717 Radiation Detector

[Grumpy Old Man]

Just got in my new order from Sportsman's Guide which included a 90 pill bottle of 32.5 mg KI. While I was checking out when ordering this product they did the usual thing of "people who bought this also bought ......". Lo and behold there was a 717 CD Radiation detector for $99 (cheaper if you belong to the Buyer's Club). So I picked one up to fill that big hole in my preps when it comes to radiation. Basically on this unit the geiger-mueller tube is completely enclosed in the base of the machine. It runs on one D cell battery which means I'll have to buy a new rechargeable battery set-up as the one I have is for AAA & AA batteries. All in all I'm very pleased with this acquisition.

BTW for our purposes 1 Roentgen (R) is approximately equal to 1 Rem (Roentgen equivalent man). I won't go into the conversions of Grays and Sieferts. I stick to what I learned originally and screw the SI units!

[Twitchy]

IF that is calibrated I may just head over there myself...

[Grumpy Old Man]

The meters very seldom drift out of calibration. This was NIB as the electronics are up to date. When I was an RSO I was sent to Troxler school in Arlington TX to learn repair and calibration of nuclear densometers and detection devices. The densometers were the only ones that really drifted owing to half-life of the Cesium source (~30 years). If you know your typical background radiation you can check that way. I have friends who are still dirt cops so I'll check the calibration by using one of their densometers.

[Twitchy]

The meters very seldom drift out of calibration. This was NIB as the electronics are up to date. When I was an RSO I was sent to Troxler school in Arlington TX to learn repair and calibration of nuclear densometers and detection devices. The densometers were the only ones that really drifted owing to half-life of the Cesium source (~30 years). If you know your typical background radiation you can check that way. I have friends who are still dirt cops so I'll check the calibration by using one of their densometers.

You could make a quick buck calibrating machines...

[bacpacker]

It's not a bad job. I did it for a few years.
Grumpy, I'm not familiar with the 717, what all does it measure? I've been considering a surplus Bicron and get an Alpha and beta-gamma probe, just for rough counting. Easy to work on and pretty simple to use for general survey's

[AlphaTea]

I too have a little experience with the 717 and some of its cousins.
For the most part, you get what you pay for.
I have seen folks buy these things expecting more than they got.
Stated accuracy is + 20%.
I worked in the RP Calibration Lab for about 16 years and I would try to get a decent Calibration for friends (on my own time). It was rare to get one that was able to get the 20%.
Generally we would adjust it at 50% full scale and check it at 20% and 80% of scale. Not always linear, but hey, it was usable.
You have to remember that these were made back in the early '60s. The technology is VERY rugged and reliable.
They were made for the average Joe to use, not professionals who might need very precise readings.
That being said i have a few suggestions:
Dont use rechargeable batteries. Voltage varies too much. They were designed for the old style carbon batteries, but alkaline will be just fine.
Do not store it with the battery installed. Too many people forget to turn it off when done which causes dead batteries which leak. Also if stored in a hot area (car trunk, attic etc) the battery my not fare well. Remove the battery after use.
The 717 has a remote use feature (case separates) try to minimize using this. While the cable was usually OK the connectors were sometimes weak.
Being an Ion Chamber type detector, it has limitations. Temperature and barometric pressure will effect the reading. Usually calibrated to 22C and 760mm Hg (room temp at sea level). Every 1000ft in elevation increase will cause about a 5% increase in the reading. Hotter temp makes readings higher too.
It is imperative that you keep the inside of the meter dry. VERY dry.
Buy a Photon Micro-light or equivalent and tape it to the handle. I usually used shrink tube. Meter is no good in the dark or low light if you cant read it.
YMMV

[Grumpy Old Man]

Ditto what AlphaTea said. I checked this last night against my buddy's troxler case which has a TI of 0.3. The lower end of the scale (0.01X) is way out of whack, at higher scales (1X and 10X) it was OK, but just. BTW I was checking the Cesium source. The lower end of the scale is problematical. As has been pointed out above this is not a super fine instrument. KI4U will calibrate for $92, which is more than I have in the instrument, so I will probably do that. But I still don't expect good results on the lower end. The CDV 717 was designed primarily for surveys on the high end after a nuclear event. That being said, this will be used to get an initial reading which I can then plug into TOM's spreadsheet to calculate decay rates and when it will be safe to go out.

