Analyzing physical characteristics and shielding efficiency for non-lead medical radiation shielding sheets improved using PMMA

ABSTRACT

Recently, the research for replacing heavy lead goods, such as medical radiation shielding sheets with environmentally friendly shielding materials has been widely carried out. The use of tungsten injected into the base material of polyethylene resin may be a good alternative for manufacturing lightweight shielding sheets. However, the increase of the mass ratio of tungsten in the shielding sheets is accompanied by the degradation of their physical properties such as tensile strength and flexibility. In this report, we have tried to fix this problem by adding Polymethyl Methacrylate (PMMA) to the mixing process of materials. If the portion of the added PMMA is 20%, it leads to a 25% increase of the particle packing ratio while there is a simultaneous 28% enhancement of tensile strength compared to before adding it. In the final test for shielding efficiency, it also turned out that the increase of the particle packing ratio for tungsten exhibits the same shielding efficiency as that of 0.2?mmPb. This consequence may imply that mass production of sheets that can prevent scattering rays in the medical radiation frequency range is possible through the calender process using a 0.3?mm tungsten sheet.     

光学窗口电磁屏蔽性能分析与验证

为分析不同基底材料光学窗口电磁屏蔽性能,以Kohin的等效薄膜模型为基础,考虑电磁波在材料2个界面中的多次反射和折射,得到电磁波界面反射系数,利用matlab编写程序计算相同网栅、不同厚度、不同材料的屏蔽效率曲线,分析了厚度和材料对光窗屏蔽效率的影响。为验证仿真数据的准确性,在ZnS基底上制作了周期为500 μm、线宽为15 μm,电阻≤20 Ω的测试样片,测试其在8 GHz～18 GHz频段的电磁屏蔽效能。通过对比可看出:测试与理论计算数据较符合,误差约为2 dB～4 dB,计算数据可以预估光学窗口电磁屏蔽性能,为后续的设计工作提供参考。     

An international perspective on radiological threats and the need for retrospective biological dosimetry of acute radiation overexposures

The widespread use of ionizing radiation sources (machine-generated or from the decay of radioactive materials) across many disciplines including medicine, industry, and academia, has led to hundreds of instances in which one or more persons received an acute radiation overexposure. Successful medical diagnosis and management of these victims rested in part on a rapid, accurate determination of absorbed dose, which in many cases must be retrospective, due to the paucity of useful dosimetry data. This has led to the development of a number of biological dosimetry techniques to determine absorb dose retrospectively. The frequency of these accidental overexposures, however, has failed to serve as the impetus for the development of a cadre of experts in this field and an expansion in the number and availability of centers to perform the more sophisticated analysis necessary to accurately determine absorbed dose. Meanwhile, the world has seen an increase in the number of lethal terrorist events with time and there is realistic concern that the perpetrators of these events strongly desire to employ the specter of acute radiation overexposure in the future to induce mass panic in their target population. To that end, if any of these organizations achieves success, the existing capacity for rapid, accurate retrospective determination of absorbed dose may be overwhelmed, resulting in sub-optimal outcomes for the victims of such an event and potential mismanagement of medical resources designated for their care. This paper reviews existing techniques for retrospective biological dosimetry and diagnosis in relation to past experiences with overexposures, explores potential malevolent overexposure scenarios, and examines the need for public authorities to enhance national capabilities in light of the growing risk of an incident that will result in multiple acute radiation overexposures.     

Overview of novel techniques for radiation protection and dosimetry

Generally, the main approaches for assessing the radiation protection (RP) quantities in neutron fields are: i) the use of an instrument with a response to the protection quantity quasi-independent of energy; ii) neutron spectrometry; iii) microdosimetry.The techniques based on the first approach include rem-meters, superheated emulsions and the electronic personal dosemeters. Passive rem-meters have recently been developed for assessing the ambient dose equivalent in pulsed neutron fields around particle accelerators for hadrontherapy and research. Most of these instruments are characterised by a response extended to high-energies (up to a few GeV). An example is given by the GSI-ball, which employs a pair of LiF TLDs as a thermal neutron detector. It is likely that passive instruments will play a fundamental role also for monitoring the neutron fields generated by ultra-high intensity lasers, where the duration of a single pulse is of the order of hundreds femtoseconds.Arrays of tissue-equivalent proportional counters (TEPCs) of a millimetric/sub-millimetric physical size have been developed both for assessing the quality of therapeutic radiation beams and for estimating the RP quantities in low-intensity fields, which may limit the use of conventional microdosemeters. Very satisfactory results were obtained with GEM-based TEPCs and gas microstrip detectors (GMDs). Moreover, mini-TEPCs have been constructed and tested for measuring the quality of hadrontherapy beams (BNCT included). Silicon microdosemeters have also been demonstrated to be very promising for characterizing proton and ion beams for radiation therapy and for estimating the occurrence of single event effects in space applications.     

