On December 23, 2013, a man who goes by the YouTube username KillYour0TV took a Geiger counter to Pacifica State Beach in San Francisco and detected disturbing levels of radiation as he approached the ocean. The video has gone viral. He explains:

Background radiation reading is 30 CPM. Near the ocean it's 150 CPM. The moister (sp) coming from the ocean waves seems to be what makes the Geiger Counter jump up 5X. This is not normal at all.

The video title suggests he attributes the heightened radiation to the nuclear disaster at Fukushima Daiichi.

Is his reading accurate? Is there evidence to suggest the radiation results from the Fukushima Daiichi disaster?

  • 2
    I assume "moister" means moisture, not monster!
    – Golden Cuy
    Commented Jan 2, 2014 at 23:55
  • 1
    There are actually two different claims here, first explicit, that the elevated radiation is from Fukushima, second, implied, that this level of radiation is dangerous (wording is kind of FUD, going with ambiguous "disturbing level")
    – vartec
    Commented Jan 3, 2014 at 11:09
  • 1
    This is all pretty meaningless without the relevant context such as what are the normal background counts in the area. "normal" radiation levels vary by far more than this in different geological environments. And counts isn't much use for measuring the harm of radiation: you need to know what type and strength (alpha, beta, gamma radiation and what energy each has).
    – matt_black
    Commented Jan 3, 2014 at 17:06
  • Also, the sea naturally contains a high enough concentration of uranium that some people seriously suggest "mining" it. Commented Jan 5, 2014 at 10:15
  • Item 5 of theprovince.com/touch/story.html?id=9406811 addresses this claim.
    – Golden Cuy
    Commented Jan 22, 2014 at 11:16

3 Answers 3


Is his reading accurate?

Most likely, yes. There's quite a lot of naturally occurring uranium, thorium and radium in California. As Thunderf00t (Phil Mason) points out in his video, Panic as Fukushima radiation 'found' on Californian beach, magnetic black sand is well known for containing elements like thorium, and you can see the CPM rise when the man walks over black sand and the levels decrease nearer the water.

Is there evidence to suggest the radiation results from the Fukushima Daiichi disaster?

No. After seeing that video, Dan Sythe tested soil samples taken from the beaches in Half Moon Bay and here are his findings:

The radionuclides are in the NORM class of radioactive substances, not from Fukushima. NORM stands for Naturally Occurring Radioactive Material. We put a sample in a Multichannel Analyzer and found Radium 226 and Thorium 232. See the measured spectra below.

Radioactive spectrum from California Beach

If the sand were contaminated by radiation from Fukushima it would show Cesium 137. See spectra below from contaminated area of Fukushima Prefecture. The same instrument is identifying Cesium 137 rather than Radium and Thorium.

Radioactive spectrum of Fukushima sample

A 2008 paper Radioactivity of sand from several renowned public beaches and assessment of the corresponding environmental risks, took samples from California beaches and found notable concentrations of Ra226, Th232, and K40.

enter image description here


Firstly, "Counts per minute" is essentially meaningless since every device registers counts differently.

As Wikipedia points out;

Counts are only manifested in the reading of the measuring instrument, and are not an absolute measure of the strength of the source of radiation. Whilst an instrument can display at a rate of cpm, it does not have to detect counts for one minute, as it can infer the total per minute.

Additionally, significant radiation leakage from Fukushima is unlikely to have even reached the West coast of America yet.

“Ocean simulations showed that the plume of radioactive cesium-137 released by the Fukushima disaster in 2011 could begin flowing into U.S. coastal waters starting in early 2014 and peak in 2016. Luckily, two ocean currents off the eastern coast of Japan — the Kuroshio Current and the Kuroshio Extension — would have diluted the radioactive material so that its concentration fell well below the World Health Organization’s safety levels within four months of the Fukushima incident. But it could have been a different story if nuclear disaster struck on the other side of Japan.”

