Radiation, neutron

The neutron is a particle of mass m = 1.0098 dalton, with a zero electrical dipole (or smaller than 10 16 esu), a spin 1/2 and a magnetic moment which is equal to — 1.91 nuclear magneton, where 

We may now introduce the polarization factor associated with a flux of N neutrons. Here, the polarization vector is3 

A beam of monocinetic neutrons, propagating along the incident direction OZ is characterized by 

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Criticality Precautions. The presence of a critical mass of Pu ia a container can result ia a fission chain reaction. Lethal amounts of gamma and neutron radiation are emitted, and a large amount of heat is produced. The assembly can simmer near critical or can make repeated critical excursions. The generation of heat results eventually ia an explosion which destroys the assembly. The quantity of Pu required for a critical mass depends on several factors the form and concentration of the Pu, the geometry of the system, the presence of moderators (water, hydrogen-rich compounds such as polyethylene, cadmium, etc), the proximity of neutron reflectors, the presence of nuclear poisons, and the potential iateraction with neighboring fissile systems (188). As Httle as 509 g of Pu(N02)4 solution at a concentration Pu of 33 g/L ia a spherical container, reflected by an infinite amount of water, is a critical mass (189,190). Evaluation of criticaUty controls is available (32,190). 

The spectroscopic techniques that have been most frequently used to investigate biomolecular dynamics are those that are commonly available in laboratories, such as nuclear magnetic resonance (NMR), fluorescence, and Mossbauer spectroscopy. In a later chapter the use of NMR, a powerful probe of local motions in macromolecules, is described. Here we examine scattering of X-ray and neutron radiation. Neutrons and X-rays share the property of being found in expensive sources not commonly available in the laboratory. Neutrons are produced by a nuclear reactor or spallation source. X-ray experiments are routinely performed using intense synclirotron radiation, although in favorable cases laboratory sources may also be used. 

Neutron radiation is emitted in fission and generally not spontaneously, although a few heavy radionueleides, e.g. plutonium, undergo spontaneous fission. More often it results from bombarding beryllium atoms with an a-emitter. Neutron radiation deeays into protons and eleetrons with a half-life of about 12 min and is extremely penetrating. 

Neutron Radiation. See under Radiation Effects on Explosives, Propellants and Pyrotechnics... 

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]

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. 

Alpha, beta, gamma, and neutron radiation are summarized below. 

In this region, there is a linear relationship between the number of ion pairs collected and applied voltage. A charge amplification of 104 can be obtained in the proportional region. By proper functional arrangements, modifications, and biasing, the proportional counter can be used to detect alpha, beta, gamma, or neutron radiation in mixed radiation fields. 

Protection Against Neutron Radiation Up to 30 Million Elec-... 

Witherspoon, J.P. 1969. Radiosensitivity of forest tree species to acute fast neutron radiation. Pages 120-126 in D.J. Nelson and F.C. Evans (eds.). Symposium on Radioecology. Proceedings of the Second National Symposium. Available as CONF-370503 from The Clearinghouse for Federal Scientific and Technical Information, Natl. Bur. Standards, Springfield, VA 22151. 

Neutron production, plutonium, 77 585 Neutron radiation, high pressure, 13 431 Neutron-radiography (N-radiography), 77 418... 

Keywords gamma rays bursts supernovae stars neutron radiation processes non-thermal ... 

PE foams containing gold particles which can be moulded or machined into shapes are being developed for applications where atomic particle reflectance or absorption is needed. Uses in neutron radiation environments and in ion implantation technology are envisaged. Uses may also develop from the high electrical conductivity of gold. 

Small-scale, tabletop nuclear fusion devices, known as compact accelerator neutron generators, are routinely used as a source of neutron radiation. By design, however, these devices consume more energy than they release. The beam of neutrons generated by these devices can be used to identify the elemental composition of amaterial.The coal industry uses such beams to measure the sulfur content of coal in real time as the coal moves over conveyor belts. The cement industry similarly uses these beams to judge the quality of cement mixes. These fusiongenerated neutrons are also used to identify the elemental composition of nuclear wastes and for the detection and identification of explosives. 

Levy, Herley and co-workers at Brookhaven National Laboratory have been studying the effects of X-ray, gamma rays and neutron radiations on AP (Refs 163,208,211,224, 228,240, 241,244,255 258). Neutron effects studies... 

Neutron Irradiation on Military Grade Ammonium Perchlorate , BRL-MR-2448, Ballistic Res Labs, Aberdeen Prov Grnd, Md (1975) (AD-B003210L) 235) C-W. Nelson A.W. Barrows, Short Lived Bum Rate Changes in Neutron Radiation Experiments , BRL-MR-2475, Ibid (1975) (AD-B003940L) 236) P.L. Morgan et al, Biblio-... 

J.R. Ward J J. Rocchio, Effect of Neutron Radiation on the Rate of Ammonium Perchlorate Decomposition Reactions Involved in Combustion , Ibid, paper 6.4, pp 271—80 (1975) 246) Ibid, Effect of Neutron Radia-... 

Peak Breadths And Reflection Profile Function. As has been mentioned, the individual reflection profiles tend to be broad for polymers. With both x-ray and neutron radiation the peaks exhibit large peak-widths. In a neutron diffraction pattern of isotactic polypropylene (A. Immirzi, work in progress) the peak width at half maximum, K j, had values ranging from 0.60° at 20= 14° to 1.00° at 26= 43° (X= 1.542 A), whilst, with the same... 

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