The National Institute of Standards and Technology (NIST) intends to negotiate, on a sole source basis, under the authority of FAR 13.106-1(b) (1), with Anton Paar, 1 0215 Timber Ridge DR, Ashland, Virginia, for the purchase of an UV Light Curing System for an existing Anton Paar MCR 502 WESP Rheometer, needed by the Security Technologies Group at NIST. The Security Technologies Group (STG) within the Materials Measurement Science Division conducts research on complex and emerging material systems relevant to body armor and ceramic additive manufacturing (AM). These materials, including densely filled composite formulations, ceramic photopolymer slurries, and UV-curable polymer composites, exhibit properties that depend strongly on processing history, including shear, temperature, cure conditions, and microstructural evolution. A critical measurement need in these efforts is the ability to quantify UV-curing rheokinetics during photopolymerization under controlled conditions relevant to manufacturing processes and end-use performance. These measurements are required to assess viscosity increase, gel point, modulus evolution, and cure kinetics during UV exposure, while directly correlating these responses with curing parameters such as light intensity, wavelength, and exposure profile. The STG seeks to add a UV light-curing system, an optical accessory, for the existing Anton Paar MCR 502 WESP stress-controlled shear rheometer, Serial Number 83291166, located in Building 220, Room A218, on the NIST Gaithersburg campus. The system must enable simultaneous UV irradiation and rheological testing with temperature control and calibrated wavelength and intensity options. This integration creates unique requirements for the optical accessory Sole source determination is based on the need to purchase an optical accessory for the existing Anton Paar MCR 502 WESP stress-controlled shear rheometer. Purchasing a non-factory system and attempting to modify it to fit the existing rheometer runs the risk of violating the warranty and service contracts on the existing rheometer, or potentially rendering it inoperable. In addition, based on past experience with custom instrument modifications, it will likely take at least 100 person hours to identify, setup, and configure any new software packages, and to modify custom software to support the new accessory, which may be difficult or impossible to interface with the existing instrument control software. In addition, it will take about 4 person hours to train all of the users on the new software and protocol. The cost to the government for these 104 person hours is estimated to be approximately $20K. In addition, the requirement to support and operate two software packages during testing will likely require at least 32 person hours annually, at a cost of approximately $4K annually. Considering both initial costs and reoccurring costs for a 10 year life of the UV accessory results in a cost to the governm…