS

5. Introduction BSS counts (+ uncertainties) Guess hypothesis (physical models, parameterized spectrum, MC simulation) Unfolding (FRUIT) Altering guess hypothesis till “guess” counts counts are sufficiently in agreement with measured counts Spectrum

6. Introduction ERBSS spectrometry at Vesuvio (ISIS) NIM A 612 (2009)143–148 Radiation Measurements 45 (2010) 1205-1212

7. Introduction NESCOFI@BTF Goal Providing devices for “real-time” spectrometry of neutron producing facilities over the whole energy interval of production (eV - GeV) with similar measurement performance as the Bonner spheres. Condensing the characteristics of a BSS in TWO single moderator devices embedding multiple active thermal neutron detectors: SP2 Spectrometer with isotropic response CYSP Directional spectrometer Fields of application Research accelerators, industry, medical, aerospace, homeland security, cosmic rays measurements

8. Introduction Project breakdown Stage 1 Theoretical design of the instruments Response matrix calculation Manufacturing and testing passive prototypes Stage 2 Setting up active thermal detectors (TNDs) Stage 3 Manufacturing and testing the final spectrometers equipped with active TNDs.

9. Stage 1 The SPherical SPectrometer SP2 • Thirty-one thermal neutron detectors along three axes of a 25 cm sphere. • Positions: radius 0.0 (centre), 5.5, 7.5, 9.5, 11 and 12.5 cm (external) • Response defined as average reading of detectors at the same radius • An internal 1 cm thick lead shell (3.5 to 4.5 cm) to enhance high-Energy response • Isotropic response for practical purposes Pb NIM A 613, 127-133 (2010) NIM A 677, 4-9 (2012) R = 0 - 5.5 - 7.5 - 9.5 - 11 - 12.5

10. Stage 1 The SPherical SPectrometer SP2 - Response matrix

11. Stage 1 Response matrix verification (PTB, 144 keV to 14.8 MeV) Tests at different mono-chromatic energies performed with Dy activation foils. Overall uncertainty estimated as ±3%

12. Stage 1 Response matrix verification (TSL-Uppsala, 50-180 MeV)

13. Stage 1 The CYlindrical SPectrometer CYSP • Seven TNDs along the axis • Spectral resolution and lateral rejection • HPDE Collimator 50 cm diam x 30 cm h Hole diameter 16 cm, B-plastic lined • Capsule for detectors: 20 cm diam, includes one cm lead disk (high-E) • Air holes to increase deep response HDPE AIR Pb B-plastic

14. Stage 1 CYSP response matrix 1 2 3 4 6 5 7

15. Stage 2 Active detectors Constraints (1) Miniaturization (≈1 cm) (2) Sensitivity such to allow responding from Sv/h to Sv/h (3) Excellent photon rejection (4) Low-cost (31 TNDs in a single spherical device) Two types of TNDs (different levels of cost/sensitivity): TNPD pulse detector (~0.04 cm2), producing a PHD TNRD rate detector, giving a DC voltage level that is proportional to the thermal neutron fluence rate. Lowest measurable thermal neutron flux ≈ tens cm-2 s-1

16. Stage 2 Fabrication and testing facilites Commercially available solid state devices are made sensitive to thermal neutrons through a customized physico-chemical process Each detector is individually calibrated in a known thermal neutron field. Batch reproducibility ±5%

17. Stage 2 The “rate detector” TNRD The device. The active area is one cm2 and overall dimensions are 1.5 cm x 1 cm x 0.4 cm. This signal is amplified in a low-voltage electronics module (developed by the project team) and acquired by a PC through an ADC. Typical calibration coefficient (93±3) cm-2 s-1 mV-1. Linearity Tested in ex-core thermal column at the ENEA Casaccia (Rome) Triga reactor • Linear response de 7E+2 - 2E+5 cm-2 s-1. • Uncertainty better than 4% • Minimum detectable flux < 50 cm-2 s-1. The measurement range can be changed by modifying the gain of the amplification module.

18. Stage 3 Manufacturing and testing the final spectrometers equipped with active TNDs. lateral protection B-plastic collimator detectors capsule for detectors

19. Stage 3 Manufacturing and testing the final spectrometers equipped with active TNDs. • CYSP was fabricated and tested with: • a continuous-spectrum Am-Be source • (0.1 - 11 MeV) • monochromatic beams at NPL (0.144 to 16.5 MeV)

20. Stage 3 Signal processing = + Analog module designed within the project Eight channels (Bias regulator + Preamp +amp) 8 channel digitizer Simultaneous acquisition of up to eight detectors (Labview based)

21. Conclusions • Conclusions 1. Broad-energy interval neutron spectrometry at beam-lines can be performed “on-line” with similar performance as those of the ERBSS 2. Two prototypal single-moderator neutron spectrometers, called SP2 and CYSP, were designed in the framework of the INFN project NESCOFI@BTF. 3. New active thermal neutron detectors developed 4. Testing phase Done for the CYSP In progress for CP2

22. Conclusions End of 2014 / NEURAPID project ETHERNES Extended THERmal NEutrons Source A thermal pile at INFN-LNF for thermal neutron detector testing with Uniformity area 30 cm x 30 cm