Composites made with boron might be absorbers of low energy neutrons, and could be used for structural materials for spacecraft. Polyethylene/boron nitride composites were fabricated using conventional polymer processing techniques, and were evaluated for mechanical and radiation shielding properties. The boron nitride powder surfaces were also functionalized to improve interfacial adhesion. Addition of neat boron nitride to an injection molding grade HDPE increased the tensile modulus from 588 to 735 MPa with 15 vol % filler. The bonding of a trifunctional alkoxysilane to the powder surface prior to processing increases the composite modulus to 856 MPa at the same loading. Scanning electron microscopy of fracture surfaces verified that the silane-treated powders had improved adhesion at the filler/polymer interface. Radiation shielding measurements of a 2 wt % boron nitride composite were improved over those of the neat polyethylene.

Neutrons are a by-product of high-energy x-ray radiation therapy ͑threshold for ͓␥ , n͔ reactions in high-Z material ϳ7 MeV͒. Neutron production varies depending on photon beam energy as well as on the manufacturer of the accelerator. Neutron production from modern linear accelerators ͑linacs͒ has not been extensively compared, particularly in terms of the differences in the strategies that various manufacturers have used to implement multileaf collimators ͑MLCs͒ into their linac designs. However, such information is necessary to determine neutron dose equivalents for different linacs and to calculate vault shielding requirements. The purpose of the current study, therefore, was to measure the neutron spectra from the most up-to-date linacs from three manufacturers: Varian 21EX operating at 15, 18, and 20 MV, Siemens ONCOR operating at 15 and 18 MV, and Elekta Precise operating at 15 and 18 MV. Neutron production was measured by means of gold foil activation in Bonner spheres. Based on the measurements, the authors determined neutron spectra and calculated the average energy, total neutron fluence, ambient dose equivalent, and neutron source strength. The shapes of the neutron spectra did not change significantly between accelerators or even as a function of treatment energy. However, the neutron fluence, and therefore the ambient dose equivalent, did vary, increasing with increasing treatment energy. For a given nominal treatment energy, these values were always highest for the Varian linac. The current study thus offers medical physicists extensive information about the neutron production of MLC-equipped linacs currently in operation and provides them information vital for accurate comparison and prediction of neutron dose equivalents and calculation of vault shielding requirements.

For CSI treatments delivered with a Mevion single-gantry proton therapy system, we found measured neutron dose was consistent with dose equivalents reported for CSI with other proton beamlines.

The fission Time Projection Chamber (fissionTPC) is a compact (15 cm diameter) two-chamber MICROMEGAS TPC designed to make precision cross section measurements of neutron-induced fission. The actinide targets are placed on the central cathode and irradiated with a neutron beam that passes axially through the TPC inducing fission in the target. The 4π acceptance for fission fragments and complete charged particle track reconstruction are powerful features of the fissionTPC which will be used to measure fission cross sections and examine the associated systematic errors. This paper provides a detailed description of the design requirements, the design solutions, and the initial performance of the fissionTPC.