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 and a 30km radius from the, 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 and )The 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.Note. 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.
World's Smallest Geiger Counter - The following two circuits are an improvement over the older circuits below. The circuits are shown generating 500 volts but they may be modified to supply a couple of hundred to nearly 1000 volts by changing the zener diodes.
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. (updated 2011-06-07, see below)Trying to build a D.I.Y Geiger Counter, I have been experimenting with various circuits to generate the High Voltage that Geiger-Mueller Tubes require (most operate around 500V D.C). There are many circuit diagrams out on the net. I've built several. One challenge is finding a proper coil (or transformer) that has the right properties to let the inverter function in the way the voltage boost is sufficient.
Another challenge is stabilizing the high voltage and lastly have a low current consumption (for battery use). During my experiments, some circuits required more than 150mA @ 5V D.C this is definitely too much for battery use. Others were a lot more conservative, but could not generate sufficiently high voltage (just 450V D.C, just the low threshold of the G.M. Tube I have, but I prefer operating the tube at the center of the plateau).I didn't have good results with the diode-cascade type of voltage-doubling.In the end, I had good result with a circuit, built with a CCFL (backlight) H.V.
Transformer scrapped from a power-supply board of a (defective) Dell or BenQ TFT Monitor. On this perticular PSU board, there are 4 of these Transformers (located on the left edge of the board):4 CCFL transformers.On this board, there are also some very good Transistors 2SC5707, designed for switchmode circuits.I used one of these as oscillator for my HV inverter circuit.Here is the final circuit diagram of the H.V. Geiger-Meuller tubes (note: there is a small update, see below). The primary winding of the transformer is brought in resonance at its optimum efficiency point, around 55kHzIn my experimental setup, the circuit draws just a few milliamps out of a 5V supply, delivering 550V to a G.M. The complete D.I.Y Geiger Counter circuit, with PIC16F628A microcontroller and a 16x2 LCD screen draws 5mA from 5V D.C.Your mileage may vary, depending on differences and tolerances of the components used. Hello Johan,I think the circuit could work with many transformers, as long as it has a primary coil (probably split in halfs or with a center tap, I use them in series), a feedback coil and a secondary coil. The secondary coil will have to have many more windings to give the right amount of voltage multiplication.
Pay attention to the right 'phase' of the windings, otherwise the oscillator won't oscillate;-)Re. The transistors: others will probably work too (it's just an oscillator circuit working at around 50-60kHz), but I got the best results with this type.Good luck with building and let me know your results please.RG.