Radiotherapy out-of-field dosimetry: Experimental and computational results for photons in a water tank

The first objective of this work was to check and select a set of four kinds of passive photon, dosimeters (two thermo-luminescence dosimeter (TLD) types, one radiophotoluminescence (RPL) dosimeter and one optically stimulated luminescence (OSL) dosimeter) together with a common measurement protocol. Dosimeters were calibrated in a reference clinical linear acccelerator beam in a water tank at a reference facility at the Laboratoire National Henri Becquerel (CEA LIST/LNE LNHB, Saclay. Radiation qualities of 6, 12 and 20 MV were used with standard calibration conditions described in IAEA TRS 398 and non-standard conditions. Profile and depth dose ion chamber measurements were also made to provide reference values. Measurements were made in a water tank into which pipes could be inserted which held dosimeters in pre-determined and reproducible positions. The water tank was built to enable investigation of doses up to 60 cm from the beam axis. A first set of experiments was carried out with the beam passing through the tank. From this first experiment, penumbra and out-of-field dose profiles including water and collimator scatter and leakage were found over three orders of magnitude. Two further sets of experiments using the same experimental arrangement with the beam outside the tank, to avoid water scatter, were designed to measure collimator scatter and leakage by closing the jaws of the collimator. Depending on the energy, typical leakage and collimator scatter represents 10–40% and 30–50% of the total out-of-field doses respectively. It was concluded that all dosimeters can be used for out-of-field photon dosimetry. All show good uniformity, good reproducibility, and can be used down to low doses expected at distances remote from the subsequent radiotherapy target volume.     

Signal processing for radiation dosimetry using EPR in dental enamel: comparison of three methods

We are reporting an alternative method of extracting useful dose information from complex EPR spectra of dental enamel. Digital differentiation of the initial first derivative spectrum followed by filtering is used to clearly distinguish the radiation-induced signal from the native background signal. The peak-to-peak height of the resulting second derivative of the signal is then measured as an indication of absorbed dose. This method does not require preliminary elimination of the native background signal, and is not effected by any uncertainty in the determination of the background signal or by errors resulting from the subtraction of two signals of comparable magnitude. Ten enamel samples were irradiated with known doses in the range of 250–10⁵ mGy. There was agreement for all the samples, within the typical experimental error of ±10% for EPR dosimetry in dental enamel, between the doses determined by two common techniques using native signal subtraction and the doses determined by the new second derivative method proposed here.     

Correlation between mechanoluminescence and lyoluminescence in gamma-irradiated KBr:Ce3+ phosphor for radiation dosimetry

Comparative study of mechanoluminescence (ML) and the lyoluminescence (LL) of γ-irradiated coloured powder of KBr:Ce³⁺ (0.1–10 mol%) phosphor is reported in this paper. Correlation between mechanoluminescence and lyoluminescence is observed, based on the formed colour centre due to γ-irradiation. All samples were prepared by a wet-chemical method. Single isolated ML and LL glow curve is observed in all samples. The variation of peak ML and LL intensities with gamma rays exposure and with different concentration of Ce³⁺ doped in KBr:Ce³⁺ is studied. The ML and LL intensities are found to be dependant on concentrations of Ce³⁺ and gamma radiation dose. The variation of peak ML and LL intensities of KBr:Ce³⁺ (0.5 mol%) with different gamma dose is found to be sublinear upto 1.5 kGy high dose and then the intensity becomes saturated. Negligible fading in the prepared sample is observed.     

TL and OSL dosimetric properties of Opal gemstone for gamma radiation dosimetry

In this work, the response of the natural material Opal was studied in relation to its thermoluminescence (TL) and optically stimulated luminescence (OSL), after exposure to the gamma radiation of a ⁶⁰Co source. The structure of the powdered Opal was verified using the X-ray diffraction, scanning electronic microscopy and energy-dispersive X-ray spectroscopy techniques. The material, in its stone form, was turned into powder and mixed to Teflon (also in powder) in three different concentrations, and then pellets were manufactured. The aim of this work was to evaluate the response of these pellets in high-doses of gamma radiation beams, and to observe their possible application as dosimeters, using the TL and OSL techniques. The dosimetric properties of the samples were analyzed by means of different tests, as: TL emission curves and OSL signal decay curves, reproducibility of TL and OSL response, minimum detectable dose, TL and OSL dose–response curves (5 Gy–10 kGy), and fading. The results obtained in this work, for the TL and OSL phenomena, demonstrated that the pellets of Opal + Teflon present an adequate performance e possibility of use as dosimeters in beams of high-dose gamma radiation.     

