MCNSI MeetingMCNSI Meeting

Detector Optimisation for the Cold Powder Diffractometer DMC

Grenoble, 26 May, 2005

U. Filges Laboratory for Material and

DevelopmentsPaul Scherrer Institut

CH-5232 Villigen

MotivationMCNSI MeetingGrenoble, 26 May 2005

DMC detector is about 25 years old- no spares available

detector performance\design is not state of the art (BF3, pressure)

View on DMC at SINQ

Schematic Design of DMC

Schematic design of the cold powder diffractometer DMC and McStas Model

MCNSI MeetingGrenoble, 26 May 2005

Virtual Experiment

McStas instrument file for the DMC instrument including cold source, neutron guide and all components of the diffractometer including sample Na2Ca3Al2F12 – virtual experiment

comparison of measured and calculated data

- measured and calculated data agree very well

- sample Na2Ca3Al2F12; height: 30 mm; diameter: 10 mm

Bragg peak resolution

16 Bragg peaks including symmetrically equivalent reflections (range of 20 – 100 degree)

MCNSI MeetingGrenoble, 26 May 2005

used wavelength: 2.567 Å

Simulation result IMCNSI MeetingGrenoble, 26 May 2005

Comparison of simulated and measured data: part 20 – 62°

Simulation result IIMCNSI MeetingGrenoble, 26 May 2005

Comparison of simulated and measured data: part 62 – 100°

Simulation result IIIMCNSI MeetingGrenoble, 26 May 2005

Comparison of peak resolution for Bragg peaks 28.98° (left) and 51.4° (right)

Optimized Detector Parameters

decreasing the detector-sample distance from presently 1.5 m to a smaller distance=> increasing intensity; decreasing instrument resolution

detector height – from 9 cm of the present detector to 30 cm of the new detector system

MCNSI MeetingGrenoble, 26 May 2005

BF3 Detector replaced by a He-3 detector under higher pressure

Changing the Detector HeightMCNSI MeetingGrenoble, 26 May 2005

Comparison of PSD images of the 9cm/30cm-detector for bragg reflections 35.73° , 51.42° and 90.2°

G = 3.4

Changing the Detector – Sample Distance

MCNSI MeetingGrenoble, 26 May 2005

radius

r [m]

intensity gain

Ir/I1.5m

loss of resolution Rr/R1.5m

total Gain

Gt=GDH+GDSD

1.2 1.243 1.158 4.2

1.25 1.206 1.090 4.08

1.3 1.152 1.085 3.89

1.35 1.106 1.042 3.74

1.4 1.081 1.035 3.65

1.45 1.028 1.014 3.47

Comparison of intensity gain vs. loss of resolution for bragg reflection 41.49°

Ongoing ProjectsMCNSI MeetingGrenoble, 26 May 2005

component development extension of Guide_tapering component – avoid direct view to the guide entry multi-pipe window component

continuation of FOCUS intercomparison (McStas/Vitess) including the new 2D-Detector

SINQ – hall extension sector 50; in opposite to the present guide hall