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Techniques for CollectorsAmptek Mini-XRF

1st Jul 2010 04:31 UTCHenry Barwood

I just finished assembling and calibrating an Amptek Mini-XRF constructed using their X-123 detector/MCA and a Mini-X Xray source (Ag target). I was able to identify elements from Ca up, but am having difficulty with the lighter elements (F - K). Amptek suggests using the unit in a vacuum to reduce/eliminate air absorbtion. The detector is sensitive down to F. Looks like I'll have to construct a vacuum chamber to house the whole unit. Fortunately, it is only 8-10 inches across and about 2 inches high. The detector is very sensitive and I got excellent ED peaks for a sample of iron ore that was sub-milligram in size. I hope to be able to chemically identify tiny crystals when I get a vacuum chamber constructed.

1st Jul 2010 11:32 UTCRock Currier Expert

Henry, I appreciate what you are doing and I just want you to know that when you get it up and running I have a few hundred unknowns that need testing and all my friends and the members on mindat have lots more. Just thought you might like to know in case you run short of samples to keep you machine running.

2nd Jul 2010 01:39 UTCHenry Barwood

Rock, the offers of assistance keep pouring in! Everyone needs analyses done. If Amptek would design a modular unit about 1/10 the price of the separate components, they would sell like hotcakes!

2nd Jul 2010 09:28 UTCRock Currier Expert

Henry,

Some years ago the company that made Bart Cannons probes went out of business, and they had a functioning unit for sale for about 10K along with lots of extra spare parts. Bart Cannon came down to LA and we went over to look at it. It even included a 5 foot or so rolling container for liquid nitrogen. I could have afforded to buy it at the time, and I even had a mostly empty garage with a 50 amp power panel in it that could have run the thing. Bart tried to encourage me to buy it, I think more to keep it out of the hands of potential competitors as much as anything else. Bart didn't buy it, but he did buy an extra vacuum chamber and a pallet full of various spare parts which I shipped him. I took one look at the mass of electronics that went along with the unit and decided that there was no way at that time in my life that I was going to learn to be an electrical engineer to keep it running. But it would be very cool to be able to go back to that particular garage and crank up my own probe. Also it would impress the hell out of my customers. All in all I think I made the right decision. This was back in cold war days and I have always wondered what a soviet spy would have thought peeking into Bart's basement, in very middle class neighborhood would have thought about that mass of instrumentation clicking and winking away, that only their most advanced research institutes had access to.

2nd Jul 2010 12:31 UTCHenry Barwood

Hi Rock,


I'm certain my neighbors think that I'm some sort of mad scientist. When we moved to our new house last year, I brought all my instruments out of storage and moved them into the shop beside the house. The fellows who moved them asked me what they were, and when I told them XRD, XRF, etc., they just had a blank look. I look for odd stuff on eBay that no one else has a clue what it is. Of course, I have to hide my bids from my wife!


BTW, I started gathering parts for the vacuum chamber for the EDXRF. I'm also working on a an updated, and extremely sensitive, optical spectrometer for work in the NIR. I should complete both projects before they send me off to the rest home!

2nd Jul 2010 20:45 UTCDean Allum Expert

Henry.


This may be a dumb question, but rather than going through all the trouble of creating a vacuum chamber which introduces the complication of sample positioning; would a helium-filled glove-box be adequate to avoid the air absorption issue?


Please keep us posted on this equipment. I hope you post an article with pictures. There are a lot of us out here who have been looking at that mini-XRF kit!


-Dean Allum

2nd Jul 2010 22:19 UTCHenry Barwood

Dean,


Actually Helium was my first choice, but have you priced He lately? The vacuum chamber will have a significant initial cost, but then it will not represent a continuing drain on my funds. I built a sample holder that positions the sample at the focus of the X-ray and SDD intersection. All I have to do is place a grain on the slide mount and insert it into the holder.


The Amptek devices are excellent, but the diodes are very fragile. If you plan on working with one, you have to be very, very careful not to touch the Be window. The Mini-X X-ray source has, so far, been easy to use and very effective. I would not recommend buying the FP software. A very similar program from NIST is free.

13th Jan 2011 20:09 UTClilo

Good day...congrats on setting up your amptek kit. I am thinking of doing the same...a few questions though...what did you use for the shielding?


Can you post the link to the NIST software?


