Radon Detector (English)

Principle of radon detection

Radon and uranium series

Let's consider the radioactive element of radon (Rn, atomic number Z=86, mass number A=222). Radon emits α-particle (α-decay) with a half life of 3.8 days. Why such a radioactive element with the short half-life exists around us? Because radium-226 (Ra, Z=88, A=226) which is the parent nucleus of radon has the long half-life of 1600 years. Is it true? Who made radon?
If we trace back to the uranium decay chain, we can finally reach the element of uranium-238. Since uranium-238 has the half-life of 4.5 billion years, uranium-238 does not readily decrease. 4.6 billion years has passed since the solar system was born, therefore the number of uranium-238 has became almost the half of original one in number. (When were uranium created? It will be another long story..., but let me explain it briefly. There was a star before the formation of the solar system, and when the star burned out, a supernova explosion happened. In that moment, the elements with heavy mass like uranium is supposed to be created. Study on when and how the elements were created in the history of universe since the Big Bang is one of the latest research theme.) The radioactive elements like uranium-238 remain so much on earth. The half of the heat of the earth's interior is at least due to the decay heat of radioactive elements like uranium, which is convinced by the measurement of the amount of neutrino.

Now, let's go back to the original subject. Radon-222 changes into polonum-218 (Po) by α-decay in the half-life of 3.8 days. Then polonium-218 becomes lead-214 (Pb) in the half-life of about 3 miniutes, and Pb-214 becomes polonium-214 through the twice of β-decays in the half-life of 27 min. and 20 min. and so on. Please look at the figure below. It shows a grand history starting from uranium-238 to a stable element of lead-206!
In the experiment, measuring a radon emitted from ore picked up in hot springs, and also confirming radon coming from any stone and soil around us, with the high sensitive radon detector we developed is a main subject.


Ionization of radiation

As you know, there are three typical types of radiation, such as α-ray, β-ray, and γ-ray. It is written in the science textbook at high school that the α-ray is the nucleus of helium (He), the β-ray is electron or position, and γ-ray is an electromagnetic wave. The important thing is each radiation has a large energy of several MeV (million electron volt). An energy scale in chemical reactions is about several eV, but the radiation has a million times as high as energy scale. It is obvious that the world of nuclei has different order of magnitude in energy compared to chemical reaction.

Have you ever solved the wave function on an electron in a hydrogen atom? It is a famous model called Bohr atom.
The figure below shows a solution for an electron bound around nucleus with positive charges of +Ze. In the case of a hydrogen, we can set Z=1, and the binding energy is 13.6eV for the principal quantum number n=1, where the spread of the wave function for the electron is 0.53eV.

(under construction)


Electrostatic collection method

electrostatic2.png PD_can.png

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Last-modified: 2014-08-12 (火) 15:03:54 (1259d)