The BAND-GEM detector Financial support from CNR; ESS pre-construction in-kind contract GEM G. Croci on behalf of G. Croci 1,2,3, A. Muraro 1, G. Grosso 1, E. Perelli Cippo 1, G. Albani 3, C. Cazzaniga 3, G. Claps 4,, F. Murtas 4, M. Rebai 2,4, M. Tardocchi 1, C. Höglund 5,6, L. Hultman 6, J. Birch 6, R. Hall-Wilton 6,7, Xiao-Xiao Cai 5,8, I. Llamas Jansa 5,8 and G. Gorini 3,4 1 Istituto di Fisica del Plasma (IFP-CNR) – Via Cozzi 53, Milano, Italy 2 INFN – Sez. Di Milano-Bicocca – Piazza della Scienza 3, Milano, Italy 3 Dipartimento di Fisica, Università degli Studi di Milano-Bicocca – Piazza della Scienza 3, Milano, Italy 4 INFN – Laboratori Nazionali di Frascati –Via Fermi 40, 0044 Frascati, Italy 5 European Spallation Source ESS AB, P.O. Box 176, SE Lund, Sweden 6 Department of Physics, Chemistry and Biology (IFM), Thin Film Physics Division, Linköping University, SE Linköping, Sweden 7 Mid-Sweden University, SE Sundsvall, Sweden 8 IFE: Institute for Energy Technology, Box 40, 2027 Kjeller, Norway

SHOULD WE DETECT THERMAL NEUTRONS WITH GEMS? GEMs offer the following advantages High rate capability (up to MHz/mm 2 ) suitable for high flux neutron beams like at ESS Submillimetric space resolution (suited to experiment requirements) Time resolution from 5 ns (gas mixture dependent) Possibility to be realized in large areas and in different shapes Radiation hardness Low sensitivity to gamma rays (with appropriate gain) GEM detectors born for tracking and triggering applications (detection of charged particles) but if coupled to a solid state converter they can detect Thermal Neutrons  10 Boron converter Neutrons are detected using the productus (alpha,Li) from nuclear reaction 10 B(n,alpha)7Li Face 3 He world shortage G. Croci et Al JINST 7 C03010; F. Murtas et Al, JINST 7 P07021; G. Croci et Al, NIMA 720, 144; G. Croci et Al, NIMA, 712, 108; G. Croci et Al, JINST 8 P04006; G. Croci et Al, NIMA 732, 217; G. Albani et Al, JINST 10 C04040; G. Croci et Al, EPJP 130, 118 G. Croci et Al, EPL, G. Croci et Al, Prog. Theor. Exp. Phys. 083H01;

OUTLINE THE BANDGEM DETECTOR Principle of operation Detector Simulation Results LOKI-ESS LOKI Demonstrator

Boron Array Neutron Detector BANDGEM Thermal neutron detector

Scheme and Principle of operation 5 Padded Anode n α e- α 10 B 4 C n Al 2 O 3 Alumina Lamellas coated on both sides with 10 B 4 C θ Using low θ values (few degs) the path of the neutron inside the B 4 C is increased  Higher efficiency when detector is inclined 10 cm 6 cm 2 mm Triple GEM Cathode 3D Lamella System EdEd

The lamellas 6 Material = Allumina (Al 2 O 3 ) 6 cm 12 cm 2 mm A lamella is composed by 15 strips

10 B 4 C Coating on the lamellas 7 A 1 μm 10 B 4 C coating has been deposited on both sides of the lamella and on all the 15 strips The resulting coated lamellas Deposition done by Dr. Carina Hoglund In total more than 50 lamellas have been coated 50 Lamellas are necessary to assembly the first detector prototype Coatings are slightly conductive ρ = 696 Ω*cm

Detector Assembly 8 The full Lamella System. A total of 48 lamellas have been mounted mounted. Their distance is 2 mm Assembly with Triple GEM detector 128 Pads of area 6x12 mm 2 have been used as anode

BANDGEM simulation Numerical Simulation of Neutron conversion efficiency and electron extraction B4C=2mm GAS=2mm 2mm Volumetric Simulation (1000 e-) Diffusion ON Good Electron 1000, Out Electron 263 Percentage 26.3 Volumetric Simulation (1000 e-) Diffusion OFF Good Electron 1000, Out Electron 486 Percentage 48.6

10 Detector test at IFE (JEEP II Reactor, RD2D beamline) E d = 230 V/cm E t1 =E t2 = 3 kV/cm; E i = 5 kV/cm Mixture Ar/CO2 70%/30% 230 cc/min Carioca chips FPGA-LNF Motherboard Angle = 7 degrees V GEM = 980 V

High Voltage Scan – Working point 11 E d = 230 V/cm E t1 =E t2 = 3 kV/cm; E i = 5 kV/cm Mixture Ar/CO2 70%/30% 230 cc/min VGEM working point values are higher than usual one (870 V) Neutron energy E n = 34.5 meV Need to understand the gamma ray background component. On-site measurment with a gamma source

12 Angular scan Neutron energy E n = 34.5 meV Beam size = 9 mm x 9 mm The counting rate depends on the angle between the beam and the lamellas. There is about 0.5of systematic error settings due to the mechanics The 3 He tube in front of the GEM is counting n/s with an efficiency of 87% at this neutron energy. It is fully in the beam