Keen to know if the vacuum chamber worked for the light elements?

13th Jan 2011 23:16 UTCHenry Barwood

Hi Lilo,


I am still constructing the vacuum enclosure. It has gone through a couple of design changes, and is now a small chamber that fits on the end of the X-ray and the Detector. Since the two units are of differing diameters and shapes, and are set at a 45 degree angle, it has been fairly difficult to construct. I hope to have the first prototype assembled and ready for testing in a few weeks.


I used thin Lead sheet as a shielding material and it worked quite well.


I'll have to dig up the URL of the NIST software and see if I can send it to you.

15th Jan 2011 08:38 UTClilo

Hi Henry,


You can post to me directly at lilo49er@y7mail.com


lilo

15th Jan 2011 15:21 UTClilo

Nevermind, I found the program at the NIST XRF Download Page. The program is called nrlxrf. It is distributed in fortran source code. I managed to compile it after a lot of modification to the code. I am guessing this is the program you are referring too. Mostly for calculating compositions from peaks which have to be input manually or in a file.

16th Jan 2011 03:55 UTCHenry Barwood

Hi Lilo,


The version I have runs under Windows XP and will accept a variety of input formats. I will not be able to retrieve it from my office until at least Tuesday (it is installed on a lab laptop). Glad you could get the older Fortran version running. A little Unix code is about hte best I can manage!

4th Feb 2011 00:54 UTCAngela Rostan

Has anyone used the Thermo Scientific Niton XRF Analyzer for mineral identification? It is rather pricey at $1,500 per week and I believe it is a requirement, depending on the state you live in, to have a license since the equipment contains radioactive material. Any other suggestions would be greatly appreciated.

10th Feb 2011 02:57 UTCHenry Barwood

Thermo makes units now with a mini X-ray tube rather than the old radionuclide sources. I personally would not fool with the radioisotope driven XRF units. I strongly suspect that the learning curve for using one of these units is greater than a week!

28th Feb 2011 04:23 UTCBart Cannon

The Electron Probe that Rock was referring to was an ARL SEMQ owned by EMTEK, the company that ARL sold their closing inventory to.


They were located in Santa Clarita in 1988, and have been out of business since. Advanced Microbeam in Vienna, Ohio have taken over the service and modernization of ARL probes.


I got the probe operating in the EMTEK office and it sold to Western Michigan University in Grand Valley, Michigan. Kevin Cole was to be the user. I'm not sure if they ever got it running at their place.


I started building a large chamber vacuum based, x-ray induced XRF unit a few years ago. X-ray induced XRF has a much lower minimum detection limit than than electron induced XRF. I was tasked to provide a benign analytical circumstance to get some x-ray spectra from the spear point lodged in 9,300 year old Kennewick Man's ilium. The project went nowhere because the tribe's and the conservatuers were afraid the vacuum would disintegrate the bones.


I proved that there would be no harm by analyzing similar old bones in an EDAX Eagle III x-ray microprobe. This is an expensive piece of gear. It has x-ray optics that produce a 50 micron x-ray beam, a micrscope to locate the beam area and a precise stage translator.


It has helium, air, and vacuum paths. The helium path gets you down to silicon, but to get down to sodium you need a vacuum path.


I would not recommend using Henry's approach. For what he is going to pay you could buy a pretty good SEM with a liquid nitrogen based EDS system and ten years of liquid nitrogen. Plus you'd get a working vacuum system with sodium or better detection, and x-ray lateral resolution of one or two microns, and SEM quality imaging.


I've been down this road.


And Rock, thanks for loaning me your van and your best "toadie" for the EMTEK project ! I am forever in your debt.

4th Mar 2011 00:44 UTCHenry Barwood

Holy Smokes, Bart, I would love to have any of the systems you mentioned, BUT, where I live service/repair on such instruments is nonexistent. I picked the Amptek system because it is a simple system. My only mistake was overestimating the Z detection capabilities of the air system. Now I have to cobble together a vacuum chamber for sample analysis. With it, I should get down to Na. The biggest problem has been making the chamber fit the Amptek configuration.

4th Mar 2011 12:27 UTCBart Cannon

Henry,


I would guess that you bought the AMPTEK x-ray gun, the AMPTEK detector and pre-amp and the AMPTEK pulse processor and multichannel analyzer.


