Neutrons from special nuclear material

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. 

The atom s structure has a nucleus at the center, surrounded by a cloud of electrons. Inside the nucleus are two types of particles, neutrons (electrically neutral) and protons (positively charged). Under special experimental conditions, neutrons can be released from the nucleus. They are useful for creating new radioactive materials or for producing large amounts of nuclear energy. 

The name comes from the Latin Polonia, meaning Poland, the home country of Marie Curie, one of its discoverers. It was discovered by Marie Curie (1867-1934) and Pierre Curie (1859-1906) in 1898 when they were studying uranium and other radioactive materials found in pitchblende. Polonium is very rare, and, although some exists naturally, most polonium is manufactured in nuclear reactors. Polonium is very dangerous even in minute quantities because of its level of radioactivity. It is a very good source of alpha radiation and, if combined with beryllium, produces neutrons. It is thus used as a thermoelectric source for specialized applications such as satellites. 

Advanced fuel assembly (AFA) has been developed both for replacement of standard fuel at the operating reactors, and for new nuclear power plants with advanced WWER. The main difference of AFA, being the most effective as to economy, from standard fuel is application of only zirconium stmctural materials in the assembly active part. This allowed (in combination with specially developed refuelling patterns) to reduce the specific consumption of uranium approximately by 13%. Application of gadolinium burnable absorber instead of boron absorber allows to reduce this index by approximately 5% more. Application of AFA allows also to reduce enrichment of makeup fuel. Using of uranium-gadolinium fuel allows to reduce neutron fluence to the reactor vessel, to improve flexibility of fuel cycle, to exclude expenses for operation and storage of burnable absorber rods. 

Another advantage of neutrons over X-rays comes from the fact that neutrons are particles with a nuclear spin. The interaction of this with the electronic spin of a sample allows the determination of the magnetic stmcture of magneticaUy-active compounds. For example, in this way it is possible to distinguish between parallel and anti-parallel spins in ferromagnetic and antiferromagnetic materials [63]. This topic is beyond the scope of this book, so we refer to a more specialized text [64]. 

Boranes, boron clusters, and in particular, carboranes are of special interest due to their unique properties that cannot be found in organic counterparts. These uniqne properties are based either on the element boron, due to its electron deficiency, or on the structnral featnre of the cluster compound. Borane clusters as a class of materials have a wide range of potential applications. This is not only due to their unique electronic and nuclear features the fields of application, to name but a few, range from materials science through medical applications to catalysis, which will be described in more detail below [13]. Carboranes can be applied as liquid crystals in electro-optical displays [14], non-linear optics [15], and ion-selective electrodes [16] in the materials science arena. If carboranes are vaporized and fired at high temperatures they create boron films that are applied in Tokamak reactors for nuclear fusion [17]. Boranes have furthermore found application in airbag propellant systems in cars [18], as the stationary phase in gas chromatography [19] and in metal ion extraction systems, for example, for nuclear waste [20]. In medical applications, boron neutron capture therapy (BNCT), a special field of anti-cancer therapy, is noteworthy. 

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