History by history statistical estimators in the BEAM code system
History by history statistical estimators in the BEAM code system
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DOI：
10.1118/1.1517611
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发表时间：
2002-12-01
期刊：
影响因子：
3.8
通讯作者：
Rogers, DWO
中科院分区：
文献类型：
--
作者：
Walters, BRB;Kawrakow, I;Rogers, DWO
在BEAMnrc和DOSXYnrc程序中实现了按历史的方法来估计不确定度，取代了统计批次的方法。该方法根据主要病史对计分数量(例如，剂量)进行分组。当使用相空间源时，该方法根据产生入射粒子的主要历史对它们进行分组。这就需要向相空间文件添加标记(负能量)，以指示由新的初级历史生成的第一个粒子。新方法大大减少了不确定度估计中的不确定性。新方法从所有的评分数组中去掉了一维(保存每批结果)，导致内存需求减少了2倍。考虑了相空间源中粒子之间的相关性。与不确定性有任何重大影响的唯一关联是粒子回收引入的关联。未能考虑到这些相关性可能会导致对不确定性的严重低估。以前通过将所有回收颗粒放在同一批中来计算回收相关性的方法确实奏效了。当相空间源重新启动时，新方法和批处理方法都没有考虑入射粒子之间的相关性，因此必须避免重新启动。
A history by history method for estimating uncertainties has been implemented in the BEAMnrc and DOSXYnrc codes replacing the method of statistical batches. This method groups scored quantities (e.g., dose) by primary history. When phase-space sources are used, this method groups incident particles according to the primary histories that generated them. This necessitated adding markers (negative energy) to phase-space files to indicate the first particle generated by a new primary history. The new method greatly reduces the uncertainty in the uncertainty estimate. The new method eliminates one dimension (which kept the results for each batch) from all scoring arrays, resulting in memory requirement being decreased by a factor of 2. Correlations between particles in phase-space sources are taken into account. The only correlations with any significant impact on uncertainty are those introduced by particle recycling. Failure to account for these correlations can result in a significant underestimate of the uncertainty. The previous method of accounting for correlations due to recycling by placing all recycled particles in the same batch did work. Neither the new method nor the batch method take into account correlations between incident particles when a phase-space source is restarted so one must avoid restarts.