Intercomparative study on low energy electron beam dosimetry

Studies of dose intercomparison and dose estimation of low energy electron beams from 150 to 300 keV have been conducted to unify and standardize the methods of dosimetry and dose estimation as an activity of Low-Energy Electron-Dose Measurement Committee which started in Japan in 1985. The transfer dosimetry with thin film dosimeters by mail was found to be useful for dose intercomparison between irradiation plants and unification of dose estimation methods. A simple dose calculation formula as a function of basic irradiation parameters, proposed for rough dose estimation, was also checked on the basis of the result of the dose intercomparison.     

小剂量电离辐射对生物体的作用

本文调研了国内外有关小剂量电离辐射对生物体作用的实验研究。许多实验结果指出,辐射引起生物体近期辐射损伤的阈值一般不低于01Gy,并且小剂量电离辐射对机体免疫功能有促进作用,小剂量预辐照后能对大剂量辐照产生适应性。因此,有学者提出小剂量有益的观点,很具有启发性。然而由于对小剂量辐射生物效应的资料掌握不够,对小剂量照射还需要继续进行深入的研究。     

D.C.-electrical conductivity as a method for monitoring radiation curing of unsaturated polyester resins-II. Influence of electrical field and dose rate

The course of radiation crosslinking of unsaturated polyester resins was followed by measuring electrical conductivity change. Both the electrical field strength and dose rate influenced the crosslinking. The electrical field somewhat increased the reaction rate possibly due to the orientation of a polar polyester chains. To investigate the effect of electrical field, the samples were irradiated to different doses at different field strengths, from 2.5 to 250 kV/m and then extracted in benzene to determine the extent of crosslinking. The extraction analysis of irradiated samples confirmed the influence of electrical field observed in conductivity measurements. The electrical field effect depended on the dose rate. Three dose rates were applied 3.05, 0.354 and 0.096 kGy/h. The medium dose rate gave the highest reaction rate (on dose scale). Faster decrease of free styrene content with radiation dose than increase of gel content at higher dose rate implies partial styrene graftng or homopolymerization. The higher the electrical field the more pronounced were the effects of dose rate.     

湖北省国控点天然γ辐射空气吸收剂量率研究

使用我国新一代X-γ剂量率测量仪对湖北省9个国控点进行了天然γ辐射空气吸收剂量率的测量,建立了剂量率与剂量当量的数学模型,计算了9个国控点地区人均年有效剂量当量。结果表明,9个国控点地区的剂量率在59.336～141.638 nGy/h,天然γ辐射致公众人均年有效剂量当量为0.390～0.931 mSv;9个国控点地区天然γ辐射均属正常天然本底水平。     

环氧树脂E-44的电子束固化研究

涂层的传统固化方法是热固化,此种固化过程耗时长达数十小时,生产效率很低,电子束固化是以电子加速器产生的电子束(EB),对样品进行辐照,使其固化的过程,与热固化相比,它有许多优越性,如电子束固化涂料体系时,树脂不需要溶剂的稀释,产生挥发性有机物质少,环境污染小;     

Kinetics of diffusion-free radiation graft polymerization of styrene onto polyethylene

The diffusion-free radiation graft polymerization of styrene onto polyethylene has been studied. The grafting rate shows a dependence on monomer which is far different than what has been assumed. Further, the dependence on monomer changes with increasing dose rate as does the dependence of grafting rate on radiation dose rate. Three different regions of behavior are defined: (1) a region of low dose rate where the grafting rate is 1/2-order in dose rate and 3/2-order in monomer; (2) a region of intermediate dose rate where the grafting rate is intermediate between 1/2-and zero-order in dose rate and 5/2-order in monomer; and (3) a region of high dose rate, where the grafting rate is independent of dose rate and at least 5/2-order in monomer. Various possible mechanisms responsible for these effects are discussed, including the effects of viscosity on the initiation and termination reactions, the possibility of ionic graft polymerization, and energy transfer.     