Or, I'll get blown up in the event and you guys can divvy up my remaining preps.

ETA: This is for gamma radiation.

[AlphaTea]

Ditto what AlphaTea said. I checked this last night against my buddy's troxler case which has a TI of 0.3. The lower end of the scale (0.01X) is way out of whack, at higher scales (1X and 10X) it was OK, but just. BTW I was checking the Cesium source. The lower end of the scale is problematical. As has been pointed out above this is not a super fine instrument. KI4U will calibrate for $92, which is more than I have in the instrument, so I will probably do that. But I still don't expect good results on the lower end. The CDV 717 was designed primarily for surveys on the high end after a nuclear event. That being said, this will be used to get an initial reading which I can then plug into TOM's spreadsheet to calculate decay rates and when it will be safe to go out.
Or, I'll get blown up in the event and you guys can divvy up my remaining preps.
ETA: This is for gamma radiation.

I was having a little trouble deciphering what you actually did here.
When you are calibrating, or checking the calibration, you cant just put the instrument in a radiation field and check all the ranges with just one doserate. Each range has its own cal pot. To get a source with enough activity to check the high scale, you would need a source that emmited 2-2.5R/hr @ ~20 inches from the source. You aint gonna find that.
That high of a doserate will have to be in a well type calibrator or a box calibrator (like a safe).
Most of the range type calibrators I have used usually had a max (usable) doserate of about 200mR/hr. You could then use a DR(r)^2 calculation to get the lower doserates.
My advice?
Pony up the bucks and have KI4U do it for you.
If anybody is interested I can show you how to make your own check source for the lower range to at least check the operability of your meter.

[Grumpy Old Man]

I was having a little trouble deciphering what you actually did here.
When you are calibrating, or checking the calibration, you cant just put the instrument in a radiation field and check all the ranges with just one doserate. Each range has its own cal pot. To get a source with enough activity to check the high scale, you would need a source that emmited 2-2.5R/hr @ ~20 inches from the source. You aint gonna find that.
That high of a doserate will have to be in a well type calibrator or a box calibrator (like a safe).
Most of the range type calibrators I have used usually had a max (usable) doserate of about 200mR/hr. You could then use a DR(r)^2 calculation to get the lower doserates.
My advice?
Pony up the bucks and have KI4U do it for you.
If anybody is interested I can show you how to make your own check source for the lower range to at least check the operability of your meter.

What I was doing was using the cesium source in the backscatter position just to see if the instrument was functioning. It wasn't meant to try and calibrate, just to see how it was working. That source isn't very strong but it can give a good idea of what needs to be done. That was where the detachable feature was useful. And yeah $92 is cheap at KI4U. It beats $150+ for my nukalert (which also has a battery shelf life).

[AlphaTea]

What I was doing was using the cesium source in the backscatter position just to see if the instrument was functioning. It wasn't meant to try and calibrate, just to see how it was working. That source isn't very strong but it can give a good idea of what needs to be done. That was where the detachable feature was useful. And yeah $92 is cheap at KI4U. It beats $150+ for my nukalert (which also has a battery shelf life).

Cool. as long as you understand you are doing a response check, not in any way should this be used to adjust the meter. Any adjustments should be done in a controlled environment where the field strength, backscatter and geometry effects have been accounted for.
I have a couple of those Nukalerts. Matter of fact I have one of the prototypes. Accuracy on them is actually pretty decent across the range once they settle in.
Wifey used to keep one in her purse but she stopped because the chirping was driving her nuts. Seems they dont like quick temperature changes and during the winter her in NY her purse could change temps quickly. Getting it cold makes it think there is a radiation field nearby.
Anyway NukAlert.com has a battery/calibration deal where you get a new case (they get scratched up after a while), battery and desiccant change and a new calibration for $35.
Mine are better than 10 years old and still chirp. I occasionally check them at work