Diamond detectors in Bonner Spheres A Novel Approach for Real-time Neutron Spectroscopy

Università degli studi di Roma Tor Vergata Dottorato di Ricerca in Ingegneria dei Microsistemi XXIV ciclo Diamond detectors in Bonner Spheres A Novel Approach for Real-time Neutron Spectroscopy Candidate: Rosaria Villari Tutor: Prof. E. Milani Coordinator: A.A. 2012/2013 Prof. A. Tucciarone 1

2 spheres: Outline Outline Introduction Activity carried-out in the present Phd: Response functions calculation Tests & simulations with a single Bonner Sphere Bon-dia tests & simulations Conclusions & Perspectives Scientific activities during Phd period

spheres: Introduction Bonner spheres technique for neutron spectrometry Set of Polyethylene spheres of different diameters detector sensitive to thermal neutrons placed at the center of each sphere 3 Increase of Ø sphere Detector sensitivity peak shifts towards high energies From the reading of each sphere (M i ) once known its response function R i (E) F(E) obtained through deconvolution M 1 = R 1 (E)F E (E).. M n = R n (E)F E (E)

Bonner spheres: advantages & drawbacks ADVANTAGES wide energy range (thermal to GeV) relatively easy to use isotropic response good n/g discrimination (depending on the sensor) high or low efficiency (depending on the sensor) DRAWBACKS poor energy resolution lengthy measurements bulky equipment uncertain deconvolution Diamond detectors in Bonner spheres: Introduction 4 Thomas, Rad. Meas. 85 (2010) Zimbal, NEUDOS-11(2009)

spheres: Introduction Bonner spheres: thermal neutron detectors PASSIVE SENSORS Activation foils TLD - Insensitivity to g - Operation in pulsed field 5 ACTIVE SENSORS 6 LiI(Eu) scintillator He 3 proportional counter - poor g discrimination (scint) - Pile-up effects - No harsh environment - Sensitive only to thermal neutrons Can we overcome these limitations using diamonds?

spheres: Introduction 6 Benefits in using diamond based neutron detectors in Bonner spheres Real-time response to both high energy & thermal neutrons Insensitivity to g rays and EM field Stability & reproducibility High temperature operations Radiation hardness

SCD- 6 LiF: Mechanism of neutron detection Ag contact Al contact Fast Neutrons n 6 LiF CVD Intrinsic CVD B-doped HPHT substrate 9 Be Diamond detectors in Bonner spheres: Introduction 7 Thermal Neutrons n 6 LiF CVD Intrinsic T CVD B-doped HPHT substrate Fast neutrons n + 12 C + 9 Be 5.7 MeV Thermal neutrons n + 6 Li Tritium + + 4.8 Mev E Tritium = 2.73 MeV ; E = 2.06 MeV 6 Li (n, )T 12 C (n, ) 9 Be Marinelli et.al App. Phys. Letter 89 (2006)

What? Develop & Characterize Bon-dia: a novel real-time neutron detection system based on Bonner spheres & diamond detectors How? Monte Carlo simulations Diamond detectors in Bonner spheres Experiments under neutron irradiation Why? Overcome limitations of Bonner spheres with active detectors Extend the range of applications of diamond based neutron detectors 8

9 spheres: Outline Outline Introduction Activity carried-out in the present Phd: Response functions calculation Tests & simulations with a single Bonner Sphere Bon-dia tests & simulations Conclusions & Perspectives Scientific activities during Phd period

MCNP5 calculations Diamond detectors in Bonner spheres: Response functions MCNP input file Geometry modelisation (cells, surfaces) Materials description (chemical comp.,density) Selection of nuclear data libraries Source specification Particle transport setting (particles, cut-off, phys.,..) variance reduction Tally specifications MCNP parallel run Check for statistical output results Optimisation of variance reduction Analysis of output results 10

Response functions calculations Aluminum Y-Z X-Z N source SCD LiF Polyethylene Lead ~300 different input files ~3000 h computing time Diamond detectors in Bonner spheres: Response functions 11 MCNP models Bonner spheres of 3, 5, 8, 10,12 with & without Pb SCD- 6 LiF Monoenergetic irradiation En <20 MeV

spheres: Response functions 12 Output Neutron spectra in SCD for different spheres 6 Li (n, )T & 12 C (n, ) 9 Be response vs. E n at various. vs. at various E n Reaction rate R J 20MeV 0 ( E) ( E) de J N 0J

