[en] Small ultracold neutron cooling and heating during long storage in closed traps have been observed in recent experiments. It is shown that neutron quasielastic scattering due to the diffusive motion of hydrogen at the surface of adsorbed hydrogenous contaminations of the surface may be a possible reason for the spread in the energy of ultracold neutrons during long storage in closed traps

[en] Different inelastic processes of ultracold neutrons (UCN) losses in traps are considered. A hypothesis of the de Broglie singular wave-packet description of the neutron wave-function to explain anomalous losses of UCN is proposed. An experiment to check the hypothesis and its results are discussed

[en] A monoenergetic focused neutron beam has been produced by utilizing the endoenergetic heavy ion reactions on hydrogen. To realize this, the projectile heavy ion energy should be taken slightly above the threshold energy, so that the excess energy converted to the neutron energy should be very small. In order to improve the capability of the focused neutron beam, some hydrogen stored metal targets have also been tested. Separating the secondary heavy ions (associated particles) from the primary ions (accelerated particles) by using a dipole magnet, a rf separator, and a particle identification system, we could directly count the produced neutrons. This will leads us to the possibility of realizing the standard neutron field which had been the empty dream of many neutron-related researchers in the world. (author)

[en] We have developed a multi-group Monte Carlo neutron transport code using C++ and the Parallel Object-Oriented Methods and Applications (POOMA) class library. This transport code, called MC++, currently computes k and α-eigenvalues and is portable to and runs parallel on a wide variety of platforms, including MPPs, clustered SMPs, and individual workstations. It contains appropriate classes and abstractions for particle transport and, through the use of POOMA, for portable parallelism. Current capabilities of MC++ are discussed, along with physics and performance results on a variety of hardware, including all Accelerated Strategic Computing Initiative (ASCI) hardware. Current parallel performance indicates the ability to compute α-eigenvalues in seconds to minutes rather than hours to days. Future plans and the implementation of a general transport physics framework are also discussed

[en] This paper examines the use of quasirandom sequences of points in place of pseudorandom points in Monte Carlo neutron transport calculations. For two simple demonstration problems, the root mean square error, computed over a set of repeated runs, is found to be significantly less when quasirandom sequences are used (open-quotes Quasi-Monte Carlo Methodclose quotes) than when a standard Monte Carlo calculation is performed using only pseudorandom points

[en] The inelastic neutron acceleration (INNA) by long living isomeric nuclei is studied. The theoretical estimates of the INNA cross-sections for thermal neutrons for a number of isomers give the values in the range 0.1-10²b. Inelastic acceleration of thermal neutrons was observed by ^152mEu and ^180mHf, and confirmed the high value of the INNA cross-sections. As a result of the high probability of acceleration some isomeric nuclei ^113mIn, ^115mIn, are not usual moderators but accelerators of neutrons. The use of the INNA reaction for the study of high excited levels and the nature of various nuclear hindrances are discussed. (orig.)

[en] The macroscopic thermal neutron absorption cross section for small samples was calculated in framework of diffusion theory and poisoning technique. The theoretical formulae agree with the experimental data. (author). 6 refs., 3 figs

[en] Effects of non-exponential transmission 14.6 MeV neutrons have been studied by using time-of-flight techniques for Bi nuclei. The causes of possible excursion, statistical and systematical errors were discussed

[en] A semi-automatic pre-processing technique is proposed to classify the experimental data for a reaction into one or a small number of large data groups, called main cluster(s), and to eliminate some data which deviate from the main body of the data. The classifying method is based on a technique like pattern clustering in the information processing domain. Test of the data clustering formed reasonable main cluster(s) for three activation cross sections. This technique will be helpful tool in the neutron cross section evaluation. (author)

[en] The simplified P_N (SP_N) equations have previously been proposed, implemented, and tested as an inexpensive transport correction to diffusion theory. Although the theoretical foundation of the SP_N equations is weak, the computational results that have been obtained are impressive. Low-order SP_N results often capture more than 80% of the transport corrections to diffusion theory. In this paper, we provide a theoretical foundation for the SP_N equations by showing that they are high-order asymptotic solutions of the transport equation in a physical regime in which diffusion theory is the low-order asymptotic solution. (In other words, the SP_N equations represent high-order asymptotic corrections to diffusion theory). We also reformulate the conventional SP_N equations into a canonical form, which greatly simplifies the determination of boundary conditions and solution procedures. Finally, we give computational results comparing diffusion, SP_N, and S_N solutions