And even when it does, the levels of radioactivity will fall well below a level that is likely to be significantly harmful to health.

Tentatively assuming a value of 10 petabecquerel (PBq) for the net 137Caesium (Cs) input during the first weeks after the Fukushima incident, the simulation suggests a rapid dilution of peak radioactivity values to about 10 Bq/m³ during the first 2 years, followed by a gradual decline to 1–2 Bq/m³ over the next 4–7 years. The total peak radioactivity levels would then be about twice the pre-Fukushima values. “While this may sound alarming, these levels are still lower than those permitted for drinking water,” said Böning.

Quite what is causing his geiger counter to register a different rate as he approaches the ocean is unclear. Perhaps it's something to do with moisture in the air because there's no reliable indication that it has anything to do with radiation.

  • It does have a bit too do with radiation, as linked in my answer, there is naturally occurring radiation in these beaches. Every other part of your answer is correct, and to some degree, even your last statement. Commented Apr 4, 2014 at 16:08

This video shows a background reading of 30 to 40 cpm. From the manual the specifications of the geiger counter are known. It detects alpha, beta and gamma radiation with a pancake tube, however alpha radiation is blocked by air within 4cm and not detected. Assuming Cs-137, as most other detectors are calibrated against this source and the given tube characteristics, a dose rate of ~90 nSv/h is obtained. This is in perfect agreement with natural background radiation expectations.

Now taking the 150 cpm reading, you get 450 nSv/h. As you are not 24hours/365 days in this radiation field, it may considered safe, depending on your local legislation. However, this level is indeed above the background. This readings are out of the error band and statistically significant. And the video shows a distance correlation to the the beach.

Update 1: According to this article "Health officials respond to beach radiation scare" there is now an official investigation.

County health officials first learned of the radiation levels last week, and they sent their own inspector on Dec. 28 to Pacifica with a Geiger counter. Using a different unit, the county inspector measured the beach to have a radiation level of about 100 micro-REM per hour, or about five times the normal amount.

Note: 100 microRem/h=1 microSievert/h. So the original video even underestimated the radiation by a factor of 2.

Although the radiation levels were clearly higher than is typical, Peterson emphasized that it was still not unsafe for humans. A person would need to be exposed to 100 microREMs of radiation for 50,000 hours before it surpassed safety guidelines by the Occupational Safety and Health Administration, he explained.

100 microREM/h times 50 000 hours makes 5 REM or 50 mSv. This is outside of The 2007 Recommendations of the International Commission on Radiological Protection of 1 mSv artificial dose rate for common people. For the US special regulations apply. Your yearly combined dose should not exceed 5 mSv. Within 5 000 hours in a 100 micro REM radiadion field you get your yearly "save" dose.

So maybe you should avoid this confirmed hot spot beach West of San Mateo, south of Princeton Harbor. Or limit your visit to approx. 3 hours a day.

Update 2:

A recent Half Moon Bay Review article interprets the readings with the occurrence of radioactive Thorium in the black sand

“It’s not considered a radiation hazard, so long as you’re not eating it, and you’re not living on it, 24/7.”

  • Welcome to Skeptics! Please provide some references to support your claims. This single anecdote is insufficient to be convincing.
    – Oddthinking
    Commented Jan 6, 2014 at 6:22
  • Please specify your 'single anecdote'. Commented Jan 6, 2014 at 7:26
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    A single guy with a single Geiger counter making a single trip to a single beach is a single anecdote.
    – Oddthinking
    Commented Jan 6, 2014 at 7:56
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    "safe, depending on your local legislation", lol, I thought that would depend on medical science, not lawyers :-P
    – vartec
    Commented Jan 6, 2014 at 12:19
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    And from the same newspaper hmbreview.com/news/radioactive-sands-known-for-years/… here is an article saying scientists have known about high radiation levels at that beach for 50 years - it's apparently caused by high thorium in the sand.
    – Mark
    Commented Jan 18, 2014 at 22:17

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