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Robust shielding for intense, high-energy neutron and gamma sources is necessary to reduce radiation fields to a level safe for people. This is particularly challenging for high-energy mixed radiation... Robust shielding for intense, high-energy neutron and gamma sources is necessary to reduce radiation fields to a level safe for people. This is particularly challenging for high-energy mixed radiation fields because most traditional shielding materials cannot efficiently shield both gammas and neutrons. Such shielding using traditional materials can be heavy and bulky, often consisting of layers of materials targeted at attenuating specific types and energies of radiation. This makes installation, moving, and design challenging and expensive, often requiring special procedures and support structures. A reduction in the overall weight and volume of shielding material while retaining effectiveness is desirable in many industries employing strong radioactive sources. Shielding is often plagued by gaps between shielding materials and against structures or surrounding canning. Complex and expensive shielding may be required to account for these gaps that represent weak points in a shield. A shield that effectively fills such a hypothetical gap, obviating the need for supplemental shielding is desirable. Beyond this consideration, there is no requirement for the form of the material (e.g., granular, aggregate, spherical, sheet, blocks, liquid). A new material or approach to address the challenges described above is requested for submission. Any recommended material(s) should have the ability to effectively shield neutron and gamma radiation; alpha and beta radiation are of secondary concern. Required characteristics include: Ability to maximize the attenuation of several MeV gamma and fission neutron sources. Ability to withstand temperatures of 180 F without significant material property degradation for a time period of at least 10 years. Affordable in material acquisition, installation, and maintenance. Scalable in production such that 25 cubic feet can be produced and installed. Desired, but not required characteristics include: Scalable production and installation to 1000 cubic feet at an approximate cost of $4k per cubic foot or less. Some compressibility or capability of expansion to fill a space in which it is installed. Attenuation of several MeV gamma and fission neutron by more than a factor of 1000 through the depth of 1 foot. Low off-gassing in a mixed neutron/gamma radiation field in the desired temperature range. A high thermal conductivity. Ability to withstand temperatures is desirable up to 550 F without significant material property degradation. Non-toxic when being fabricated (e.g., cut, milled). Minimize material activation that produces penetrating radiation after use. Low thermal expansion coefficient. Does not require special precautions for safe handling or storage. High-damping to reduce mechanical vibrations. All proposals should specifically identify the technological gap and address how the work proposed may lead to the implementation or development of an improved shielding material.