Source Rack Research Articles

Universal strategy study of applying passive metasurfaces to an intra-DC wireless-optical interconnection

Free-space optical (FSO) communication can reduce the routing complexity of data center networks (DCNs), not only ensuring high-capacity optical switching, but also owning similar flexibility to the wireless connectivity. Presently, mainstream wireless-optical switching units (WOSUs) have adopted serial beam control for unicasting. As a two-dimensional planar structure composed of meta-atoms with special electromagnetic properties arranged in a certain way, a passive metasurface (PMF) has strong parallel beam regulating capability. In this paper, we propose a wireless-optical intra-DC interconnection scheme based on PMFs. Through a real PMF chip, by adjusting the polarization of an incident beam, the power distribution between normal and abnormal reflected beams can be controlled. When both reflected beams are assigned with power, we obtain a pair of beams reflected in parallel, thus simultaneously communicating with two racks. In fact, we can perform 1-to-N (N≥2) multicast by using cascaded PMFs, and 1-to-N means that each source rack can communicate with N destination racks, i.e., a wide communication coverage range. However, the cascaded PMFs may result in huge chip costs and high accumulated power loss. In this paper, we only demonstrate the 1-to-2 communication ability of our PMFs, so the communication coverage may be still limited. Hence, by introducing electrostatic drive to control the PMF rotation, each source rack can achieve a wider communication coverage range than before. As a result, all racks within the coverage range have the ability to establish communication links with the source rack. To this end, we also design a neural network to mimic the PMF rotation, further improving the communication capability between racks. We then propose a DCN-topology reconfiguration algorithm supporting the coexistence of unicasting and multicasting, in order to make real-time decisions on the matching between FSO ports with minimized latency. Finally, we established a proof-of-concept prototype system to demonstrate the parallel beam control of our PMF. The test results show that the angle error is less than 0.1°, satisfying the accuracy requirements of WOSUs, and our PMF always has a good polarization response with the insertion loss of less than 2 dB under various azimuth angles or rotation planes.

Dosimetry studies for an optimized reloading of a panoramic Cobalt-60 source using FLUKA Monte Carlo code

The Cobalt-60 source used at the Tunisian Gamma Irradiation Facility is nearing the end of its useful life. Due to the current low dose rates, the irradiation process takes a long time. To address exposure time and cost issues, source racks need to be reloaded to improve the quality of the exposure process. This work aims to find the optimal new configuration for future reloading of the Cobalt-60 source rack and to evaluate the dose rate distribution in the vicinity of the Irradiator and the Dose Uniformity Ratio (DUR) in a dummy product. When keeping old pencils, the optimal configuration will need to be adjusted to accommodate the new Cobalt-60 pencils. The replenishment method developed using FLUKA-based Monte Carlo code involved the addition of six new pencils: three in the upper top (outer) holder of the source rack and three in the lower bottom (inner) source holder. The spatial distribution of dose rates in the vicinity of the source rack before and after reloading was evaluated. For the radiation processing, the maximum and minimum absorbed dose in the dummy product were estimated to calculate the DUR value. The DUR value for a single-use medical product is about 2.5. The results obtained before and after reloading show that the spatial distribution of the dose rate is uniform for the proposed configurations, and has a value of approximately 0.4 kGy/h after reloading at the conveyor belt location.

Dose mapping of the 60Co gamma irradiation facility and a real irradiated product – Measurements and Monte Carlo simulation

A model of the 60Co gamma irradiation facility in Croatia has been developed using the Monte Carlo code PHITS for particle transport. For the high dose rate area (i.e. inside the source rack), the calculated dose rate distribution was compared with the measurements performed with the chemical ethanol-chlorobenzene dosimeters and good agreement was observed with a relative difference of up to 6%. For the low dose rate area (i.e., outside the source rack), the calculated dose rate distribution was compared with previous simulation (using Geant4) and experimental (using ionisation chamber) study and good agreement was observed with a relative difference of less than 5%. The application of the PHITS model in everyday practice has been successfully tested on a real product, a medical implant, commonly irradiated inside the source rack for the purpose of sterilization. It was found that the simulation and experimental dose maps agree very well. Both methods can be used and will improve everyday work in both radiation processing and research.