Neutron energy distribution Diamond detectors in Bonner spheres: Response functions 13 N energy spectra 3.0E-04 bare FE(cm 2 ) 2.0E-04 1.0E-04 12 0.0E+00 1.E-09 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 Energy (MeV) Moderation in Polyethylene 14 MeV n irradiation

spheres: Response functions Cumulative Neutron energy distribution 14 Cumulative N distribution (%) 100 0'' 3'' 80 5'' 8'' 10'' 12'' 60 12''+Pb 40 20 0 1.E-09 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 Energy (MeV) 14 MeV n irradiation

spheres: Response functions 15 Total Neutron fluence 1.E-03 8.E-04 8 10 F (cm -2 ) 6.E-04 4.E-04 3 5 12 2.E-04 bare 0.E+00 0 5 10 15 20 E inc (MeV)

Response functions Diamond detectors in Bonner spheres: Response functions 16 6 Li (n, )T R/at/F a (10-24 cm 2 ) 500 400 300 200 100 3 bare 5 8 12 10 0 1.E-06 1.E-04 1.E-02 1.E+00 1.E+02 12 '' 10 '' 8 '' 5 '' 3 '' bare E inc (MeV)

Response functions Diamond detectors in Bonner spheres: Response functions 17 600 100keV 6 Li (n, )T 2.5 MeV R/at/F (10-24 cm 2 ) 400 200 1eV 14 MeV 0 0 1 2 3 4 5 6 7 8 9 10 11 12 diameter of Bonner sphere (inch)

Response functions Diamond detectors in Bonner spheres: Response functions 18 0.20 R/at/F a (10-24 cm 2 ) 0.15 0.10 0.05 10 8 bare 3 5 R/at/F a (10-24 cm 2 ) 0.15 0.10 0.05 0.00 10 MeV 12 MeV 16 MeV 20 MeV 14 MeV 0 1 2 3 4 5 6 7 8 9 10 11 12 13 diameter of Bonner sphere (inch) 0.00 12 12 C (n, ) 9 Be 5 10 15 20 E inc (MeV) E> 5.7 MeV 12 '' 10 '' 8 ''

19 spheres: Outline Outline Introduction Activity carried-out in the present Phd: Response functions calculation Tests & simulations with a single Bonner Sphere Bon-dia tests & simulations Conclusions & Perspectives Scientific activities during Phd period

Tests description Diamond detectors in Bonner spheres: 20 Single Bonner shere tests DDL 4.7x4.7 x 0.5 mm + 6 LiF Optimised for Fast EXPERIMENTS DDL & SCD- 6 LiF in 6 Bonner sphere tested under 14 MeV (DT) neutron irradiation at the Frascati Neutron Generator (FNG) Response to fast & thermalised neutrons Neutron spectrum measurements through activation foil techniques SCD- 6 LiF Ø1.8 mm 30 mm + 6 LiF Optimised for Thermal

spheres: 21 Single Bonner shere tests Simulations description MCNP INPUT Detailed 3-D input model of experimental assembly and FNG target FNG neutron source distribution optimisation of variance reduction techniques different models for: MCNP OUTPUT - Activation foils neutron spectra - Diamond detector reaction rates in the foils reaction rates of 12 C(n, )& 6 Li(n, )T reactions in detector

spheres: 22 Single Bonner shere tests Neutron spectra calculation & validation cumulative N distribution % 100 80 60 40 20 0 1.E-09 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03 E (MeV) air Au Ni Al Nb Fe Polyethylene df/de (n/cm 2 /MeV) 1.E+14 1.E+12 1.E+10 1.E+08 1.E+06 1.E+04 MCNP calculation Activation foil unfolded spectra 1.E-09 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 E (MeV) Average Deviation CAL/Act foils unfolded (EXP) ±3% Verification of the reliability of MCNP predictions

spheres: 23 Single Bonner shere tests Reaction rates Reaction rate (10-24 /at/n) 1.E-02 1.E-04 1.E-06 1.E-08 C-12 (n,a) Li-6 (n,t) 1.E-10 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 E (MeV)

Experimental assembly detector Diamond detectors in Bonner spheres: 24 Single Bonner shere tests FNG target 20 cm Bonner sphere (Ø6 ) Note: No scientist has been irradiated during this experiment

Counts DDL Spectra Diamond detectors in Bonner spheres: Tests with a single Bonner sphere 25 6 Li(n, )T T+ peaks Component C/F air (cm 2 ) Thermal 7.81 x10-5 Fast 5.12 x10-5 12 C(n, ) 9 Be FAST Well resolved peak Channels THERMAL Poor Response & T peaks not resolved