Natural indoor gamma background in Coonoor environment of South India

Indoor natural radiation dose existing in dwellings of Coonoor have been estimated using thermoluminescent dosimeters. TLDs are displayed in indoors and are replaced after three-month period. The seasonal averages of the dose rate and the annual effective dose equivalent are calculated from the measured results. Geographical and seasonal variations as well as the differences between indoor to outdoor dose rates have also been studied. Very good correlation exists between the indoor dose rates measured by TLD and environmental radiation dosimeter with correlation coefficient of 0.91. The annual effective dose equivalent to the Coonoor population due to indoor gamma radiation was estimated to be 970 mSv/y for the period of 1997–1998.     

Use of maximum temperature for correction of alanine dosimetry in electron beams

Alanine dosimetry is well characterized for irradiation temperature response. In use, alanine absorbed dose response is corrected for the irradiation temperature. The temperature used to correct alanine dosimetry absorbed dose response in electron beams has historically been the mean temperature occurring during irradiation (Sharpe and Miller, 2009). At lower absorbed doses, the change in temperature is relatively low; thus the absorbed dose response correction due to temperature is small. However, industrial electron beam processing often requires higher absorbed dose measurements where the change in temperature can be very large and the corresponding dose response correction for alanine becomes significant. This paper compares the impact of the temperature correction based on the use of a mean irradiation temperature (Sharpe and Miller, 2009) versus the use of a maximum irradiation temperature on the absorbed dose measurement. The results of this comparison indicate that the use of a mean temperature correction for higher absorbed doses measured with temperature corrected alanine dosimetry introduces a bias in the absorbed dose estimate.     

Investigation on the electron-beam curing of vinylester resin

A typical vinylester resin, Derakane 411-350, was electron-beam (EB) cured without initiators. The curing process was investigated by gel-fraction testing, FTIR and Raman spectroscopies. Both dynamic numerical analysis and positron annihilation life spectroscopy were utilized to analyze the microstructure of resin samples irradiated with different doses and dose rates. Resin irradiated with the same dose at a low dose rate achieved a higher degree of cure than those samples irradiated with a high dose rate. Resin irradiated with low dose rates had a lower free-volume fraction with smaller interstices and a more uniform microstructure. The glass-transition temperature of the resin increased with increasing irradiation dose. The mechanical properties of the EB-cured resin confirmed the analysis of changes in microstructure arising from irradiation.     

The operator dose assessment of landmine detection systems using the neutron backscattering method

Personal safety issue is one of the major limitations in landmine detection by nuclear techniques. In this paper, the dose rate received by the operator of different hand-held landmine detection systems using the neutron backscattering method was investigated. Monte Carlo method was used to simulate a computational model of the body, instruments with different shielding configurations and soil with various moisture contents. The effective dose received by the different organs of the operator has been estimated by using two different approximation methods including average equivalent dose and dose equivalent assessment. The results obtained by these two methods were compared. The common results showed that the operator dose rate depends on the facility shielding, soil moisture level, and source-to-operator distance. Also, although the absorbed dose received by most organs generally decreases as a function of source to operator distance, for some organs such as kidneys and lungs it firstly increases when source-to-operator distance increases up to 0.7–1.2 m and after that the absorbed dose decreases. Furthermore, the results showed that the effective dose received by the operator has its maximum value when the source to operator distance is 0.60 m.     

