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Determination of X-ray flux using silicon pin diodes.

Owen RL, Holton JM, Schulze-Briese C, Garman EF - J Synchrotron Radiat (2009)

Bottom Line: Accurate measurement of photon flux from an X-ray source, a parameter required to calculate the dose absorbed by the sample, is not yet routinely available at macromolecular crystallography beamlines.These experiments have shown that a simple model based on energy deposition in silicon is sufficient for determining the flux incident on high-quality silicon pin diodes.The derivation and validation of this model is presented, and a web-based tool for the use of the macromolecular crystallography and wider synchrotron community is introduced.

View Article: PubMed Central - HTML - PubMed

Affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.

ABSTRACT
Accurate measurement of photon flux from an X-ray source, a parameter required to calculate the dose absorbed by the sample, is not yet routinely available at macromolecular crystallography beamlines. The development of a model for determining the photon flux incident on pin diodes is described here, and has been tested on the macromolecular crystallography beamlines at both the Swiss Light Source, Villigen, Switzerland, and the Advanced Light Source, Berkeley, USA, at energies between 4 and 18 keV. These experiments have shown that a simple model based on energy deposition in silicon is sufficient for determining the flux incident on high-quality silicon pin diodes. The derivation and validation of this model is presented, and a web-based tool for the use of the macromolecular crystallography and wider synchrotron community is introduced.

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Log–log plot of the photoelectric cross section, μpe/ρSi (units: cm2 g−1), of silicon as a function of incident X-ray energy.
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fig2: Log–log plot of the photoelectric cross section, μpe/ρSi (units: cm2 g−1), of silicon as a function of incident X-ray energy.

Mentions: Using equation (1) and the relationship I = ϕQ, where I is the photo-induced current and Q is the charge created in an interaction for X-rays of energy E incident on a silicon diode, the photoconversion ratio can be expressed in the formwhere A pe is the photoelectric cross section of silicon, e is the electronic charge3 and ∊ is the energy required to generate an electron–hole pair defined in §1.5. The quantity A pe is tabulated for all elements by the NIST XCOM program (http://physics.nist.gov/PhysRefData/Xcom/Text/XCOM.html) and is plotted for silicon as a function of energy in Fig. 2 ▶. Fitting a third-order polynomial in the log–log domain reproduces XCOM data to better than 1% in the range 5–40 keV and allows A pe to be expressed in the formfor silicon. Equations (2) and (3) therefore enable the beamline photon flux to be related to the current induced in the diode solely in terms of the beamline energy and the thickness of the diode.


Determination of X-ray flux using silicon pin diodes.

Owen RL, Holton JM, Schulze-Briese C, Garman EF - J Synchrotron Radiat (2009)

Log–log plot of the photoelectric cross section, μpe/ρSi (units: cm2 g−1), of silicon as a function of incident X-ray energy.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2651761&req=5

fig2: Log–log plot of the photoelectric cross section, μpe/ρSi (units: cm2 g−1), of silicon as a function of incident X-ray energy.
Mentions: Using equation (1) and the relationship I = ϕQ, where I is the photo-induced current and Q is the charge created in an interaction for X-rays of energy E incident on a silicon diode, the photoconversion ratio can be expressed in the formwhere A pe is the photoelectric cross section of silicon, e is the electronic charge3 and ∊ is the energy required to generate an electron–hole pair defined in §1.5. The quantity A pe is tabulated for all elements by the NIST XCOM program (http://physics.nist.gov/PhysRefData/Xcom/Text/XCOM.html) and is plotted for silicon as a function of energy in Fig. 2 ▶. Fitting a third-order polynomial in the log–log domain reproduces XCOM data to better than 1% in the range 5–40 keV and allows A pe to be expressed in the formfor silicon. Equations (2) and (3) therefore enable the beamline photon flux to be related to the current induced in the diode solely in terms of the beamline energy and the thickness of the diode.

Bottom Line: Accurate measurement of photon flux from an X-ray source, a parameter required to calculate the dose absorbed by the sample, is not yet routinely available at macromolecular crystallography beamlines.These experiments have shown that a simple model based on energy deposition in silicon is sufficient for determining the flux incident on high-quality silicon pin diodes.The derivation and validation of this model is presented, and a web-based tool for the use of the macromolecular crystallography and wider synchrotron community is introduced.

View Article: PubMed Central - HTML - PubMed

Affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.

ABSTRACT
Accurate measurement of photon flux from an X-ray source, a parameter required to calculate the dose absorbed by the sample, is not yet routinely available at macromolecular crystallography beamlines. The development of a model for determining the photon flux incident on pin diodes is described here, and has been tested on the macromolecular crystallography beamlines at both the Swiss Light Source, Villigen, Switzerland, and the Advanced Light Source, Berkeley, USA, at energies between 4 and 18 keV. These experiments have shown that a simple model based on energy deposition in silicon is sufficient for determining the flux incident on high-quality silicon pin diodes. The derivation and validation of this model is presented, and a web-based tool for the use of the macromolecular crystallography and wider synchrotron community is introduced.

Show MeSH
Related in: MedlinePlus