Jerome Verbeke

Adding new features in a peer-to-peer distributed computing framework

The aim of P2P computing is to build virtual computing systems dedicated to large-scale computational problems. This kind of architecture will contain several thousands of computing nodes, which need to be organized. Moreover, the architecture will deal with nodes dynamism and network scalability. JXTA proposes an underlying infrastructure, which builds a virtual network of peers on top of a physical network. This structure allows, among other features, to create peer groups. JNGI, which is one of the first P2P decentralized computing platforms, is already using these groups to structure the computing system. This article aims to demonstrate how to build new types of groups called similarity groups into the JNGI project. A similarity group is a peer group where all the peers have common characteristics like CPU speed or memory size. This is done in order to increase the relevance of task dispatching and therefore to increase the performance of JNGI.

Analysis of decay dose rates and dose management in the National Ignition Facility.

AbstractA detailed model of the Target Bay (TB) at the National Ignition Facility (NIF) has been developed to estimate the post-shot radiation environment inside the facility. The model includes the large number of structures and diagnostic instruments present inside the TB. These structures and instruments are activated by neutrons generated during a shot, and the resultant gamma dose rates are estimated at various decay times following the shot. A set of computational tools was developed to help in estimating potential radiation exposure to TB workers. The results presented in this paper describe the expected radiation environment inside the TB following a low-yield DT shot of 1016 neutrons. General environment dose rates drop below 30 &mgr;Sv h−1 within 3 h following a shot, with higher dose rates observed in the vicinity (∼30 cm) of few components. The dose rates drop by more than a factor of two at 1 d following the shot. Dose rate maps of the different TB levels were generated to aid in estimating worker stay-out times following a shot before entry is permitted into the TB. Primary components, including the Target Chamber and diagnostic and beam line components, are constructed of aluminum. Near-term TB accessibility is driven by the decay of the aluminum activation product, 24Na. Worker dose is managed using electronic dosimeters (EDs) self-issued at kiosks using commercial dose management software. The software programs the ED dose and dose rate alarms based on the Radiological Work Permit (RWP) and tracks dose by individual, task, and work group.

Threat Detection of Radioactive Contraband Incorporating Compton Scattering Physics: A Model-Based Processing Approach

The detection of radioactive contraband is a critical problem in maintaining national security for any country. Gamma-ray emissions from threat materials challenge both detection and measurement technologies significantly. The development of a sequential, model-based Bayesian processor that captures both the underlying transport physics of gamma-ray emissions including Compton scattering and the measurement of photon energies offers a physics-based approach to attack this challenging problem. The inclusion of a basic radionuclide representation of absorbed/scattered photons at a given energy along with interarrival times is used to extract the physics information available from noisy measurements. It is shown that this representation leads to an “extended” physics-based structure that can be used to develop an effective sequential detection technique. The resulting model-based processor is applied to data obtained from a controlled experiment in order to assess its feasibility.

PLANNING TOOLS FOR ESTIMATING RADIATION EXPOSURE AT THE NATIONAL IGNITION FACILITY

Abstract A set of computational tools was developed to help estimate and minimize potential radiation exposure to workers from material activation in the National Ignition Facility (NIF). AAMI (Automated ALARA-MCNP Interface) provides an efficient, automated mechanism to perform the series of calculations required to create dose rate maps for the entire facility with minimal manual user input. NEET (NIF Exposure Estimation Tool) is a web application that combines the information computed by AAMI with a given shot schedule to compute and display the dose rate maps as a function of time. AAMI and NEET are currently used as work planning tools to determine stay-out times for workers following a given shot or set of shots, and to help in estimating integrated doses associated with performing various maintenance activities inside the target bay. Dose rate maps of the target bay were generated following a low-yield 1016 D-Tshot and will be presented in this paper.

Simulating and optimizing a peer-to-peer computing framework

The aim of P2P computing is to build virtual computing systems dedicated to large-scale computational problems. JXTA (JuXTApose) proposes an underlying infrastructure on which JNGI (Jerome, Neelakanth, Greg, and Ilya: first names of the creators), one of the first P2P decentralized computing frameworks is built. In order to test this framework, we have built a tool named P2PPerf which allows us to study the behavior of JNGI and to optimize it according to our simulation results.

Post-Shot Radiation Environment Following Low-Yield Shots Inside the National Ignition Facility

Abstract A detailed model of the Target Bay (TB) at the National Ignition Facility (NIF) has been developed to estimate the post-shot radiation environment inside the facility. The model includes large number of structures and diagnostic instruments present inside the TB. These structures and instruments are activated by the few nanosecond pulse of neutrons generated during a shot and the resultant gamma dose rates are estimated at various decay times following the shot. The results presented in this paper are based on a low-yield D-T shot of 1016 neutrons. General environment dose rates drop to below 3 mrem/h within three hours following a shot with higher dose rates observed at contact with some of the components. Dose rate maps of the different TB levels were generated to aid in estimating worker stay-out times following a shot before entry is permitted into the TB.

Using similarity groups to increase performance of P2P computing

This article aims to demonstrate how to build new types of groups called similarity groups into the JNGI project. This is done in order to increase the relevance of task dispatching and therefore to increase the performance of JNGI.

Simulation of the Post-Shot Radiation Environment in the National Ignition Facility

Abstract The National Ignition Facility at Lawrence Livermore National Laboratory is the world’s largest and most energetic laser system for inertial confinement fusion. The NIF is designed to perform shots with varying fusion yield (up to 20 MJ or 7.1 × 1018 neutrons per shot). A large number of diagnostic instruments are present inside the target chamber (TC) and target bay (TB) during shots. The gamma dose rates due to neutron activation are estimated at various decay times following the high-yield (20-MJ) shots. Several components, like the snout assemblies of the diagnostic instrument manipulators and target positioners are inserted inside the TC, close to the target during the shot. These components represent major sources of gamma decay after retraction outside the TC. Five days after a 20-MJ shot, dose rates near the highly activated (retracted) parts are on the order of 1 mSv/h and dose rates within the TB outside the TC but at distance from the retracted components drop to about 50 to 70 μSv/h. The dose is dominated by decay of 24Na (T1/2 = 14.95 h) and waiting for two additional days drops the dose rates significantly. Seven days following a 20-MJ shot, dose rates in the immediate vicinity of the retracted components drop to <0.2 mSv/h and the general ambient dose rates within the TB (away from retracted components) near the TC drop to <10 μSv/h. Dose rates at much larger distances from the TC (near TB wall) are an order of magnitude lower. Detailed radiation transport simulations are performed to create detailed dose rate maps for all floors inside the TB. The maps are used to estimate worker stay-out times following shots before entry is permitted into the TB.

Characterization of Fissile Assemblies Using Low-Efficiency Detection Systems

We have investigated the possibility that the amount, chemical form, multiplication, and shape of the fissile material in an assembly can be passively assayed using scintillator detection systems by only measuring the fast neutron pulse height distribution and distribution of time intervals

Monitoring Spent or Reprocessed Nuclear Fuel Using Fast Neutrons

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