I expect that you probably paid $16K. Am I close?


I would love to have that system, but it's more than I can afford as an accessory to my other gear.


Do you know what the x-ray spot size will be? I think you would be lucky if it was as small as 200 microns.


Knowing your passion for mineral analysis, I think that you will probably end up with an SEM and EDS system eventually.


When I bought my first old ARL EMX-SM from the first moon rock era, I knew nothing about electronics and vacuum systems. I found a guy from Boeing to teach me about vacuum, and another guy from Boeing to show me how to adjust the electron beam and tune the wavelength dispersive X-ray spectrometers. I think the training cost about $700. I trained myself in electronics, vacuum and x-ray detectors. I've never had a service engineer in my lab since 1984.


You could do the same, and you could get a working SEM and EDS system for less than $3K.


I would be happy to give you some over the phone help, though I am sure that you could find a guy in your area for some inexpensive in the lab help.


There are many labs getting rid of their older SEMs in order to have state of the art instruments that have computer controlled everything.


The modern insturments require annual licenses, and can't really be repaired inexpensively since they are full of proprietary control boards, and there is a huge turnover in manufacturer take-overs of existing SEM companies. Service engineers on modern gear pack around large boards and swap them out to find the fix. Costs about $4K per board even if the fault is a 20 cent transistor. The service call will be $5K.


I know of many AMRAY 1200 SEMs from 1974 to 1980 which are still running.


In fact I have one in my garage with a PGT detector. Price ? $1,000 plus shipping. But you could surely do better than that locally.


Please keep me posted on your system. I'm quite interested, and if some of my current gear blows out beyond cheap repair, AMPTEK is certainly an option I will investigate for replacement.

4th Mar 2011 20:06 UTCHenry Barwood

Hi Bart,


I actually used some research funds to purchase the Amptek parts. It was a one-time allocation that I will not see again. The collimator on the X-ray source is 2 mm. They have narrower ones, but for my use, 2 mm was sufficient.


I wish I had your optimism about SEM/EDS units. I've worked with energy and wavelength dispersive analysis for 30+ years and a good technician is essential to good results! I do agree that modern "service" engineers are little more than board changers.

25th Mar 2011 22:24 UTCBob Rock

I recently got myself one of the "low cost" chinese desktop xrf units. It only operates in air, so is restricted for K to Bi. I use in combination with petrography and XRD, so is adequate for my purposes.

26th Mar 2011 01:10 UTCHenry Barwood

Hi Bob,


You might try putting baggie over it and flooding the detector with Helium. Would improve the low-Z detection limit.

26th Mar 2011 06:42 UTCBob Rock

Might do that as a last resort. I will have take a closer look at the the guts, there may be a way to introduce a vacuum around the detector. The software has a vacuum option...hmmm, must mean something.

30th Mar 2011 06:54 UTCBob Rock

Practically, the XRF will do Ti to Bi. I can't find any way to introduce a vacuum. He flush might work, something to try later....

Only templates for Au, Ag, Pt and Pd are provided. I am adding other elements using pure reference samples. The software handles the calculations, but is a little tricky to set up correctly.

1st Apr 2011 07:49 UTCBob Rock

How effective is increasing the voltage at detecting lower concentrations of heavy elements. Also, would it improve the low z detection limit?

1st Apr 2011 21:57 UTCHenry Barwood

I assume you are talking about increasing the voltage of the X-ray tube. I don't know how yours is set up, but the Amptek system allows any voltage to be programmed into the tube. Pre-programmed setting is 40KV, but for lighter elements anything above 20KV is overkill.

13th Apr 2011 09:53 UTCBob Rock

My XRF is setup for 35KV and 60microamperes current, set by the manufacturer. It's a gas proportional spectrometer, so does not have the resolution of the Amptek.


I have scanned about 30 reference samples of elements, pure analytical reagents with known concentration.


I have the following options for calculating concentrations:


1. Net Areas

2. Gross Areas

3. Pure spectrum (single element)

4. Pure spectrum (multi element)


My understanding is that

net areas calculates the areas under peaks of interest and converts them to concentration

pure spectrum (single element) uses some type of k ratio calculation


I am not sure what gross area and pure spectrum (multi element) are for


So far, it works great for qualitative and semi quantitative elements. I have not done enough tests for evaluating quantitative results


What calculation method would you guys use for this type of spectrometer for quantitative analysis?

