How gamma radiation processing systems are benefiting from the latest advances in information technology

This paper discusses how gamma irradiation plants are putting the latest advances in computer and information technology to use for better process control, cost savings, and strategic advantages.

Some irradiator operations are gaining significant benefits by integrating computer technology and robotics with real-time information processing, multi-user databases, and communication networks. The paper reports on several irradiation facilities that are making good use of client/server LANs, user-friendly graphics interfaces, supervisory control and data acquisition (SCADA) systems, distributed I/O with real-time sensor devices, trending analysis, real-time product tracking, dynamic product scheduling, and automated dosimetry reading. These plants are lowering costs by fast and reliable reconciliation of dosimetry data, easier validation to GMP requirements, optimizing production flow, and faster release of sterilized products to market.

There is a trend in the manufacturing sector towards total automation using “predictive process control”. Real-time verification of process parameters “on-the-run” allows control parameters to be adjusted appropriately, before the process strays out of limits. Applying this technology to the gamma radiation process, control will be based on monitoring the key parameters such as time, and making adjustments during the process to optimize quality and throughput. Dosimetry results will be used as a quality control measurement rather than as a final monitor for the release of the product. Results are correlated with the irradiation process data to quickly and confidently reconcile variations. Ultimately, a parametric process control system utilizing responsive control, feedback and verification will not only increase productivity and process efficiency, but can also result in operating within tighter dose control set points.     

Effect of γ irradiation on optical properties of Ce-doped phosphate and silicate scintillating glasses

A set of Ce³⁺ activated silicate- and phosphate-based scintillating glasses were submitted to γ irradiation in the ⁶⁰Co radioisotope source “Calliope” (ENEA-Casaccia in Rome, Italy) in the dose range between 1 and 250 Gy (3.7 Gy/h). The effect of ionising radiation was probed by transmission measurements performed before and after each irradiation on all analysed samples. From these data, the radiation-induced absorption coefficient was calculated, proportional to the density of colour centres induced by irradiation in the solid matrix. Results are discussed by taking into account the possible dependence of radiation hardness on the composition of glass matrix.     

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.     

Theoretical evaluation of dose distribution in product in radiation processing plants

An analytical method has been developed for the computation of dose rates at any number of points in the product material in a radiation processing plant in which radioactive source pencils are arranged in a rectangular vertical frame. Exposures from each individual source pencil and the movement of the product box was taken into consideration for the evaluation of absorbed dose. The validity of the computational method was tested for one of the existing irradiator already in operation. Excellent agreement was achieved between the computation and measured values of doses received by the product material. The method was then applied in the design of a new irradiator and was found very useful to arrive at optimum source size and target size. Hence, this method is being adopted for the design of all forthcoming ⁶⁰Co irradiation plants in India.     

Irradiation plant control upgrades and parametric release

This paper reviews an integrated PC irradiation plant control system which is one of the most advanced available. The system controls the entire irradiation process from ‘goods in’ through to dosimetry and the production of post-irradiation documentation. Product processing speeds are automatically calculated by reference to validation data which ensures that the dose requirements are met. Detailed product tracking and data logging of all plant activities ensures traceability of the entire irradiation process. The paper demonstrates how the system effectively enables parametric release of products since the critical processing parameters are automatically set, monitored and recorded and are directly linked to the validation of these parameters.     

Leakage neutrons and X-rays in a therapeutic microtron facility

Measurements of dose equivalent rate distribution in a medical microtron facility were done for neutrons and X-rays originated from 14 MV or 8 MV X-ray irradiation by the microtron. Measured data are described with empirical formulas for convenience of quantitative reconstruction of the data. A formula consisting of a simple power function agrees well with measured data except for thermal neutrons, and is understood to describe the dose rate separating into the scattered and unscattered components in the case of the point source. The thermal neutron distribution in the maze is described with another formula of an exponential function. A discrepancy was observed between the X-ray distribution in the maze from 14 MV X-ray irradiation and that from 8 MV irradiation. This is estimated to be caused by a contribution of capture gamma-rays increasingly emitted in the case of 14 MV X-ray irradiation.     

