Biomedical subjects

J S Bull

Publications and source records attributed to J S Bull.

6 recordsLinked to original sources

PubMed2006

Proton radiography applications with MCNP5.

A modified version of MCNP5 has been developed to treat continuous-energy proton transport. This work is summarised in companion papers by Hughes et al. and Bull et al. (in these proceedings). An intrinsic part of this development effort has involved testing, verification and validation of a capability for simulating proton radiographs. This paper presents the results of calculations simulating various different test objects and the effects of alternative physics models. The significant physics processes include elastic scattering, multiple coulomb scattering, collisional energy-loss and straggling, magnetic fields and attenuation owing to nuclear interactions. Comparisons with experimental data are presented.

Algorithms↗

PubMed2001

Radiation safety systems for accelerator facilities.

The radiation safety system RSS) of an accelerator facility is used to protect people from prompt radiation hazards associated with accelerator operation. The RSS is a fully interlocked, engineered system with a combination of passive and active elements that are reliable, redundant and fail-safe. The RSS consists of the access control system (ACS) and the radiation containment system (RCS). The ACS is to keep people away from the dangerous radiation inside the shielding enclosure. The RCS limits and contains the beam/radiation conditions to protect people from the prompt radiation hazards outside the shielding enclosure in both normal and abnormal operations. The complexity of an RSS depends on the accelerator and its operation. as well as associated hazard conditions. The approaches of RSS among different facilities can be different. This report gives a review of the RSS for accelerator facilities.

Humans↗

PubMed1997

Groundwater activation at the Superconducting Super Collider: a new design model.

A groundwater activation model was developed for use in designing the accelerators at the Superconducting Super Collider Laboratory. This model is based on the concept of a 4-m-thick "activation zone" surrounding the accelerator enclosure, which contains over 99% of the soil activation caused by beam losses. Empirical shielding formulae based on computer simulations indicate that the soil activation in the activation zone decreases exponentially with distance from the tunnel enclosure. From this assumption, the average activation in the activation zone is derived. It is shown that the average activity concentration in the activation zone is equal to the activity concentration 1 m from the accelerator enclosure. The activation concentration in the water averaged over the volume of the activation zone is compared to the drinking water standards. The goal of this model is to meet the drinking water regulatory standards by averaging the activation in the activation zone. Groundwater activation concentrations have been calculated for the Super Collider utilizing experimental measurements of production cross sections and leachability factors. Comparison is made to the groundwater activation criterion for both routine and accidental beam losses.

Equipment Design↗

PubMed1997

Leaching of accelerator-produced radionuclides.

Leaching of radionuclides produced in soil and rock by high energy proton-induced radiation was studied for the SSC site. Comparison was made with predictions of a Monte Carlo code CASIM and previous results for the Fermilab site. The principal long-lived radionuclides were 3H and 22Na in agreement with Fermilab results. A few other radionuclides were present at lower concentrations in a subset of the samples. For example, 134Cs was detected in a few SSC water samples. Leaching from SSC chalk was dependent on previous weathering and on leaching time. The more soil-like marl and shale were leached more rapidly. Results of this study, in conjunction with the SSC groundwater model, show that adequate groundwater protection would have been maintained for an accidental loss of the entire proton beam at a point in the SSC Collider tunnel. Early warning techniques developed are directly applicable to soil activation monitoring at other facilities.

Cesium Radioisotopes↗

PubMed1987

Disruption of the jejunal migrating motor complex by gastric distension and feeding in the dog.

1. The jejunal motor response to gastric distension has been quantified in the conscious dog and compared with that of feeding in order to determine the role of the physical bulk of a meal in the conversion from fasted to fed motor activity. 2. In six dogs gastric distension abolished the cyclical migrating motor complex (m.m.c.) and evoked a pattern of continuous irregular jejunal motility similar to that seen postprandially, but only after a latency of 21.5 +/- 2.7 min compared to that of 7.1 +/- 1.2 min for the response to feeding. Computer analysis of distension and fed jejunal motility revealed similar distributions of intervals between contractions and contraction amplitudes with comparable mean values for both. 3. In two dogs with antrum and corpus surgically divided distension of the corpus had a similar effect on jejunal motility although the latency to both distension and feeding were considerably less. 4. By varying the period of distension it has been possible to control accurately the duration of the jejunal motor response and so assess its effectiveness in disrupting the timing of the m.m.c. The return to m.m.c. cycling following deflation was independent of preceding complexes. The occurrence of the post-distension activity front was closely related to the act of deflation itself (R = 0.94) following a latency of 26.2 +/- 2.1 min (n = 39). 5. It is concluded that the bulk of a meal contributes significantly to the early part of postprandial motility and is capable of disrupting the timing of subsequent migrating motor complexes.

Animals↗

PubMed1985

The effect of intraluminal tryptophan and phenylalanine on small intestinal motility in the conscious dog.

The effect of D- and L-isomers of tryptophan and phenylalanine on fasting motor activity of canine jejunum were investigated. Only L-tryptophan had any effect on jejunal motility. The concentration of L-tryptophan required to elicit a motor effect in 50% of animals was estimated at 28 mM. 50 mM-L-tryptophan stimulated jejunal motility after a latency of 4.5 +/- 0.7 min. The pattern of motility was similar to that evoked by feeding but continued for only 41 +/- 5 min and failed to disrupt the normal timing of the interdigestive migrating motor complex (m.m.c.). The duration of the subsequent phase II of the complex was, however, significantly reduced. Multiple infusion of L-tryptophan also failed to disrupt the timing of the m.m.c. These data are consistent with the hypothesis that specific breakdown components of protein digestion are implicated in the stimulation of postprandial motor activity. The mechanisms involved in the motor response to L-tryptophan are discussed.

Animals↗