Human Eye Can Detect Cosmic Radiation

Well, not in the way you think.

I recently found this video of an appearance of astronaut Scott Kelly on The Late Show with Stephen Colbert. During this segment, he talked about the fact that when he went to sleep on the Space Station and closed his eyes, he occasionally detected flashes of light. He attributed it to the cosmic radiation  passing through his body, and his eyes in particular.

Check out the video at minute 3:30



My first inclination is to say that this is similar to how we detect neutrinos, i.e. the radiation particles interact with the medium in his yes, either the vitreous or the medium that makes up the lens, and this interaction causes the ejection of relativistic electron and subsequently, a Cerenkov radiation. The Cerenkov radiation is then detected by the eye.

Of course, there are other possibilities, such as the cosmic particle causes an excitation of an atom or molecules when they collided, and this then caused a light emission. But Scott Kelly mentioned that these flashes appeared like fireworks. So my guess here is that it is more of a very short cascade of events, and probably the Cerenkov light scenario.

This, BTW, is almost how we detect neutrinos, especially at Super Kamiokande and all the neutrino detectors around the world. Neutrinos come into the detector, and those that interact with the medium inside the detector (water, for example), cause the emission of relativistic electrons that move faster than the speed of light inside the medium. This creates the Cerenkov radiation, and typically, the light is blueish white. It's the same glow that you see if you look in a pool of fuel rods in a nuclear reactor.

So there! You can detect something with your eyes closed!

Zz.

Is Radiation Dangerous?

Believe it or not, there are still people out there who get scared witless and going out of their minds with their phobia about "radiation". I get questions related to this often enough that whenever I find info like this one, I want to post it here.

Don Lincoln decides to tackle this issue regarding "radiation". If you have little knowledge and idea about this, this is the video to watch.



Zz.

She's Still Radioactive!

She, as in Marie Curie.

This article examines what has happened to the personal effects of Marie Curie, the "Mother of Modern Physics".

Still, after more than 100 years, much of Curie's personal effects including her clothes, furniture, cookbooks, and laboratory notes remain contaminated by radiation, the Christian Science Monitor reports.

Regarded as national and scientific treasures, Curie's laboratory notebooks are stored in lead-lined boxes at France's national library in Paris.

While the library allows visitors to view Curie's manuscripts, all guests are expected to sign a liability waiver and wear protective gear as the items are contaminated with radium 226, which has a half-life of about 1,600 years, according to Christian Science Monitor.

What they didn't report, and this is where the devil-is-in-the-details part is missing, is what level of radioactivity is given off by these objects. You just don't want to sign something and not know the level you will be exposed to (which, btw, if you work in the US or at a US National Lab, a RWP (radiation work permit) must be posted at the door detailing the type of radiation and the level of radiation at a certain distance).

I suspect that this level is just slightly above background, and that's why they are isolated, but not large enough for concern. Still, the nit-picker in me would like to know such details!

Zz.

Teaching Radioactivity

A series of videos from the Institute of Physics (IoP) that teach elementary radioactivity.

Zz.

Fukushima: Fact Versus Fiction

A video of a panel dialog on the nuclear disaster at the Fukushima nuclear power plant.



Zz.

Traces of Radiation from Japan?

So I read this CNN news this morning about slightly higher radiation levels that could possibly come from Japan.

But, on a portion of its website dedicated to tracking such radiation, the Environmental Protection Agency noted Wednesday that these and other readings "show typical fluctuation in background radiation levels" and -- thus far -- "are far below levels of concern."

Sampling from a monitor in Colorado -- part of a national network of stations on the lookout for radioactivity -- detected miniscule amounts of iodine-131, a radioactive form of iodine, the state's public health and environmental department said Wednesday in a press release.

On the same day in Portland, Oregon, tiny quantities of iodine-131 were also detected by an Environmental Protection Agency air monitor, Oregon public health officials said.

Now, the physicist in me started asking "It's one thing to detect slightly higher-than-normal radiation, it is another to actually know the source of such radiation." How can one verify a statement that says ".. trace amounts of radioactive particles that have likely drifted about 5,000 miles from a quake and tsunami-damaged nuclear power plant in Japan.. " Is the detection of such iodine isotopes rather uncommon, so much so that their detection now can be plausibly linked to the nuclear accident in Japan? Can someone who is an expert in this field clarify this?

Zz.

Radiation

As expected, whenever something like this occurs, the fear (be it warranted or not) about radiation resurfaces once again. It is also a good time to educate the public a little bit on what radiation is, and the fact that we, human beings, live with it every single moment of our lives.

This news article looks at everyday sources of radiation that we live with.

With the help of CU physicists, 7NEWS tested everyday objects with a Geiger counter, a device that detects radiation levels.

We held the meter against the buildings on campus, a post office mailbox, electronic devices, even a banana with potassium. All of the objects caused the meter to beep and show levels of radiation, but only in trace amounts.

"These parts of the country are actually naturally blessed with a slightly higher level of radioactivity," said Nesbitt. "Low is good, but zero is just not what you're ever going to find in everyday life."

People who have an unreasonable fear of "radiation" should look at this article and accompanying video. Often, these are the very same people who put granite countertops in their homes. I'm not saying that such material is unsafe. I'm saying that ALL of us have accepted a certain level of radiation that we live with.

Zz.

Airport X-Ray Backscatter Scan May Miss Hidden Objects

I've mentioned in a couple of blog entries regarding the airport full-body scans and the physics surrounding them (see here and here). We once again won't address the "emotional" issues associated with those machines. But we can certainly address issues related to physics.

