Radiation induced polymerization of Vinylbenzoate–II. Study of the molecular weights of polymers

Abstract

In this study, the molecular weights of the polymer from vinyl benzoate has been reported for different dose rates and different temperatures. The mol.wt. remains around 4000. With increasing dose, the molecular weight increases to about 14,000. The degrees of polymerization and the kinetic chain lengths calculated from the experimentally determined G _R values have been compared which show that the kinetic chain length is larger than the D ^? Pn.

From a plot of the (D ^? Pn)^?1 vs. R _p , an intercept is obtained which is equal to 3.25 × 10^?2 which is higher than obtained in conventional polymerization. By examining the effect of temperature on mol.wt., the dependence of R _p on dose rate and the absence of induction period it has been concluded that chain transfer occurs to impurities that are generated during radiolysis.     

Indications of bulk property changes from surface ion implantation

In the majority of cases, the effects of ion implantation are confined close to the implant zone but, potentially, the resultant distortions and chemical modifications could catalyse relaxations extending into the bulk substrate. Such possibilities are rarely considered but the present data suggest that high dose ion implantation of ZnO has induced bulk changes. Surface implants with Cu and Tb strongly modified the low temperature bulk thermoluminescence properties generated by X-ray irradiation. Suggestions are proposed for the possible mechanisms for bulk relaxations and structural characteristics, which may indicate where such instability may occur in other lattice structures.     

Synthesis,Persistent Luminescence,and Thermoluminescence Properties of Yellow Sr3SiO5:Eu2+,RE3+ (RE=Ce,Nd, Dy,Ho, Er,Tm, Yb) and Orange‐Red Sr3−xBaxSiO5:Eu2+, Dy3+ Phosphor

Sunlight‐excitable orange or red persistent oxide phosphors with excellent performance are still in great need. Herein, an intense orange‐red Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ persistent luminescence phosphor was successfully developed by a two‐step design strategy. The XRD patterns, photoluminescence excitation and emission spectra, and the thermoluminescence spectra were investigated in detail. By adding non‐equivalent trivalent rare earth co‐dopants to introduce foreign trapping centers, the persistent luminescence performance of Eu²⁺ in Sr₃SiO₅ was significantly modified. The yellow persistent emission intensity of Eu²⁺ was greatly enhanced by a factor of 4.5 in Sr₃SiO₅:Eu²⁺,Nd³⁺ compared with the previously reported Sr₃SiO₅:Eu²⁺, Dy³⁺. Furthermore, Sr ions were replaced with equivalent Ba to give Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ phosphor, which shows yellow‐to‐orange‐red tunable persistent emissions from λ=570 to 591 nm as x is increased from 0 to 0.6. Additionally, the persistent emission intensity of Eu²⁺ is significantly improved by a factor of 2.7 in Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ (x=0.2) compared with Sr₃SiO₅:Eu²⁺,Dy³⁺. A possible mechanism for enhanced and tunable persistent luminescence behavior of Eu²⁺ in Sr_3?xBa_xSiO₅:Eu²⁺,RE³⁺ (RE=rare earth) is also proposed and discussed.     

Prompt isothermal decay of thermoluminescence in MgB4O7:Dy,Na and LiB4O7:Cu,In dosimeters

According to standard delocalized kinetic models of thermoluminescence (TL), when an irradiated sample is held at a high temperature T, the isothermal TL signal will decay with a characteristic thermal decay constant λ which depends strongly on the temperature T. This prediction of standard delocalized kinetic theory is investigated in this paper by studying two TL dosimeters, MgB₄O₇:Dy, Na and LiB₄O₇:Cu, In (hereafter MBO and LBO correspondingly). In the case of LBO it was found that the thermal decay constant λ of the main dosimetric TL peak follows exactly the predictions of standard delocalized kinetic theory. Furthermore, the thermal activation energy of the main peak evaluated by the isothermal decay method is in full agreement with values obtained from initial rise and glow curve fitting methods. However, in the case of MBO it was found that the thermal decay constant λ varies little with the isothermal decay temperature T. In order to explain these unusual results for MBO, the TL glow curves and isothermal decay curves were analyzed using analytical expressions derived recently from a radiative tunneling recombination model. Based on the different behavior of the two TL dosimeters, it is suggested that the isothermal decay of TL at high temperatures can be used to discriminate between radiative delocalized recombination and radiative localized recombination processes.     

Thermoluminescence and optically stimulated luminescence in various phases of doped Na2SO4

The dependence of optically stimulated luminescence (OSL) and thermoluminescence (TL) response due to crystal phase in Cu and Cu,Mg-doped Na₂SO₄ was studied. Study shows that the slowly cooled samples which crystallize in phase V show good OSL sensitivity whereas the quenched samples of Na₂SO₄ which crystallize in phase III irrespective of doping show no OSL sensitivity. However, during storage when phase III samples get converted to phase V, samples show OSL sensitivity comparable to freshly prepared samples in phase V. Hence, it is observed that TL–OSL properties of doped Na₂SO₄ are phase dependent .This study will be helpful in developing OSL phosphors in which phase plays an important role in deciding the desired properties.     

