The closest book game December 21, 2006
Posted by dorigo in Blogroll, books, games, internet, italian blogs, language, personal.6 comments
By monitoring incoming links today, I found 10 from http://backreaction.blogspot.com/ , and had a look. She had indeed linked me, and I found out it was an invitation to act on a game posted by clifford first.
So the game is, take the closest book to you right now, go to the fifth sentence on page 123, write the following three sentences in the blog, and tag three people.
The closest book to me in English (also visible from the picture in the previous post, if you have good eyes) is “Late Roman Painting” by my father, the late Wladimiro Dorigo. I’m quite happy to post three sentences from my father here.
“In the crypt of the Five Saints, in the Cemetery of Callistus, the only portrait of a praying figure which remains almost intact (though damaged) for inspection is that of ‘Dionysas’, so called from the inscription Dionysas in pace. It may well be affirmed, with De Walt, that every specific trace of impressionism has disappeared from this countenance. Its facial planes are so separated from the physiognomical lines of eyes, nose or mouth as to amount to a formal dissociation which is wholly expressionist.”
Wow that was long! Three sentences in pure Dorigo style. Now who should I tag ? Let’s see.
Ok, let’s take Gordon ( http://gordonwatts.wordpress.com ), Zerocold ( http://zerocold.wordpress.com ), and gattostanco ( http://gattostanco.diludovico.it/) .
This was fun!
Waiting for you December 21, 2006
Posted by dorigo in food, personal, social life.8 comments
The three large pans of lasagne (one containing bucatini with mushrooms and meat sauce, one with pine nuts and ham, and a third “regular” one) are ready to go. The calamary are done. The tuna steaks with olives are baked. Polenta is on its way. The large chunk of roast-beef is waiting to be sliced. An obnoxious amount of tartines with caviar, salmon, crevettes are all set in their trays. Some 20 liters of good to very good wine are waiting, either on the table (the reds) or out of the window (the whites and the cartizze).
All we are still missing is the guests! In 20 minutes they will start coming. You sure you cannot make it tonight ?
Radon contamination and Poisson statistics December 21, 2006
Posted by dorigo in games, mathematics, personal, physics, science, travel.add a comment
Two weeks ago I was coming back from a trip to Chicago and I was carrying my pocket digital gamma dosimeter, something I still do when I travel on a plane. Upon walking through the corridor leading to the stairs to my apartment, I noticed that the thing beeped three times in the matter of 20 seconds or so, and the other day I decided I would investigate whether there is Radon contamination in my basement.
Radon is a inert gas emitted by the decay of Thorium, a radioactive material contained in traces in the ground. Radon is heavy and mildly radioactive itself. It accumulates over time in poorly ventilated areas such as basements, and it can stick to plastic surfaces quite easily.
My digital dosimeter records x-ray radiation and has a window of sensitivity roughly in the right region to detect decay products of radionuclides such as Radon. If set at the maximum sensitivity, it beeps every 100 nanoRems of integrated gamma dose. That means about 20+-6 seconds of exposure, under normal conditions (but beware, background radiation depends on the region of the world where you are, as well as on your latitude). By beeping three times in 20 seconds it was giving a signal, or was it a statistical fluctuation ?
I investigated the matter by going back to the basement, and taking notes of the number of beeps given in 5 minutes. The count was 22 (2.2 microRems), while outdoors it counts 15 (1.5 microRems) in the same time interval. Now the question arises, is the measurement indicating a significant contamination of Radon or just another fluke ?
If you just followed Statistics 101 and are thinking at Christmas presents with the other side of your brain, you might come out with “22 is not significantly different from 15, after all these are random counts and they are subjected to Poisson statistics, so 22 is really 22+-sqrt(22), 15 is 15+-sqrt(15), and 22+-4.6 is not so different from 15+-3.9″. Wrong.
Sure, gamma collection is a random process, but the counter does not beep every time it sees a gamma. Rather, it beeps once it collects a certain dose. For what you know, a 100 nanoRem beep could arise from one photon, or 100. In the former case you would be right in your error estimates, in the latter you would be off by a factor of 10. Further, not every photon will release the same amount of energy in your counter - but that is a unnecessary detail and I’ll neglect it here.
What we know, as I stated at the beginning, is that in normal conditions a beep occurs every 20+-6 seconds (yes, I did construct a histogram of timings to get that information). What that means is a 30% relative uncertainty on 20 seconds. That must imply that 20 seconds, or 100 nanoRems, are integrated with an equivalent number of counts which fluctuates by 30%. The number whose square root is 30% of its value is, of course, 10. So we can eyeball that 100 nanoRems are on average obtained by 10 photon counts.
Equipped with that information, we can now evaluate the significance of our 2.2 microRem/1.5 microRem difference. If 100 nanoRems are 10 counts, then on average 2.2 microRems are 220 counts. So we are really talking about 220+-15, and 150+-12. These two numbers are incompatible at almost 4-sigma level. We conclude that my basement indeed has Radon contamination, and that the radiation level in it is 1.5+-0.1 times larger than it is outdoors.
Did I know 5 minutes would have been enough to detect a significant signal before performing the experiment ? No, since I did not know how much of a signal I would be observing. But I did know that I would have been sensitive to a 20-30% increase with a 5′ exposure. Knowledge is power…
