Amendment_I.docx

AMENDMENT I (SB1341-16-RQ-0168)

The purpose of this amendment is to address vendor question and answers as follows:

Question (1) For the case that a detector with 3He as converter gas is offered, can 3He for the detector be provided by NIST?

Answer: NIST will be able to request an allocation of 3He gas from the DOE/NNSA for this project. With the approved allocation, the offeror will be able to purchase the gas directly from a supplier (Linde).

Question (2) A multi-wire Proportional Counter (MWPC) can meet the specifications as listed in the solicitation with the exception of specification 6 on page 2 (detection uniformity) and operation test 5 (detection uniformity on page 4), a MWPC can meet the requirements on detection uniformity in the direction parallel to the anode wires. Perpendicular to the anode wires, however, the readout electronics are sensitive to the fact that in a MWPC the pulses are formed very near to the anode wires (charge multiplication by avalanche processes). If these pulses are readout with pixel sizes well below 1 mm (as required for the system) than any homogeneous radiation is detected – in the direction perpendicular to the anode wires-with a strong modulation with maxima at the anode wire positions (accounting for typical wire pitches of ~1mm to 2mm).

Answer: The requirement for detection uniformity should be interpreted as it relates to the spatial resolution of the detector, not the readout pixel size. That is, when the detector is illuminated with a uniform neutron field (for example, by the scattering from an isotropic sample such as light water), the recorded neutron counts per unit time and per spatial resolution area, does not vary by more the 20 % over the entire active area of the detector.

Question (2a) Thus, the question arises whether MWPC’s are generally excluded as possible candidates for the detector.

Answer: MWPC’s are not excluded as possible candidates for the detector (see answer to question 2b below).

Question (2b), If MWPC’s are not excluded the question of maximal anode wire pitch arises. What is the maximum anode wire pitch acceptable?

Answer: Assuming that the distance between anode wires (anode wire pitch) determines the spatial resolution perpendicular to the anode wires, the maximum anode wire pitch is 1.5 mm (to meet specification 2) Question (3) For VSANS applications the requirement is for excellent detection uniformity together with high spatial resolution.

Would a detector be considered which

a. would meet these requirements over its entire active area

b. with the exception of “dark lines (dead areas with a length of 450 mm and a width of about 2 mm)” and a pitch of ~ 30 mm (in total 4 dark lines in the case of a 150 mm wide active area)?

Answer: A detector with 2mm of dead space (dark lines) every ~ 30 mm would be acceptable if the total active length is at least 150 mm. Hence the detector would have to have an active width that extends ~ 160 mm to meet this requirement.

Question (4) In accordance with specification 2 the optimum spatial resolution is given by <= 1 mm × 1 mm. Would the VSANS instrument benefit from a position resolution well below 1 mm (e.g. 0.3 mm) in one direction (over 150 mm) and if so, would the Government review the optimum spatial resolution?

Answer: The VSANS instrument would not benefit from position resolution well below 1 mm. Spatial resolution of ~ 1 mm x 1 mm is optimal, although, as stated in specification 2, spatial resolution of 1.5 mm x 1.5 mm is acceptable.