Requirements for synthetic diamond devices for radiotherapy dosimetry applications

CVD diamond is a remarkable material for the fabrication of radiation detectors. Radiation hardness, chemical resistance and high-temperature operation capabilities of diamond motivate its use for fabrication of devices operating in hostile environments such as that encountered in nuclear industry and high energy physics. Its potentialities for such applications have been well documented and recent studies have led to the developments of a few applications that are addressing specific industrial needs.One particular interest of diamond stands in the fact that its atomic number is close to that of human tissues. This implies that the response of a diamond device to radiation is close to that received by the human body. Its thus enables the straightforward measurement of the dose for radiotherapy applications. However, this requires high reproducibility and linearity. It is widely observed that radiation exposure is modifying the initial performances of diamond detectors and priming devices is therefore required to obtain the required linearity. However, the nature of defects in the material strongly influences the type of priming required. This paper will address this problem from the study of trapping levels and their influence on the device response. We present here the current status of the development of polycrystalline diamond for this type of application, and propose new techniques of improving the material characteristics toward the optimisation of ionisation chamber performances as well as that of thermoluminescent dosimeters for the particular field of radiotherapy applications.     

Analysis of weathering effects in automotive coatings using thermoluminescence

Thermally stimulated luminescence (TL) can be used to detect damage in the early stages of degradation after artificial weathering, and to analyze the efficiency of stabilizers used in automotive coatings. TL is particularly suitable for this task due to its inherent high sensitivity to structural, morphological, and chemical changes in macromolecular chains. In this work, TL measurements were carried out for different automotive coatings to follow their degradation progression during artificial weathering. The TL results demonstrate high sensitivity to parameters like stabilizers, matrices, hardeners, and weathering time, and provide an opportunity to monitor the early stages of damage in polymers, which therefore reduce the time required for further outdoor weathering tests.     

Thermoluminescence glow curve analysis and kinetic parameters of Dy-doped BaSi2O5 phosphor

In this paper,Dy³⁺incorporated BaSi₂O₅phosphors were synthesized by gel co mbustion method and characterized by X-ray diffraction(XRD).The effects of various heating rate s on thermoluminescence(TL)kinetics and glow peak temperatures of Dy³⁺incorporated BaSi₂O₅phosphors exposed toβirradiation at room temperature were investigated.The glow curves of the phosphor exposed toβ-irradiation(0.1-100 Gy)consist of four main peaks located at 87,130,271,and 327℃and exhibit a good linearity between 0.1 and100 Gy.Three experimental techniques including variable heating rate(VHR),repeated initial rise(RIR),peak shape(PS)and computerized glow curve deconvolution(CGCD)were employed to determine TL kinetic parameters.Our findings indicate that the TL glow peaks of the phosphor obey first-order kinetics.Analysis of the main dosimetric peaks through the techniques mentio ned above indicates that activation energies(E)and pre-exponential factor(s)are in the range of 0.80-1.50 eV and 1.15×10⁸-3.28×10¹³s^-1.Additionally,it is found that the temperature of the glow peaks shifts toward the higher temperatures and the TL intensity smoothly decreases as the heating rate increases.The effect on the TL intensities and glow peak temperatu res of the heating rate is discussed in terms of thermal quenching.     

Preparation and characterization of Ce0.95Zr0.05O2 nanopowders obtained by sol–gel and template methods

Ce_0.95Zr_0.05O₂ nanopowders have been prepared by a standard Pechini-type sol–gel process and by using polymethyl methacrylate (PMMA) colloidal crystals as template. The effects of these different synthesis routes, on the structure and microstructural features of the nanopowders, were evaluated by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific surface area measurements. For both preparation routes, the XRD analysis has shown that a cubic fluorite structure is formed with a crystallite size of ∼45–50 nm. The SEM images indicate that the powder obtained by the sol–gel Pechini-type process, is constituted by aggregated nanoparticles with relatively uniform shape and size, whereas the powder synthesized as inverse opal exhibits the formation of macropores with a mean size of ∼130 nm. The specific surface areas of the powder samples obtained by the Pechini-type sol–gel and inverse opal methods are ∼56 m² g⁻¹ and ∼90 m² g⁻¹ respectively. Additionally, the thermoluminescence (TL) signal of the synthetized samples has been measured in order to examine its potential application in the field of dosimetry of ionizing radiations.     