Synthesis of titanium boride nanoparticles and fabrication of flexible material for radiation shielding

A numerical simulation for a radio frequency (RF) thermal plasma torch was carried out to identify the temperature and velocity distributions and determine the optimal design of a plasma system based on the coil turn and torch inner diameter parameters. Then, the optimized conditions of five coil turns and a torch inner diameter of 64 mm were applied to synthesize titanium boride nanoparticles. The major crystal structure of the synthesized titanium boride nanoparticles was TiB₂, with TiB as a minor phase and an average particle size of 42 nm. Subsequently, the gamma-ray shielding performance was analyzed using synthesized titanium boride nanoparticles. Flexible shielding materials were fabricated using a hydrogel to load the synthesized nanoparticles. The attenuation coefficient of the titanium boride nanoparticle flexible material was 0.238 cm⁻¹, and the half-value layer was 2.91 cm.     

辐照和电流注入下电缆耦合响应的计算

 采用传输线模型,利用时域有限差分方法计算了辐照和电流注入两种试验环境中电缆屏蔽层电流对芯线的耦合响应,并对响应规律进行了研究。计算结果表明：电流注入时近端负载电压峰值最小,辐照时次之,电流注入时远端最大;负载电压峰值、负载能量与屏蔽层电流源幅度等比例变化;相比较前沿的变化而言,改变屏蔽层电流源前沿对负载电压峰值和负载能量的影响不大;屏蔽层电流源半高宽较小时,负载电压峰值、负载能量与半高宽是非线性关系,屏蔽层电流源半高宽较大时,负载电压峰值、负载能量与半高宽成线性关系;电缆较短时,改变电缆长度对负载电压峰值有影响,而电缆较长时,只会影响电缆负载能量。     

辐照和电流注入下电缆耦合响应的计算

采用传输线模型,利用时域有限差分方法计算了辐照和电流注入两种试验环境中电缆屏蔽层电流对芯线的耦合响应,并对响应规律进行了研究。计算结果表明：电流注入时近端负载电压峰值最小,辐照时次之,电流注入时远端最大;负载电压峰值、负载能量与屏蔽层电流源幅度等比例变化;相比较前沿的变化而言,改变屏蔽层电流源前沿对负载电压峰值和负载能量的影响不大;屏蔽层电流源半高宽较小时,负载电压峰值、负载能量与半高宽是非线性关系,屏蔽层电流源半高宽较大时,负载电压峰值、负载能量与半高宽成线性关系;电缆较短时,改变电缆长度对负载电压峰值有影响,而电缆较长时,只会影响电缆负载能量。     

Monte Carlo calculations of the energy deposited in biological samples and shielding materials

The energy deposited by gamma radiation from the Cs-137 isotope into body tissues (bone and muscle), tissue-like medium (water), and radiation shielding materials (concrete, lead, and water), which is of interest for radiation dosimetry, was obtained using a simple Monte Carlo algorithm. The algorithm also provides a realistic picture of the distribution of backscattered photons from the target and the distribution of photons scattered forward after several scatterings in the scatterer, which is useful in studying radiation shielding. The presented method in this work constitutes an attempt to evaluate the amount of energy absorbed by body tissues and shielding materials.     

Thermoluminescence characterization of functionalized grafted polymers and its application for radiation dosimetry at low doses

Functionalized polymers were prepared by radiation-induced graft copolymerization of binary monomer system acrylic acid/acrylamide (AAc/AAm) onto low-density polyethylene (LDPE) and polypropylene (PP) films using direct radiation-grafting technique. Sulfonation was carried out for the prepared grafted copolymers using concentrated sulfuric acid (97%) at 60 ^°C for 15 min. The grafted and sulfonated grafted films found to have good properties such as thermal stability and hydrophilic properties. The sulfonated grafted films found to have a better hydrophilic character than the grafted ones due to ionic character resulted by this conversion. The thermoluminescence (TL) characteristics of a set of grafted and sulfonated films have been studied with regard to their use as off-line dosimeters in radiotherapy. The structural characterization has been performed by means of infrared spectroscopy. Their TL responses have been tested with radiotherapy beams of ⁶⁰Co photons in the dose range 0.1–7 Gy. The dosimetric characterization has yielded a very good reproducibility and is independent of the radiation energy. The TL signal is not influenced by the dose rate and exhibits a very low thermal fading. Moreover, the sensitivity of the samples compares favorably with that of the standard TLD100 dosimeters. Finally, at the same dose, the TL response for LDPE-g-P (AAm/AAc) films is higher than the PP-$g$-P(AAm$/$AAc), and the sulfonated grafted films are more sensitive to radiation than the grafted ones.     

