Geiger counter :
Geiger counter with LCD (excerpt from my graduation work y. 2011)
This is a continuous electronic detector alpha, beta and gamma particles/radiation. It provides continuous information about the instantaneous intensity of radiation and quanta of ionizing radiation. Its main display section is both a digital display activity in the base unit activity Becquerel, also using an analog display measuring instrument in units of dose equivalent Sievert per hour (mSv / h) in the two ranges indicated in the characteristics of the device. As the main element is a measuring device used in this Geiger tube of mica window, which allows good penetration of alpha particles. For separation of the individual types of radiation are used to handle the probe, they are able to brake alpha particles and beta. For alpha radiation shielding, just plastic or paper box and beta radiation shielding is used as a plastic window, and 1 mm thick layer of lead to block the braking radiation, which occurs when passing a light material such as plastic. Radiation can be measured with this probe to a value 1000uSv / h, for measurement of larger doses, it would be necessary to use another GM tube, theoretically up to 50MBq enabling range counter pulses. Values ​​given dose equivalent valid and are calibrated only for the measurement of beta and gamma radiation (ideally for radioisotope Cs137) alpha radiation coefficient value multiplied by 20 times. The value of digital imaging in Bq by this unit is similar to the value on an analog meter in SCP / h, but not a direct conversion of the value depends on the measurement geometry and distance from the source, therefore the value in SCP derived from calibration radioisotope Cs137, while activity in Bq is constant and vary the geometry of the measurement and the probe is therefore merely indicative.

And now something of the structure itself ... the pictures you can see the first version of the dosimeter that was larger and had a less efficient source of high voltage.
A second, smaller version is perfect, miniaturized and has an effective source of high voltage ( my design).

Obrázek č.10 – fotografie měřící sondy

--- Photos : second, better versionu ---

3.1 Technical specification

Table n.1

Photo n . 12 – Block scheme

3.3  Measuring

When measuring radiation by this device, I was focused on verification exponential activity, depending on the distance from sources.ï I also examined the absorption of radiation in various materials.These experiments I have as a radiation source used several radioactive sources which are available without a special license .

The following table shows the measurement of activity by the distance of the probe from the source, using radionuclide (cca.400ug) 226Ra.

Table 5 - activity measurements, the probe by the distance from the source (source: 226Ra)

Graf č. 1 - Activity, by measuring distance

            Table n. 6 – Materials absorption (zdroj: 226Ra/ beta/gamma)

As anomaly appears Bismuth although a larger atomic weight than lead absorbs radiation approximately three times less than plumbum.Reason its a crystalline nature, when the rapid cooling, crystals formed.

           Graph n. 2 - Different materials absorbtion č. 6 (Supply: 226Ra)

Table n. 7 - Different materials absorbtion č. 6 (Supply: 226Ra)

Graph n. 3 - Different materials absorbtion (Supply : uraninite)