热释光材料LiF：Mg,Ti,LiF：Mg,Cu,P和MgSO4的正电子湮没特性

测量了经＾６０Ｃｏγ辐照的热释光材料ＬｉＦ：Ｍｇ，Ｔｉ，ＬｉＦ：Ｍｇ，Ｃｕ，Ｐ和ＭｇＳＯ４的正电子湮没寿命谱，所有寿命谱都分成三个成分，两种不同掺杂的ＬｉＦ样品，其τ２成分寿命参数十分接近，表明正离子空位对寿命谱影响较小，并且观察到，在剂量范围为０．０５－１ｋＧｙ内，τ２成分寿命参数随剂量按相反趋势发生较小的变化，等时退火实验表明，ＭｇＳＯ４样品的τ２和τ３成分与硫酸基有关，其大小可参取决于Ｍｇ＾     

The effect of impurities on TL emission wavelengths of NaCl crystals

We report emission spectra during thermoluminescence of NaCl crystals doped with Eu, Sr, Ca, Cr and Ni impurities. Crystals were irradiated at ambient temperature with X- or γ-rays prior to measurement. Isometric plots in the wavelength range 200–800 nm reveal only small differences in patterns of TL emission for pure samples and samples doped with Eu, Sr and Ca. However samples doped with Cr and Ni show significant variations characterized by suppressed emission between 390 nm and 520 nm. This is discussed in terms of the efficiency of colouration of the crystals and the state of aggregation of impurity–vacancy dipoles.     

天然钾长石热释光峰的动力学特性研究

研究了天然钾长石的热释光动力学特性与γ射线辐射剂量的关系，用不退火处理样品和用不同剂量辐照的方法，观测到位于１６０℃和２４８℃的两个热释光峰。前者峰高与γ剂量有关。后得峰高基本不随γ剂量而变化，经退火处理后的样品，只存在与剂量有关的发光峰，１６０℃的发光峰形和峰浊都不随γ辐射剂量增加而变化，用初台升温法测定该发光峰的激活能级为１．０ｅＶ，用一般级动力学方程拟合得到的动力学级数表明该发光峰非常接近二     

EFFECT OF HEATING RATE ON NONLINEARITY OF DOSE RESPONSE IN TL BY KINETICS MODEL

ＥＦＦＥＣＴ　ＯＦ　ＨＥＡＴＩＮＧ　ＲＡＴＥ　ＯＮ　ＮＯＮＬＩＮＥＡＲＩＴＹ　ＯＦ　ＤＯＳＥ　ＲＥＳＰＯＮＳＥ　ＩＮ　ＴＬ　ＢＹ　ＫＩＮＥＴＩＣＳ　ＭＯＤＥＬＬｉｕＸｉａｏｗｅｉ（刘小伟）ａｎｄＫ．Ｎ．Ｙｕ（余君岳）（ＤｅｐａｒｔｍｅｎｔｏｆＰｈｙｓ...     

Thermoluminescence of BaFCl_xBr_（1－x）：Sm System and Assignment of Their Glow Peaks

ＴｈｅｒｍｏｌｕｍｉｎｅｓｃｅｎｃｅｏｆＢａＦＣｌ_ｘＢｒ_（１－ｘ）：ＳｍＳｙｓｔｅｍａｎｄＡｓｓｉｇｎｍｅｎｔｏｆＴｈｅｉｒＧｌｏｗＰｅａｋｓＣｈｅｎＷｅｉ；（陈伟）；ＳｕＭｉａｎ－Ｚｅｎｇ；（苏勉曾）（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ，...     

The persistent energy transfer of Eu and Mn and the thermoluminescence properties of long-lasting phosphor Sr3MgSi2O8:Eu, Mn, Dy

Eu²⁺, Mn²⁺ and Dy³⁺ co-doped long-lasting phosphors Sr₃MgSi₂O₈ were prepared by a solid-state reaction under a reductive atmosphere. Fluorescence spectra demonstrated that the weak red emission resulting from the forbidden transition of Mn²⁺ could be enhanced by the energy transfer from Eu²⁺ to Mn²⁺. The energy transfer between Eu²⁺ and Mn²⁺ was systematically investigated. The phosphorescence spectra revealed that Eu²⁺ could persistently transfer its energy to Mn²⁺ after removing the excitation source. The duration of Mn²⁺ can prolong to more than 2 h. The thermoluminescence spectra were used to characterize the ability of the trap to trapping the carriers. By the analysis of the ionization potentials, the roles of Mn²⁺ and Dy³⁺ in the afterglow process were discussed. A possible afterglow mechanism was presented and discussed.