A simple ion chamber to measure radioactivity

I built Charles Wenzel's simple ion chamber. It creates an electric field inside the can via a battery. A wire in the center of the can, isolated from the can, is connected to a transistor pair called a Darlington, essentially a pair of amplifiers. When ionizing radiation creates an ion in the can, the electric field drives the ion towards either the can or the wire, depending on the charge of the ion. This creates a very small current which barely turns on the darlington to allow the voltmeter to measure a small change in voltage.






I could easily up the voltage on the chamber by snapping in more 9V batteries.


You can also light things up nicely: I had 122V DC at my disposal, although I wouldn't recommend running it for very long. Based on a rough calculation, the 40W lamp would run for an hour on this battery set, but the batteries aren't meant to source this much current (about 1/3 Amp).



I had an easy way of changing the chamber voltage, 9 volts at a time, so I measured the quiescent voltage and the voltage with a smoke detector alpha particle source in the chamber. I sealed the chamber by placing it on a sheet of aluminum foil.

Voltage	Null voltage	alpha source
36V	4.8mV	9.1mV
45V	7.1mV	14.9mV
54V	11.3mV	20.6mV
63V	23.4mV	41.5mV
72V	1230mV	1915mV
81V	12000mV	12000mV

Dear Blogger, why do you mess my table so?

Mt. St. Helens webcam

A wonderful service from the National Forest Service is a webcam showing Mt. St. Helens from Johnson Ridge Observatory--and now it's gone to a much higher resolution. It'll be interesting to see what sort of near-infrared performance the new NetCam XL camera has. The old camera would occasionally pick up the invisible glow of the hot dome at night.

Watch the slow growth of the reemergent lava dome in this movie from last year. (Others here).

Surplus lens

Yes, I had already bought this lens on my last American Science and Surplus trip. The most useful purchase that trip was a UV/IR blocker window--I'm using several of them in various projects. They were on sale at the store.

Astronomy communities

The media has globbed onto the existence of planned astronomical communities where bad lighting design is not allowed by rules and housing covenants. These are new places, places only needed in the recent past, because of the horrendous growth of light pollution. Continued light pollution increases of 5-10% per year mean the end of the visibility of the stars in just a few decades. Already 2/3rds of Americans haven't seen the Milky Way. By 2025 there will simply be no more dark sky in the United States. Simply no place. Current arguments about "why don't you move your scopes to a dark place" are ignorant by this measure and besides, are the people who created the light pollution paying for relocation? Destruction of useful observatories like Mt. Wilson and the current degradation of Palomar by misinformed politicians who'd rather be concerned about aesthetics than efficiency and science:

(Mayor Dick Murphy) said he also supports the change for aesthetic reasons: "People think they're ugly."

Astronomers also are concerned about a plan before the council to replace some hooded streetlights with decorative acorn-shaped lamps in various historic districts. The acorn lamps allow most of their light to shine upward, to the sky.

"They are blantantly inefficient," said Paul B. Etzel, director of the nearby Mount Laguna Observatory. "It's a 19th century solution to a 21st century problem."

Critics also point to higher costs. Getting rid of the low-sodium lights would cost nearly $2.8 million and raise the city's power bill by a half-million dollars a year, according to a city report.

This alley has 4 250W lights plus a 150W streetlight within a thirty foot radius. A resident of this building can't get the city to remove or shield any of the lights.

Which constellation lost will make people realize the sky is gone? Orion? The asterism of the Big Dipper? Already seeing the Pleiades is tough in Chicago, and the faintest star of the Big Dipper is getting difficult to see.

I've seen it first hand in a place that doesn't need anymore light, yet we in Chicago increase the energy use in lighting by leaps and bounds whenever the mayor needs re-election or a University president feels to rule by fiat. I can only hope people will eventually realize spending tens of thousands of dollars for just the light that goes up into the sky (yes, really) is not smart for a campus nor the millions of dollars per year for a city like Chicago. The nation as a whole wastes--not uses, but wastes--$5 billion a year or more in outdoor lighting that doesn't hit its target.


Would you want to live with this light outside your bedroom, giving you breast cancer?

People think that brighter lighting decrease crime--but it doesn't, period, and in fact, I was shocked to discover someone actually checked: Brighter alley lights in Chicago increased crime in the alleys by 21% percent: Each of the three crime categories experienced an increase in the number of
reported incidents between the pre and post- installation period. Violent Index offenses
increased 14 percent (119 to 136), property Index offenses increased 20 percent (30 to
36) and non-Index offenses increased 24 percent (279 to 347). All this, using 160W more per fixture (there's 175,000 of them in the city), adding 28 Megawatts to the "Greenest" city.

Radioactive Bananas?

