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.

Thursday, June 30, 2011

Borssele NPP gets permit for MOX fuel

Borssele NPP gets permit for MOX fuel

Sadly, today I heard in the news that EPZ's* request to allow use of MOX fuel in the 30 year old Borssele NPP was granted by Dutch Ministry of Economic Affairs (MinEZ). Publication here.
*EPZ is the operator of the Borssele NPP.
We believe this decision is a very serious mistake! MOX fuel is 2.000.000 times more dangerous than enriched Uranium fuel. That's 2.000.000 times a higher health risk ! All of this for Economic gain (MOX fuel is cheaper than regular Uranium enriched fuel).
It is now time to object!
Quote from the "definitieve beschikking":
Belanghebbenden kunnen tot en met 11 augustus 2011 beroep bij de Afdeling
bestuursrechtspraak van de Raad van State instellen.
Als belanghebbende kan worden aangemerkt diegene die rechtstreeks door
het besluit in zijn of haar belangen wordt geraakt en eerder een zienswijze heeft
ingebracht over het ontwerp van het besluit of redelijkerwijs niet kan worden
verweten eerder geen zienswijze daarover te hebben ingebracht.
De beschikking treedt na afl oop van de beroepstermijn in werking, tenzij voor deze
datum een verzoek wordt gedaan tot het treff en van een voorlopige voorziening.
Het beroepschrift moet worden gemotiveerd en voorzien zijn van een naam, datum
en het adres van de indiener.
Het beroepsschrift moet worden gericht aan de Afdeling bestuursrechtspraak van
de Raad van State, Postbus 20019, 2500 EA ‘s-Gravenhage. Het verzoek tot het treff en
van een voorlopige voorziening moet worden gericht aan de voorzitt er van de
Afdeling bestuursrechtspraak van de Raad van State. Voor de behandeling van een
beroep of een verzoek om een voorlopige voorziening is griffi erecht verschuldigd.
Inlichtingen over de procedure en de hoogte van het griffi erecht kunnen worden
verkregen bij de Raad van State, telefoon 070 - 426 44 26.

Wednesday, June 8, 2011

Disassembly and repair of FH40T geigercounter

After the malfunctioning of my FH40T geigercounter, it became clear that the probable cause was a gradual loss of High Voltage. Probably due to bad capacitors (loss of capacity or leak) in the voltage doubler / rectifier stage.
To reach the components concerned, the circuit boards need to be removed from the FH40T's housing.
To make removal possible, several wires need to be unsoldered.
To document the situation, to be able to connect all wires after repair of the circuit, I took this series of  pictures:

I've replaced all three 0.025µF / 400V capacitors, a 0.01µF / 250V capacitor and the three 100µF / 4V / 6V electrolytic caps (the meter averaging caps and supply filtering cap) too, as they probably have lost their capacity due to drying out.
After re-assembly of the unit, it seems to be working again, so the operation succeeded ! H.V. measured 500V at the FHZ55/500 stabilizer tube and it's glowing softly.