Thermoluminescence and optically stimulated luminescence studies on LiMgPO4 crystallized by micro pulling down technique

LiMgPO₄ (LMP) crystals were grown by micro pulling down technique. Samples were irradiated with different β-particle doses of the ⁹⁰Sr/⁹⁰Y source. Thermally and optically stimulated luminescence spectra were measured with the automatic Risø TL/OSL-DA20 reader under the different modes of stimulation. The dose–response dependence, reproducibility, the lowest measurable dose and short-time fading were investigated. TL and OSL dose–response of LiMgPO₄ crystals was found to be linear up to around 1 kGy, what makes this material suitable for high dose measurements. Discrepancies between successive measurements did not exceed 10%, regardless of the applied growth parameters. The lowest measurable dose, defined as three standard deviations of the signal of unexposed detector, was determined around 0.5 mGy. About 73% of the initial OSL signal value was measured 24 h after the irradiation. For longer periods of time the level of signal stabilizes so that there was no further loss of signal observed. In case of TL, the level of signal does not stabilize and decreases to 69% within 2 weeks after the irradiation. The obtained results tend to suggest that LiMgPO₄ crystals may be considered as promising dosimeters for both personal and high dose dosimetry.     

Thermally assisted OSL (TA-OSL) reproducibility in Al2O3:C and its implication on the corresponding thermoluminescence (TL) reproducibility

Thermally assisted optically stimulated luminescence (TA-OSL) method is an excellent advancement of high-dose luminescent dosimetry with involvement of very deep traps. This specific method has been reported to be very efficient for the cases of anion deficient alumina doped with carbon and quartz. Nevertheless, reproducibility and sensitivity changes have been previously studied only for the case of quartz. In the present study, reproducibility was studied in both terms of quantitative and qualitative features, such as signal intensity and glow curve shape respectively, for both TL and TA-OSL signals on various TLD 500 dosimeters. Finally, for the case of the TL signal, sensitivity changes were studied with and without applying TA-OSL, towards studying the impact of the TA-OSL on the main dosimetric TL signal.     

三硝基间苯三酚1,5-二氨基四唑盐的制备、晶体结构及热分析

通过1,5-二氨基-1,2,3,4-四唑（DAT）与等摩尔的2,4,6-三硝基-1,3,5-苯三酚（TNPG）反应,制备了新型离子型含能化合物DATH⁺TNPG^-。通过X射线单晶衍射、元素分析、FT-IR光谱和¹H NMR对其进行了表征。晶体结构测试表明：该化合物的晶体属于单斜晶系,P2(1)/c空间群,a = 1.3399(3),b= 0.47088(9),c = 2.0127(4) nm,β= 92.83(3) ^o,V = 1.2684(4) nm³, Z= 4。在氢键、静电引力和范德华力的作用下该化合物形成了稳定的三维网状结构。对DAT和DATH⁺TNPG^-晶体进行了DFT-B3LYP/6-31G**周期性计算研究,得到其Mulliken电荷分布和重叠布居,从理论上说明DAT质子化位置是在四唑环的N(4)原子。采用TG-DTG和DSC技术对目标化合物的热分解进行了研究,并采用Kissinger和Ozawa-Doyle法对热分解过程的非等温反应动力学进行了计算。     

泡沫红外消光影响因素的实验研究

通过红外光谱实验和红外热成像实验,研究了影响泡沫红外消光的因素,结果表明:泡沫溶液的红外光谱特征决定红外光谱吸收峰位,且溶质浓度越高,吸收越强;泡沫结构是造成光线强烈衰减的重要原因,透射光强随光线穿过泡沫液膜界面的次数成指数衰减,泡沫直径越小,达到相同遮蔽效果的泡沫溶液的用量就越少;当泡沫直径远大于入射光线波长时,透射比随光束大小变化不大;泡沫溶液升温可在一定程度上增强泡沫的红外吸收强度.各因素影响程度从大到小的次序为:泡沫结构,红外光谱特征,内充气体折射率,泡沫直径,温度.     

Low-temperature synthesis of ZnO nanonails

Wurtzite ZnO nanonails on silicon substrate were successfully synthesized by thermal vapor transport and condensation method at a low temperature without a metal catalyst. Pure Zn powders were used as raw material and O₂/Ar powders as source gas. The products were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results show that the deposited nanostructures include aligned ZnO nanonails. The ZnO nanonails, with crystalline cap and small-diameter shafts, grow along the c-axis. The optical properties have been revealed by photoluminescence spectra. We considered that the ZnO nanonails growth is a vapor-solid process.     

闪电光电信号的同步观测与闪电类型模式识别

 利用宽带电场仪和光学纹波探头，对2006年夏季广东省从化地区发生的自然闪电的光电信号进行了同步观测，并对结果进行了统计分析。统计结果表明：闪电光信号脉冲的发生时间和峰值到达时间总是滞后于电信号，并且脉冲上升沿和宽度也比电信号宽；云闪的光信号在上述特征参数的滞后量、上升沿时间和脉宽时间差要比地闪回击放电大。从闪电光电信号时域信号特征的角度，利用BP人工神经网络，对闪电类型进行了模式识别研究。总体识别结果基本上能够满足要求，但是由于云闪放电过程比较复杂，获得的数据较少，所以对云闪识别的效果并不理想。     

Study of a new Lif:Mg,Cu,P formulation with enhanced thermal stability and a lower residual TL signal

This paper presents results obtained for a new LiF:Mg,Cu,P (HMCP) preparation with modified Mg and Cu concentrations. The shape of the HMCP glow curve shows minimal differences for annealing in the range from 523 to 543 K for 10 min. The thermoluminescence (TL) readout value remained stable when annealed in the range from 513 to 543 K for 10 min. The new formula allows heating of the material to higher temperatures than that originally employed for the well-known GR-200A dosemeter, practically without losses in sensitivity. The TL sensitivity is approximately half of that for the GR-200A, and still 29-fold greater than that for the TLD-100 dosemeter, and the residual signal is approximately five-fold lower than for the GR-200A. These results indicate that the new TL material shows enhanced thermal stability and a lower residual TL signal at a small TL sensitivity cost. The heat treatment temperatures are related to concentrations of Mg and Cu in LiF:Mg,Cu,P.     

基于GEM探测器的时间投影室TPC的讨论

自20世纪90年代以来, GEM探测器以其高电子倍增、高空间分辨和高计数率等优势在粒子物理和辐射成像等领域得到了广泛和深入的研究, 具有广阔的应用前景. 如果将GEM作为读出探测器应用在时间投影室TPC系统上, 和传统的读出方式比较起来, 既有许多优点也有许多挑战. 目前世界上有许多机构正在研究将此方案用于将来的大型正负电子对撞机ILC. 本文论述了这些研究课题的概况, 讨论了TPC的各项关键性能指标与GEM探测器的关系及存在的问题.     

基于GEM读出的TPC工作气体的研究

针对TPC中对于电子漂移的要求, 结合Garfield软件, 研究了我们所研制的TPC原型所用的工作气体. 分析了不同气体对于电子漂移的寿命、漂移速度、横向和纵向扩散, 以及电离特性等参数的影响; 结合分析论证, 得到了以Ar, CH₄和CF₄为主要成分的气体作为工作气体时TPC的性能指标. 并且测试了该气体中的读出GEM探测器的能量分辨率、气体增益等性能参数, 获得了很好的结果.