Modelling and optimization of dosimeters in the product box for commissioning dosimetry at gamma irradiator using Voronoi Diagram algorithm

The complexity of the geometrical configuration of a product box and source rack demands an efficient and straightforward methodology for positioning dosimeters in desired planes of the product box to optimise its dose profile. The gamma dose profile generated in the Y-set of commissioning dosimetry depends on the geometry of the selected planes of the product box. The present work attempts to model a product box using a Voronoi diagram-based algorithm for optimising the number of dosimeters in the desired planes of the product box. Discrete dosimeter positions in vertical planes of the product box were used to construct the Voronoi diagram and Delaunay triangulation to model the product box. The Voronoi vertices were computed using a perpendicular bisector algorithm from the discrete coordinates of positions of dosimeters. The Voronoi vertices of the plane of the product box were chosen to optimise the position of dosimeters. The ceric-cerous dosimeters were used to measure the absorbed doses in the product box to validate the algorithm. The overdose ratio calculated was estimated as the average maximum dose and the average minimum dose from the vertices of the Voronoi diagram, and the position of dosimeters put as per conventional strategy in the plane of the product box. The results estimated from the proposed methodology are very close to the conventional dosimetry with a better dose uniformity ratio. The overdose ratio calculated from the Voronoi approach (DUR = 1.06) was found to be improved compared to the estimated overdose ratio (1.07) of the conventional Z-set dosimetry. The present work established the advantages of using the Voronoi Diagram in commissioning dosimetry to ease the dosimetry process.

Solid-state 360° optical beamforming for reconfigurable multicast optical wireless communications.

Optical wireless communication is an attractive technique for data center interconnects due to its low latency line-of-sight connectivity. Multicast, on the other hand, is an important data center network function that can improve traffic throughput, reduce latency, and make efficient use of network resources. To enable reconfigurable multicast in data center optical wireless networks, we propose a novel 360° optical beamforming scheme based on the principle of superposition of orbital angular momentum modes, emitting beams from the source rack pointing towards any combination of other racks so that connections are established between the source and multiple destination racks. We experimentally demonstrate the scheme using solid state devices for a scenario where racks are arranged in a hexagonal formation in which a source rack can connect with any number of adjacent racks simultaneously, with each link transmitting 70 Gb/s on-off-keying modulations at bit error rates of <10-6 at 1.5-m and 2.0-m link distances.

Optimization of source pencils loading plan with genetic algorithm for gamma irradiation facility

The arrangement pattern of source pencils on the source rack determines the quality of the dose field in a gamma irradiation facility. An optimum source loading plan can achieve a uniform dose distribution and utilize the radiation energy with high efficiency. This study proposed a methodology to optimize source loading plans using genetic algorithms. In a case study of a planar source rack which is typically used in most gamma irradiation facilities, the single objective optimization of source loading plans for minimizing dose uniformity ratio was accomplished with simple genetic algorithm, while the multi-objective one for minimizing dose uniformity ratio and maximizing average dose simultaneously was performed with NSGA-II. The loading plans gained by the genetic algorithms resulted in a 16.0% reduction in dose uniformity ratio and an increase of 5.4% in average absorbed dose compared to the probable random plan. The improvement allows the products to absorb the gamma dose more uniformly and utilizing cobalt-60's energy with higher efficiency.

Simulation of the multi-purpose gamma irradiator dose distribution based on the GEANT4 and GPU system

