Photon Factory Activity Report 2004 #22 Part B (2005)
Atomic and Molecular Science

15A/2003G060

Simultaneous measurement of SAXS and absorption factor by use of
Si PIN photodiode installed in direct beam stopper (2)Yoshitada TANAKA, Takeshi MORITA*, Yoshihiro TAKAHASHI, Keiko NISHIKAWA
Chiba Univ., Yayoicho, Inage-ku, Chiba 263-8522, Japan

Experimental
The transmittance of direct beam was monitored bysilicon PIN photodiode (Hamamatsu Photonics, S5106)
connected to a pico-ammeter (Keithley Instrument, 6485).
The detector was covered with aluminum foil to shut out
room light, and cupper sheet was set on the photodiode toattenuate X-ray intensity to proper intensity for thedetector. Since surface of the detector is larger than thecross section of direct beam, the detector was covered
with lead sheet to cut scattered X-ray. Figure 1 shows
photograph of the detector set at frame in vacuum
chamber of BL-15A. The distance between sample anddetector was about 2 m. Incident X-ray intensity wasmonitored by ionization chamber.
It takes one minute to be stable intensity of X-ray after
open the shutter. After stabilizing intensity of X-ray, thesignal was flowed as follows: the Picoammeter-V/F
converter-counter.
Simultaneous measurement of SAXS and absorption
factor was carried out for super critical CHF3 along an
isotherm at 311.4 K and pressures between 4.08 to 8.25
MPa.
Results and Discussion
Figure 2 shows the measured absorption factor, µl, atvarious densities of super critical CHF3. As shown in Fig.
2, the measured µl shows good proportional relation todensity. This indicates that the measurements wereaccurately performed in wide density range. This method
is applicable to other samples. This apparatus enables us

simultaneous measurement of SAXS intensity andabsorption factor of a sample.

Fig. 1 Photograph of the detector set at frame invacuum chamber of BL-15A.

2
1.5

µl

Introduction
Small-angle X-ray scattering (SAXS) pattern and themagnitude of the scattering intensity sensitively dependon correction of background intensity and of absorption,
both of which are made by use of absorption factor, µl,
where µ is the linear absorption coefficient of a sample
and l is its length. Here, we report the apparatus formeasurement of the factor by use of photodiode installed
in a direct beam stopper. Our method for thedetermination of the factor, which is simply constructedby a beam stopper with a pinhole and a one dimensional
detector, was described previously.[1] However, themethod is not enough in stability and accuracy. Althoughanother method has been tried using two ionizationchambers, this method increases background due to pathof ionization chamber, or we have to obtain SAXS signals
and the absorption factors by turns. The new method issuperior in an in-situ measurement of SAXS intensities
and absorption factor of the sample.

10.5
000.5
1density (g/cm3)

Fig. 2 Relation of absorption factor, µl, and fluid
density of super critical CHF3 measured by Si PIN
photodiode installed in a direct beam stopper.
Acknowledgement
The authors are grateful to Dr.Kazuki ITO (SPring-8)
for helpful discussion in the design of the sensor.
References[1] K. Nishikawa et al., J. Phys. Chem.B, 101,1413(1997).
*moritat@faculty.chiba-u.jp

Users' Report5