Gamma Spectrometry Forum

Mini xray xrf

I have done xrf before using Am241 sources .Covers a wide range from 7 kev to 50 kev.
This time with xray with xray generating tube
My xray energy is powered by about 30 kvp transformer.Max current is 100 microamp max
Unable to measure high votage cos my voltmeter max is 1000v only
Not sure using 1000 ohm resistor can overcome this ,,Haven't tried
I guess it is between 20 to 30 kvp
Input voltage about 18 volts.
Xray energy spectrum is a 15 kev single peak with no bestrahlung spread .This was measured by exploranuim 130 and scintillion detector.
But enough for low energy XRF production less than 15 kev

SETUP
RAP 47 set at 750 volts using GS2000 pro
Rap47 is placed inside a iron cylinder with some Pb tape near the crystal end to block incident xray background
Aluminium sheet at exit site of xray collimator to block off low unwanted xray energies.
Thermimo software
Russian tube with high voltage without filament current.Sorry no pics cos it will mess up if I remove it .
I carefully put inside the xray collimator to prevent high voltage arcing.
Xray collimator to generate a beam of xrays with less scatter.
SHIELDED with a radpad material(Sb polymer enough to block 15 kev xrays)
Inspector usb geiger counter inside box to hear xray so that I know its working and control exposure time
A leaded glass with lead sleeves to protect myself from any backscatter
These xrays are quite intense .
MY Insp usb geiger counter and exploranium 130 really buzz loudly even placed 3 feet away.
Being low energy it is more hazardous so I have sheild adequately
I was hoping to get good results for the low energy like Cu and below but I got mixed results

PROS
Fast results for low Z elements like Cu which normally is slower with Am241
Expecting better resolution on these low xrf peaks

CONS
SMALL metal sheets less than 5 do not work
Geometry and positiong of samples important
Works best with flat metal sheets
Limited to xrf energy less than 15 kev
I am still trying to improve my setup by trial and error
Prior to this I was using a bulky ludlum collimator to house my RAP 47 but this was taking up a lot of space,difficulty positioning my samples etc
This iron cylinder matching the size of my Rap47 is functionally better to focus on the xrf.
Besides danger of xray I encounter arcing so I ensure wires are well insulated...yet those electrons jump to nearest conductor.I dont touch any metals nearby when shooting
See pics for some of the elements
Thanks for listening
TARAY

Anonimous wrote: ↑

24 Nov 2019, 20:30

Mini xray xrf

CUT
I guess it is between 20 to 30 kvp
Input voltage about 18 volts.
Xray energy spectrum is a 15 kev single peak with no bestrahlung spread .This was measured by exploranuim 130 and scintillion detector.
But enough for low energy XRF production less than 15 kev

Hi,
i think there is something wrong with tube energy output characterization , an x-ray tube put out bremsstrahlung plus characteristic lines of the electron beam target material, roughly the bremsstrahlung energy peak is 1/3 max voltage tube input.
Unfortunately scintillation detectors under 100KeV energy , even the LEG probe like the RAP47, exhibit too much poor resolution for doing XRF analysis, so the near 15KeV energy peak you are seeing is the bremsstrahlung peak.

Nice setup!

Beware of scattered x-ray…….

Ya
My input voltage is only about 20 plus Kvp
I need about 50 to 100 to excite the anode assuming its tungsten to release characteristic xrays
So I have to settle for bestrahlung peak only
I am unable to generate that 50 plus kvp due to my transformer limitation max 30 kvp.
Don’t won’t to push it beyond recommended limits.
Thanks

Taray,

If your tube outputs 15 keV x-rays and we assume a high Z target then your power supply is probably only giving you 15kV under load.

I am also keen to explore XRF using a scintillation detector, but I'm thinking of buying an LaBr or CeBr crystal, These crystals are normally very expensive, but since you only need a 1 mm slice for XRF the cost should not be much less. Also the internal radiation in LaBr would be irrelevant in such a thin slice.

LaBr3 usually has a resolution of 2.5% to 3.5% @ 662 keV, so I assume it is also better at low energies.

Steven

Taray,

If your tube outputs 15 keV x-rays and we assume a high Z target then your power supply is probably only giving you 15kV under load.

I am also keen to explore XRF using a scintillation detector, but I'm thinking of buying an LaBr3 or CeBr3 crystal, these crystals are normally very expensive, but since we only need a 1 mm slice for XRF the cost should be much less. Also the internal radiation in LaBr3 would be irrelevant in such a thin slice.

LaBr3 usually has a resolution of 2.5% to 3.5% @ 662 keV, so I assume it is also better at low energies.

Steven

Hi Steven,
The use of LaBr3 or CeBr3 is not possible for xrf because the resolution in the low energy area is worse than NaI(Tl).
E.g. NaI(Tl) gives 18%@30KeV and 11%@60KeV, CeBr3 20%@30KeV and 13%@60KeV, same for LaBr3 that also has an other problem that is the Beta's background (<200KeV)in the low range is so high that will spoil the xrf readings.
These High resolution crystals are very good but only in the range >200KeV therefore useless for xrf.
Luuk

Steven Sesselmann wrote: ↑

25 Nov 2019, 16:41

Taray,

If your tube outputs 15 keV x-rays and we assume a high Z target then your power supply is probably only giving you 15kV under load.

Hi Steven, the bremsstrahlung peak is roughly 1/3 of input voltage, so tube input should be in excess of 30kV.

Ciro
My transformer states 12 volts for +30 kev
My input is 18 volts
So it should excess 30 kv
Like I said before I am unable to measure my high voltage .Just making an estimate.
Good maths
Taray

Checked up what happens if one gives more input voltage than recommended.
It will lead to insulation failure ,transformer saturation and arcing and the output voltage will not be linear although higher .
Of course the transformer can burnout
I acquired a single 12 volt battery recently and will check if there is any difference .
I transiently check once with 27 volts without significant change in X-ray energy.
Taray

Taray,

I fond some information here; https://www.arpansa.gov.au/understandin ... tion/x-ray

It seems consistent with Ciro's comment above, the main bremsstrahlung peak is around 1/3 of maximum, where the maximum energy is the input voltage times charge.

Steven