Counts SCD-LiF spectra Diamond detectors in Bonner spheres: Tests with a single Bonner sphere 26 6 Li(n, )T T 12 C(n, ) THERMAL Channels & T peaks are resolved SCD better resolution than DDL C/F air (cm 2 ) 5.57 x10-5

27 spheres: Outline Outline Introduction Activity carried-out in the present Phd: Response functions calculation Tests & simulations with a single Bonner Sphere Bon-dia tests & simulations Conclusions & Perspectives Scientific activities during Phd period

Bon-dia Diamond detectors in Bonner 28 spheres: Bon-dia SCD- 6 LiF produced in Tor Vergata University lab Set of Bonner sphere provided by INFN 4, 5, 8, 10 and 12 +Pb Bon-dia tested under 14 MeV neutron irradiation at FNG SCD#1 30 mm thick+1.2 mm 6 LiF SCD#2 35 mm thick+1.2 mm 6 LiF

Spectra of Bon-dia Counts/Yield 9.E-12 8.E-12 7.E-12 6.E-12 5.E-12 4.E-12 3.E-12 2.E-12 1.E-12 SCD #1 4'' 5'' 8'' 10'' 12''+Pb Diamond detectors in Bonner spheres: Bon-dia 29 0.E+00 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 Energy (MeV) 14 MeV yield 3x10 13-9x10 13 n counts sphere diameters T peak resol: 5.8±0.8 % Stability: (±20keV, 1%)

Spectra of Bon-dia Diamond detectors in Bonner spheres: Bon-dia 30 Counts/Yield 9.E-12 8.E-12 7.E-12 6.E-12 5.E-12 4.E-12 3.E-12 2.E-12 1.E-12 0.E+00 4'' 5'' 8'' 10'' 12''+Pb 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 Energy (MeV) SCD #2 counts sphere diameters T peak resol: 6.2± 0.3 % (#2) Stability (±20keV, 1%) Reproducibility (± 8%) Counts/Yield 9.E-12 8.E-12 7.E-12 6.E-12 5.E-12 4.E-12 3.E-12 2.E-12 1.E-12 4'' SCD#1 12''+Pb SCD#1 4'' SCD#2 12''+Pb SCD#2 SCD #1 &#2 0.E+00 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 Energy (MeV)

31 spheres: Bon-dia Response of Bon-dia 7E-10 6E-10 Total SCD#1 Counts/Yield 5E-10 4E-10 3E-10 Total SCD#2 Tritium SCD#1 Tritium SCD#2 R(d)=a ln(d)- b 2E-10 1E-10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Bonner sphere diameter (inch) 2.5 2 Total SCD#1/SCD#2 Total #1/#2 1.00±0.04 Tritium #1/#2 1.03±0.05 Ratio 1.5 1 Tritium SCD#1/SCD#2 Total/Tritium SCD#2 Total/Tritium 1.99±0.13 0.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Total/Tritium SCD#1 Bonner sphere diameter (inch)

spheres: 32 Single Bonner shere tests MCNP5 Simulations description MCNP INPUT Detailed 3-D input models of experimental assembly and FNG target FNG neutron source distribution optimisation of variance reduction techniques different models for MCNP OUTPUT 4, 5, 8, 10 and 12 +Pb Neutron fluence & spectra Reaction rate of 6 Li(n, )T of SCD- 6 LiF in the different spheres >7000 h computing time

MCNP models Diamond detectors in Bonner 33 spheres: Bon-dia

spheres: Bon-dia Neutron fluence calculation 34 8.E-05 6.E-05 Total E>5.7 MeV E<1eV F (cm 2 ) 4.E-05 2.E-05 Air 1.E-06 0 2 4 6 8 10 12 14 Bonner sphere diameter (inch)

Study of Bon-dia calculated response Counts/F a (cm 2 ) 1.E-03 1.E-04 1.E-05 1.E-06 EXP-SCD#1 EXP- SCD#2 CAL-MCNP5 Diamond detectors in Bonner spheres: Bon-dia 6 Li(n, )T 3 4 5 6 7 8 9 10 11 12 13 diameter of Bonner sphere (inch) Calculation Assumptions theorical number of 6 Li atoms all the,t particles are collected The calculation systematically overpredicted the experiment 35 +Pb

spheres: Bon-dia Causes of overestimation 36 Geometrical effect n 6 LiF CVD Intrinsic CVD B-doped HPHT substrate T ~ 50% of the secondary particles are collected Exact amount of 6 Li is unknown Response of Bondia Correction of geometric effect 6 Li m eff from calibration in thermal reference field

