Uncertainties related to in situ gamma-ray spectrometry measurements have been widely acknowledged. Despite being commonly used in exploration, the evaluation of the uncertainty range of K, U and Th gamma spectrometry field measurements is generally limited due to the lack of corresponding laboratory measurements. Estimating uncertainty, however, is essential to ensure reliable and accurate results.

In this paper, we establish a set of procedures to acquire gamma-ray spectrometry data while minimizing uncertainty, based on high-resolution lithostratigraphy and composite gamma-ray logging techniques. We compare the concentration of radionuclides measured in situ in 250 selected sites in outcrops of the Lower and Middle Jurassic sedimentary successions of the Lusitanian Basin to the concentration of radionuclides in representative samples collected from the same outcrops and analysed in the laboratory.

The global radiometric dataset obtained for K, U and Th is similar between field and laboratory gamma spectrometry measurements, which are correlated. The root-mean-square deviation was determined for K, U and Th, and the error of the field measurements was estimated at 0.6%, 1.4 and 2.5 ppm, respectively. We calculated the relative error (RE) between laboratory and field data. If we use the interquartile range of the RE to distinguish outliers in each radionuclide dataset, approximately 8%, 6% and 10% of the K, U and Th field measurements correspond to outliers. Conversely, 92%, 94% and 90% of the samples offer reliable field data for K, U and Th, respectively. The RE is similar between K and U, with a mean of 0.73 and 0.69, respectively, and is higher for Th (with a mean of 1.29). Higher RE values are also observed in dolostones (D), dolomitic limestones (DL), limestones (L) and marly limestones (ML). Lower RE values are linked to sandstones (S) and fine-grained siliciclastic (F-g.S) lithologies, with a mean value of 0.19, 0.33 and 0.25 for K, U and Th, and 100% of reliable data.

As the accuracy of field gamma-ray measurements varies with lithology, field procedures must be adjusted for lithological variability to reduce uncertainty. Given that the RE decreases with an increase in layer thickness, thicker sedimentary layers should be favoured when measuring K, U and Th concentration in field campaigns.

与原位伽马射线能谱测量相关的不确定性已得到广泛认可。尽管通常在勘探中使用，但由于缺乏相应的实验室测量值，因此对K，U和Thγ谱仪野外测量的不确定性范围的评估通常受到限制。但是，估计不确定性对于确保可靠和准确的结果至关重要。

在本文中，我们基于高分辨率的岩相地层学和复合伽马射线测井技术，建立了一套在获取伽马射线光谱数据的同时将不确定性降至最低的程序。我们比较了卢西塔尼亚盆地中侏罗世沉积演替层露头中250个选定地点的原位测量的放射性核素浓度与从同一露头收集并在实验室中分析的代表性样品中的放射性核素浓度。

在野外和实验室伽马能谱测量之间获得的有关K，U和Th的全球辐射数据集是相似的，它们之间是相关的。确定了K，U和Th的均方根偏差，现场测量的误差估计分别为0.6％，1.4和2.5 ppm。我们计算了实验室和现场数据之间的相对误差（RE）。如果我们使用RE的四分位数范围来区分每个放射性核素数据集中的离群值，则K，U和Th场测量值中大约有8％，6％和10％对应于离群值。相反，分别有92％，94％和90％的样本分别提供了K，U和Th的可靠现场数据。该REK和U之间相似，均值分别为0.73和0.69，Th值更高（平均值为1.29）。在白云岩（D），白云质石灰石（DL），石灰石（L）和马来石灰石（ML）中也观察到较高的RE值。较低的RE值与砂岩（S）和细粒硅质碎屑岩（Fg.S）岩性有关，K，U和Th的平均值分别为0.19、0.33和0.25，并且100％是可靠数据。

由于现场伽马射线测量的精度随岩性而变化，因此必须针对岩性的变化调整野外程序，以减少不确定性。鉴于RE随着层厚度的增加而降低，因此在野战活动中测量K，U和Th浓度时，应优先选择较厚的沉积层。