Paxton A, Nickles R, DeWerd L
University of Wisconsin, Madison, WI.
Med Phys. 2012 Jun;39(6Part20):3856. doi: 10.1118/1.4735740.
This work takes advantage of a newly-determined, low-uncertainty branching ratio of the internal pair production component of Y-90 decay to spectroscopically assay the activity of a Y-90 microsphere sample with a coincidence detection system (CDS).
The CDS pairs a HPGe detector with a large NaI detector. The system is able to electronically filter the bremsstrahlung continuum from the photon spectrum by gating the energy signal from the HPGe with the coincidence signal. This reduces the uncertainty in the spectra measurement compared to measurements with a single HPGe detector. A series of pulsers were used to correct for counting losses. A geometric characterization was completed to find the optimal source position for measurements. An efficiency calibration of the CDS was completed using a Na-22 standard source. To validate the measurement accuracy of the CDS, the activity of a Y-90 standard activity solution from the NIST SRM program was determined and compared to the value given by NIST. The CDS was then used to determine the activity of a Y-90 microsphere sample. This value was compared to the 3.0 GBq value given by the manufacturer.
The activity determined with the CDS was within 2.6% from the given activity of the NIST SRM source, which is within the expanded uncertainty associated with the CDS measurement. The activity of the Y-90 microsphere sample was determined to be 3.72 GBq +/- 1.9%. This is 19% higher than the manufacturer-stated activity of 3 GBq. This is outside the manufacturer-stated uncertainty of +/-10%.
The ability of CDS to determine the activity of a Y-90 source has been validated with comparison to a NIST Y-90 standard activity solution. The use of the CDS has been extended to determine the activity of a Y-90 microsphere sample.
本研究利用新测定的、不确定性较低的钇-90衰变内对产生成分的分支比，通过符合探测系统（CDS）对钇-90微球样品的活度进行光谱分析。
CDS将一个高纯锗探测器与一个大型碘化钠探测器配对。该系统能够通过用符合信号对来自高纯锗的能量信号进行选通，从光子能谱中电子过滤轫致辐射连续谱。与使用单个高纯锗探测器的测量相比，这降低了能谱测量的不确定性。使用一系列脉冲发生器来校正计数损失。完成了几何特征描述以找到测量的最佳源位置。使用钠-22标准源完成了CDS的效率校准。为验证CDS的测量准确性，测定了美国国家标准与技术研究院（NIST）标准参考物质（SRM）计划中的钇-90标准活度溶液的活度，并与NIST给出的值进行比较。然后使用CDS测定钇-90微球样品的活度。将该值与制造商给出的3.0吉贝可（GBq）值进行比较。
用CDS测定的活度与NIST SRM源的给定活度相差在2.6%以内，这在与CDS测量相关的扩展不确定度范围内。钇-90微球样品的活度测定为3.72 GBq±1.9%。这比制造商声明的3 GBq活度高19%。这超出了制造商声明的±10%的不确定度。
通过与NIST钇-90标准活度溶液比较，验证了CDS测定钇-90源活度的能力。CDS的应用已扩展到测定钇-90微球样品的活度。