SCD- 6 LiF calibration 37 Diamond detectors in Bonner spheres: Irradiation in thermal field Reference thermal neutron field 300 SCD 250 200 T Counts 150 100 50 INMRI-ENEA Casaccia - SCD-LiF - Gold foil 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Energy (MeV) FWHM 200 kev (6.75 ± 0.34)x10-5 Counts/ F (cm 2 ) 6 Li m eff =0.62±0.03 μg

spheres: Bon-dia C&E Response to 14 MeV neutrons 38 Counts/F a (cm 2 ) 3.0E-05 2.5E-05 2.0E-05 1.5E-05 1.0E-05 5.0E-06 0.0E+00 EXP-SCD#1 EXP- SCD#2 CAL-MCNP5_calibration&geometrical effects 6 Li(n, )T 3 4 5 6 7 8 9 10 11 12 13 diameter of Bonner sphere (inch) +Pb Response 5x10-6 to ~2x10-5 counts/f air Monte carlo simulations well reproduce the experimental behaviour

39 spheres: Outline Outline Introduction Activity carried-out in the present Phd: Response functions calculation Tests & simulations with a single Bonner Sphere Bon-dia tests & simulations Conclusions & Perspectives Scientific activities during Phd period

Conclusions The use of diamond detectors in Bonner spheres has been studied for the first time through experiments under neutron irradiations & MCNP5 simulations Effectiveness of the real- time detection system of both high energy & thermal neutrons has been assessed through the reported experimental and calculation studies Stability, reproducibility and reliability of diamond sensors for real-time measurements inside Bonner spheres have been shown The experimental results are well reproduced by Monte Carlo simulations Diamond detectors in Bonner 40 spheres: Conclusions Calculated response functions can be used to determine the neutron spectrum with unfolding codes Bon-dia is a promising system for the improvement of the capabilities and applications of Bonner sphere tecniques (Publication in preparation for EPL on Bon-Dia)

Outlook&Perspectives Optimisation of Bon-dia Diamond detectors in Bonner 41 spheres: Perspectives o Use of thicker SCD + large area to increase the efficiency o Combination of two SCD: a thick one optimised for fast + 1 thin one optimised for thermal o Adaptation of unfolding codes to manage the double response functions o Extension of response function to GeV regions o Dose Response calculations

Outlook&Perspectives Bon-dia applications Real-time operations in: o o o o o nuclear reactors accelerators spallation neutron sources fusion machines space applications Thanks to unique features of diamond detectors: o o o o o insensitivity to g-rays and EM field radiation hardness high temperature operation stability& reliability fast & thermal real-time measurements Diamond detectors in Bonner 42 spheres: Perspectives The tissue equivalent property of diamond may be also exploited for dosimetric purposes

43 spheres: contributors Contributors Dr. M. Angelone (ENEA) Dr. R. Bedogni (LNF, INFN) Prof. M. Marinelli (University of Tor Vergata) G. Pagano (ENEA) Dr. A. Pietropaolo (ENEA) Dr. M. Pillon (ENEA) Dr. F. Pompili (University of Tor Vergata) Dr. M. Vadrucci (ENEA) Dr. G. Verona Rinati (University of Tor Vergata) Dr. C. Verona (University of Tor Vergata)

44 spheres: Outline Outline Introduction Activity carried-out in the present Phd: Response functions calculation Tests & simulations with a single Bonner Sphere Bon-dia tests & simulations Conclusions & Perspectives Scientific activities during Phd period

45 spheres: 2009-2014 2009-2014 Scientific Activity summary 63 Publications on peer reviewed journals 35 Technical Reports 1 monographic contribution on a book 5 Lectures 9 Oral/Invited to international conferences 25 Collaborations with national and International research institutions, organisations and universities further scientific activities and appointments

46 spheres: 2009-2014 Scientific activities 2009-2014 Nuclear analysis with MCNP Monte Carlo code on ITER (International Thermonuclear Experimental Reactor, Cadarache, France), JET (Joint European Torus, Culham, UK), DEMO (Demonstration fusion power plant), FAST (Fusion Advanced Studies Torus, Italy) and JT-60 SA (JT-60 Super Advanced, Japan) projects. Benchmark experiments at FNG for nuclear data and code validations. Development and experimental validation of advanced code for 3-D shutdown dose rate calculations in fusion reactors: Advanced D1S method Design of Gas Electron Multipliers (GEM) detectors for neutron diagnostics in fusion

spheres: 2009-2014 47 Grazie Un Bon-dia comença en el matí