Geo,

Getting only 1800 counts/sec ?in 600 sec is saying something is
not quite right with the setup. Not separating the Fe and Ni Kb and Ka is also
not right but may? be related to the low count rate. Before you go any further
find out why you’re getting the low count rate. This spectra should come in in ?30
sec count. ?I suspect the beam flux is too low (what’s the collimator diameter
and where is the micro-focus point?) and if you haven’t moved the detector
closer to the target ?that may be the problem as well.? Get rid of the lead shield
setup and set up the geometry by hand without it (but keeping ?shielding between
you and it). Play around getting an optimal geometry and beam current. Start by
getting the detector closer to the target.? I’d think running ?a test with and
without the plastic cap on the low energy end would be interesting test to see
as well. Use a Si target.

Dud

?

Baby steps- a 304 stainless bolt from the shop.


Geo

?

Yes, the exciter flux is very low. Only 20 uA and in the beam port right now are 3 ea. 1.6mm Aluminum plates (solid) and then a 4.75mm plate with a 1mm hole in the center. I'm please with the clean patterns, even tho slow. This is a Si-PIN, not an SDD.?

I did machine a new part the other day that connects the Al and Pb? cylinders together, that allows the sensor to be considerably close to the center of the chamber. Not that? it maters very much, as the beam can be positioned anywhere on the floor of the chamber.

?

Also today, a trip to the garage yielded a good thick aluminum part that can be turned on the lather to make the lid-liner,

With luck, the lid will be finished tomorrow and work on the permanent collimator started.

Geo

----- Original Message -----
From: Dude <dfemer@...>
To: [email protected]
Sent: Tue, 04 Feb 2020 19:52:13 -0500 (EST)
Subject: Re: [XRF] Stainless Steel XRF

?

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Geo,

Getting only 1800 counts/sec ?in 600 sec is saying something is
not quite right with the setup. Not separating the Fe and Ni Kb and Ka is also
not right but may? be related to the low count rate. Before you go any further
find out why you’re getting the low count rate. This spectra should come in in ?30
sec count. ?I suspect the beam flux is too low (what’s the collimator diameter
and where is the micro-focus point?) and if you haven’t moved the detector
closer to the target ?that may be the problem as well.? Get rid of the lead shield
setup and set up the geometry by hand without it (but keeping ?shielding between
you and it). Play around getting an optimal geometry and beam current. Start by
getting the detector closer to the target.? I’d think running ?a test with and
without the plastic cap on the low energy end would be interesting test to see
as well. Use a Si target.

Dud

?

Baby steps- a 304 stainless bolt from the shop.


Geo

?

?

?

Geo,

Why is there ?4.8mm of Al attenuator in the beam path? ?What is the
no collimated diameter of the micro-focus beam on the target? Is it well
aligned with the 1mm collimator, if 颈迟’蝉 not you’ll have ?a lot of attenuation.?
Collimation usually uses 2 ?separated collimators and sometimes one on the
detector. ?Start simple, no collimator, no attenuators. Look at the beam
diameter at the target plane. Set up the collimation to get the beam diameter
you want at the target plane. ?Then move the Detector close to the target say
about 1 – 2cm. ?Take a shot using the lowest beam current and look at Dead Time.
You should be able to count at 40Kcps and have good resolution and count time.?
Play with the beam current. Play with Detector distance to target.

Your comment “…allows the sensor to be considerably close to the center of the
chamber. Not that? it maters very much” ?What is considerably
closer? It matters very much. The beam will expose a small circle on the target
that will fluoresce over a solid angle. The flux in is proportional to the flux
out. The percentage of that signal your detector will get is directly dependent
on the distance from the target and that solid angle. Close up its 1/r, at a
distance it falls as 1/r2.? Remember the time distance shielding thing

?Do a sensitivity analysis. What gets the best signal? What changes
things the most? – where do I optimize my effort? Is it Distance, geometric angle
between beam and detector, collimation, need for attenuator, what size beam
spot do I want on the target, what s that get me in count time etc.

The problem here is not the difference between a SDD and a SI-PIN 颈迟’蝉
the set up geometry and the shield system limiting you to very poor performance.

Dud

KK7IF

?

?

?

?

" Geo,Why is there ?4.8mm of Al attenuator in the beam path? "

?

Two reasons, the first is to selectively block the lowest energies from the tube (to help the detector see less noise at the area of interest below 15keV, then the top layer is to control beam spreading and provide a clear path (1mm hole) for the beam I want to strike the target.

?

Some of the same thought went into the Am_X8 to reduce the 13.9 +17.74 but leave the 59.5 pretty much unaffected flux-wise.

?

Geo

?

----- Original Message -----
From: Dude <dfemer@...>
To: [email protected]
Sent: Wed, 05 Feb 2020 00:25:05 -0500 (EST)
Subject: Re: [XRF] Stainless Steel XRF

?

Geo,

Why is there ?4.8mm of Al attenuator in the beam path? ?What is the
no collimated diameter of the micro-focus beam on the target? Is it well
aligned with the 1mm collimator, if 颈迟’蝉 not you’ll have ?a lot of attenuation.?
Collimation usually uses 2 ?separated collimators and sometimes one on the
detector. ?Start simple, no collimator, no attenuators. Look at the beam
diameter at the target plane. Set up the collimation to get the beam diameter
you want at the target plane. ?Then move the Detector close to the target say
about 1 – 2cm. ?Take a shot using the lowest beam current and look at Dead Time.
You should be able to count at 40Kcps and have good resolution and count time.?
Play with the beam current. Play with Detector distance to target.