Gamma irradiation systems are used extensively in the industry in order to sterilize medical devices, disinfect hygienic products and increase the shelf life of agricultural products. The method of gamma irradiation is superior to the older methods of heat or chemical treatment because it is by far a simpler operation. In this method, only one parameter, the exposure time is controlled, whereas in the other mentioned methods five or six different parameters need to be controlled. The design of irradiation systems generally includes the size and the location of products, and the arrangement of source rack pencils. In order to optimize the design of the gamma irradiation systems, it is needed to study the product’s dose distribution in a wide range of densities. The Monte Carlo algorithm is an effective way for simulating the irradiation systems which is being used by a variety of codes. Since this method requires a high computation time, it is necessary to speed up the simulation and design the systems by various methods such as using graphics processing units which having a highly parallel design makes them more suitable for algorithms that process a large number of data than central processing units. In this work, a GEANT4-based computational code is developed to adapt on the GPU using the CUDA programming. Since the developed GEANT4-based code utilizes a graphical processor of NVIDIA (in particular a series GTX660 Ti NVIDIA’s GPU), it leads to speed up the process of simulation. Using this computational technique, a IR-136 gamma irradiator is simulated and the results of the simulation are benchmarked against previously published work. In the present work, a new setup of the industrial irradiator system is considered. The results of the simulations using CPU and GPU are compared with the available experimental dosimetry data. The dose calculation in the new setup is significantly faster using GPU in comparison to the GEANT4 code performed by CPU. The system specification used in both the routine GEANT4 code performed by CPU and the GEANT4-based algorithm performed by GPU are the same. The results show that computational speed when using GEANT4-based code with GPU is superior to using GEANT4 code with CPU, and the deviation between the two sets of data is less than 3%. The speed-up factor is averagely about 3300.

Two-Aggregator Topology Optimization Using Single Paths in Data Center Networks

This paper focuses on the data aggregation problem to two aggregators in a data center network under the constraint that each source rack must use a single path to each aggregator. We derive bounds on the approximation ratios of two classes of aggregation algorithms- Restricted 1-Round (R1R) and Restricted 2-Round (R2R). We achieve tighter bounds for the problem with additional constraints on the inputs. We propose another strategy using the 2Chain topology for k = 2, where k denotes the maximum degree of each top-of-rack(ToR) switch (number of uplinks in a ToR switch) in the data center and show that the optimal 2Chain cannot have an aggregation time greater than that of the optimal R1R and R2R topologies. For k ≥ 4, we propose a 1-round aggregation algorithm (1R) that uses trees for aggregation. Experimental results illustrate that 1R, R2R and R1R reduce the aggregation time by up to 85, 67 and 67 percent respectively for k = 4 relative to the two-round aggregation algorithm proposed by Wang et al. Moreover, for k = 2, the 2Chain can reduce the aggregation time up to 42 and 24 percent respectively relative to R1R and R2R.

Optimizing the Gamma Process.

This article will discuss opportunities to improve the efficiency of cobalt-60 (Co-60) utilization within a gamma irradiator. It will show how redistributing the Co-60 within the source rack may lead to improved throughput or dose uniformity within a product. It presents examples of modifications to the equipment within the source pass; these include reduction in the carrier wall thickness and changes to the product stack size. It will discuss the process of scheduling and present ideas of how to optimize both the order of the products and transitions between the products to maximize process efficiencies.

Monte Carlo validation of dose mapping for the Tunisian Gamma Irradiation Facility using the MCNP6 code

In this paper, we develop a three-dimensional configuration of the Tunisian Gamma Irradiation Facility (TGIF) to determine the spatial distribution of gamma absorbed dose rates in the irradiation area at the 60Co source rack. The results are obtained by using the MCNP6 code. Experimental measurements of the gamma absorbed dose rate are performed in order to be compared with the calculated results. Two dosimetry systems are employed to perform measurements: red and amber perpex and cellulose triacetate (CTA). The results of MCNP6 simulations are compared to the absorbed dose measurements for the following experiments: (1) estimation of the 60Co source rack position, (2) isotropy verification of gamma-ray emission, (3) isodose curves of the absorbed dose rate inside the irradiation room, (4) absorbed dose rate distribution in air on four vertical planes, (5) absorbed dose rate distribution in air on four horizontal planes versus increasing distance from the source axis. The root mean square error (RMSE) is employed to check the discrepancy between MCNP6 simulation and dose measurements. The values of RMSE for all experiments vary from 0.5 to 2.6%, showing good agreements between the measured and calculated results. This agreement reveals that the developed model of the TGIF is accurate. It inspires the possibility to use the model on an irradiation processing and a reload of the facility.

