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A VIDICON SYSTEM FOR REAL TIME DIFFRACTION STUDIES

P. Bösecke, D. Ercan, C. Riekel

To cite this version:

P. Bösecke, D. Ercan, C. Riekel. A VIDICON SYSTEM FOR REAL TIME DIFFRACTION STUD- IES. Journal de Physique Colloques, 1986, 47 (C5), pp.C5-175-C5-181. �10.1051/jphyscol:1986523�.

�jpa-00225840�

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JOURNAL DE PHYSIQUE

Colloque C5, supplement au n o 8, Tome 47, aoOt 1986

A VIDICON SYSTEM FOR REAL TIME DIFFRACTION STUDIES

P. B~SECKE, D. ERCAN and C. RIEKEL

Institut fiir Technische und Makromolekulare Chemie, Bundesstrasse 45, 0-2000 Hamburg 13, F.R.G.

Resum6

-

Un s y s t b

2

base d'un Vidicon 2 6t6 d & e l d pour des 6tudes de diffraction en temps r&l sur l'anneau de stockage D3RIS (DESY). I1 est possible d'accumuler jusqu's 256 diagramnes de 51 2x51 2 pixels avec une

&oire et une unit6 arithm6tique. Avant transfert, la moyenne sur quatre points est calcul6e et on effectue une mise a l'khelle sur 256 niveaux de gris. Le temps minimum de transfer d'un diagramw de 256x256 pixels est environ 2 s.

Abstract

-

A Vidicon system has been developed for real time diffraction studies at the storage ring D3RIS (DFSY). Up to 256 digitized frames of 512x512~2 bytes can be accumulated by a memory and an arithmetic logic unit, Prior to storage on disc, every four pixels are averaged and scaled to 256 grey levels. Minimum transfer tine per frame of 256x256 pixels to disc is about 2 s.

ZD-detectors are useful in order to accelerate the rate of data collection in applications reaching from single crystal- to real time-diffractcinetry during phase transformations. Thus the possibility to study anisotropic scattering phenc~nena occurring for example during crystallization processes of polymers opens new possibilities to Werstand the dynamics of structural processes./l/

High data collection rates are encountered especially at high intensity X-ray sources, such as a storage ring. Here the temporal limitation in the study of irreversible structural processes is determined by the time necessary to perturb the sample. Atemporal resolution in the order of a few seconds is often sufficient for such exgeriments /I/.

The present article describes an operaticail data-collection system, installed at the polymer beamline of HASYLAB (DESY) and which is canposed of a Vidicon camera, an on-line digitizer and a PDP 1 1/24 ccmputer. It allows to transfer 2D-pictures (frames) -with a 256x256 grid and 256 intensity levels- in about every 2 seconds. The principal application of this system lies in real time diffraction studies of structural processes in polymers. It could, hawever, also be adapted to single crystal diffractanetry.

11.1 The Vidicon Camera/2,3/

Vidicon tubes for X-ray diffractim experiments have been described by a n W r of authors./4-ll/ We use a Westinghouse SIT-Vidicon tube (TEM 4321~) which has been develop63 for low light level astronomical applications. The camera is shown schematically in Fig. I .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986523

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JOURNAL DE PHYSIQUE

Fig. 1

-

Schematic diagram of the Vidicon Camera.

( BAS is the German abbre- viation for a ccmposite signal, which includes picture signal, blanking, horizontal, vertikal and equalizing pulses )

Remote control

I

cabinet

) pz-1

Conversion of X-rays ( X = 1.551 ) into visible light is done by a

-

30 prn thick

layer of ZnS:Ag or Gd S 0:% (

-

10pm ) which covers the surface of a fiber-optics plate (&&mess of fibers: about 10pm ;light transmission: about 60% -Galileo Optics-; diameter of the photo cathode: 80 mm)

The tension between photo ca-e and target can be varied between 0 and -1 2 KV.

This allows to obtain a gain factor of up to 2100. In practice, the tension is usually chosen in such a way, that the strongest peak does not saturate the target.

