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[en] I calculated neutron and gamma-ray equivalent doses leaking through a variety of infinite (laminate) slab-shields. In the shield computations, I used, as the incident neutron spectrum, the leakage spectrum (<20 MeV) calculated for the LANSCE tungsten production target at 90 degree to the target axis. The shield thickness was fixed at 60 cm. The results of the shield calculations show a minimum in the total leakage equivalent dose if the shield is 40-45 cm of iron followed by 20-15 cm of borated (5% B) polyethylene. High-performance shields can be attained by using multiple laminations. The calculated dose at the shield surface is very dependent on shield material. 4 refs., 4 figs., 1 tab
[en] The ''maximum'' unperturbed, steady state thermal neutron flux for LANSCE is calculated to be 2 /times/ 1013 n/cm2-s for 100 μA of 800-MeV protons. This LANSCE neutron flux is a comparable entity to a steady state reactor thermal neutron flux. LANSCE perturbed steady state thermal neutron fluxes have also been calculated. Because LANSCE is a pulsed neutron source, much higher ''peak'' (in time) neutron fluxes can be generated than at a steady state reactor source. 5 refs., 5 figs
[en] Neutron doses through 162-cm-thick spherical shields were calculated to be 1090 and 448 mrem/h for regular and magnetite concrete, respectively. These results bracket the measured data, for reinforced regular concrete, of /approximately/600 mrem/h. The calculated fraction of the high-energy (>20 MeV) dose component also bracketed the experimental data. The measured and calculated doses were for a graphite beam stop bombarded with 100 nA of 800-MeV protons. 6 refs., 2 figs., 1 tab
[en] At the Los Alamos National Laboratory, we have an active effort in the general area of Applied Spallation Physics Research. The main emphasis of this activity has been on obtaining basic data relevant to spallation neutron source development, accelerator breeder technology, and validation of computer codes used in these applications. We present here an overview of our research effort and show some measured and calculated results of differential and clean integral experiments
[en] We will show in this article the proposed upgrade for the lower tier water moderators for the LANSCE 1L Mark-III design. This proposal will include the introduction of pre-moderators for the high intensity moderators and a change of the decoupler from Cadmium to Gadolinium on all lower tier water moderators. We will present the influence of these changes on the integrated thermal flux and the time distribution of these moderators. As part of the upgrade of the Manual Lujan Jr. Neutron Scattering Center target (1L target) the goal was to increase the integrated thermal flux of the lower high intensity and the high resolution moderator by 20%. We will show in this paper that this goal can be achieved by introducing a pre-moderator concept on the high resolution moderators and by changing the decoupling scheme on all three moderators. Furthermore we will show that this goal can be achieved without jeopardizing the time of flight resolution of these moderators. For the all these calculations we used the radiation transport code MCNPX, which is most commonly used for this type of calculations.
[en] A liquid H2 moderator has been operational at the Manual Lujan Jr. Neutron Scattering Center (Lujan Center) since 1985. Detailed Monte Carlo calculations have been made to estimate the neutronic performance of the liquid H2 moderator cold source, using the state-of-the-art Los Alamos LAHET Code System and liquid H2 scattering kernels. The absolute neutron spectrum leaking from the moderator has been measured. In thermal equilibrium at 20 K, the moderator would convert to 100% para-hydrogen on some time frame. The authors show that the performance of the Lujan Center cold neutron source is sensitive to small fractions of ortho-hydrogen, and display these results as a function of the ortho/para H2 concentration. Integral data from the measured neuron spectrum have been combined with calculated predictions to estimate the ortho/para H2 concentration in the moderator. From these analyses, they estimate the ortho-hydrogen concentration in the liquid H2 moderator to be 6--9% at the time the neutron spectrum was measured
[en] We have investigated the possibility of implementing the idea of a beryllium reflector filter in the LANSCE 1L target Mark-III upgrade. We will present different concepts of beryllium reflector filters (megaphone, chevron and swiss-cheese concept) and their effect on the integrated cold flux and the time distribution of the lower tier hydrogen flux-trap moderator as a function of the three instruments, (SPEAR, LQD and Asterix) which are served by this moderator. As part of the LANSCE 1L target upgrade study it is the declared goal to increase the cold flux (E < 5meV) of the lower tier partially coupled liquid hydrogen moderator by a factor of two. This goal is proposed to be achieved by adding a pre-moderator system to the moderator and by implementing the cold beryllium reflector concept. The cold beryllium reflector filter concept was tested in an experiment at the weapons neutron research (WNR) facility at LANSCE in January 2003 by Pitcher et al. Based on the success of this experiment it was then decided to implement this concept into the 1L target Mark-III upgrade. In this context a series of Monte Carlo transport calculations was performed to optimize the cold neutron flux.