2015 Cameca Users Meeting Background characterization – must account for background shape...

2015 Cameca Users Meeting

Background characterization – must account for background shape

CurvatureSpectrometer efficiencyNatural Bremsstrahlung shape

InterferencesFrom elements in the excitation volumeFrom elements fluoresced from a distance – can be 10s to 100s of microns

Absorption edges

S K edge

S Kb S Ka

Bi Mα


‘Holes’

Compositional variation within phase of interest

2012 Workshop: Dating Tectonic Events using Monazite/Xenotime



‘Holes’

Compositional variation within phase of interest


Curvature and interferences…






54000 55000 56000 57000 58000 59000 60000 61000 62000 63000 640000.80

1.00

1.20

1.40

1.60

1.80

2.00

PbMb

f(x) = 174.740050889563 exp( − 8.39654354896111E-05 x )f(x) = 261.71092066823 exp( − 9.07497725717837E-05 x )

f(x) = NaN exp( NaN x )f(x) = NaN exp( NaN x )f(x) = NaN exp( NaN x )f(x) = NaN exp( NaN x )f(x) = NaN exp( NaN x )Pb-M region on GdPO4

Ultrachron VLPETExponential (Ultrachron VLPET)Ultrachron LPETExponential (Ultrachron LPET)Ultrachron PET (1 bar Poly)

wavelength (sin-q * 105)

inte

ns

ity

(c

ps

/nA

)

Intensity Scaling Curvature 1.0 -7.238 2.42 -8.465 5.14 -4.369 5.10 -5.161 4.00 -7.652 5.52 -9.075 1.67 -8.466






Ti Kα1 (2)

Th Mα

Th Mβ

High net intensity (pk-bkg) and large pk/bkg

Major element analysis is primarily characterization of peaks…


Measured net Int.20% error, ~350ppm error

Correct net Int.

Trace element analysis is primarily characterization of background…


Curvature and interferences…



How do we know the analysis is correct ?

Analysis of elemental concentration

Test against secondary standard of “known” composition

Secondary must be appropriate for monazite, etc.

REE phosphateThU

Very difficult to find or make homogeneous trace element secondary standard


If you can’t check against a known value, then try for a zero result in something appropriate that doesn’t have any of the trace element of interest (blank).

Clearly,“If you can’t analyze something, then see if you can analyze nothing…”

“Because, if you can’t do nothing right, then you can’t do anything.”

A start for assessing accuracy…Blank analysis


Test for Pb in synthetic GdPO4 (no Pb flux!)Savitsky – Golay low pass filter


Savitsky – Golay low pass filter


Blank test for Pb


Blank test for Pb

Background offsets Pb

(sinθ*105) ppm sd

+/- 200 2 12

+/- 500 -40 14

+/- 1000 -79 7

+/- 2000 -54 6

Regressed -4 10


Determination of background intensity by the multipoint method

Fit via exponential or polynomial regression


Determination of background intensity by the multipoint methodBlank testing…

GdPO4 PrPO4Avg all Std dev. Avg all Std dev.

0.0041 0.0048 -0.0059 0.00330.0117 0.0024 0.0123 0.00180.0004 0.0027 0.0006 0.0016

0.0033 0.0096 -0.0086 0.00280.0133 0.0015 0.0129 0.00190.0012 0.0042 -0.0022 0.0016

-0.0019 0.0096 -0.0130 0.00260.0093 0.0015 0.0102 0.0019

-0.0089 0.0044 -0.0126 0.0017

Multipt bkg

UTh

Pb

2-pts bkg, EXP.

UThPb

2-pts bkg, LIN.

UThPb




Interferences and absorption edges…It’s not just background, but background on interference correction measurements also


Interferences and absorption edges…


Interferences and absorption edges…How do we measure the interference correction?








































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2015 Cameca Users Meeting Background characterization – must account for background shape...

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