Two-Aggregator Topology Optimization Using Multiple Paths in Data Center Networks

This paper focuses on the data aggregation problem to two aggregators in a data center network under the constraint that each source rack must use a single path to each aggregator. We derive bounds on the approximation ratios of two classes of aggregation algorithms– Restricted 1-Round (R1R) and Restricted 2-Round (R2R). We achieve tighter bounds for the problem with additional constraints on the inputs. We propose another strategy using the 2Chain topology for k = 2, where k denotes the maximum degree of each top-of-rack(ToR) switch (number of uplinks in a ToR switch) in the data center and show that the optimal 2Chain cannot have an aggregation time greater than that of the optimal R1R and R2R topologies. For k $\geq$ ≥ 4, we propose a 1-round aggregation algorithm (1R) that uses trees for aggregation. Experimental results illustrate that 1R, R2R and R1R reduce the aggregation time by up to 85, 67 and 67 percent respectively for k = 4 relative to the two-round aggregation algorithm proposed by Wang et al. Moreover, for k = 2, the 2Chain can reduce the aggregation time up to 42 and 24 percent respectively relative to R1R and R2R.

Research and design of the moving system for the cobalt-60 industrial irradiator

On the way of localization of Cobalt-60 industrial irradiators, Research and Development Center for Radiation Technology (VINAGAMMA) has successfully designed and manufactured the first version of Co-60 industrial irradiator, VINAGA1. The second version of Co-60 industrial irradiator has been studied and designed by VINAGAMMA in the frame of the scientific project No. ĐTCB.02/15/TTNCTK. The nucleus of a Co-60 industrial irradiator is a mechanical system inside an irradiation room namely a tote box moving system. This report presents the tote box moving system designed by VINAGAMMA. The tote box moving system contains 52 tote boxes with the dimensions of 50 cm (w) × 70 cm (l) × 150 cm (h) that are moving around the source racks in the manner of 4 passes and 2 levels. The irradiator with this tote box moving system has good specifications: The minimum time of an irradiation cycle is 1h 20 min. and the dose uniformity ratio (DUR) at the product densities of 0.1 g/cm3 and 0.5 g/cm3 is 1.4 and 1.8, respectively. Radiation energy utilization efficiency at the product densities of 0.1 g/cm3 and 0.5 g/cm3 is 19.7% and 48.8%, respectively. These specifications meet the requirements for a multi-purpose Co-60 industrial irradiator and the present irradiation requirements in Vietnam.

Network topology optimisation for data aggregation using multiple paths

In this paper, we develop algorithms for the data aggregation problem which arises in the context of big data applications that employ the MapReduce operation. For the case when source racks can send their data to the aggregator using multiple paths, we show that an aggregation tree topology that minimises aggregation time can be constructed in a polynomial time. We also consider the problem of constructing aggregation trees that minimise total network traffic subject to the primary constraints that the aggregation time is minimised. The heuristics for this problem is presented and the experiments show that allowing multiple paths reduces aggregation time by up to 99% related to the aggregation trees constructed using the LPT rule. This reduction in aggregation time, however, comes with up to 35% increase in total network traffic when the racks have more than two optical links and up to 98% increase in total network traffic when each rack has two optical links.

Retrospective dosimetry with the MAX/EGS4 exposure model for the radiological accident in Nesvizh-Belarus

On October 26, 1991 a fatal radiological accident occurred in a 60Co irradiation facility in the town of Nesvizh in Belarus. Following a jam in the product transport system, the operator entered the facility to clear the fault. On entering the irradiation room the operator bypassed a number of safety features, which prevented him from perceiving that the source rack was in the irradiation position. After the accident average whole body absorbed doses between 8 and 16 Gy have been determined by TLD measurements, by isodose rate distributions, by biological dosimetry and by ESR measurements of clothes and teeth. In an earlier investigation the MAX/EGS4 exposure model had been used to calculate absorbed dose distributions for the radiological accident in Yanango/Peru, which actually represented the simulation of exposure from a point source on the surface of the body. After updating the phantom as well as the Monte Carlo code, the MAX/EGS4 exposure model was used to calculate the absorbed dose distribution for the worker involved in the radiological accident in Nesvizh/Belarus. For this purpose, the arms of the MAX phantom had to be raised above the head, and a rectangular 60Co source was designed to represent the source rack used in the irradiation facility. Average organ absorbed doses, depth-absorbed doses, maximum absorbed dose and average whole body absorbed dose have been calculated and compared with the corresponding data given in the IAEA report of the accident.