Your comment “…allows the sensor to be considerably close to the center of the
chamber. Not that? it maters very much” ?What is considerably
closer? It matters very much. The beam will expose a small circle on the target
that will fluoresce over a solid angle. The flux in is proportional to the flux
out. The percentage of that signal your detector will get is directly dependent
on the distance from the target and that solid angle. Close up its 1/r, at a
distance it falls as 1/r2.? Remember the time distance shielding thing

?Do a sensitivity analysis. What gets the best signal? What changes
things the most? – where do I optimize my effort? Is it Distance, geometric angle
between beam and detector, collimation, need for attenuator, what size beam
spot do I want on the target, what s that get me in count time etc.

The problem here is not the difference between a SDD and a SI-PIN 颈迟’蝉
the set up geometry and the shield system limiting you to very poor performance.

Dud

KK7IF

?

?

?

?

_._,_._,_

Geo,

You use XRF filters to remove tube artifacts, Brem, ?and
fine tune low energy response. The filters are used in conjunction with the
tube voltage and the filter material is tailored for the absorption edge for
the analytes you are interested in. ?Putting a 4.8mm block of Al will reduce
the 50 kV intensity by a factor 0.6, at 30 kV the beam is attenuated down to
0.2. At 20 kV its gone at 0.012.? The only thing 颈迟’蝉 doing is killing your
beam intensity (count time) and shape resulting in excitation only by the highest
energies.? For looking at a broad band range of elements don’t use a filter.
When looking to reduce noise select a filter and beam kV tailored to that
material of interest.? Filters are used to maximize the sensitivity to
different groups of elements.? They are not thick, they are thin, a couple of um
to mils, and are single or layered composite of Al , Ti, Cu, C, Pd, In, etc.?
Filters are used to tailor the excitation ?energy range. The filter is designed
to absorb x-rays with energies immediately above the absorption edge of the filter
material.? Lower energy x-rays and the much higher energy x-rays will make it ?through.?
This reduces the Brem just above the absorption edge.? For an Al filter (not a 4.8
mm! but a mil or so), the absorption edge of Al is 1.56 keV so the Ka of the lower
Z elements Mg (1.2 keV) and Na (1.0 keV) will be absorbed by filter while the
region just above that will have a very low background allowing better
sensitivity to elements from Si (1.7 keV) to Ca (3.7) due to the lower brem.
Above that the higher energies are unaffected.? The filter is used to help pull
up the sensitivity in energy ranges defined by the element’s Z.

The ?only thing you are doing with the Al block is
reducing the total excitation flux rate, lowering the low energy flux rate and killing
the low energy element sensitivity while increasing the count time.

Take the Al filter out. ?If you’re getting Sum peaks then
attenuate the beam but use the beam current first.

?

Dud

?

?

?

Dud, I'll look at the link tomorrow, thanks. Meantime, per your request,? my? module gives a 10mm round beam at the surface of the brass port that is part of the module. 3 inches away the spot it still circular and has spread to 25mm.

?

?

Geo

?

----- Original Message -----
From: Dude <dfemer@...>
To: [email protected]
Sent: Wed, 05 Feb 2020 19:19:29 -0500 (EST)
Subject: Re: [XRF] Stainless Steel XRF

?

Geo,

You use XRF filters to remove tube artifacts, Brem, ?and
fine tune low energy response. The filters are used in conjunction with the
tube voltage and the filter material is tailored for the absorption edge for
the analytes you are interested in. ?Putting a 4.8mm block of Al will reduce
the 50 kV intensity by a factor 0.6, at 30 kV the beam is attenuated down to
0.2. At 20 kV its gone at 0.012.? The only thing 颈迟’蝉 doing is killing your
beam intensity (count time) and shape resulting in excitation only by the highest
energies.? For looking at a broad band range of elements don’t use a filter.
When looking to reduce noise select a filter and beam kV tailored to that
material of interest.? Filters are used to maximize the sensitivity to
different groups of elements.? They are not thick, they are thin, a couple of um
to mils, and are single or layered composite of Al , Ti, Cu, C, Pd, In, etc.?
Filters are used to tailor the excitation ?energy range. The filter is designed
to absorb x-rays with energies immediately above the absorption edge of the filter
material.? Lower energy x-rays and the much higher energy x-rays will make it ?through.?
This reduces the Brem just above the absorption edge.? For an Al filter (not a 4.8
mm! but a mil or so), the absorption edge of Al is 1.56 keV so the Ka of the lower
Z elements Mg (1.2 keV) and Na (1.0 keV) will be absorbed by filter while the
region just above that will have a very low background allowing better
sensitivity to elements from Si (1.7 keV) to Ca (3.7) due to the lower brem.
Above that the higher energies are unaffected.? The filter is used to help pull
up the sensitivity in energy ranges defined by the element’s Z.

The ?only thing you are doing with the Al block is
reducing the total excitation flux rate, lowering the low energy flux rate and killing
the low energy element sensitivity while increasing the count time.

Take the Al filter out. ?If you’re getting Sum peaks then
attenuate the beam but use the beam current first.

?

Dud

?

?

?