BAND-GEM Istituto di Fisica del Plasma, IFP-CNR – Milano Dipartimento di Fisica, Università di Milano-Bicocca INFN, LNF e Sezione di Milano-Bicocca ESS, Lund Linköping University Further help from HZ Geesthacht ISIS detector group Beam time at LLB and IFE Financial support from CNR; ESS pre-construction in-kind contract

SHOULD WE DETECT THERMAL NEUTRONS WITH GEMS? 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  10Boron converter Neutrons are detected using the productus (alpha,Li) from nuclear reaction 10B(n,alpha)7Li GEMs offer the following advantages High rate capability (up to MHz/mm2) 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)

WORK IN PROGRESS (STARTED MAY 2011) MEASUREMENT OF GEM RATE CAPABILITY IN A HIGH FLUX NEUTRON BEAM GEM DETECTORS FOR NEUTRON DIFFRACTION MEASUREMENTS HIGHER EFFICIENCY -> BANDGEM DETECTOR A POSSIBLE APPLICATION IN ESS

MEASUREMENTS OF GEM DETECTOR RATE CAPABILITY IN A HIGH FLUX NEUTRON BEAM

GEM detector for thermal neutrons (bGEM) Triple GEM detector equipped with an aluminum cathode coated with 1μm of B4C Exploits the 10B(n,α)7Li reaction in order to detect thermal neutrons ΔV GEM = ΣVGEM = 870 V Gain ≈ 100 Ar/CO2 70%/30% (5 l/h) n α Detector Schematics B4C coated aluminium cathode mounted on its support B4C coated aluminium cathode assembled inside the bGEM chamber layout Natural B: Low efficiency detector: 1% Enriched 10B: 5% efficiency

* *Borated cathode from HZ Geesthacht

GEM DETECTORS FOR NEUTRON DIFFRACTION MEASUREMENTS

Test of bGEM detector for neutron diffraction measurements bGEM with enriched borated cathode Cd mask and rough collimator The bronze sample is different The same bGEM position (90°) was no longer available  FOCUSSING Cd mask (not really visible, but it is there…..) Cd slabs to cover the GEM sides Cd collimator Incident neutron beam Transmitted neutron beam INES (ISIS) sample pos. GEM position

Efficiency comparison with corresponding 3He tubes GEM GEM 3He 3He 1st test (natural B) He3 rate x25 GEM rate 2nd test (enriched 10B) He3 rate x8 GEM rate

bGEM (time) resolution Resolution OK by adding up data from pads that lie on the same Debey-Scherrer cone, i.e. constant Lsenϑ Counting area ToF [us] FWHM (us) All GEM 12648,66 229,9 Focussed GEM 12714,22 79,43 3He 12673,94 77,43

BAND-GEM DETECTOR Borated Array Neutron Detector = BAND

Scheme and Principle of operation θ Al2O3 Triple GEM Cathode 3D Lamella System Ed α α 10B4C 10B4C e- 10B4C 10B4C Al2O3 Padded Anode Alumina Lamellas coated on both sides with 10B4C Using low θ values (few degs) the path of the neutron inside the B4C is increased  Higher efficiency when detector is inclined

10B coating: Chewbacca’s ancestor coating machine Chewbacca being inaugurated in Linköping

Detector Assembly The full Lamella System An aluminium cathode (few microns thick) has been mounted on top

Detector test with X-Rays Test with X-Rays (in IFP-lab) Detector completed

Detector test at IFE (JEEP II Reactor, RD2D beamline)  

Beam Profile Ed = 230 V/cm Et1=Et2= 3 kV/cm; Ei = 5 kV/cm Mixture Ar/CO2 70%/30% Angle = 10 degrees VGEM = 980 V 6 mm 12 mm

Efficiency c comes from   c comes from   where if λ=λ0=1.54 A ε=ε0=0.15 for 10 degrees and ε=ε0=0.20 for 7 degrees

POSSIBLE APPLICATION @ ESS: LOKI (Small angle neutron scattering) 2 Å< λ < 12 Å 25 cm Beam Trapezoidal Triple GEM detector Borated Lamellas of different lenghts Minimise frame thickness especially near the n beam At least 6 BAND-GEM modules Detectors tilted by a few degrees

Conclusions The rate capability measured with GEM+electronics is about 40 MHz/mm2 The GEM detector can be used as diffractometer and its time resolution matches those of 3He tubes BAND-GEM detector tested in a thermal neutron beam. Next: optimize efficiency/ gamma discrimination trade-off Trapezoidal geometry for LOKI Explore lamella materials other than alumina (OK but fragile)