Radiation on California Beachesカリフォルニアビーチにおける放射線量

[UPDATE 3/2014: The CDPH did their own study and confirmed our findings below, the report of their findings can be found here]

In December this rather shocking video titled “Fukushima radiation hits San Francisco! (Dec 2013)” was posted to YouTube

To date it’s been viewed almost half a million times, and countless articles have been written referencing it as evidence, source, etc.. However the claims made in the video are inaccurate. Not that the beaches aren’t radioactive – they are – however this is a natural phenomenon that has been documented for over 50 years, a fact which is easily googleable to anyone interested. Unfortunately it seems that the creators of that video, and the media publications that have run with the story, haven’t been interested enough to spend a few minutes doing any research.

In the 2008 paper Radioactivity of sand from several renowned public beaches and assessment of the corresponding environmental risks by Radenkovic, et al, published in the Journal of the Serbian Chemical Society, notable concentrations of Ra226, Th232, K40 were found in LA-area beaches (see table 1). Going back even further 1959, Tracing Coastal Sediment Movement By Naturally Radioactive Minerals is a report by Kamel & Johnson, from Berkeley, which states “This radioactive thorium is added naturally at discrete places along the coast where rivers flowing through thorium rich granite out- crops reach the coast or where the thorium rich granite itself outcrops at the sea coast.”

As there is readily available information that these beaches should naturally show higher radioactive levels than nearby surrounding areas, any claim about outside cause or influence would first need to rule out these documented radioisotopes. Dan Sythe, CEO of International Medcom (whose Inspector device is featured in the video) and self professed “truth junkie,” was concerned about these reports and immediately had soil samples taken from the beaches in Half Moon Bay where the video was created to identify the cause of these higher levels. Using a SAM 940 Multichannel Analyzer he found the sand to contain NORM levels of Radium 226 and Thorium 232 – in line with what would be expected based on the previously linked papers. He did not find any Caesium which would indicate contamination from Fukushima. He documented his findings on the Geiger Counter Bulletin, in a post titled California Beach Radiation Not From Fukushima. Here are actual shots of the measurements:

Sand from beaches in Half Moon Bay,
showing levels of Radium 226 and Thorium 232.

Sand from beaches in Fukushima,
showing levels of Caesium 137.


Also worth noting is that while normal background levels around California are between 30-60 CPM, and measurements have been taken on these beaches in Half Moon Bay (as well as other spots along the west coast) of upwards of 200 CPM, this is still far less than what a person is exposed to on a typical commercial airline flight where levels are regularly over 800 CPM for the duration of the flight. 200 CPM is within the level you would expect to measure from a granite counter top, or a building with some kinds of exposed brick.

So the actual science here immediately disproves claims that there is radiation from Fukushima hitting the beach in any detectible levels. Yet – an important distinction – as many existing scientific models show that trace, though detectible levels will reach the coast in the next few years, a topic we’ll address in a future post.

It’s also worth discussing some of the other points brought up in the above video, as they seem to be the cause of much stress for many people. The video accurately shows that levels increase on the beach, and decrease towards the water line, which indicates that it’s not the water itself that is the source of the readings, otherwise the levels would continue to rise as the geiger counter was brought closer to the water. Additionally, it’s not the air, because in that situation the entire area would have higher levels – the entire beach, the path, the roadway, sidewalks – everything would have a higher level. Since it’s very clear that the elevated readings are restricted to specific areas, that’s evidence that the source is on/in the surface.

To document this we’ve sent a Safecast team with our own bGeigie Nano’s to the area and expect to have detailed maps/data back from them shortly and will amend this post when we have it.[2014年3月に更新:CDPH(カリフォルニア州公衆衛生局)は、自ら研究を行い、下記のようにセーフキャストの調査結果を確認しています。その調査結果の報告書はここで見ることができます]




これらのビーチは、近接する周辺地域よりも放射能レベルが高いのは当然であろうという情報は容易に入手できるので、外的要因や外的影響に関するいくつかの主張は、まずこれらの文書化された放射性同位元素(ラジオアイソトープ)情報を排除しているのでしょう。インターナショナル・メドコム社(同社のインスペクターが動画内で登場している)の最高経営責任者であり、「真実に取り憑かれた者」と自称するダン・サイス(Dan Sythe)氏は、これらの報告書について関心を持ち、すぐさま、この高い数値の原因を特定するために、動画が作成されたハーフムーンベイのビーチから土壌サンプルを検出しました。サイス氏が見つけだした SAM 940「マルチチャンネルアナライザー」を使用することによって、ラジウム226とトリウム232というNORM(天然起源放射性物質)が含まれている砂を発見しました。それは、過去に発表された関連の論文から予測していたことでした。Hサイス氏は、福島からの汚染を示すいかなるセシウムも発見しませんでした。彼は、カリフォルニアビーチの放射線は福島からではない というタイトルの投稿を、ガイガーカウンターブルテン(Geiger Counter Bulletin)にしました。実際の測定写真は、以下の通りになります。





ですから、実際の科学では、福島から検出可能な数値の放射線がカリフォルニアビーチへ到達するなどという話はただちに誤りであると証明できます。しかし、ひとつの重要な特徴として、多くの既存の科学的モデル は、検出可能な数値は今後数年間でこのカリフォルニアの海岸に到達するだろうという証拠を示しており、そのトピックこそ、私たちが今後の取り組んでいくものです。

また、このビデオに登場した、このことが多くの人に多大なストレスを与えたという点にも議論の余地があります。この動画は実際に、数値がビーチで上昇し、水位線に向かって減少していることを示しています。つまり、これは水そのものが数値の原因ではないことを示しているにもかかわらず、ガイガーカウンターを水に近づけて持っていくと数値が上がり続けるようになっています。加えて、その数値の原因は空気ではありません。なぜなら、そのような状況であれば、その周辺一体のエリアは高い数値であるはずです。 ビーチ、車道、歩道の全てにおいて高い数値がでるはずです。上昇する測定値が特定の領域に限定されているということはとても明確ですので、その原因が表面上あるいは下に存在しているという証拠になります。


(翻訳: Kohei Watanabe)

About the Author

Sean Bonner


Sean Bonner is a co-founder and Global Director of Safecast. Based in Los Angeles, he's an Associate Researcher at the Center For Civic Media at the MIT Media Lab and a Shuttleworth Fellow.