Beyond the issue of radiation dosage, the other issue here is the effectiveness of such machine in detecting hidden objects underneath one's clothing. This question came up recently upon the publication of a new study[1] that showed (mainly via simulation), that depending on the type of material and where it is hidden on the body, such objects can missed in such a body scan. This new study was covered and reported here.

According to the report, the reasons contraband might not be detected are because of the X-ray exposure level produced by the scanner combined with how a substance such as plastic explosives are placed on a persons body. Those factors can prevent the material from being detected by the scanner, the study says. In addition, “because front and back views are obtained (in a scan), low Z (metal) materials can only be reliably detected if they are packed outside the sides of the body, or with hard edges, while high Z materials are well seen when placed in front or back of the body, but not the sides.”

You may read the actual paper at the link listed at the bottom of this blog entry. Of course, the TSA has a standard response to something like this:

Nonetheless, the TSA says, “Advanced imaging technology is a proven, highly-effective tool that safely detects both metallic and non-metallic items concealed on the body that could be used to threaten the security of airplanes.”

“TSA employs many layers of security that work collaboratively to form a system that gives us the best chance to detect and disrupt the evolving threats we face,” the agency’s statement says.

That is a non-statement that doesn't address the scientific study. A proper rebuttal would be to send a rebuttal paper to address the specific result of the paper. That's the only way the scientific result can be disputed, not by basically saying "it is effective because I said so". That might work in politics, but it doesn't work at all in science. And this is a scientific issue. The TSA should commission a study to either verify or dispute this work, not issue some bland, generic replies that really didn't say anything worthy.

Zz.

[1] L. Kaufman and J.W. Carlson J. Transp. Secur. DOI 10.1007/s12198-010-0059-7 (a copy of the paper is available, at this moment, here).

The Physics of X-Ray Backscattering at Airports

I'm back and severely jet-lagged. So it'll be a couple of days before I'm back up to speed with what's been happening. But yours truly got his first full-body scan at O'Hare on this past trip. Yippee!

I couldn't figure out if it was the X-ray backscattering or the millimeter wave technology. I was about to ask one of the TSA's officer what it was, but they were all rather busy at that time, and I was already "loitering" about the area for a few minutes. After giving it a thought, I decided not to risk raising suspicion about being too curious about the scanning technology and left.

Anyway, if anyone wants to look at the issue surrounding the millimeter wave technology, check out an earlier blog entry. Ars Technica has a good article covering the x-ray backscattering technology.

Happy traveling!

Zz.

Full Body Scans At Airports

Obviously, the biggest news in the traveling world lately is the controversy surrounding the full-body scans at airports around the world. There are people who don't want to go through it, opting instead for a full body pat down (which in itself could be highly intrusive).

Now, there are various reasons why people don't want to have the full body scans, ranging from privacy matters all the way to safety. Physics can't address issues on privacy matters - it is a personal decision and what you are comfortable with. However, physics can certainly address the latter, which is the radiation safety issues. This is where I see many people are getting either the wrong information, or not realizing what they accept to be "safe" and what isn't.

What makes it a bit confusing is that, at least in the US, there are two types of full-body scans. There is one called the X-ray backscattering scan, and the other being the Millimeter-Wave scan. The former uses weak x-ray to do the scan. The TSA has cited studies in which the amount of radiation received during such a scan is equivalent to about 2 minutes of flight time at high altitude. There's some questions about this number, and some even quote it to be as long as 1/2 hour. Regardless of the number, it is still less than what you get with a dental x-ray, and certainly less than what you would get over a typical airplane flight. So one has to consider, just like having a medical x-ray, if this is an acceptable risk, or not. This is a personal judgment, but it should be decided upon a clear understanding of the radiation amount received IN COMPARISON with others that one has already accepted.

Now, the latter uses non-ionizing radiation, typically in the GHz range. So this is safe as far as "radiation" is concerned. Yet, there are those who are not aware of this. See this blogger, for example.

One report from a very credible source (a famous health author whom I know quite well) reveals that TSA officers told her the naked body scanners don't even emit X-rays. "It's a myth," the officer said. "There are no X-rays from those machines."

Really? Then how do they work? Are they MAGIC? Do TSA officers cast a magic Spell of X-Ray Vision on the air travel passengers like some sort of Dungeons & Dragons adventure?

No, it could easily mean that that scanner is the Millimeter-wave imaging scanner, and it is completely accurate that there are no x-rays from the machines. BTW, there is a very nice paper describing the physics of this technique that you should read if you're interested in this:

D.M. Sheen, et al., IEEE Trans. Microwave Theory and Tech. v.49, p.1581 (2001).

I think people need to make an informed decision here, rather than repeating the same irrational decision that's based on rumors and half-truths. If you know the difference between x-ray backscattering and millimeter wave scans, and you also know how much radiation you get when compared to other types of radiation, then go ahead and decide if you want to skip the scan and do a pat down. But don't decide based on confusing the two types of scans, or simply not knowing the level of radiation that you get when compared to other types that you've already accepted as part of your life.

And don't use the safety card to hide behind other issues. If you dislike the scan because you don't want an image of your pseudo-naked self being displayed on a screen somewhere, then argue it on that point, not on concerns about "safety".

Zz.

How To Build A Cloud Chamber

More fun instructional videos from Jefferson Lab. This time, they teach you how to build a simple cloud chamber.



So, talking about safety, shouldn't the woman wear safety glasses, especially when the isopropanol is being squirted? The MSDS that was referred to indicated that one should wear eye protection, and gloves.

Read my previous blog entry to see other videos in this series.

Zz.