Are bananas radioactive? We've all heard they are rich in potassium, good to eat to restore electrolyte balance in the human body, but since they have potassium they're bound to have some potassium-40 in them, like our own bodies do.

How much ⁴⁰K? Bananas have 400-450mg of potassium; interestingly the state of Colorado says potatoes are a better source (750mg per medium potato). Potassium-40 is isotopically 0.01177% of natural potassium, so that's 0.05mg or 50ug of ⁴⁰K.

***This sentence was the error in the original post:
The specific activity of potassium-40 is about 30Bq/g (A Becquerel is one radioactive event per second), so there is only 1.5 Bq in a single banana. ***

In fact, the specific activity of potassium-40 is 258,000 Bq/g. 30Bq/g is the specific activity of generic potassium; that is, potassium that has 0.01177% K-40.
So, the banana actually has 13.5Bq.

It's not detectable, by me at least. My body has 4000Bq of K-40, but the geiger counter doesn't change from background when I'm near it. The geiger counter didn't see the bunch of bananas either.

Sorry, Kristin, the counter didn't move.

It does move for pure potassium chloride though.

The Japan nuclear plant earthquake leak

Robert Merkel does the calculations on the leaks from the nuclear power plant in Japan and makes the point most media missed: the leak of water into the ocean wasn't anything. The media missed the much larger release into the atmosphere--nearly 300 million becquerels, or about 3000x times the amount of radioactive material. (A becquerel is one atom disintegrating per second). But looking only at the total amount of radioactivity doesn't tell the whole story. A release of the noble gas krypton-85, for instance, does not really accumulate in organisms in any way; while a release of iodine-131 would concentrate and damage your thyroid. Half-lifes and the particular radiation emitted is also important in consideration: the weak beta electrons (~18keV) from tritium decay is considered not as hazardous as a multi-MeV alpha particle from polonium-210.

The reprocessing of nuclear fuel rods in France releases huge amounts of krypton-85 into the air: 1.8 × 10^17 Bq in 1994 alone.

The 90,000 becquerels of whatever went into the ocean (I am guessing it was tritium) is actually not that much: your own body has about 4000Bq of potassium-40 and 3000Bq of carbon-14 in it; in addition, at least here, tritium is allowed to be diluted by large amounts of river water in Illinois.

The end result is the release wasn't a lot; it sounded like a lot from the numbers, but that's due to the definition of a Becquerel more than anything else. The reality is most people don't have much of an education on radioactivity, and this affects how they irrationally perceive a risk.

All of this is really just a minor detail though, when the real issue is any delay or hiding of release information, which according to the press is endemic in the Japanese nuclear industry.

UPDATE: I've found descriptions of the leaks here. The spent fuel pool water sloshed onto the floor and leaked out via cabling. The second leak, to the atmosphere, was iodine and radioactive dust from a main exhaust line.

Personal update

I haven't been posting lately. suffering from a bizarrely strong summer cold, plus work stuff ( I can finally say, after a long legal silence, that my workplace is going with Aquabrowser as the next generation library catalog, which I am administering the boxes it runs on).

An interesting tidbit showed up this week in the blog logs: Google has re-indexed its images again, bringing my violet image of the solar spectrum back to its rankings. Previous to March, it was the first hit for the term "blue-violet". For whatever reason (I believe some stupid google war site misappropriated the image), it disappeared then, dropping monthly hits to my blog by 3,000. The image is now #4; although the hit goes through the same stupid site. The direct link for the blue-violet image is this.

Quantum Mechanics and Dick Cheney

bwhahaha. A good one.

Seen at SciAm Blog.

A Trip Back in Time and Space -- Harvard's Cosmos

The New York Times has a good article on a dedicated effort to digitize the Harvard Observatory plate archive.

I hope Chicago eventually does the same with the Yerkes collection. With the closing of the Yerkes Library, much of the plate collection is coming down to campus, although I don't know how much of the telescopic plate collection is coming. Yerkes has a fantastic historical photo collection of observatories, instruments, and astronomers.

Philosophia Naturalis #11

My post on the opening of Nevada Solar One got mentioned in Philosophia Naturalis #11, hosted at Highly Allochthonous. Philosophia Naturalis is a collection of blog posts about the physical sciences, hosted each month at a different site.

weird battery chemistry

A computer UPS status report.

On seeing this, my first thought was, "I really hope there is no actinium in this UPS."

My second thought was, "I wonder what sort of electrochemical potential a Pb-Ac battery would have."

Geiger counter clicker schematic

By long-delayed request, a schematic of the geiger counter clicker unit I built to supplement the Aware Electronics RM-70. I'm not very good at creating electrical schematics, so please be gentle.

Schematic in TinyCAD.


Schematic as PNG.