Neutron spectrum parameters in irradiation channels of the Nigeria Research Reactor-1 (NIRR-1) for the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-NAA standardization

Summary The first nuclear research reactor in Nigeria has been commissioned for neutron activation analysis and limited radioisotope production. In order to extend its utilization to include the k₀-standardization method, the following neutron spectrum parameters in inner and outer irradiation channels were determined by the “Cd-ratio for multi-monitor method”: the thermal-to-epithermal flux ratio, f, and the epithermal flux shape factor, α. Neutron spectrum parameters determined in the inner irradiation channel B2, are: α = -0.052±0.002 and f = 19.2±0.5. For the outer irradiation channel B4, the neutron spectrum parameters were found to be α = +0.029±0.003 and f = 48.3±3.3. The results are compared with the neutron spectrum parameters of other reactor facilities with similar core configuration such as the Slowpoke and Miniature Neutron Source Reactor facilities available in the literature.     

The operational benefits of integrated PC control of gamma irradiation plants

Compared with the traditional PLC control systems used on many gamma irradiation plants, the semi-intelligent decision making capabilities of a fully integrated PC control system can bring many benefits to the plant operator.

The authors will describe how plant operation is fully automatic with the PC control providing all the input-output data required to run the plant efficiently and safely. Detailed product tracking, with live on-screen data, can be incorporated to give both plant operator and product manufacturer complete confidence in the irradiation process. Advanced features such as on-line diagnostics and mechanical part failure prediction are also described.

Also available is automated dosimetry, reducing the opportunity for human error, whilst at the same time saving on staff costs and providing highly professional dose validation reports and comprehensive routine dosimetry documentation.

The benefits of PURIDEC's PC control system are not only available with its new plants. The system can be supplied as an upgrade to plants of all ages and design giving the current operator all the benefits described in the paper.     

Application of egs4 computer code for determination of gamma ray spectrum and dose rate distribution in gammacell 220

The EGS4 a Monte Carlo electron-photon transport simulation package together with a locally developed computer program “GCELL” has been used to simulate the transport of the gamma rays in Gammacell 220. An additional lead attenuator has been inserted in the chamber, has been included for those cases where lower dose rates were required.

For three cases of 0, 1.35 and 4.0 cm thickness of added lead attenuators, the gamma spectrum, and dose rate distribution inside the chamber have been determined. For the case of no attenuator present, the main shield around the source cage has been included in the simulation program and its albedo effects have been investigated.

The calculated dose rate distribution in the Gammacell chamber has been compared against measurements carried out with Fricke, PMMA and Gafchromic film dosimeters.     

Optimization of electron beam crosslinking of wire and cable insulation

The computer simulations based on Monte Carlo (MC) method and the ModeCEB software were carried out in connection with electron beam (EB) radiation set-up for crosslinking of electric wire and cable insulation. The theoretical predictions for absorbed dose distribution in irradiated electric insulation induced by scanned EB were compared to the experimental results of irradiation that was carried out in the experimental set-up based on ILU 6 electron accelerator with electron energy 0.5–2.0 MeV.The computer simulation of the dose distributions in two-sided irradiation system by a scanned electron beam in multilayer circular objects was performed for various process parameters, namely electric wire and cable geometry (thickness of insulation layers and copper wire diameter), type of polymer insulation, electron energy, energy spread and geometry of electron beam, electric wire and cable layout in irradiation zone. The geometry of electron beam distribution in the irradiation zone was measured using CTA and PVC foil dosimeters for available electron energy range. The temperature rise of the irradiated electric wire and irradiation homogeneity were evaluated for different experimental conditions to optimize technological process parameters. The results of computer simulation are consistent with the experimental data of dose distribution evaluated by gel-fraction measurements. Such conformity indicates that ModeCEB computer simulation is reliable and sufficient for optimization absorbed dose distribution in the multi-layer circular objects irradiated with scanned electron beams.     

Comparative study on degradation of ethylene-propylene rubber for nuclear cables from gamma and beta irradiation

Considering safety is the priority concern of nuclear power plants, equipment qualification testing of the nuclear components manufactured should be paid special attention to. Thereinto, equivalent conversion (1:1) from the absorbed beta doses to gamma doses is a rule of thumb for irradiation qualification testing of the polymers used as nuclear cables, however whether it is reasonable and applicable to Chinese domestic polymers still requires investigation. In this paper, both gamma and beta irradiation testing with the actual dose rates and total absorbed doses in China Advanced Passive (CAP) series nuclear power plant was performed upon one domestically manufactured ethylene-propylene rubber intended for nuclear cable insulation in China. The mechanical and the electrical properties before and after irradiation were measured to compare the extent and the trend of degradation between the two irradiation types, and related oxidation degradation mechanism especially its attenuation along the thickness was quantitatively addressed.     

