The sediments deposited in Lake Kevojärvi (69°45N, 27°00′E) in northernmost Finland were investigated for radioactivity. Freeze cores recovered from the 35-m deep basin has preserved a distinct succession of annual laminations deposited between 1909 and 2015. The basic varve structure is composed of a detrital snowmelt layer and an organic-rich post-snowmelt layer lying on top of the snowmelt layer. The past nuclear events have been preserved in the lake sediment. In order to study these, sediment freeze with annual sediment laminations were recovered from the lake bottom and measured for gamma emitting radionuclides. A total of 53 sediment subsamples, each incorporating sediment from one to two varves i.e. sediment deposited during one to two years, were taken for gamma spectroscopy measurements using low-background HPGe detector system. The measurements showed large variations in ¹³⁷Cs and ²⁴¹Am concentrations between different laminae marking different nuclear events in history. This highly resolved profile revealed a detailed record of anthropogenic radioactive fallout from atmospheric nuclear weapons testing during 1950s and 1960s and the Chernobyl accident in 1986. The measured ¹³⁷Cs concentrations varied between 0.6 and 229 Bq/kg dry weight (dw) while the measured ²⁴¹Am concentrations varied between 0.6 and 6.4 Bq/kg dw. The ¹³⁷Cs showed downward migration in the sediment column since ¹³⁷Cs was also found in varves dating before 1945. The first clear increase in ¹³⁷Cs concentration was observed in 1956 varve and the ¹³⁷Cs concentrations were found to peak in the 1964, 1970 and 1986 varves. The ²⁴¹Am was first observed in 1957 varve and the concentrations peaked in 1960–1962, 1964 and 1970 varves. This demonstrated that ²⁴¹Am can be a complementary chronostratigraphic marker to ¹³⁷Cs in sediment. A time delay of one to two years was observed between the years of intensive atmospheric nuclear weapons testing and the increased ¹³⁷Cs and ²⁴¹Am concentrations in the sediment varves. In the ²¹⁰Pb concentrations long-time periods of low (~1930–1950 and ~1990–2000) and high concentrations (~1950–1980) were observed. The reason for large variation was the amount of sediment input. The Constant rate of supply (CRS) model results showed good agreement with the varve counting. The model results showed that the ²¹⁰Pb deposition has been constant over the last 80 years and no effect of climate change to the ²¹⁰Pb deposition was observed.

调查了芬兰最北端的Kevojärvi湖（69°45N，27°00′E）中的沉积物的放射性。从深达35米的盆地中回收的冻核保留了1909年至2015年之间沉积的一系列明显的年叠层。基本的瓣膜结构由碎屑融雪层和位于融雪顶部的富含有机物的融雪后融雪层组成层。过去的核事件已保存在湖泊沉积物中。为了研究这些问题，从湖底回收了具有每年沉积物分层的沉积物冻结物，并测量了伽马发射放射性核素。使用低背景HPGe检测器系统对总共53个沉积物子样本进行了伽玛光谱测量，每个子样本都包含一到两个阀门的沉积物，即在一到两年内沉积的沉积物。不同层之间的¹³⁷ Cs和²⁴¹ Am浓度标志着历史上不同的核事件。这一高度解析的资料揭示了1950年代和1960年代大气核武器测试和1986年切尔诺贝利事故的人为放射性沉降的详细记录。测得的¹³⁷ Cs浓度在0.6至229 Bq / kg干重（dw）之间变化，而测得的²⁴¹ Cs浓度在²⁴¹ Bq / kg干重之间。Am浓度在0.6至6.4 Bq / kg dw之间变化。的^137个Cs的显示在沉积物柱向下迁移，因为^137个Cs的也于1945年varves之前约会中的第一个明显的增加发现¹³⁷ Cs的浓度在1956年纹层和观察到¹³⁷发现Cs浓度在1964、1970和1986年的阀门中达到峰值。在²⁴¹上午被在1957年首次观察到纹层和浓度1960年至1962年，1964年和1970年达到高峰varves。这表明²⁴¹ Am可能是沉积物中¹³⁷ Cs的补充年代地层标记。在密集的大气核武器试验与沉积物中的¹³⁷ Cs和²⁴¹ Am浓度增加之间，观察到了一到两年的时间延迟。在²¹⁰长期观察到铅的浓度处于低水平（〜1930–1950和〜1990–2000）和高浓度（〜1950–1980）。变化很大的原因是泥沙输入量。恒定供给率（CRS）模型结果与阀门计数显示出良好的一致性。模型结果表明，在过去的80年中²¹⁰ Pb的沉积一直保持恒定，并且未观察到气候变化对²¹⁰ Pb沉积的影响。