1. Introduction

X-ray single crystal structure analysis is known as the easiest and most direct approach to investigatingthe structure of the solid state. Rigaku has marketedfour-circle X-ray diffractometer systems (AFC) as astandard analysis tool in this field for many years.Rigaku has also been offering imaging-plate-mounted two-dimensional X-ray diffractometers (R-AXISseries), designed for protein structure analysis, as ahigh-speed data collection system for smallmolecules. Now, aiming primarily at small moleculesingle crystal structure analysis, Rigaku hasdeveloped a new instrument, the IP-mountedWeissenberg camera R-AXIS RAPID.

Other area detector systems typically use MoKaradiation for small molecule analysis in order tocompress the diffraction data because of the limitedapertures of these instruments. The cylindrical geo-metry of the IP in the R-AXIS RAPID extends the

scanning range (2θ) to 140°, allowing measurementof complete data sets using CuKα radiation.

A newly developed software package unifies theequipment control and data processing functions, sothat even a novice can collect data for structureanalysis without a detailed knowledge ofcrystallography. The imaging plate employed is of atype characterized by high sensitivity and low noise,so even exceedingly small crystals can be measured in a short time, thus meeting broad analytical needs from general users and professionals alike.

2. Features

(1) The X-ray tube assembly and thegoniometer are combined into a single unit tomake intense incident X-rays obtainable.

(2) The user may choose either a sealed tubeor a rotating anode X-ray source, depending onthe intended use and budget.

43 The Rigaku Journal

The Rigaku Journal

Vol. 15/ number 2/ 1998

Product Information

X-ray Single Crystal Structure Analysis System

R-AXIS RAPID

(3) As shown in Fig. 1, a newly developed 3χ goniometer permits automatic axial alignment.High-speed measurement by the screenlessWeissenberg method is practicable in addition tooscillation photography.

(4) A broad scanning range of -60 to ±140° inthe circumferential direction and ±45° in the axial direction is obtained by the use of a cylindricalimaging plate. Accordingly, a complete data setsuitable for publication in Acta Crystallographica C can be measured with not only MoKα but alsoCuKα radiation.

(5) The vertical arrangement of the IP makes a compact system with good access to the sample.

(6) A high-speed readout system significantly reduces the dead time.

(7) The double photomultiplier system hasattained a sensitivity of 1 x-ray photon/pixel and a dynamic range of 106 or more and less than 1 x-ray photon of read noise.

(8) Automatic measurement can be madeusing newly developed software.

Vol. 15 No. 2 1998 44

Fig. 1.

X-ray generator X-ray generator Sealed tube Rotating anode

Max. rated output 3 kW 18 kW

X-ray shutter Rotary shutter

Dimensions 570W x 1560 H x 780 D mm 600 W x 1700 H x 1000 D mm

X-ray tube Mo, Cu (optional)

Camera section System Vertical Weissenberg camera

Monochromator Flat graphite crystal

Camera length 127.38 mm

Angle measuring range -60 ~ +144° (circumferential direction) ±45° (axial direction)

Collimator 0.3 mm, 0.5 mm, 0.8 mm double pinhole

Beam stopper To be installed right behind crystal

CCD camera for sample observation ¼” color, to be displayed on host CPU

Goniometer System 3-axis Eulerian goniometer

ω -85 ~ +265° (in 0.002° steps)

χ -15 ~ +55° (in 0.001° steps)

φ -180 ~ +360° (in 0.002° steps)

Axial intersection precision Within φ20µm

3. Hardware Specifications

4. Software

The newly developed fully automatic datacollection software AUTO incorporates bothequipment control and data processing functionstogether. As a result, the measuring conditions can be

automatically determined, allowing inexperiencedscientists to collect useful diffraction data. Measure-ment and data processing will follow consecutively.Fig. 2 shows a flowchart of measurement. Theoperator has only to mount a sample and enter certainmeasuring conditions and the sequence of processing

45 The Rigaku Journal

IP readout system Readout system Internal circumference readout (optics rotation) system

Number of IPs One

Detection area 465 mm x 258 mm

Pixel size 100 x 100 µm; 100 x 150 µm; 200 x 200 µm

Number of pixels 4500 x 2560; 4500 x 1700; 2250 x 1280

Output data 23MB; 16MB; 6MB

Readout time 100 sec; 70 sec; 50 sec

Excitation light source Semiconductor laser (max. Rated output 30 mW)

Detector Dual photomultiplier

Readout sensitivity 1 x-ray photon/pixel

Dynamic range 1 ~ 106 (0 ~ 1048480)

IP erase time 20 sec

Duty time 140 sec (at 100 x100 µm)

Controller Function X-ray exposure, readout, sequence control of data transfer

IP data readout High-speed 16 bits linear ADC

Interface for control RS232C

Interface for data SCSI2

Dimensions 900 W x 1950 H x 1000 D mm 1050 W x 1950 H x 1000 D mm

Host CPU IRIS O2

CPU 64 bits RISC (R5000) or equivalent

Main memory 96 MB

Magnetic disk 2GB (for system) + 4GB (for data)

Auxiliary memory 4-time speed CD-ROM drive (built-in)

Magnetic tape 2GB DAT drive

Display 17” monitor

Laser printer Printer that can handle postscript

Computer desk Computer desk, chair, table top...one each

Host CPU dimensions 800 W x 1270 H x 730 D

steps from Index to Scale will then be executedautomatically.

