Neutron detectors for the NMX instrument 16.03.2015 Dorothea Pfeiffer on behalf of the ESS detector group

Content Collaboration for NMX detector development NMX instrument and requirements Detectors for NMX Gd-Neutron measurements Schedule

Collaborations and people ESS detector group Dorothea Pfeiffer (CERN) – Coordinator Filippo Resnati (CERN) – Detector R&D Thomas Kittelmann (Lund) – Computing and Simulations Scott Kolya (Lund) - Electronics Carina Hoeglund (Linkoping) - Coatings Linda Robinson (Linkoping) - Coatings ESS joined RD51 in 2013 CERN MPGD group world wide leading in R&D Discussions with CERN thin film experts from TE-VSC

The macromolecular crystallography instrument NMX

29.06.2012 Dorothea Pfeiffer

Detectors and sample environment

Reflections of example crystal Purpose of the NMX instrument is to determine structures of proteins, in particular location of hydrogen atoms in the structure

TOF separation of reflections

ESS pulse shape and intensity 16.66 Hz pulse rate, duty cycle of 1:25 Time averaged flux at NMX sample

Detectors for NMX

Challenges and History 200 um beyond state of art for time resolved detector High rate requirements with up to MHz/cm2 In original instrument proposal for NMX: Gd-MSGC developed by HZB as in-kind partner with a 10 yr history Ca. 24 months ago: HZB ordered to cease development ESS detector group prioritized this development Idea: Replace MSGC with GEM Engaged with CERN as strong, stable, long term collaborative partner Joined RD51, Strong R&D collaboration and community

Thermal neutron converters Isotope Crosssection [barns] Reaction Range 3He 5333 n + 3He -> 3H (191 keV) + 1H (573 keV) Q= 0.76MeV Rp = 5.7 bar cm 6Li 940 n + 6Li -> a (2.06 MeV) + 3H (2.73 MeV) Q = 4.79 MeV Rt=130 mm 10B 3835 n + 10B -> 7Li*(0.84 MeV) + a (1.47 MeV) + g (0.48 MeV) (93%) Q=2.3 MeV -> 7Li (1.16 MeV) + a (1.78 MeV) (7%) Q=2.79 MeV Ra = 3.14 mm 157Gd 259000 n + 157Gd -> 158Gd + g (79, 181, 944 keV) + conversion electron spectrum (29-182 keV) Q=7.94 MeV lce = 11.6 mm Good neutron converters have a high cross section for thermal neutrons The neutron capture creates a charged particle that can be easily detected The converter has to have the correct thickness so that a maximum of the charged particles can escape and reach the gas volume

Geant4 Gadolinium Simulations 25 meV neutrons Scoring of electrons that cross boundary between converter and drift Drift backwards 0.25 – 50 um Converter Drift forwards Geant4 simulations to evaluate different converter materials and thicknesses Natural Gd, 155 Gd, 157 Gd, Gd2O3 and enriched Gd2O3 were simulated

Gd thickness and efficiency 155 Gd: 9 um optimal (44%) 157 Gd: 3 um optimal (35%) Nat. Gd: 6 um optimal (19%) 15 % with 1 detector

Electron spectra natural Gd 157 Gd conversion electrons (in converter) Mean: 67 keV Mean: 60 keV conversion electrons (in converter) MeV MeV natural Gd 157 Gd Mean: 69 keV Electrons arrived in drift Mean: 54 keV MeV MeV

Measurement at IFE in Norway

Gd-GEM backwards setup

Gd-GEM configuration Standard triple-GEM detector operated at gain of 5000 (730 uA) 250 um natural Gd as cathode with 50 um thick Cu tape 10 mm drift gap Drift field of 700 V/cm

IFE measurement setup Slits 1 Slits 2 Gd-GEM neutrons He3 tube

Spectra and detection efficiency Spectra comparable to simulated spectra for 10 mm drift First estimation of neutrons detection efficiency: >= 9 % Neutron rate with beam of 2cm x 2cm and He3 tube in front of GEM: 11 kHz Rate in GEM with beam of 2cm x 2cm (without He3 tube): 4.7 kHz Background rate in GEM with beam of 2cm x 2cm with Cd sheet in front: 3.7 kHz

Electron tracking The conversion electrons leave long more or less straight tracks in the drift space Centroid calculation not sufficient to determine position Tracking method like uTPC method is needed to determine the start point of the track Fit more complicated than in case of alpha particles (see talk by F. Resnati) X - view Y- view

Track map Beam collimated to 3mm x 10mm Detector rotated with respect to collimation Effects of 50 um copper tape clearly visible Graph shows start of track in x versus start of track in y Signal to background ratio of around 10:1

Position resolution 2cm x 2cm beam Resolution with very simple method (last time bin over threshold): 1.4 mm Improvement likely with better fit, better collimation and less background

Position resolution 2mm x 2mm beam Resolution with very simple method (last time bin over threshold): < 1 mm Improvement likely with better fit, better collimation and less background

Results and outlook Gd-GEM detector works Detection efficiency is with >= 9% around the expected one of 15% from simulations Tracking of electrons works in principle, but method has to be refined Position resolution in the mm range does not meet requirements of 200 um yet Setup limited: Improvements likely with better collimation, lower background and better fit In backwards configuration, scattering of neutrons from readout board and three GEM foils influences resolution Faster readout electronics needed

Electronics - ASICs Being evaluated ASIC used for R&D Being evaluated Courtesy: S. Kolya Dorothea Pfeiffer – Second Special Workshop on Neutron Detection with MPGDs 16.03.2015

Sam says: Thank you for your attention !