Brief Description of NDP Instrumentation

 Shown below is a schematic depicting one (of many) simplified configuration for a NDP chamber. Other NDP configurations may include:  sample stage motion,  neutron focusing lenses, multiple detectors or detectors in a coincident configuration, sample changers, other neutron monitors, etc.  The neutron monitor is placed in the vacuum chamber but may be placed at the entrance window of the chamber. Some configurations do not use a neutron monitor but, rather, use a standard that is analyzed in series with the samples.  In addition, vacuum pumps and vacuum gauges are required as well, as electrical feed thorough connections into the vacuum to supply power or collect signals. These could include detectors, motion controllers, pre-amplifiers, samples, and other equipment. A review of the literature shows many approaches used for the instrumentation and analysis.

The photograph below shows a former configuration of the NDP Chamber at the NIST Center for Neutron Research. A cold neutron beam (<5 meV, ~1 cm diameter) flows from the neutron source through the blue shielding and passes through the stainless steel vacuum chamber. The neutron beam at the sample position is described in some detail here. Non-reacted neutrons continue through the chamber to be captured in the beam stop enclosed in additional radiation shielding. Some neutrons are scattered by the chamber windows, sample, support structure, etc. during the measurement.  During NDP measurements this chamber typically is held at a pressure of  <2E-03 Pascal (<1E-05 Torr).