Configuration of an alpha–gamma coincidence spectrometer for utilization of safeguards measurements

An alpha–gamma coincidence spectrometry (AGCS) system was developed at the International Atomic Energy Agency's (IAEA) Safeguards Analytical Laboratory (SAL) in order to improve the detection of alpha–gamma emitting radionuclides of relevance for safeguards, such as ²³⁹Pu and ²⁴¹Am. The AGCS design was based upon a linear gate, whose resolving time is dependent upon the amplifiers’ shaping time constants (STC). A coincidence spectrum of a Pu/Am sample was acquired which showed that the AGCS system could be utilized in safeguards measurements.     

Monte Carlo simulation of a PhosWatch detector using Geant4 for xenon isotope beta–gamma coincidence spectrum profile and detection efficiency calculations

A simulation tool has been developed using the Geant4 Toolkit to simulate a PhosWatch single channel beta–gamma coincidence detection system consisting of a CsI(Tl)/BC404 Phoswich well detector and pulse shape analysis algorithms implemented digital signal processor. The tool can be used to simulate the detector's response for all the gamma rays and beta particles emitted from ¹³⁵Xe, ^133mXe, ¹³³Xe, ^131mXe and ²¹⁴Pb. Two- and three-dimensional beta–gamma coincidence spectra from the PhosWatch detector can be produced using the simulation tool. The accurately simulated spectra could be used to calculate system coincidence detection efficiency for each xenon isotope, the corrections for the interference from the various spectral components from radon and xenon isotopes, and system gain calibration. Also, it can generate two- and three-dimensional xenon reference spectra to test beta–gamma coincidence spectral deconvolution analysis software.     

食品样品中低水平137 Cs活度浓度测量的两种方法比较

目的 比较食品中¹³⁷Cs的γ能谱分析法和放射化学分析法,并探讨两种方法的适用性。方法 采用γ能谱分析方法和放射化学分析方法(磷钼酸铵分离-β计数法)测量不同类型食品中的¹³⁷Cs,比较两种方法所需样品量、预处理制样过程以及测量探测下限,并以肉类样品为例,对比两种方法测量肉类样品中¹³⁷Cs的活度浓度及不确定度评估。结果 能谱分析法与磷钼酸铵分离-β计数法的测量结果一致,两种方法测量肉类样品的相对扩展不确定度分别是18.0%和8.0%,γ能谱分析法样品制备简单,但样品用量大预处理过程耗时,磷钼酸铵分离-β计数法的样品用量小,但需要分离纯化过程,两种方法的探测下限分别是10.6 mBq/kg (样品质量11.7 kg)和5.1 mBq/kg (样品质量2.1 kg)。结论 两种方法测量食品中低水平¹³⁷Cs结果一致,适用于食品中¹³⁷Cs的监测。     

Prospective comparison of two gamma probes for intraoperative detection of <Superscript>18</Superscript>F-FDG: in vitro assessment and clinical evaluation in differentiated thyroid cancer patients with iodine-negative recurrence

Purpose This study was aimed at evaluating the spatial resolution and sensitivity of two hand-held gamma probes. Radioguided surgery was tested in seven patients with iodine-negative differentiated thyroid cancer (DTC) recurrence using ¹⁸F-FDG PET. Methods Two gamma probes were evaluated: Clerad’s GammaSup with a collimated CsI(Tl) scintillator and Novelec’s Modelo2 with a BGO scintillator. Five measurement tests were performed following the NEMA guidelines (NU3-2004). Radioguided surgery was performed in patients with recurrent DTC and abnormal ¹⁸F-FDG uptake on preoperative ¹⁸F-FDG PET images. Patients were injected with rTSH 2 days before surgery. A mean activity of 211 MBq of ¹⁸F-FDG was injected 60 min before surgery. In vivo and ex vivo counts were recorded for suspected tumours and normal tissue. Results Spatial resolution was higher with the CsI(Tl) than with the BGO detector: 20.2–40.6 mm vs 20.6–55.3 mm from 0 to 20 mm depth. Sensitivity in air and water and through side shielding was higher for BGO but the signal-to-noise ratio was 88 and 22 with the BGO compared to 131 and 76 with the CsI(Tl) at 10 and 30 mm depth. Median in vivo SNR (tumour/non-tumour ratio) was 1.8 with both the BGO and the CsI(Tl) detector, while ex vivo ratios of 2.3 and 2.1, respectively, were obtained. Radioguided surgery allowed detection of all of the tumours identified by ¹⁸F-FDG PET images. Conclusion This study demonstrated the feasibility of high-energy photon detection with a conventional scintillator equipped with a collimator. The CsI(TI) probe detected more true events from background than did the BGO detector during surgery.     

Geochemical variation of soil–gas composition for fault trace and earthquake precursory studies along the Hsincheng fault in NW Taiwan

The present study is proposed to investigate geochemical variations of soil–gas composition in the vicinity of the geologic fault zone of Hsincheng in the Hsinchu area of Taiwan. Soil–gas surveys have been conducted across the Hsincheng fault, to look for the degassing pattern of this fault system. During the surveys, soil–gas samples were collected along traverses crossing the observed structures. The collected soil–gas samples were analysed for He, Rn, CO₂, CH₄, Ar, O₂ and N₂. The data analysis clearly reveals anomalous values along the fault. Before selecting a monitoring site, the occurrence of deeper gas emanation was investigated by the soil–gas surveys and followed by continuous monitoring of some selected sites with respect to tectonic activity to check the sensitivity of the sites. A site was selected for long term monitoring on the basis of coexistence of high concentration of helium, radon and carrier gases and sensitivity towards the tectonic activity in the region. A continuous monitoring station was established at Hsinchu National Industrial Science Park (HNISP) in October 2005. Preliminary results of the monitoring station have shown possible precursory signals for some earthquake events.     

Pulse sequence and timing of contrast‐enhanced MRI for assessing blood–brain barrier disruption after transcranial focused ultrasound in the presence of hemorrhage

Purpose:

To optimize the timing of contrast‐enhanced magnetic resonance imaging (MRI) that best indicates blood–brain barrier (BBB) disruption induced by focused ultrasound (FUS) along with an ultrasound contrast agent (UCA) and to verify that the contrast‐enhanced spin‐echo MRI sequence can indicate the degree and location of BBB disruption in the presence of hemorrhage better than a gradient‐echo sequence.

Materials and Methods:

Sonication was applied to 12 rat brains with four different doses of UCA to cause variable degrees of hemorrhage. Two imaging sequences were performed to acquire T1‐weighted (T1W) images at two time‐points after the administration of a T1‐shortening contrast agent. The contrast enhancement at the sonicated regions was quantified and correlated against Evans blue (EB) staining.

Results:

The spin‐echo T1W images at 10 minutes post–contrast enhancement showed the best correlation with EB staining in both quantity of EB extravasation (r = 0.812; P < 0.01) and spatial distribution (r = 0.528, P < 0.01). This capability was more robust than the gradient‐echo sequence.

Conclusion:

Our results suggest that contrast‐enhanced T1W spin‐echo sequence acquired in the early phase post–contrast enhancement should be considered to monitor the degree and location of BBB disruption under the possibility of hemorrhage induced by FUS. J. Magn. Reson. Imaging 2010;31:1323–1330. © 2010 Wiley‐Liss, Inc.