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El miércoles, 26 de mayo de 2021 19:04:13 ART, Allaz Julien <[log in to unmask]> escribió:

Hi Fernando,

To cut to the chase: L-type monochromator are better to my opinion.

L-type stands for larger area monochromator. They allow for a higher collection rate of X-ray (bigger solid angle), yet they fully preserve a peak-to-background ratio equivalent to any “normal” 140 mm Rowland circle spectrometer.

H-type spectrometer (smaller R circle) offers certainly a higher X-ray count rate, but this includes also a higher count rate on the background. Hence the peak-to-background ratio is LOWER than the achievable peak-to-background ratio on L-type monochromator. As you mention, there is also a loss of energy resolution, hence a higher risk of peak or background interference issues. I have a few data on my paper on REE phosphate analysis, comparing notably REE analysis on LiF-L vs. LiF-H, or Pb on PET-L, PET-VL [Cameca only] or PET-H (check notably table 5 and figure 2):

https://iopscience.iop.org/article/10.1088/1757-899X/891/1/012001/meta

On another note, there has been several reports on H-type monochromator being more likely prone to fracturing over time. As the Rowland circle is smaller, the monochromator must be bent more (= more tension on the 2d-lattice and risk of failure).

Other important point: H-type spectrometer have some limitation on their range (~85 to 235 mm on H-type spectrometer against ~70 to 250 mm for regular 4-crystal spectrometer or for L-type monochromator). There are thus several X-ray lines you cannot reach. For instance, Ti on PET-H is just at the limit and you cannot place a low background (but this is not a problem if you use a mean atomic number background correction), and you cannot reach Si Ka on TAP-H (not that I would do this anyway in silicate as the count rate will be too way too high > 50k cps).

L-type monochromator comes to a price, but you will not regret your purchase.

Cheers,

Julien

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Dr. Julien Allaz
SEM/EPMA lab manager
Department Erdwissenschaften

Inst. für Geochemie und Petrologie

ETH Zürich
NW E 84
Clausiusstrasse 25
8092 Zürich
Switzerland

Tel: +41 44 632 37 20

Fax: +41 44 632 16 36

Email: [log in to unmask]

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On 26 May 2021, at 22:43, Fernando Colombo <[log in to unmask]> wrote:

Hi all,

there is a possibility that we can add two spectrometers to our microprobe, and we are trying to decide which could be the best combination. We perform mostly analyses on geological samples.

I would be grateful if you could tell me the difference between the L and H crystals (e.g. LiFH vs LiFL). The JEOL brochure reads that the L type is for "trace element overlaps in geology" and the H type is for "high X-ray intensity". As expected, we noticed some loss of resolution when going from the "normal" (e.g. PETJ, LIF) to H crystals (PETH, LIFH) in the spectrometers we already have. Do L-type crystals offer a better resolution than the regular crystals? How about detection limits?

I will appreciate your comments and experiences.

Thank you very much in advance,

Fernando Colombo

National University of Cordoba

Argentina

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