UTAB: a computer database on residues of xenobiotic organic chemicals and heavy metals in plants.

The UTAB Database contains information concerned with the uptake/accumulation, translocation, adhesion, and biotransformation of both xenobiotic organic chemicals and heavy metals by vascular plants. UTAB can be used to estimate the accumulation of chemicals in vegetation and their subsequent movement through the food chain. The database contains actual data from papers in the published literature dating from 1926 for organic chemicals and from 1976 for heavy metals. At present the database is comprised of more than 37,000 records pertaining to 900 different organic chemicals, 21 heavy metals, and over 350 plant species. Each record contains information on a single combination of species, chemical, and dose. Other information includes the application and destination sites, amount accumulated, rates of uptake or translocation, products and sites of biotransformation, experimental condition parameters, and the source paper. Thus, the database can be used to quickly obtain specific data pertaining to a chemical, plant species, mine spoil, etc. or it can be used for the comparative analysis of a set of data pertaining to groups of chemicals and plants.     

Standardization and regulatory control on radiation processing dosimetry in China

In 1983, in order to suit the rapid development of radiation processing, a programme of high dose standardization was initiated in China. As a result, a high dose measurement system for gamma - rays including primary standards, transfer standards and working dosimeters, has been established. In this paper, the scheme of dosimetry traceability to national standards for gamma - rays is illustrated. The aspects of standardization and the progress of dosimetry of radiation processing are also outlined.

In order to implement “the Law on Metrology of the Peoples Republic of China” and to guarantee the product quality of radiation processing. SBTS and SCTS have jointly issued “the Provisional Regulation of Metrological Supervision and Management for Radiation Processing”. A series of national standards, verification regulations and technical norms have been enacted and issued on the radiation processing dosimetry and on the approval of irradiation facilities. These documents are expected to play significant roles in the dose measurement standardization and the regularity control.     

Advancements in internationally accepted standards for radiation processing

Three subcommittees of the American Society for Testing and Materials (ASTM) are developing standards on various aspects of radiation processing. Subcommittee E10.01 “Dosimetry for Radiation Processing” has published 9 standards on how to select and calibrate dosimeters, where to put them, how many to use, and how to use individual types of dosimeter systems. The group is also developing standards on how to use gamma, electron beam, and x-ray facilities for radiation processing, and a standard on how to treat dose uncertainties. Efforts are underway to promote inclusion of these standards into procedures now being developed by government agencies and by international groups such as the United Nations' International Consultative Group on Food Irradiation (ICGFI) in order to harmonize regulations and help avoid trade barriers.

Subcommittee F10.10 “Food Processing and Packaging” has completed standards on good irradiation practices for meat and poultry and for fresh fruits, and is developing similar standards for the irradiation of seafood and spices. These food-related standards are based on practices previously published by ICGFI.

Subcommittee E10.07 on “Radiation Dosimetry for Radiation Effects on Materials and Devices” principally develops standards for determining doses for radiation hardness testing of electronics. Some, including their standards on the Fricke and TLD dosimetry systems are equally useful in other radiation processing applications.     

A theoretical model to improve the design of gamma irradiators

Improvement in the design of the source and the transport system in a multipurpose gamma irradiation plant is of fundamental importance. With this in mind we propose the implementation of a mathematical model permitting the improved design of gamma irradiators as a function of the efficiency of the facility and the parameters of the irradiation process. A linear relationship between the height of the container and the dose ratio can be deduced from the analysis of the results. Such relationship provides a useful and economic tool for calculating the most advantageous dimensions of the source and the volume of the material to be irradiated.     

Effect of gamma radiation on wheat plant growth due to impact on gas exchange characteristics and mineral nutrient uptake and utilization