乙醇对纳米多孔氧化铝薄膜热释光的影响

以乙醇-草酸混合溶液为电解液,用二次阳极氧化法制备纳米多孔Al_2O_3∶C薄膜。在制备过程中,碳的掺杂浓度可控。实验结果表明,随着碳浓度的增加,热释光强度逐渐增大;随着退火温度的升高,320℃左右的主热释光峰的强度先升高后降低。在退火温度为500℃时,主热释光峰的强度达到最大。纯草酸溶液制备的Al_2O_3薄膜的热释光剂量响应曲线在10~50 Gy是线性的,在50~100 Gy呈超线性;而乙醇-草酸混合溶液制备的Al_2O_3∶C薄膜在10~100 Gy基本呈线性。     

Effect of 100 MeV swift Si8+ ions on structural and thermoluminescence properties of Y2O3:Dy3+nanophosphor

Nanoparticles of Y₂O₃:Dy³⁺ were prepared by the solution combustion method. The X-ray diffraction pattern of the 900°C annealed sample shows a cubic structure and the average crystallite size was found to be 31.49?nm. The field emission scanning electron microscopy image of the 900°C annealed sample shows well-separated spherical shape particles and the average particle size is found to be in a range 40?nm. Pellets of Y₂O₃:Dy³⁺ were irradiated with 100?MeV swift Si⁸⁺ ions for the fluence range of 3?×?10^11_3?×?10¹³ ions cm^?2. Pristine Y₂O₃:Dy³⁺ shows seven Raman modes with peaks at 129, 160, 330, 376, 434, 467 and 590?cm^?1. The intensity of these modes decreases with an increase in ion fluence. A well-resolved thermoluminescence glow with peaks at ～414?K (T_m1) and ～614?K (T_m2) were observed in Si⁸⁺ ion-irradiated samples. It is found that glow peak intensity at 414?K increases with an increase in the dopant concentration up to 0.6?mol% and then decreases with an increase in dopant concentration. The high-temperature glow peak (614?K) intensity linearly increases with an increase in ion fluence. The broad TL glow curves were deconvoluted using the glow curve deconvoluted method and kinetic parameters were calculated using the general order kinetic equation.     

ZnS中电子陷阱能级对光生电子弛豫过程的影响

采用微波吸收法,测量了在不同助熔剂条件及不同气氛下烧制的ZnS材料受到超短激光脉冲激发后的光电子衰减过程,并且测量了材料的热释光曲线。样品A采用过量的SrCl作为助熔剂,在1150℃下灼烧制备而成;其热释光曲线显示材料中有浅电子陷阱,电子陷阱密度小,光生电子衰减过程为双指数衰减过程,快过程寿命为45ns,慢过程寿命为312ns。样品B中加入了少量的NaCl作为助熔剂;热释光曲线显示有浅电子陷阱和深电子陷阱,且都有较高的密度,其光电子寿命为1615ns。在NH₄Br气氛中烧制样品C,热释光谱显示只有浅电子陷阱形成,光电子寿命为1413ns。结果表明材料的光电子寿命和浅电子陷阱密切相关,浅电子陷阱密度越大,光生电子寿命越长,深电子陷阱对光生电子瞬态过程影响很小。     

Preliminary study of the thermally stimulated blue luminescence of ulexite

In this paper, novel results on the blue thermally stimulated luminescence (TSL) emission of ulexite (NaCaB₅O₆(OH)₆·5H₂O) have been studied. The four maxima appearing at 60, 110, 200 and 240°C on the TSL glow curves of this borate could be respectively associated to: (i) the first dehydration (NaCaB₅O₆(OH)₆·5H₂O→NaCaB₅O₆(OH)₆·3H₂O), (ii) the creation-annihilation of the three-hydrated phase, (iii) the Na-coordinated chains dehydroxylation and the starting point of the alkali self-diffusion through the lattice and (iv) the amorphisation of the lattice. These results are fairly well correlated with the differential thermal analyses (DTA), in situ thermal observations under environmental scanning electron microscope (TESEM) and thermal X-ray diffraction (TXRD) techniques.     

高剂量率单次快脉冲辐射参量测量

记述了“强光一号”高剂量率脉冲辐射装置在状态调试过程中对其出射波形和辐射剂量进行监测的基本情况，实际监测的结果与设计方监测的结果进行了比对，双方的剂量监测值基本一致，偏差在20％以内；双方的波形形状十分相似，但测量得到的波形半宽度却相差10～20ns，最后对双方束流监测产生的差异进行了定性分析。