Victoreen 450p question

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
Post Reply
Bruce Meagher
Posts: 106
Joined: Fri May 13, 2011 3:25 am
Real name: Bruce Meagher
Location: San Diego

Victoreen 450p question

Post by Bruce Meagher » Thu Jan 15, 2015 2:20 am

I recently acquired two Victoreen 450p pressurized ion chambers, but unfortunately the readings between the two differed by over a factor of four. Today I was able to check the higher ranges of these meters against the local university's calibrated Cs137 source.

Below is the data I collected:
Screen Shot 2015-01-14 at 6.09.51 PM.png
From what I understand the internal calibration constants can only be changed by 20% so clearly unit2 problems are more than just a poor calibration. Thinking there might be a problem with the electronics I swapped the ion chambers between the two units. The low readings remained with the one ion chamber and not the electronics.

If the pressurized ion chamber has lost some or all of it’s 6 atms of pressure then I believe this might explain why the readings are off by such a large factor. Has anyone seen this before?

I was thinking of trying to open the fill line to see if it has really lost it’s pressure. If this is the case maybe there's hope I can find and fix the leak and then refill.

Any thoughts or suggestions?
Victoreen 450p.jpg
Victoreen 450p
ion chamber.jpg
Ion chamber

User avatar
Richard Hull
Site Admin
Posts: 10872
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Victoreen 450p question

Post by Richard Hull » Thu Jan 15, 2015 8:29 am

That's a classic rolled, metal weld seal on the tube. What is the gas fill? 4-6 atm will require a very good valve on the stem if you refill. It would be tough to just re-seal the stem without a metal weld roller. Typically, roll seals are performed on pure annealed copper tubing, but not totally limited to that metal. It is just that the roll sealers are less costly or complex for simple copper. The weld is a cold weld or fusion of the metal, bonded under extreme pressure.

I have seen vacuum seals like this where a bit of paranoia caused the manufacturer to put a blob of solder or epoxy over the finished copper roll seal as backup insurance against slow leaks. At 6 atm, I don't know if this would work as well as with a 1atm vacuum situation.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Bruce Meagher
Posts: 106
Joined: Fri May 13, 2011 3:25 am
Real name: Bruce Meagher
Location: San Diego

Re: Victoreen 450p question

Post by Bruce Meagher » Mon Jan 19, 2015 8:38 am

Yes the fill tube looks to be cold welded. The fill gas on the 451 ion chambers is nitrogen with a pinch of argon. I have yet to confirm that the same fill gas and ratio was used in the 450p. I believe some of the newer pressurized ion chambers have a schrader valve for easy pressure relief (and therefore less hassle and cost in shipping). I’m going helium leak test the chamber to see if I can identify the leak location.

Bruce

Bruce Meagher
Posts: 106
Joined: Fri May 13, 2011 3:25 am
Real name: Bruce Meagher
Location: San Diego

Re: Victoreen 450p question

Post by Bruce Meagher » Wed Mar 15, 2017 1:27 am

I finally got around to refilling this ion chamber. I used an 1/8” swagelok compression fitting on the copper fill tube. After filling it with 6 ATMs of nitrogen I pinched the tubing, cut it with diagonal cutters, and then sealed it some solder. From my research the fill gas for the Victoreen 450p is 6 ATM of a nitrogen/agron mix. The exact ratio isn't documented anywhere, but several references mentioned adding a few precent (2-5%) of argon to help flattening the energy response. I was able to recalibrate the device over all its ranges using two Cs-137 sources and the Victoreen 450-1A communicator. I currently don’t have a way to measure energy flatness over the ranges, so it could be giving a low reading when measuring low energy sources. I’ve also filled a couple of new style ion chambers with the schrader valves and they seem to come back to life as well.

After it was calibrated I hacked the ion chamber open to see what was behind the curtains. I was surprised to find some electronics inside. I was also surprised at the size of the collector (I assumed the collector would just be a small rod).
Attachments
Victoreen 450p x2.JPG
New and old style Victoreen 450p
450p ion chamber -1.JPG
450p ion chamber - 1
450p ion chamber -2.JPG
450p ion chamber - 2
450p ion chamber -3.JPG
450p ion chamber - 3
450 Communicator.JPG
Victoreen 450-1A Communicator
Cs173 source.JPG
Cs137 source

User avatar
Richard Hull
Site Admin
Posts: 10872
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Victoreen 450p question

Post by Richard Hull » Wed Mar 15, 2017 4:17 pm

Electronics is always inside the best ion chambers. It is to be remembered that fempto-ampere currents are the norm at the low end of ion chamber detection. You cannot bring that out into the real world. The critical "electrometer" front end is always contained within the ion collecting can or in a common, bonded shield box attached. This is why batteries are used to power most all ion chamber detectors. They are rather stable or more so than most electronic supply sources.

The electrometer circuitry receives the fempto-ampere low end signal via a carefully "guarded" chamber collector of relatively large collection surface area and current amplifies it to output via the multi-terminaled connector on the rear of the chamber. All ranging" is carried out in the can where ultra high ohm resistors are tapped via what must be a clean, silver or gold plated range switch external to the chamber. Here is where noise can be introduced. This is why zero'ing or balancing the electrometer bridge must be constantly re-done. The latest electronic switching can reduce this old mechanical switch sensitivity a great deal.

I have made a number of modern electrometer systems, repaired and sold many Kiethley electrometers over the years. I made a super one that approaches a zepto-amp sensitivity that works in a vacuum. The best electrometer systems can eaily detect a differential of plus or minus a few electrons. In the past, these were vibrating reed electrometers.