The charge pattern created on the Si-target is read out in the standard fast scan technique (25 frames per second with 625 lines and 5MHz Ixndwith), which represents the ulthte temporal resolution of this camera type.

In order to reduce noise and dark current it is necessary to cool the target./2,3 ,I 2/ A temperature of about 7 OC is attained routinely by a coolant liquid which is circulated arcjund the target.

The resolution of this system has been determined fran wide-angle scattering diagrams of a single-crystal to be 0.7 m vertically and 1.4 mm horizontally (full width at base)./2/ Note that these data had been digitized from frames recorded on video tape which is limited in horizontal direction by the smaller band width of the videotape ( about 3 MHz )

.

11.2 The Digitizer

The BAS-signal ( CCIR-standard ) is digitized on-line by the MBV-system

( Mcdulares-Bild-Verarbeitungs-System ) of VTE-DIGITALVIDE13 Ltd. and transferred to a PDP 11 /24 complter (Fig.2).

The digitizer operates at a scanning frequency of 10MHz and furnishes a frame of 512x512 pixel with 8-bit per pixel wery 40 ms. Accurrmlaticm of up to 256 frames is possible by an arithmetic logic unit (ALU) with integrated lookup table and two mories.

The lookup table maps the 8-bit words into prechosen 16-bit words. The AUT canbines the two 76-bit words caning frcm the lookup table and one of the two memories.

After the last accurrmlation cycle, the data are scaled dawn by dividing them through the n m b r of accumulation cycles via a bit-shifter. This is r e a d l e in view of the dynamic range which is 103./2/ The bit-shifter limits the nmber of acaurmlatians -na- to n =2" ( I <n<8) and one obtains frames with 2 bytes per pixel, where the intmaities are contained in the l m byte of the data

~10rdS.

The presence of 2 mmries allows to transfer data to the cunpter fran one of the two memories, while the other is used for frame accumulatim.

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Fig. 2

-

Schematic design of the digitizing system and the connection to the PDP 11/24 computer.

In view of the application to usually more disordered materials than encountered in single crystal diffractmetry, the present system has been developed with the aim of transferring cmplete frames to the computer, as quickly as possible and to perform a detailed data analysis afterwards.

The velocity of data transfer to the RL02 disc of the PDP 11/24 is limited by the address space of the computer (64K bytes) and the time necessary to dump the data onto disc. Furthemre, only about 19 frames of 512~512x2 bytes can be stored on a RL02 disc.

A 256x256 grid with 256 intensity levels is, however, sufficient in view of the detector resolution (see above), the size of the focus ( typically around I m ) and the dynamic range. This allws storage of about 150 frames on the disc. In order to obtain this grid, two approaches have been tested:

a) The optional half-frame transfer mcde of the MBW-system is chosen.

Frame-segments of 512x16~2 bytes are transferred to the core. Reduction to 4K bytes blocks is done by storing only every (nx4)+1 byte ( 0 <n<127), which corresponds to a suppression of the high bytes and of every second column.

16K bytes blocks are then transferred to the disc. This process is repeated 4 times and takes about 2 s.

b) Frame-segments of 512x16~2 bytes are transferred to the core. Mter averaging square blocks of 4 pixels, one obtains again a 4K bytes block. This process is repeated 32 times. Transfer to disc is again done for 16K bytes blocks.

Total transfer time is abut 3 S, in which the total transfer time from core to disc is 0.6 s.

As 75% of all pixels are suppressed in methcd a), but the transfer times are nearly equal, we prefer to use methcd b).

In addition to the frames, the intensity of an ionization chamber can be read out for each accumulated frame fran a CAMAC-mcdule./l /

In view of a possible application of the system to single crystal diffractmetry it is of interest to note that the transfer time can be reduced by transferring only a part of a frame.

Thus the transfer time into the core consists of 10ms for each program call and 2.5 ms/ K words for DMA transfer. Total transfer time of -say- one hundred (6x6) pixel-blocks (2-bytes deep) into core will be (100x10)+(3.6x2.5) ms, i.e. about 1.0s. Total transfer time to disc will be 1.0+(0.6/4) s, i.e. about I .Is. The data are then transferred to a 1600 BPI magtape which can hold about 750 frames.

