Influence of thermal neutrons

The tighter bounds on the SAW DDR reduced the uncertainty in the irradiated fracture toughness. This approach was subjected to rigorous peer review before acceptance by the Nuclear Regulator. It was successful in maintaining the margins for on-upper-shelf operation at critical locations. 

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T. Waaler, S. A. Sande, B. W. Muller, G. Schuller-Lisether, The influence of thermal neutron irradiation on the in vitro characteristics of ASA oral dosage forms—Validation of neutron activation, Eur J Pharm Biopharm 43 159-164 (1997). 

R B Jones, D J Edens and M R Wootton, Influence of thermal neutrons on the hardening and embrittlement of plate steels. Effects of Radiation on Materials 19" International Symposium, ASTM STP1366, M L Hamilton, A S Kumar, S T Rosinski and M L Grossbeck, eds, American Society for Testing and Materials, West Conshohocken, PA, 2000,366-382. 

R Moskovic and C Jordinson, Influence of thermal neutrons on embrittlement and hardening in weld metals, Modell. Simul. Mater. Sci. Eng., 1999, 7, 503-523. 

One of the varieties of malignant tumor radiotherapy is neutron capture therapy (NCT) (De Stasio et al., 2001). NCT is a cancer therapy that uses radiation from the reaction of capturing thermal neutrons by or Gd isotopes, previously accumulated in tumor cells (Detta and Craickshank, 2009 Turanska et al., 2010). The result of thermal neutron interaction with isotopes is a significant cytotoxic effect caused by the influence of the products of nuclear reaction on cancer cells. 

One of the main tasks of nuclear-reactor safety research is assessing the integrity of the reactor pressure vessel (RPV). The properties of RPV steels and the influences of thermal and neutron treatments on them are routinely investigated by macroscopic methods such as Charpy V-notch and tensile tests. It turns out that the embrittlement of steel is a very complex process that depends on many factors (thermal and radiation treatment, chemical compositions, conditions during preparation, ageing, etc.). A number of semi-empirical laws based on macroscopic data have been established, but unfortunately these laws are never completely consistent with all data and do not yield the required accuracy. Therefore, many additional test methods are needed to unravel the complex microscopic mechanisms responsible for RPV steel embrittlement. Our study is based on experimental data obtained when positron annihilation spectroscopy (PAS) and Mdssbauer spectroscopy (MS) were applied to different RPV steel specimens, which are supported by results from transmission electron microscopy (TEM) and appropriate computer simulations. 

Impurity atoms resulting from nuclear reactions. Their influence on the properties of a solid is generally very similar to that of the same impurities introduced in a chemical way. Only thermal neutrons are able to produce them in any appreciable amount even in this case, and as far as the irradiated material does not contain elements with a large cross section, like boron-10 or lithium-6, the concentration of the produced impurities quite generally remains negligible. 

Fast moving neutrons emitted from a radioactive source (usually Radium-Berrylium or Americium-Beryllium) upon collision with a particle having mass nearly equal to its own, like hydrogen atom in the soil, release their energy and gets thermalized or slowed down. The thermalized neutrons are detected by a detector and recorded on a scalar. Usually BFg gas is used as detector of slowed down neutrons. Increased thermalization indicates higher water content of the soil. The zone of influence is normally about 15-20 cm arormd the detector. 

Shazali 1, Van t Dack L, Gijbels R (1987) Determination of precious metals in ores and rocks by thermal neutron activation/y-spectrometry after preconcentration by nickel sulfide fire assay and coprecipitation with tellurium. Anal Chim Acta 196 49-58 Stembeck J, Sjodin A, Andreasson K (2002) Metal emissions from road traffic and the influence of resuspension—results from two tunnel studies. Atmos Env 36 4735-4744 Sun Y, Guan X, Du A (1998) Determination of platinum group elements by inductively coupled plasma-mass spectrometry combined with nickel sulfide fire assay and tellurium coprecipitation. Spectrochim Acta B 53 1463-1467... 

Certainly one of the most interesting applications lies in the control of architecture (control of hole and electron injecting and active layers) in very thin electroluminescent devices. The existence of a precursor polyelectrolyte Pre-PPV (39,90,91) of the electroluminescent material poly(p-phenylene-vinylene) (PPV) (92) makes it possible to fabricate polyion multilayer film architectures, in which the Pre-PPV can subsequently be converted to PPV by thermal annealing (19,34-38,87,88,93). The first electroluminescent devices have been prepared and it was found that devices as thin as 13 nm emit light (88). Tum-on voltages of less than 2 V are required to generate light (35) and even an influence of the film architecture on the luminescent properties has been observed (88). However, the structural details of these films are presently not understood and it is not clear how device properties are influenced by film composition and architecture. We have recently shown that the thermal conversion of Pre-PPV to PPV can be carried out with preservation of a layered structure. These results were obtained by neutron reflectometry on... 

The apparatus consists of encapsulated and sealed nuclear (radioactive source), thermal neutron detectors and a read-out instrument. The detectors are sensitive to outside influences therefore, any other source of neutron radiation is kept at least 10 m from the apparatus during use. The area around the apparatus should also be kept free of large amounts of hydrogenous material, such as water, plastics or asphalt during use. 

The effects of temperature changes (para. 671(a)(vi)) on the stability of fissile material form or on the neutron interaction properties are required to be examined. For example, uranium systems dominated by very low energy (thermal) neutrons have an increase in neuUon multiphcation as the temperature is reduced. Temperature changes may also influence the package integrity. The temperatures which should be considered include those resulting from ambient condition requirements specified in para. 676 and those of the tests (paras 728 or 736, as appropriate). 

The starting nuclide (deuterium) is present in natural water with an isotope abundance of 0.015%. An additional formation of during reactor operation by the nuclear reaction H (n, y) can be neglected because of the small neutron capture cross section of this reaction. Even if one does not take into account the water exchange which takes place during plant operation, an increase in the natural concentration of only 0.002 to 0.0035% would occur during one fuel cycle such an enhancement is too small to influence production to any measurable extent. The thermal neutron capture cross section for the formation of from amounts to about 3.6 10 cm (MaxweU spectrum). In the PWR primary coolant, between 40 and 150 GBq per fuel cycle are produced by this reaction, depending on the primary coolant volume, the water volume of the active zone in the reactor core and other parameters. 

Thus the influence of extra thermal neutron absorption placed in a thermal reactor is very strong at the center, where the flux is high. In a slab reactor, for example, the statistical weight for absorption would fall off as cos x, (The implications of this behavior are discussed further in subsequent analysis when the one-velocity model is considered in detail.)... 

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