About this blog

About this blog

During the recent events in Fukushima - Japan, it soon became clear that the authorities are not very informative to civilians regarding radiation exposure values. Authorities seem to be witholding information, perhaps to avoid panic.??

So I got the urge to be able to detect and measure radiation by my own, especially since I live within a 15km radius from the NPP of Borssele and a 30km radius from the four reactors of Doel NPP, Belgium.

Browsing the internet, I found some relatively cheap ex-army radiation detectors at an army-dump shop. One of them appeared to be suitable to even detect the (usually low) background radiation levels: A Frieseke & Hoepfner FH40T Geiger counter (fitted with a FHZ76V energy-compensated geiger-mueller tube), sensitive to γ (gamma) radiation and β (beta) radiation over 0.25MeV.The FHZ76V tube actually contains a Valvo 18550 tube, which is equivalent to Centronics ZP1320, Mullard Mx164 and LND-713 (found in this Probe Selection Guide and here)

The specs of the ZP1320 tube claim a sensitivity of 9cps/mR/h for Cs-137 (540cpm/mR/h). For 'normal' background (0.025-0.045mR/h) this results in a counting rate of approx.10-20cpm.. Where I live, I measure values varying between 4cpm up to 25cpm. This variation is caused by the randomness of the decay of radioactive elements.


The unit R in this text means Roentgen, a depricated unit of radiation exposure. Nowadays it is better to use S.I units. The Gray (Gy) and Sievert. The official conversion between Roentgen and Gray is:

1 R = 8.77 mGy
1 Gy = 115 R

For sake of simplicity, in our calculations we simply use 1R = 10mGy and 1Gy= 100R. And so is 10µR = 0.1µSv.
This approximation is good enough for this experiment.

I've built a PIC16F628-processor based interface / pulse-counter, that counts the pulses and converts them to mR/h values and transmits them out of an RS232 port. This interface is then connected between the Geiger counter and a small PC, running Linux. On the PC, a simple script runs that reads the values from the RS232 port (one measurement value every 111seconds) and stores the entries in an RRD database and the graphs are made with rrdtool.

There are 3 types of radiation:
α (alpha) decay is helium nucli being released, (beta) decay is electrons (β-) or positrons (β+) and γ (gamma) decay is electromagnetic radiation (like X-rays).
This Geiger-Mueller tube is only sensitive to β and γ radiation. The calibration is only correct for the γ radiation (662keV) emitted from Cs-137 .

I am now on the lookout for a device that can detect alpha radiation too. But the current situation in Fukushima has stirred up the market (crazy prices, run out of stock) for detection devices so I better wait until better times.

Friday, May 20, 2011

Russian Pancake tube SI-8B / СИ8Б

From Ebay, I acquired a N.O.S (new old stock) Russian Pancake GM tube SI-8B / СИ8Б.
It has a diameter of 8cm and is very sensitive:
A quick test showed a background radiation count between 3 and 10 CPS (counts per second), compared to between 3 and 10CPM with my FHZ76V tube !! This is a 60-fold higher count rate !!
I'll do some more tests and measurements soon.

The specifications sheet are in Russian language. 
If somebody can translate these specification sheets from Russian to English or German, I would very much appreciate that! Please leave a comment!
Update: Katze typed the Russian text of the datasheet in a wordprocessing document, which can now be easily translated, so many thanks to Katze for this great job :-) .
Here is the translation:

Counter Beta radiation SI8B (hereinafter counter) is used to register the soft beta-radiation in radiometric devices.
Climatic performance U3.I.
Solo 15170 Date of manufacture OKT 1990
Circuits connecting the electrodes with the findings
Designation Name of the output electrode
            I Free
            3 Cathode
            5 Free
            7 Anode
Basic electrical and radiometric parameters
The slope of the plateau of the counting characteristics,%, not exceeding: 0,3
Sensitivity of the counting rate, imp.s-1.A-1.kg: 1.3 * 10E12 ... 1.9 * 10E12
Sensitivity of the counting rate (imp / uR): (350 ... 500)
The slope of the voltage-current characteristics,%, not more: 1,25
Amplitude voltage pulse, V, no less than: 20
Own background, imp / s, max: 2
Effectiveness of registration of beta radiation,%: 50 ... 85
Current sensitivity, uA: 8 ... 15 (at P = 12.9 * 10E-10 A / kg (5 uR / s))
Operating range voltage, V: 360 ... 440
Maximum operating speed counting, pulses / s: 3400
Maximum operating current, mA: 18.2
The maximum permissible exposure dose of gamma radiation, A / kg: 21.5 * 10E-6 (for 1 min)
The maximum permissible exposure dose of gamma radiation (R / h): (300) (for 1 min)

Precious metals are not contained.

The content of non-ferrous metals in a counter:
Nickel - 3.6 grams per 4-pin.
Acceptance Information
Counter SI8B meets specifications 0D0.339.388 TU.
TCI Stamp
At re-manufactured _________ date
I. After you remove the meter from the package carefully remove the protective cover and visually check to make sure that the counter has no express mechanical defects (cracks of mica, chipped enamel).

The counter can be taken only at the base. Is strictly forbidden to touch mica window.
2. The inclusion of the counter is made by feeding the anode voltage 390.
3. During operation of the counter values that determine the mode of operation, should not exceed the maximum allowable value.
Doing so may lead to loss of counters performance.

Manufacturer of SI8B

No comments:

Post a Comment