THE THEORY OF PHOTODYNAMIC THERAPY DOSIMETRY: CONSEQUENCES OF PHOTO-DESTRUCTION OF SENSITIZER

Photodynamic dose is defined as the area under the curve of sensitizer level plotted as a function of light dose. This is a photochemical definition of dose. We will show that this definition is useful in predicting photobiological response. The photodestruction of sensitizer during photodynamic therapy is shown to result in an upper limit on the photodynamic dose which can be delivered by an unlimited light dose. This limit results in the opportunity to make total photodynamic dose uniform to considerable depths (one to two centimeters). The existence of thresholds for permanent tissue damage allows protection of normal tissue from the large light doses required to achieve this limiting dose deep in the tissue. Higher sensitizer levels in the tumor permit tumor destruction while the normal tissues are protected. A clinical trial to determine the proper level of injected dose necessary for these results is required. This theory of photodynamic therapy (PDT) dosimetry is tested in the DBA-SMT experimental mouse tumor system. Combinations of drug and light which are not reciprocal but are nearly equal by this theory are shown to give equivalent tumor control at seven days post treatment. Reciprocal combinations of drug and light fail to give equivalent results when they ae selected using the theory to choose a combination where reciprocity should fail.     

Neutron and gamma ray doses from a 252Cf brachytherapy source in a water phantom

Axial and radial doses of Neutrons and gamma rays from an Isotron ²⁵²Cf Brachytherapy source were calculated in a Water phantom using Maienshein’s prompt fission gamma rays data and Maxwellian neutron energy spectrum. It was observed that neutron dose due to the source casing thickness does not contribute significantly to the total dose. Further the calculated secondary gamma ray dose rate is very small compared to the calculated primary gamma dose rate. Neutron and secondary gamma ray dose calculated in this study agree with the published data. Results of this study will be presented here.     

Poly(N-vinylpyrrolidone) hydrogels: 1.Radiation polymerization and crosslinking of N-vinylpyrrolidone

POLY(N-VINYLPYRROLIDONE) HYDROGELS: 1 RADIATION POLYMERIZATION AND CROSSLINKING OF N-VINYLPYRROLIDONE). The effects of irradiation dose on the conversion of vinylpyrrolidone (VP) with various concentration and other characteristics such as Gelation Dose (Dg), Degree of Swelling (DS) and Equilibrium Water Content (EWC) have been investigated. Aqueous solution of vinylpyrrolidone with several concentrations such as 5, 10, 20, 40, 60, 80 and 100 Wt % were irradiated by using gamma rays of Cobalt-60 source with a dose rate of 0. 139 Gy/s. After irradiation, parameters such as conversion of vinylpyrrolidone, gelation dose, degree of swelling, and equilibrium water content were analyzed. Results show that the conversion of VP to PVP was almost 100% at a dose of 2 kGy. The gelation dose of PVP depends on initial content of monomer. Degree of swelling of gels with concentration of 10 % was 55 at the dose of 10 kGy and 30 at the dose of 40 kGy. The lowest value of degree of swelling is 15. At the range of irradiation dose of 10 to 40 kGy the EWC of gel was found to be 98 to 94 %.     

Dose dependence of the radiothermoluminescence intensity of polyethylene crystalline regions

The dose dependence for the intensity of all radiothermoluminescence peaks of polyethylene crystalline regions has been studied in the dose (D) range of 1.3?C30 kGy. The initial portion of the dose dependence curve at doses below 5 kGy has the same pattern for all the peaks; the first derivative is dI/dD > 0 at D = 0 and only decreases with the dose. This type of the dependence suggests that charge traps present in the polymer (in intracrystalline regions) at low doses have existed before irradiation. These traps can be regular segments of polymer chains in the crystalline regions. As the dose increases, radiation-induced traps appear and the dose dependence curves for peak intensities become dissimilar. Some of them show a decrease in intensity with the dose, others reach a limiting value and further do not vary in intensity, and the third ones display a permanent intensity rise.     