Radiation-induced modifications of point defects in quartz crystals and their application in radiation dosimetry

Different types of impurity-related point defects in crystalline quartz are known to exhibit various spectroscopic signals. When exposed to ionizing radiations, these defect centers get modified and new species of point defects are formed. This paper presents a study and discussion of radiation-induced modification of point defects in natural as well as cultured quartz, with an emphasis to use this material for radiation dosimetry up to a range of a few Mrad.     

OSL and TL in TLD-100 following alpha and beta irradiation: Application to mixed-field radiation dosimetry

The optically stimulated luminescence (OSL) of LiF:Mg,Ti (TLD-100) following irradiation by beta and alpha particles was investigated by measurement of the excitation and emission spectra of OSL and comparison with thermoluminescence (TL) characteristics. The OSL excitation spectra of all the samples following both beta and alpha irradiation are very similar.Identical emission bands with very similar relative intensities following both beta irradiation and alpha particle irradiation have been recorded in the OSL induced in nominally pure LiF mono and TLD-100 polycrystals. The identical excitation and emission bands in the doped and pure crystals are strong evidence indicating that the observed OSL is due to an intrinsic trapping structure. The OSL has indeed been previously attributed to F₂ centers and F₃⁺ centers.The preferential excitation of OSL compared to TL following high ionisation density (HID) alpha irradiation is naturally explained via the identification of OSL with the “two-hit” F₂ or F₃⁺ center, whereas the major component of composite TL glow peak 5 is believed to arise from a “one-hit” complex defect. This discovery allows near-total discrimination between HID radiation and low ionisation density (LID) radiation and may have significant potential in mixed-field radiation dosimetry.     

Interaction of biological and nonbiological surfaces. New opportunities for research and technologies using synchrotron radiation

The applicability of synchrotron radiation to implementation of medical ideas associated with introduction of nonbiological objects into a human body—implants, drug nanocapsules, and X-ray therapeutic means (metal nanoparticles and nanocrystalline phosphors and scintillators)—is considered. Synchrotron radiation presents new possibilities of analyzing the surface with a resolution comparable to the sizes of biological nanostructures involved in interactions such as chemical and biochemical modification of implant surfaces in vitro; activation of implant surface integration with biological tissue in a tissue culture (in vitro) and in vivo; biochemical modification of therapeutic nanoparticle surface in vitro; immunocamouflage by host proteins; attachment of “molecular targets”, i.e., antibodies, to target tissue to provide targeted delivery vehicles; and local activation of X-ray therapeutic drugs and drug nanocapsules in biological tissues. A functional block diagram of a medical technological station is given.     

BiodosEPR-2006 Meeting: Acute dosimetry consensus committee recommendations on biodosimetry applications in events involving uses of radiation by terrorists and radiation accidents