The experiment was conducted to determine the effect of gamma radiation on plant growth and development, flag leaf gas exchange characteristics such as net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) and activity of key carbon and nitrogen assimilating enzymes like Rubisco, starch synthase (SS) and nitrate reductase (NR) in field grown wheat. Grains of cultivar PBW-343 were exposed to a ⁶⁰Co (Cobalt-60) gamma source at a dose range from 0 to 500 Gy (Gray). Gas exchange characteristics of flag leaf were measured using Infrared Gas Analyzer (IRGA), while mineral nutrients were analyzed spectrophotometrically. Our results show that an irradiation treatment, in general, caused an improvement in plant growth and yield characteristics such as shoot and root mass, root length and surface area, leaf area and chlorophyll SPAD index, tiller number and grain yield. However, irradiation exceeding 5 Gy reduced the magnitude of radiation advantage for most of the investigated physiological and biochemical traits. No germination was recorded at 500 Gy irradiation dose. A dose-dependant increase in shoot Fe in radiated plants up to 25 Gy reflected its higher plant root to shoot translocation which may yield micronutrient rich grains. At higher dose of 100 Gy, there was a drastic reduction in flag leaf membrane stability index (MSI), photosynthesis, Rubisco, NR, and nutrients like K, P, Mg, Fe, and Zn. Starch synthase enzyme activity was unaffected by gamma irradiation indicating that the negative effect of high dose (100 Gy) on the grain yield were caused by the adverse effect of radiation on the gas exchange attributes particularly photosynthesis, carbon, and nitrogen assimilation efficiency and the plant uptake of mineral nutrients. The study concludes that gamma radiation at a low dose (25 Gy or lower) stimulates, while a high dose (100 Gy and above) inhibits plant growth and development of wheat. The adverse effect at 100 Gy and beyond could be attributed to the poor carbon and nitrogen assimilation efficiency and the plant uptake of mineral nutrients, all of which are the ultimate determinant of plant health.     

Predictive aging results in radiation environments

We have previously derived a time-temperature-dose rate superposition methodology, which, when applicable, can be used to predict polymer degradation versus dose rate, temperature and exposure time. This methodology results in predictive capabilities at the low dose rates and long time periods appropriate, for instance, to ambient nuclear power plant environments. The methodology was successfully applied to several polymeric cable materials and then verified for two of the materials by comparisons of the model predictions with 12 year, low-dose-rate aging data on these materials from a nuclear environment. In this paper, we provide a more detailed discussion of the methodology and apply it to data obtained on a number of additional nuclear power plant cable insulation (a hypalon, a silicone rubber and two ethylene-tetrafluoroethylenes) and jacket (a hypalon) materials. We then show that the predicted, low-dose-rate results for our materials are in excellent agreement with long-term (7–9 year) low-dose-rate results recently obtained for the same material types actually aged under bnuclear power plant conditions. Based on a combination of the modelling and long-term results, we find indications of reasonably similar degradation responses among several different commercial formulations for each of the following “generic” materials: hypalon, ethylene-tetrafluoroethylene, silicone rubber and PVC. If such “generic” behavior can be further substantiated through modelling and long-term results on additional formulations, predictions of cable life for other commercial materials of the same generic types would be greatly facilitated.     

Flux calculation in LSNAA using an <Superscript>241</Superscript>Am-Be source

The CITATION code based on neutron diffusion theory is used for flux calculation inside voluminous sample in prompt gamma activation analysis with an isotopic neutron source (²⁴¹Am-Be). The code used the specific parameters related to energy spectrum source, irradiation system materials (shielding, reflector, etc.), geometry and elemental composition of the sample. The flux distribution (thermal and fast) was calculated on three-dimensional geometry for the system: source, air, and polyethylene and water cylindrical sample of 125 liters. The thermal flux was calculated in series of points inside the sample, and agreed with the results obtained by measurements with good statistical uncertainty. The maximum thermal flux was measured at distance of 4.1 cm and calculated at 4.3 cm by the CITATION code. Beyond a depth of 7.2 cm, the ratio of thermal flux to fast flux increases up to twice and allows us the optimization of the detection system in the scope of in-situ PGNAA.     

Numerical simulation of annealing of dose effects in radiation-induced conductivity of polymers

Numerical simulation of dose effects in radiation-induced conductivity in polymers and of roomtemperature annealing of these effects was performed in the formalism of the generalized Rose-Fowler-Vaisberg model, which allows for bipolar electron transport of charge carriers and for generation of radiationinduced traps. It was shown that neither the distinct dose effect nor its long annealing time can be explained unless the radiation-chemical aspect of irradiation is taken into account. It was found that satisfactory fit of theoretical prediction to published data for a number of polymers (PS, PET, LDPE, polyvinylcarbazole) can be achieved in the case of the reasonable choice of the parameter for the injection of radiation-induced traps (free radicals), although certain difficulties are met. This coincidence is attainable if the other parameters of the model are fixed and their values have been determined in independent experiments.