Charging Unit, Individual Dosimeter No.1

[PSValves]

I found this unusual item on my local antiques market. It came with very little information beyond the name plate - the vendor could only tell me that if I cranked the handle and stuck your finger in the hole, I'd be electrocuted. This was more than enough to persuade me to part with my £5.

Closer examination and a bit of googling reveals it's a hand-powered charger for personal radiation dose meters that use a quartz fibre and a decaying electrostatic field to record cumulative radiation dosage. I guess these units (both the dosimeters and the charger) were pretty common a few decades ago, around hospitals, nuclear power stations and the military.

Inside there appears to be a dynamo and a (physically) large capacitor. There's also a rotary switch which is apparently used for discharging the dosimeter. Cranking the handle generates in the region of 200v across C1 and C2.

Although the circuitry is apparently simple, the principle of operation isn't clear to me. The component linking the dynamo to the capacitor (GEC branded, cream coloured) is a mystery - it seems to have more than 30MOhms resistance, no measurable capacitance and doesn't see to be a diode either...anyone know what it does?

The capacitor box appear to contain two 1uF caps (possibly a third, low-value cap too), connected via the rotary switch to the output connector. What's going on here?

Ideally I'd like to try and find one of the original dosimeters that was used with this charger so I can see it working - if anyone point me in the right direction, or indeed shed any light on this old gadget, I'd be very grateful.

[GrimJosef]

I used to use those dosimeters at work. They were wonderful things - very, very well insulated capacitors with an internal electroscope attached which were charged up by your supply then discharged by the radiation they encountered. Different capacitances and electroscope leaf stiffnesses, presumably, gave different sensitivities. The looked a bit like a short fountain pen only much more 'industrial' of course. The charger could be connected to one end and they were read by looking into the other end which had an optical assembly in it.

VB

[Bazz4CQJ]

I recall there being lots of them about in the late 60's (though I never saw a charger) in the radio junk shops in Leeds, but I have not seen one since. As Grim described, bit like a fattish fountain pen in plain aluminium tube, and sort of like a microscope to look through. Maybe Birkett's in Lincoln?

[HamishBoxer]

Yes,i think Birketts and also a lot of amateur radio rallies sold them.

[McMurdo]

I've got a feeling I have a large quantity of those dosimeters that came from a fire brigade disposal sale, I'll try to dig one out though they might be in a collapsed shed

I have a large quantity of those dosimeters

Well at least you can charge them now, seriously, what is the charge voltage for them, can't be too high given the photos of the charger.

[PSValves]

Originally Posted by McMurdo

I've got a feeling I have a large quantity of those dosimeters that came from a fire brigade disposal sale, I'll try to dig one out though they might be in a collapsed shed

That'd be really cool - hopefully they're not too squashed.

----------------

I've had a proper look at the charger this evening with the 'scope. I incorrectly stated that it had a dynamo - it's actually an alternator. The cream-coloured cylinder definitely is a diode. I'm guessing it's perhaps a stack of selenium rectifiers in a case? Anyhow, this charges the 1uF cap to about 250v. The charge is then transferred in 1nF chunks using the dual pole switch, which is vibrated by the rotary dial on the side of the unit.

Unfortunately the storage cap looses it's charge fairly rapidly - far to quickly to charge up your dosimeter. Easily fixable though, I guess.

[cmjones01]

The alternator looks very similar to the ones found in some military field telephones, though I don't know off it's exactly the same. I have a Telephone Set 'F' Mk II in a bakelite case which contains a very similar unit. Any telephone experts care to comment?

Chris

[McMurdo]

Looks like a ringer magneto to me. I have a quantity of Field Tele-L sets that have them in

[wave solder]

These Dosimeters were known as Quartz fibre dosimeters.

http://en.wikipedia.org/wiki/Quartz_fiber_dosimeter

The charging unit I have has a lever on the side so you could charge or discharge the dosimeter.

http://www.orau.org/ptp/collection/d...ketchamdos.htm

[PSValves]

Originally Posted by McMurdo

Looks like a ringer magneto to me. I have a quantity of Field Tele-L sets that have them in

Could be. The pictures of ringer magnetos I've seen online all have external gears though. This one either lacks gears altogether, or they're inside the magneto housing.

[marlowradio]

There was a chap on Ebay selling these, I belive his username was y3sjk. I have no connection with the seller other than buying a couple of EX-Mod clothing from him.

Steve

[McMurdo]

Internal pic of magneto similar to one in OP

(Courtesy of The Russell Barnes Collection)

[PSValves]

Looks very similar to what I have here, Kevin.

Out of interest, do you know how much current these little dynamos will supply?

[Gridiron]

I bought a Charging Unit No 2 and some dosimeters at a Radiophile auction, this lot included a strange looking dosimeter (see photos) with a red plastic dome on the end and a right angle connection which doesn't appear compatible with the charger. Does anyone have any informtion about this dosimeter?
The charger is dated 1957.
Mike.

[radiotechnician]

Originally Posted by GrimJosef

I used to use those dosimeters at work. They were wonderful things - very, very well insulated capacitors with an internal electroscope attached which were charged up by your supply then discharged by the radiation they encountered. Different capacitances and electroscope leaf stiffnesses, presumably, gave different sensitivities. The looked a bit like a short fountain pen only much more 'industrial' of course. The charger could be connected to one end and they were read by looking into the other end which had an optical assembly in it.

Here is a wind up charger. I have the fountain pen detector, somewhere.

The lucite window caught the light, so you could see where to position
the quartz fiber to reset it to zero.

The little canister was a kit of adapters for various sticks, I believe.

It may have been made in 1959.

Winding it one way, moved the fibre one way, and reverse, the other.

It is a cunning electrostatic device.

The magneto in the larger unit looks like a British type I remember in
a radio remote control unit for a wireless set.