22nd Apr 2011 13:16 UTCBart Cannon

I thought that I would mention how cheap good vacuum pumps are, and how easy it is to make a vacuum chamber.


Every university has pallet loads of used vacuum pumps. Many are perfectly good, and can achieve adequate vacuum to detect sodium without the need for a diffusion pump. The pallets of vacuum pumps here at the U.W. in Seattle often sell for less than $100. I have some good pumps that I would give away.


I have an old Kevex XRF unit. Its vacuum chamber is a sliding drawer about 2"x1"x3". The beam is fat, but a sample holder could be made out of plastic to eliminate stray spectra.


A larger chamber is easy to build out of thick plexi-glas, and using a fluorescent target you could see your beam diameter and location.


I still believe that eventually Bob and Henry will buy an old SEM and interface their Amptek detectors.


There is no work-around for the image and analysis resolution obtained by an SEM.


I also have some SEMs that I would give away. They all need a little work, but that's fun of it.

23rd Apr 2011 00:12 UTCHenry Barwood

Hi Bart,


I would love to be able to have an SEM/EDS machine at my disposal, but I teach at a "second tier" university with very limited research funds. The mini-XRF will likely be as close as I get to one.


My experiences with fixing SEM's was entirely negative and I doubt I have enough time and resources left to tackle that kind of a project.


I do hope to have an XRD operational by summer. I like using a powder camera for mineral identification. I've worked with them so much that they hardly seem time consuming and they do provide reasonably definitive identification of a mineral species. If you happen to have EDS/WDS data also that is confirmation of the identify of the mineral.


At one time I had a micro XRF that Phillips/Norelco made for their vacuum spectrograpth. Left it behind during a move and it is likely in a landfill somewhere. Wish I had it now. It did pretty good spot analyses, and was WDS.


Henry

16th May 2011 12:18 UTCBob Rock

If I want to determine the beam width and location on my EDXRF, as Bart mentioned, what type of fluorescent target would be a good choice?

17th May 2011 03:49 UTCHenry Barwood

Standard is a fragment of benitoite.

22nd Jun 2011 17:19 UTCBob Rock

I am doing a little catching up here. Sounds like dental x ray film may be more suitable for my machine. What is the story with this? Can it be opened and used in daylight, or does it need a darkroom?

22nd Jun 2011 18:43 UTCHenry Barwood

You can get pakages opf film with developer form China on eBay. They are inexpensive, but in spite of the advertisement, they do require a darkroom to develop. At least, I've not been able to get them to work in full light. they are quite sensitive and will show a focal spot nicely if you note the positiion of the film accurately.

23rd Jun 2011 05:32 UTCBob Rock

Thanks for the tips Henry. Use of a dark room is only a minor inconvenience.

26th Jun 2011 20:52 UTCGene

Rock Bob - Which low cost Chinese XRF tabletop system did you get? Could you tell me how much you paid and the contact as I am wanting a tabeltop XRF setup.

26th Jun 2011 20:53 UTCGene

Rock Bob - Which low cost Chinese XRF tabletop system did you get? Could you tell me how much you paid and the contact as I am wanting a tabeltop XRF setup.

27th Jun 2011 00:37 UTCBob Rock

Hi Gene,


I am not sure what you are wanting the XRF for? The XRF I have is advertised on the Internet as a Gold Testing Unit for around US$7000.00. I purchased direct from the Chinese. The model number is EXF7200.


The XRF comes with templates for quantitatively determining gold, silver, platinum and palladium. It will also detect other elements from Ti to Bi qualitatively. These can be identified by looking up their energies in the periodic table. I wrote my own templates for identifying the other elements. I might add an article on this XRF unit later.

27th Jun 2011 00:47 UTCHenry Barwood

Hi Bob,


Just a guess, but when I looked into these units a few years back, they used imported Amptek Peltier cooled diodes for the sensor. Most of the cost of these XRF's is likely those same diodes. Wish the Chinese would start manufacturing the things, then we might see a drop to several hundred rather than several thousand dollars.

27th Jun 2011 01:22 UTCBob Rock

Hi Henry,


Yes, they have several models, some of which use the Amptek Peltier Cooled Diode. The lower cost XRF's use gas proportional counters as the detector. The major cost would be the detector and x-ray tube.
 
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