Dear Julien,
Thank you so much for your very clear explanation.Best,
Fernando
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
###########################Dr. Julien Allaz
SEM/EPMA lab manager
Department ErdwissenschaftenInst. 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 36Email: [log in to unmask]
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 ColomboNational University of CordobaArgentina**** JEOL Probe Users Listserver
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