5. Measurement Example

Fig. 3 shows the measurement of cytidine(C9H13O5N3) with the R-AXIS RAPID. This exampleshows the results of the oscillation photographicmethod and the screenless Weissenberg method, using both CuKα and MoKα radiations as the X-ray source.

In the Weissenberg method, exposure is made byslowly moving the IP which is synchronized with thecrystal rotation (ω-axis oscillation) so as to preventoverlap of diffraction spots. As may be seen from Fig. 3(A) and (C), this method is a very efficient onewhich permits recording of large quantities ofdiffracted X-rays on a single IP exposure. Because the axis used for axial alignment is automatically

Vol. 15 No. 2 1998 46

AUTO FUNCTION

Crystal centering, sample name entry, etc while watching CCD camera

Determination of setting matrix from two photos ofω=0~5° and ω=90~95°, respectively

Osc/weiss: For user’s prior selection; Determination of optimalmeasurement conditions from setting matrix and latticeconstants; Calculation of completeness and redundancy.

Oscillation photo mode: Measurement of ~44 photos for an ordinary sampleWeissenberg mode: “ ~10 “

Start of measurement based on conditions automaticallydetermined by Strategy; Automatic determination of box size forintegrated reflection intensity calculation; Refinement of settingmatrix, lattice constant, etc; Integrated reflection intensity

merge:post refine:laue:scale:abscor:average:

Merge of intensity data file per frameRefinement of crystal parameters, e.g. Lattice constantsDetermination of Laue classDetermination of scale factor per frameAbsorption correctionAveraging and output of equivalent reflections

Structure analysis (Optional)

Fig. 2. Flowchart of automatic measurement

determined in the software from the result of Index the operator can be freed from complicated axialalignment work, unlike in the conventionalWeissenberg method.

CuKα radiation interacts more strongly withsamples than does MoKα radiation, and thereforedisplays higher performance in the measurement oftiny crystals. When Fig. 3(A) and (B) are compared, it

may be seen that CuKα radiation may be used tomeasure crystals having low diffracting power orlarge lattice constants (50 C or so) because it has alonger wavelength than MoKα radiation. CuKαradiation excels, furthermore, in determination ofabsolute structure by utilizing the anomalousdispersion effect. Table 1 shows the characteristics ofeach measurement mode.

47 The Rigaku Journal

MoKα CuKα

Oscillation photographicmethod

Most standard method (3~8 hrs)

Strong diffraction intensity

Crystal with large lattice parameters (~50 C)

Absolute structure determination by Anomalousdispersion effect (6~12 hrs)

Weissenberg method High-speed measurement (1~4 hrs) High-speed measurement in above conditions (4~8 hrs)

Table 1. Characteristics of each measurement mode (rough measurement time required for ordinary crystals isindicated in parentheses)

(A) Oscillation photo, MoKα, 60kV-50mAoscillation angle: 5°, exposure time: 5 min

(D) Weissenberg photo, CuKα, 60kV-50mAoscillation angle: 60°, exposure time: 5 min

(C) Weissenberg photo, MoKα, 60kV-50mAoscillation angle: 40°, exposure time: 20 min

(B) Oscillation photo, CuKα, 50kV-40mAoscillation angle: 30°, exposure time: 5 min

Fig. 3. X-ray diffraction pattern in each measurement mode (sample: cytidine C9H13O5N3)

Fig. 4 shows the structure analysis results ofcytidine (C9H13O5N3) measured by the Weissenbergmethod using MoKα radiation. The measurementtime was 60 minutes. In this case, the measurement

conditions were determined assuming that the crystalsystem is triclinic. If the Laue class is known, themeasurement time can be reduced further.

Vol. 15 No. 2 1998 48

Sample Cytidine (C9H13O5N3)

Crystal size 0.3 x 0.3 x 0.4

X-ray source MoKα 50 kV 48 mA

Measurement Weissenberg method

Exposure time 10 sec/deg (Total 60 min)

Lattice Constant13.962 14.770 5.12690.0 90.0 90.0

Crystal System orthorhombic

Laue Class mmm

Rmerge 3.2%

R 2.9%

Rw 3.0%

Fig. 4. Structure analysis result