Dating lime mortar samples using the radiocarbon (14C) method can be difficult. This is because the contamination is similar to the primary dating material (CaCO3) and consequently difficult to remove. Mortar can also have late-in-formation pyrogenic carbonate from interactions with the environment after the initial hardening phase, such as recrystallization, fire damage or delayed hardening. When 14C dating a system of primary dating material, contamination and late-in-formation pyrogenic carbonate, one approach is multi-fraction dating with conclusiveness criteria. If a sample has sufficient contamination or late-in-formation pyrogenic carbonate, the criteria evaluate the result inconclusive. To improve inconclusive results from such samples, this study investigates sample preparation by thermal decomposition. Here samples that were inconclusively dated by the authors’ traditional method, sequential dissolution with 85% phosphoric acid, are investigated further. This study finds that CO2 thermally decomposed at low temperatures contains some late-in-formation pyrogenic carbonate. By rejecting CO2 decomposed at low temperatures, Kastelholm castle and Kimito church in Finland are conclusively and accurately dated. Furthermore, a preheating method removes some late-in-formation carbonate, but not enough for a conclusive result. Finally, thermal decomposition finds difficulty in discerning binder carbonate from limestone and marble contamination.

中文翻译：

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热分解和顺序溶解的比较——石灰砂浆放射性碳测年的两种样品制备方法

使用放射性碳（14C) 方法可能很困难。这是因为污染类似于主要测年材料（CaCO3)，因此难以移除。砂浆也可能在初始硬化阶段后与环境相互作用，例如再结晶、火灾损坏或延迟硬化，从而产生后期形成的热解碳酸盐。什么时候14C 测年是一个由初级测年材料、污染和晚形成的热解碳酸盐组成的系统，一种方法是具有确定性标准的多级分测年。如果样品有足够的污染或形成较晚的热解碳酸盐，则该标准评估的结果是不确定的。为了改善此类样品的不确定结果，本研究研究了通过热分解进行的样品制备。在这里，作者进一步研究了通过作者的传统方法（用 85% 磷酸连续溶解）无法确定日期的样品。本研究发现，CO2在低温下热分解含有一些形成后期的热解碳酸盐。通过拒绝 CO2芬兰的卡斯特霍尔姆城堡和基米托教堂在低温下分解，其年代确凿而准确。此外，预热方法去除了一些晚期形成的碳酸盐，但不足以得出确凿的结果。最后，热分解发现难以从石灰石和大理石污染物中辨别粘合剂碳酸盐。