Reload of an industrial cylindrical cobalt source rack

This work presents a Monte Carlo study of the cylindrical cobalt source rack geometry of the Tunisian gamma irradiation facility, using the GEANT code developed at CERN. The study investigates the question of the reload of the source rack. The studied configurations consist in housing four new cobalt pencils, two in the upper and two in the lower cylinder of the source rack. Global dose rate uniformity inside a “dummy” product for the case of routine and nonroutine irradiation, and as function of the product bulk density, was calculated for eight hypothetical configurations. The same calculation was also performed for both of the original and the ideal (but not practical) configurations. It was shown that hypothetical cases produced dose uniformity variations, according to product density, that were statistically no different than the original and the ideal configurations and that the reload procedure cannot improve the irradiation quality inside the facilities using cylindrical cobalt source racks.

Monte Carlo studies of the Tunisian gamma irradiation facility using GEANT4 code

This paper describes a complete Monte Carlo study of the Tunisian gamma irradiation facility (CNSTN) using the GEANT4 CERN's code. The work focused on the optimization of the absorbed dose distribution inside the irradiation cell, with and without product. For this purpose, 32 different points at the middle plane of the source rack, 29 positions along Z axis and 7 critical points, were carried out using PMMA dosimeters. Then, to achieve a given bulk density, boxes loaded with “dummy” product were used. Simulated and experimental results are compared and good agreement is observed. It is shown that Monte Carlo simulation improves process understanding, predicts absorbed dose distributions and calculates dose uniformity within product.

Monte Carlo studies of the irradiator geometry of the Portuguese Gamma Irradiation Facility

This paper describes a complete Monte Carlo study of the irradiator geometry of the Portuguese Gamma Irradiation Facility, using the MCNP code. In this work, eight different source rack configurations were simulated. Routine and non-routine irradiations have been studied. For routine irradiations, both the dose per source activity and the dose uniformity remain constant for all source configurations studied. For non-routine irradiations some dependence on source configuration has been found concerning the dose uniformity in the inner rows.

Use of validation dosimetry, in source rack load planning, to improve cobalt irradiation plant efficiency

Source load planning is an important part of optimising the performance of cobalt-60 gamma irradiation plants. The best results are achieved using a complex algorithm to accurately model the radiation profile of the source. In this way operational plant performance may be predicted as a function of changes in activity distribution within the source rack. This paper describes an approach to the prediction of plant performance that is numerically simpler than attempting to calculate actual doses from first principles. It shows how validation dosimetry results can be used to validate the software-predicted dose distribution and details how this enables the load plan to be tailored to meet the specific objectives of the plant operator. Improvements in product throughput and reduced maximum to minimum dose ratios are typical.

Design of YCF-1 mobile γ irradiator

YCF-1 Mobile irradiator is designed by BINE of China. It has been put into running in YanJi city of Jilin province. It is able to be moved to border and distance places and area lumped and spreading out of agricultural products to service. It can play a important role in demonstration and extending irradiation technology in food irradiation, disinfestation, sterilization and quarantine, etc. This paper describes the features and design considerations of mobile irradiator. This irradiator adopted Cesium-137 source. The design capacity of loading source is 9.25PBq (250kCi), A half-time of Cs- 137 is 30.2 years long, exchanging source is not needed utilization rate of energy is higher, and the shielding is thinner, The Weight is lighter, The dose rate on the surface of it is 0.0025mSv/h in accordance with national standard. The internal size of irradiation room is 1800×1800×900mm (L×W×H), The sheilding of irradiation room is a steel shell filled with lead. The thickness of lead is 18cm. The irradiator is installed on a special flat truck. The size of the truck is 7000×3400×4200mm (L×W×H). The weight of irradiator is more than 80 150kw. The main components and parts of irradiator are: source, source racks and hoist, irradiation chamber, storage source chamber, the product's transport system, dose monitoring system, ventilation system and safety interlock system, etc.