13 Comparison 3 He -GEM GEM n Slits 3 He GEM is used as absorber 3 He tube has a diameter of 2.54 cm We see the same behaviuor (inverted in 3 He for the same angles). The GEM is absorbing neutrons. There are still some feautures to be understood Maxima and minima are due to the geometry of the GEM E n = 34.5 meV

14 First efficiency estimation as a function of wavelenght Where σ(λ) = λ/ λ 0 I f λ=λ 0 =1.54 A ε=0.15 for 10 degrees and ε==0.20 for 7 degrees (Angle with respect neutron direction) ε(λ) = 1 – e -cσ(λ)

BANDGEM detector for neutron diffraction measurements Incident neutron beam Transmitted neutron beam INES (ISIS) sample pos. GEM position First BANDGEM Prototype Bronze sample 90° 3 He counts about 3.4 times the BANDGEM BANDGEM/ 3 He Solid Angle Ratio = 0.45 BANDGEM 3 He Tube Same Measurement Time

Application to the European Spallation Source (ESS)

The LOKI ESS SANS Instrument

BANDGEM LOKI....Just an example of a possible LOKI vessel Configuration... BANDGEM Modules As rear detector panels Requirements for rear detector panel Rate Capability = 40 kHz/cm 2 Time resolution bettter than 1 ms Efficiency of about 60% at 4 Å X-Y Space resolution of about 4 mm Construction of BANDGEM demonstrator for LOKI as an upgrade of the first prototype

The BANDGEM umbrella for LOKI Total active area: 647 cm mm 400 mm Cathode 8 Lamellae system 96 GEM 1 6 GEM 2 2 GEM 3 2 Readout anode 2

Detector Assembly – The cake Aluminate mylar cathode Lamellas system Triple GEM Readout anode

The Front End Electronics The first protoype electronics is based on Carioca Chip. Total dimension : 3x6 cm 2 Digital Chip with 8 channels Equips the LHCb GEM detectors Fast chip – used for triggering Adapted from MWPC A new chip is being tested: the GEMINI chip. Mixed analog and digital chip that Has 16 channels/chip. This is the chip that we would like to use at ESS for LOKI BANDGEM Especially developed for GEM detectors

Conclusions First BANDGEM prototype reached an efficiency of 20% at 1.54 Å First BANDGEM prototype successfully tested as neutron diffractometer  improvement w.r.t. single layer BAND-GEM demonstrator for LOKI New simulation Higher efficiency Being designed Small area prototype ready before end 2015 Geant4 simulations on-going.

Thanks from... the BANDGEM team

Complete GEM detector system HVGEM LNF HVGEM LNF HV Filters 3 GEM detector with padded anode (Carioca Chips) 3 GEM detector with padded anode (Carioca Chips) FPGA Board LNF 128 ch FPGA Board LNF 128 ch DAQ PC 12 V PS Charged particles X Ray GammasNeutrons Current Monitor 2D monitor with pads readout Possibility to set time slices from 5 ns up to 1 s 24

Resistivity measurements of the B 4 C coatings 25 Measurement performed (using the 4 points method) on the first (preliminary) alumina sample coated by Carina with 1 μm of B 4 C Since the thickness of the sample was 1 μm the measured resistivity ρ = 696 Ω*cm The coatings can be considered as partially conductive In collaboration with CNR-IMIP

Detector Assembly (3) 26 Assembly with Triple GEM detector 128 Pads of area 6x12 mm 2 have been used as anode 6 mm 12 mm 2 mm Lamella disposition on the pads

GEM Foil The GEM foils will be realized at CERN and they will be glued to their frames using the same technique used for the production of the cathode. Each GEM foil will be sectorized in 8 sectors, in order to reduce the possible damage caused by a spark. A total of 3 GEM (triple GEM) will be installed in the detector and the gap between each GEM (Transfer gaps) is equal to 2mm. All the GEM foils will be sandwiched and glued on the upper trapezoidal frame.

Padded Anode The anode will be composed by 1024 pads. The the size of the pads is between 7.7 and 137 mm 2. The maximum pad size is similar to the one of the nGEM for SPIDER, and we have already tested the low noise level. The PADs is divided into 10 ϕ sectors, while the dimension of the PADs is constant along the y-coordinate and equal to 4mm. At the moment only the PADs were designed, while the position of the read- out electronics is still under investigation. The design of the read-out electronic position will be decided after the test of the GEMINI Chip. The anode will be glued on the GEM3 frame, and the gap between the GEM3 and the PADs (induction gap) will be equal to 2mm. y ϕ

Small Area Prototype- for testing In order to test the technology processes that will be used for the construction of the demonstrator and to validate the numerical simulation as soon as possible, it was decide to made a small scale prototype (active area=10x10 cm 2 ). 115 mm 107 mm With this detector we can test the production method of the lamellae system (it is the same of the demonstrator) and we can validate the numerical simulations. It will be composed by 25 lamellae (all with the same dimensions) and the 10x10 triple GEM system with its cathode will be the same of the actual BandGEM (and of the other 10x10 GEM detectors such as the bGEM). This should allow the production and the test of the detector up to the end of this year.