Cosmic Rays

[Don Parrish]

You are correct, some of the references were from nasa.

[Alan Emery]

I have been away for some time, but am now back and can add a bit more information about cosmic ray particles and camera sensors. The information I provided on muons remains valid, however the information on neutron defects can now be updated. Not many of the neutrons actually hit anything when they pass through the sensor but when they do they can cause permanent defects.

The most recent article I can find that has actual data (based on 23 DSLRs, 4 point and shoot cameras, and 11 cell phone cameras) as opposed to speculation is February 16, 2011 in volume 12 of “Sensors, Cameras, and Systems for Industrial, Scientific, and Consumer Applications”. Previous results showed that CMOS (APS) sensors were somewhat less vulnerable than CCD sensors. This study shows high ISO ranges cause the defects to be more noticeable thereby increasing the “rate” of observable defect. It also shows that for a given pixel size the number of defects scales with sensor size. The study also shows that defect rate increases rapidly (an empirical power law of the pixel size to be -2.5; a somewhat faster rate than just area as pixels sizes shrink). A large sensor can reach higher ISO numbers so is thereby more vulnerable than smaller sensors to cosmic ray neutron damage.

A different study looked at the relationship between altitude and latitude. Given Vancouver as a base index of “1”, Denver was “4”, Hong Kong about “.5”. The closer to the poles and the higher you are the more vulnerable is the sensor. Living in mid latitudes at moderate altitudes like Denver makes the camera 8 times as vulnerable as living at sea level in the tropics such as near Hong Kong. Other studies have shown that at altitudes reached by commercial aircraft the defect rate can be 100 times greater than at sea level.

As cameras evolve to higher resolution and faster speeds, cosmic ray particle defects will presumably be an increasingly significant design consideration for camera sensors, memory chips, and on-board computers (which also can be hit by muons and neutrons).

I still think this is a fun -- and serious -- problem. Here we are talking about quantum physics affecting our everyday lives. So far no one has actually tested the idea of a tin foil hat worn shiny side out.

Alan

[Jim Tittle]

As soon as I can get the HDMI output problem on my F3 fixed, I'll do those tinfoil hat tests.

[Don Parrish]

Would man made radiation from reactors pose a problem to the cameras in Japan ?

[Alan Emery]

Hi Don,

Japan's situation is very nasty right now, and the radioactivity scare is definitely real but with so little reliable information it is hard to know what is really happening in and around the plants. The radiation from the core will be alpha, beta, and gamma radiation. Alpha and beta won't harm cameras because the outer camera shell will stop them, but gamma radiation can if the camera is within range of the radiation (takes about 2-4 inches of lead to stop that stuff). Several explosions (probably mix of gases and superheated water) will have released particles that have ionizing radiation so if that settles on the cameras, it could do damage. Certainly people are in trouble over the long-term if the gas cloud is captured and dumped by snow or rain in any significant concentrations where people have to get food and water.

No nuclear explosion is possible with the materials in the Japanese cores -- they have not been sufficiently enriched to blow up, but they can get really hot (enough to melt steel and titanium). In Chernoble the cores were not in a heavy duty container so when the gases blew up it scattered all kinds of nasty material all over the Northern Hemisphere. A similar mess will only occur if the Japanese plants get so out of control that the melt-down destroys the containment building and then fires and gas explosions can send very bad radiation into the atmosphere. I am not too sure about the spent rods (they usually still have about 90-95% of the original energy in them) and are covered in water in what looks like swimming pools. If they are too close to the reactors, that could become a problem as well (proper storage should hold them at quite a distance, but these plants are 40 years old so who knows).

So unless the unthinkable happens, and assuming the commercial camera storage air is filtered and the warehouses have not been compromised by the quakes, warehoused cameras should be OK. Cameras in stores could be another story depending on how the store is built and if the building was damaged enough to let radioactive particles settle inside.

Alan

[Jim Michael]

If you know which radionuclides are involved you can use the nuclear wallet cards at Nuclear Wallet Cards to look at decay products of the isotopes in question and determine which decay byproducts (alpha, beta, gamma and their percentages) are formed, which isotopes result from the decay, and their half-lives, decay products, and so on.

[Alan Emery]

Hi Jim,

At Chernoble and in spent fuels, the most common problem radio-isotopes are Caesium 137 (gamma decay with half life of 30 years), Strontium 90 (Beta decay with half life of 28.8 years but seems to seek out bone) and Iodine 131 (gamma decay with half life of about 8 days goes to the thyroid which picks up iodine).

Alan