Neutron radiation shielding

There are a number of papers in the open literature explicitly reporting on the properties of boron cluster compounds for potential neutron capture applications.1 Such applications make full use of the 10B isotope and its relatively high thermal neutron capture cross section of 3.840 X 10 28 m2 (barns). Composites of natural rubber incorporating 10B-enriched boron carbide filler have been investigated by Gwaily et al. as thermal neutron radiation shields.29 Their studies show that thermal neutron attenuation properties increased with boron carbide content to a critical concentration, after which there was no further change. 

The main use of lead metaborate is in glazes on pottery, porcelain, and chinaware, as weU as in enamels for cast iron. Other appHcations include as radiation-shielding plastics, as a gelatinous thermal insulator containing asbestos fibers for neutron shielding, and as an additive to improve the properties of semiconducting materials used in thermistors (137). 

The high cross-section for thermal neutrons results in the use of boron and boron compounds for radiation shielding (14). The ease of detecting the a-particle produced when boron absorbs thermal neutrons results in the use of boron for neutron counters as weU. 

The nuclear reactor also must be shielded against the emission of radioactive material to the external environment. Suitable radiation controls include both thermal and biological shielding systems. Radiation from alpha particles (a rays) and beta particles ((3 rays) has little penetrating power, but gamma rays have deep penetration properties. Neutron radiation is, however, the primary area of risk. Typically, extremely thick concrete walls are used as a neutron absorber, but lead-lined concrete and special concretes are also used. 

Neutron diffraction on Cd compounds is not feasible, as one of the Cd nuclides (113Cd) has an extremely high absorption cross-section for neutrons, yielding an average [Pg.1255]

Another disadvantage with NRA is the requirement for very advanced high current accelerator. This accelerator wih have all of the disadvantages (large size, large weight, radiation shielding) associated with the neutron-based accelerators. 

The central storage well is a 10.16-cm pipe surrounded by 5.08 cm of lead for primary gamma shielding. The radiation dose rate at 1 m from this container with 8 sources totaling 34.6 mg 252cf in the center well was 55 mrem/h (42 mR/h gamma +13 mrem/h neutron radiation). 

Use Neutron counter, radiation shielding (in the form of boral), medicine. 

Because the total cross section of the "B-n interaction is negligible if compared with that of the °B-n interaction, let us assume that a boron-containing material used for neutron shielding is B monoisotopic (otherwise, the calculated neutron radiation length should be divided by the relative concentration of °B). In this case, in the logarithmic scale, the energy dependence of the minimal radiation length is expressed by the linear function... 

The Virus House was finished in October. Besides a laboratory the structure contained a special brick-lined pit, six feet deep, a variant of Fermi s water tank for neutron-multiplication studies. By December Heisenberg and von WeizsScker had prepared the first of several such experiments. With water in the pit to serve as both reflector and radiation shield they lowered down a large aluminum canister packed with alternating layers of uranium oxide and paraffin. A radium-beryllium source in the center of the canister supplied neutrons, but the German physicists were able to measure no neutron multiplication at all. The experiment confirmed what Fermi and Szilard had already demonstrated that ordinary hydrogen, whether in the form of water or paraffin, would not work with natural uranium to sustain a chain reaction. 

Radiation, Another safety issue for the U.S. ceramic process is radiation including gamma, alpha, and neutron radiation from plutonium and Am-241. Automation and remote handling of materials and adequate shielding are required to protect workers from radiation. 

The reactor core is surrounded by a block of concrete of very high density (density 4.14 g/cm ), the biological shield, which was also activated by the neutron radiation emanating from the reactor core (see Fig. 3). The specific Co-60 activity of the concrete achieves a maximum of 8x 10 Bq/g, which means that most of the disassembly work must be carried out remotely. 

Helium circulation and heat transfer - Cooper Neutron efficiency - Wigner Radiation Shielding - Wigner Controls - Wigner... 

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