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This section contains photographs and slide presentations that may be of interest. It is probably best to click on the slide and scroll through these presentations by hand. Otherwise they may be either to fast or too slow.

LPSD Instruments
 - The staff and consultants of Instrumentation Associates have been working with LPSD       systems since the late 1970s. 

LPSD Signal Processing  - Presented at the International Conference on Neutron Scattering, ICNS-2013 in Edinburgh, Scotland, July 8 - July 12, 2013. R. Berliner, Instrumentation Associates, Cary, NC 27518 USA.

Linear position sensitive proportional counters (LPSDs) can provide remarkably high resolution event position data. Position resolutions of 2.5 mm are routinely obtained. Arrays of LPSDs remain a cost effective way to assemble large area neutron detectors for many applications.

A simple Ohm's law analysis demonstrates that the neutron event positions can be calculated as:
                                x/L = QB/(QA+QB)

where QA and QB are the charges collected at each end of the detector from the neutron capture event, x is the event position measured from the A-end of the detector and L is the detector active length. In practice, it is not the charges that are recorded but the digitized representations of the event signals after processing by a preamplifier-amplifier-ADC chain at each end of the detector. The characteristics of the preamplifiers, the gains of the amplifiers and the zero-offsets of the ADCs can all affect the apparent position sensing response. While the preamplifier input impedance and ADC offsets tend to shift the position response transfer curve for the detector, differences in the amplifier gains between the A and B-side of the detector signal chain leads to an easily detectable nonlinear position response. These effects are of secondary importance in pulsed source applications where the position resolution requirements are often 0.5 cm – 1.0 cm but become important in reactor applications where higher resolutions are required.

The CARR High Intensity Powder Diffractometer - Presented at the International Conference on Neutron Scattering, ICNS-2013 in Edinburgh, Scotland, July 8 - July 12, 2013. 
W.Y. Yang, H. L. Du and J.B. Yang, School of Physics, Peking University, Beijing, 100871, ChinaR. Berliner and W. B. Yelon, Instrumentation Associates, Cary, NC 27518 USA.

HIPD is located on HT3 at CARR, a port that is shared with the High Resolution Powder Diffractometer. It employs a doubly bent perfect silicon (Popovici) monochromator at a 90 take-off angle and is optimized for the 511 reflection and 1.478Ǻ.  Beams at 2.31Ǻ, 1.76Ǻ, 1.17Ǻ and 1.07Ǻ are also accessible. The detector is a linear position sensitive detector array composed of 11 LPSDs, each 2.54 cm in diameter and 61 cm active length. The detector elements are clamped into a plane and mounted in a poly/borated-poly/Cd shield which is built to accommodate up to 15 LPSD elements and which rotates about the specimen position on air bearings. The detector array spans 20 2-θ with the detector array at 1.6 m from the specimen position and 30 2-θ, at the 1.05 m distance. Position encoding is by charge division. The instrument is expected to have a minimum resolution of δd/d ~3*10-3 near 90 2-θ when the detector-specimen distance is 1.6 m and δd/d ~4.5*10-3 at the 1.05 m sample to detector distance.

Data acquisition times for the full 5 – 105 spectrum at full CARR power are expected to be a few minutes.

CARR HIPD Installation - The installation of HIPD went very smoothly in no small part because we received such excellent help for the PKU and CIAE staff. While we are still waiting for CARR to operated on a regular schedule to complete the installation tests and demonstrations you can see the record of our effort here.





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