Input dropping reistors are in the 100 million megohm range with one of my systems having a calibrated 10 teraohm resistor. A fellow engineer of mine refers to these as highly calibrated open circuits, but electrometers rely on these to perform properly. FETs are replacing the venerable 5886 electrometer vacuum tube. Needless to say, normal cleanliness within the first amplifier and circuitry is not even close to good enough.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Bob Callis
Posts: 4
Joined: Fri Jun 10, 2016 11:41 pm
Real name: Bob Callis

Re: Victoreen 450p question

Post by Bob Callis » Thu Sep 13, 2018 12:04 am

I recently bought 14 of these things and to my supersize most are working to some degree or other. A couple are reading pretty far out of range and two of them read high but then when I bring a test sample close the reading drops??? Kinda strange the readings go in reverse. One is dead but I haven't had time to track down its troubles. Only one has the battery cover so I plan to make a silicone mold and see if I can make some new covers. These are going to be a fun project.

Bob

Justin Fozzard
Posts: 8
Joined: Thu Aug 24, 2017 11:11 am
Real name: Justin Fozzard
Location: Essex, England

Re: Victoreen 450p question

Post by Justin Fozzard » Thu Sep 13, 2018 9:35 am

A few years ago I worked for a company that made magnetrons, TWTs, thyratrons and other high power RF tubes. Many of the tubes were evacuated and then roll sealed using a hydraulicly operated tool. The seal had a blob of solder added afterwards to protect the assemblers from being cut by the extremely sharp edge of the seal, not for sealing slow leaks. The hydraulic tools were routinely checked by helium leak testing a sample seal made by them, and I once accidently brushed my hand against a fresh seal while testing it. I very quickly learnt how incredibly sharp they were!
Please be careful not to cut yourself on your ones.

Incidentally, we made also deuterium thyratrons with a palladium foil reservoir inside that would be electrically heated after the tube was evacuated and sealed to release controlled amounts of deuterium. Sometimes eBay has the tubes for sale and the reservoirs could be carefully recovered from them for use as a small pure deuterium source. The datasheet usually gives the required heater voltage and current for the reservoir. The deuterium isn't released until the reservoir is heated, so we could precharge them with pure gas before fitting them inside the tube.

Justin Fozzard

User avatar
Richard Hull
Site Admin
Posts: 10872
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Victoreen 450p question

Post by Richard Hull » Fri Sep 14, 2018 11:58 pm

These latter tubes are hydrogen thyratrons. I have written on this rather extensively here in these forums in the past. I have used them as high current switches in both Tesla coils and special high power discharge systems over the years. I have a boat load of these very special tubes purchased at various hamfests over the last 30 years. Most of these are used in high power radar systems and are pulled due to increasing "Jitter". Jitter is a very bad thing in radar modulators, but of no concern whatsoever in most any other usage. Thus, all such radar "jitter pulls" are 100% functional for many years to come outside of radar usage. High power lasers are another use for hydrogen thyratrons where no solid state device can serve.

The largest common glass hydrogen thyratron in common use, the 5C22, is or was available new for a bit over $1000 from Newark Electronics a few years ago. Most of my 5C22s were purchased for a few dollars. I once pondered over a pulsed fusor system around one of my ceramic hydrogen thyratrons that can handle 30kv. The horrid x-ray pulses at 1000 amps, (peak), put me off the idea, though.

Today, almost all H thyratrons are ceramic tubes. EG&G and Kuthe labs made a bunch of them. All H Thyratrons are rated in the thousands and tens of thousands of volts and can also switch thousands and tens of thousands of amps. Silly-con can't do this. These "fire bottles" will be around a long time into the future.

The classic roll seal, cold weld, copper tit on metal-ceramic vacuum items has been around a long time now.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

User avatar
Bob Reite
Posts: 277
Joined: Mon Aug 26, 2013 1:03 am
Real name: Bob Reite
Location: Wilkes Barre/Scranton area

Re: Victoreen 450p question

Post by Bob Reite » Sat Sep 15, 2018 4:42 am

I don't know, the Sylmar California DC to AC converter station got tired of all the maintenance on their insanely large mercury vapor thyratrons and when they where damaged by earthquakes, replaced them with solid state devices.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

User avatar
Richard Hull
Site Admin
Posts: 10872
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Victoreen 450p question

Post by Richard Hull » Sat Sep 15, 2018 10:57 am

Mercury vapor stuff has been replaced for some years with solid state stuff. Hydrogen thyratrons are as different as night a day. Let's say I need to switch 25kv in under 1 usec and the peak current will be 8,000 amps. The on-time I want to be about 3 usec and I want this done 800 times per second. A single H Thyratron can easily handle this job. Silly-con need not apply. H thyratrons are of no value in inverters or converters. They are multi-megawatt, peak pulse power, repetitive switches. Their rep rate and duty cycle is determined by there specs. I ran a very small Tesla coil using an H2 thyraton. I fed it with 8,000 volts DC off a charged .1ufd capacitor and at the ideal rep rate of about 400-500 hz the C.T. on my scope read 420 peak amps going into the primary. I deliberately over top loaded the resonator, thus, no spark came off. But it would light a 4 foot fluorescent tube ten feet away. I hate to think what it did to local AM reception!

Mercury vapor rectifiers were also rather low voltage items as well; although at 5kv, for some of the best, they still beat silly-con.

IGBTs are the silly-con of choice for small voltages under 1500 volts for high power operation. Heck, most mercury thyratrons were retired in the early 70's, pushed aside by big, high power SCRs.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Post Reply