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Transcript of MCNSI Meeting
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