聚乙烯醇的强化辐射交联

通常γ-辐照裂解的聚乙烯醇(PVA)在N·N’-甲基丙烯酰胺(BAM)存在下可以辐射交联。BAM/PVA体系的辐射效应可大致依辐照剂量的增加划分为三个阶段:强化辐射交联为主区,强化辐射交联与辐射裂解相抵区和辐射裂解优势区。强化辐射交联区的溶胶分数S与辐照剂量D的关系可表示为: S=(1 (1/(1-K))D_g~(2=K))-(D_g/(1-K))D~(1-K) =A-BR~(1-K)式中,D_g为凝胶化剂量;K是与BAM含量相关的常数。     

Structure property relationship of ethylene vinyl acetate copolymer grafted with triallyl cyanurate by electron beam radiation

Electron beam (EB) initiated grafting of triallyl cyanurate (TAC) onto ethylene vinyl acetate (EVA) containing 12% vinyl acetate has been carried out over a range of irradiation doses (20–200 kGy) and concentrations of TAC (0.5–5%). The grafting level, as determined from IR spectroscopy, does not change with the radiation dose at 0.5% TAC. With increase in TAC level the grafting level increases at 50 kGy dose. The gel content increases with radiation dose in the initial stage, whereas it changes marginally with the TAC level. With the increase in radiation dose or TAC level, the crystallinity decreases. The interplanar distance or the interchain distance of the grafted polymer does not change with dose or TAC level. The tensile strength is maximum at 0.5% TAC level and at the 50 kGy dose. The dielectric loss shows a maximum at 50 kGy dose and at 0.5–1.0% TAC level due to changes of polarity and the carrier chain mobility.     

Application of the ESR spectroscopy to estimate the original dose in irradiated chicken bone

The paper discusses the results of an investigation aimed to use the ESR spectroscopy as a quantitative procedure to estimate the original dose in irradiated chicken. The time stability of the ESR signal was at first carried out, to obtain a correction factor to be applied to the dose estimated with the added dose method. Our results show that this procedure gives an estimation of the original dose within ±25%.     

EFFECT OF RECEIVER ORIENTATION ON ERYTHEMA DOSE1,2

-The analysis of solar erythema dose under changing ozone amount, previously confined to the study of horizontal surfaces, is extended to include the effects of receiver orientation. A semi-empirical model is used to calculate erythema (sunburn) dose for non-horizontal plane areas under cloudless conditions as a function of latitude, season, and ozone amount. According to the model, in middle and high latitudes, surfaces with inclination angles (α) up to 45° receive at least 80% of the daily erythema dose received by a horizontal surface. Much larger reductions in daily erythema dose occur for α > 45°. which can result in a significant reduction in the latitudinal gradient of erythema dose. The amplification factor for erythema dose (Δdose/ΔO₃) varies significantly with latitude, but it is only weakly dependent upon receiver orientation. Additional calculations indicate that the amplification factor may be significantly larger for skin cancer than for erythema.     

In vivo biological behavior of 99mTc(CO)3 labeled fullerol

The increase of environmental radiation dose rate during rainfall at environmental monitoring posts (MPs) was calculated by using the correlation relationship with the dose rate at the neighboring MP. The calculated dose rate agreed with the observed one within less than 20% of the maximum increase height of the observed one for each rainfall. Furthermore, when the dose rate increased due to Krypton-85 (⁸⁵Kr) discharged from the Tokai Reprocessing Plant (TRP) at the environmental monitoring station (MS) downwind of the stack during rainfall, the dose rate due to the ⁸⁵Kr was tried to discriminate. The discriminated dose rate agreed with that calculated by the atmospheric dispersion calculation code system, SIERRA-II, using stack monitor data and local meteorological observation data.     

Effects of low dose 3H contamination on bone marrow cells of rat

Changes induced in the bone marrow cells of rats internally contaminated with tritiated water were studied by intracellular thymidine incorporation, the reduced glutathione content and the peroxide level, for the low dose irradiation domain: 0–35 cGy with dose rates in the range of 0.03–4 cGy/day. For doses below 10 cGy, the DNA precursor incorporation decreased but the reduced glutathione content and the lipoperoxides level were preserved at the control level, no matter what dose rate was used. For doses higher than 10 cGy, the thymidine incorporation has decreased irrespective of the dose rate, while the peroxides content increased with increasing dose rate.