Radiation in Goes, Zeeland (NL) - Geiger Counter: May 2011

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.

Note:

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.

Thursday, May 26, 2011

2011-05-26 21h CEST - Measurement briefly interrupted by a malfunction in the FH40T

Goes, 2011-05-26 22:19 CEST:
Tonight around 21h, the readings from the FH40T suddenly ceased. No more clicks were detected. After some initial testing, no immediate cause for this malfunction could be found, the FH40T detection electronics seemed dead but fortunately the G.M. tube was still OK.

After an interruption of about an hour, I was able to continue the measurements with a spare (D.I.Y) counter circuit that I had already built, using the same G.M. tube FHZ76V.

I''ll try to repair the FH40T in the near future, or otherwise I'll try to build new electronic circuit and integrate an LC-Display into the FH40T housing. Something which I already had planned to do, but hesitated to destroy a functional Radiation detector.

Radiation in Goes - Live graphs

Latest graphs.

Update 2011-05-26 22:19 CEST: Tonight around 21h, the readings from the FH40T suddenly ceased. No more clicks were detected. After some initial testing, no immediate cause for this malfunction could be found, the FH40T detection electronics seemed dead but the G.M. tube was still OK.

After an interruption of about an hour, I was able to continue the measurements with a spare (D.I.Y) counter circuit that I had already built, using the same G.M. tube FHZ76V.

SI8B CPM measurement

Last month's radiation graph, normal background levels.
Sun 04 sept at midnight: Raindrops leakage on GM tube and electronic circuit causing a spike and dropout of measurement. Fixed next morning.
Tue 28 june: Heavy rain and thunderstorms caused huge peak.
A lightly decreasing trend since the beginning of my measurements can be seen in the month graph. Did we experience Fallout from Fukushima before my measurements started, which is now slowly decreasing due to the half-life of the nucleides ?

Images kindly hosted by dead-men.de

Saturday, May 21, 2011

Tests with SI-8B / СИ8Б Pancake GM tube

I did some experimental measurements with my new SI-8B / СИ8Б Pancake G.M. tube/probe, to verify it's functional and to prove it's able to detect any alpha radiation.

(Update 2011-06-07 22:30 CEDST): more measurement results and photos added.

Ua=400V Ra=4.7MΩ

Background radiation, indoor..
90-126cpm, average 105cpm (with or without aluminium Beta-shield on probe).
Fertilizer (N-P-K), 100grams of granulars in a zip-bag laid on top of the probe:

with Beta-shield: 134-149cpm, average 141cpm.
without Beta-shield: 475-548cpm, average 505cpm.
Am-241 Source from Smoke detector:

with Beta-shield: 7-12cps (420-720cpm).

without Beta-shield, just a piece of paper between Am-241 source and probe (blocking alpha): 13-25cps (780-1500cpm).

without any shielding: 150-450cps (9000-27000+ cpm).
Wolfram-Thorium (red color band, 2% Thorium, 2.4mm thickness) Tungsten welding electrode:
A length (8cm) of WT20 electrode positioned across the SI-8B window:
sample1:
with Beta-shield: 253-280cpm, 268cpm average.
without Beta-shield: 521-543cpm, 530cpm average.

sample2:
with Beta-shield: 239-285cpm, 261cpm average.
without Beta-shield: 536-556cpm, 544cpm average.

Both lengths of WT20 electrode positioned side-by-side across the SI-8B window:
with Beta-shield: 356-427cpm, 389cpm average.
without Beta-shield: 941-983cpm, 963cpm average.
¹⁴C 60µC test source (Beta radiation, 0.156476MeV), in TTL6109a
"Strahlenspurgerat". Measured with the SI-8B held close to the mica window of the ionisation chamber, with the mode switch in the "R" position (so the ¹⁴C test source is exposed into TTL6109A's ionisation chamber).

with Beta-shield: 102-143cpm, 116cpm average
without Beta-shield: 3924-4360cpm, 4142cpm average

cpm = counts per minute
cps = counts per second

Photo's of experimental counter setup with SI8B, my HV inverter circuit and my Pulse-Counter / RS232- interface / LCD:

Test setup with SI8B, HV inverter and PIC pulse counter / LCD, powered by 4 NiMh coin cells

Close-up of the SI-8B mounted on a Pringles can.

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:

ECV 6343 II652 I COUNTER SI8B

LABEL

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

OPERATING INSTRUCTIONS
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