In the aftermath of a radiological terrorism incident or mass-casualty radiation accident, first responders and receivers require prior guidance and pre-positioned resources for assessment, triage and medical management of affected individuals [NCRP, 2005. Key elements of preparing emergency responders for nuclear and radiological terrorism. NCRP Commentary No. 19, Bethesda, Maryland, USA]. Several recent articles [Dainiak, N., Waselenko, J.K., Armitage, J.O., MacVittie, T.J., Farese, A.M., 2003. The hematologist and radiation casualties. Hematology (Am. Soc. Hematol. Educ. Program) 473–496; Waselenko, J.K., MacVittie, T.J., Blakely, W.F., Pesik, N., Wiley, A.L., Dickerson, W.E., Tsu, H., Confer, D.L., Coleman, C.N., Seed, T., Lowry, P., Armitage, J.O., Dainiak, N., Strategic National Stockpile Radiation Working Group, 2004. Medical management of the acute radiation syndrome: recommendations of the Strategic National Stockpile Radiation Working Group. Ann. Intern. Med. 140(12), 1037–1051; Blakely, W.F., Salter, C.A., Prasanna, P.G., 2005. Early-response biological dosimetry—recommended countermeasure enhancements for mass-casualty radiological incidents and terrorism. Health Phys. 89(5), 494–504; Goans, R.E., Waselenko, J.K., 2005. Medical management of radiation casualties. Health Phys. 89(5), 505–512; Swartz, H.M., Iwasaki, A., Walczak, T., Demidenko, E., Salikhov, I., Lesniewski, P., Starewicz, P., Schauer, D., Romanyukha, A., 2005. Measurements of clinically significant doses of ionizing radiation using non-invasive in vivo EPR spectroscopy of teeth in situ. Appl. Radiat. Isot. 62, 293–299; Weisdorf, D., Chao, N., Waselenko, J.K., Dainiak, N., Armitage, J.O., McNiece, I., Confer, D., 2006. Acute radiation injury: contingency planning for triage, supportive care, and transplantation. Biol. Blood Marrow Transplant. 12(6), 672–682], national [National Council of Radiation Protection and Measurements (NCRP), 1994. Management of persons accidentally contaminated with radionuclides. NCRP Report No. 65, Bethesda, Maryland, USA; NCRP, 2001. Management of terrorist events involving radioactive material. NCRP Report No. 138, Bethesda, Maryland, USA; NCRP, 2005. Key elements of preparing emergency responders for nuclear and radiological terrorism. NCRP Commentary No. 19, Bethesda, Maryland, USA] and international [IAEA, 2005. Generic procedures for medical response during a nuclear or radiological emergency. EPR-Medical 2005, IAEA, Vienna, Austria] agencies have reviewed strategies for acute-phase biodosimetry. Consensus biodosimetric guidelines include: (a) clinical signs and symptoms, including peripheral blood counts, time to onset of nausea and vomiting and presence of impaired cognition and neurological deficits, (b) radioactivity assessment, (c) personal and area dosimetry, (d) cytogenetics, (e) in vivo electron paramagnetic resonance (EPR) and (f) other dosimetry approaches (i.e. blood protein assays, etc.). Emerging biodosimetric technologies may further refine triage and dose assessment strategies. However, guidance is needed regarding which biodosimetry techniques are most useful for different radiological scenarios and consensus protocols must be developed.The Local Organizing Committee for the Second International Conference on Biodosimetry and Seventh International Symposium on EPR Dosimetry and Applications (BiodosEPR-2006 Meeting) convened an Acute Dosimetry Consensus Committee composed of national and international experts to: (a) review the current literature for biodosimetry applications for acute-phase applications in radiological emergencies, (b) describe the strengths and weaknesses of each technique, (c) provide recommendations for the use of biodosimetry assays for selected defined radiation scenarios, and (d) develop protocols to apply these recommended biological dosimetry techniques with currently available supplies and equipment for first responders.The Acute Dosimetry Consensus Committee developed recommendations for use of a prioritized multiple-assay biodosimetric-based strategy, concluding that no single assay is sufficiently robust to address all of the potential radiation scenarios including management of mass casualties and diagnosis for early medical treatment. These recommendations may be used by first responders/first receivers that span time-windows of (i.e. 0–5 days) after the radiological incident for three radiological scenarios including: (a) radiation exposure device (RED), (b) radiological dispersal device (RDD), and (c) an improvised (or otherwise acquired) nuclear device (IND). Consensus protocols for various bioassays (i.e. signs and symptoms recording, bioassay sampling for radioactivity analysis, nail-clipping sampling for EPR analysis and blood collection for hematology, cytogenetics, and blood chemistry analyses) are presented as Appendix materials. As stated in NCRP Commentary No. 19 [NCRP, 2005. Key elements of preparing emergency responders for nuclear and radiological terrorism. NCRP Commentary No. 19, Bethesda, Maryland, USA], multi-parameter triage (i.e. time to vomiting, lymphocyte kinetics, and other biodosimetry indicators) offers the current best strategy for early assessment of absorbed dose.     

Use of the EUR LiB 15/5 data set for radiation shielding calculations in iron

Abstract

The shielding effect of an iron sphere assembly has been tested for a Pu-α-Be neutron source placed in the center of the shield assembly. Emergent neutron and gamma spectra were measured with a stilbene scintillation counter. Discrimination between neutrons and gammas was achieved by the pulse shape discrimination technique based on the zero crossing method. Calculations have been made using the one-dimensional transport code ANISN-Westinghouse version (ANISN-W) and the EUR LiB 15/5 cross section data set. The agreement between measurements and calculations indicates that the cross section set and the calculation model are suitable for studying the iron shielding experiments over the neutron energy range 1.35–10 MeV and the gamma energy range 0.3–6 MeV. Total macroscopic cross sections for fast neutrons, linear attenuation coefficients for gamma rays and half-value thicknesses for neutrons and gammas for the whole energy range and at different energies have been obtained.