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C5-178 JOURNAL DE PHYSIQUE

For data evaluation, the VAX 11/750 ccmputer of the EMBL outstation at DESY and the program package "KOHALA'I are used at present./l3/ These programs allow a processing of the raw data (e.9. background correction), integration of reflection spots and graphic presentatim.

It is intended to replace the PDP 11 124 by a MicroVax I1 with a 456 Mbyte disc in order to be able to store more frames and to have a direct access to the data. The larger address-space will allow to transfer full frames into the core and thus further reduce the transfer time.

IV

-

EXAMPLES

A typical application of the Vidicon system is the study of phase transfonnations upon heating. Thus Fig.3 shows selected pseudo 3D-plots of orienteda-polypropylene which transforms from a highly disordered

9 phase -obtained u p n quenching

polypropylene frcm the melt- into the ordered a-phase with three characteristic wide-angle reflec- tions (110, 040, 130). The inset shms the heating curve

.

Note that the measuring tine per frame -ts-

590s (137.C) is 5.12 s (128 accumulations). No

background correction has been performed for these frames.

9 The imprtance of such a correction

can be seen in Fig.4 for a complete

- -- 1

' 1 Channels '100

frame.

Thus Fig.4a shows the structured background of the Si-tarset which seen: to be constant with fime at a Fig. 3 - Selected pseudo 3D-plots given temperature ( see below). It obtained upon heating quenched, is, hmever, slightly dependant on orientedapolypropylene (128 frames the tension of the photocathcde.

accumulated; uncorrected for back- This background is also contained in g r d scattering). The inset shaws Fig.4b which corresponds to the the variation of the sample scattering fran a Imthick, slight-

temperature. ly oriented, a-polypropylene foil.

After background subtraction (Fig.4~) the target structure has disappeared.

Note that the slight variation of the intensities along the Bragg-rings is not an artifact but due to the preferred orientation of the material.

The influence of the target temperature on the target-background is shown in Fig.5. The figure corresponds to the intensity variation along channel NO 129.

Evidently cooling reduces both the structure and the overall backgrad.

This is especially important for the observation of weak peaks, encountered for example in small angle scattering.

Thus Fig.6 shows the small angle scattering of oriented a-polypropylene (128 frames accumulated)

.

The maxima of the peaks correspod to a long perid of 290

2 .

While the previous examples correspond only to snapshots, the frames s h m in Fig.7 follaw the dynamic precess in real time, Here, a 50 &m thick foil of oriented a -polypropylene has been heated £ran 1 3 0 O ~ into the range of the melting point. The measuring time per frame -t S

-

is 5.1 2 s (1 28 accumulations), while the waiting time -t - is 4.88 s.

The melting process is found to extend

Waver

several degrees. The loss of orientation close to the melting point is indicated by an increase in the radial hlf-width of the reflections. Evidently this information would be difficult to obtain with a ID-position sensitive eetector.

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Fig. 4a

-

Background of the Si-target at 7.1° target temperature.

4b

-

Slightly oriented cx -polypropylene-foil (1 nnn thick) plus target background.

4c

-

a-Eblypropylene minus target-backgromd. The reflections shown are the 1 10, 040 and 1 30 (with increasing 2 0 -value )

a TARGET

-

BACKGROUND

I

TARGET-TEMPERATURE 128 Frames 1 5.12 s I 16.6.C

b PLUS BACKGROUND ! TARGET-TEMPERATURE

Frames l512sl 16.6.C

c

SAMPLE MINUS MCKGROUND

256 '

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JOURNAL DE PHYSIQUE

TARGET-TEMPERATURE 2h0°C

-1

0 100 200 Lines

Fig. 5

-

Variation of the target background with temperature. The frame (Fig.4a) has been cut at channel NOI 29.

Intensity

I

W ,

70 Lines 200

Channels

. .

70 Lines 200

Fig. 6

-

Small angle scattering diagrams of orientedwplypropylene at T = l D

8

(128 frames accumulated and corrected for target background). The upper pseudo 3D-plot shows two peaks close to the beamstop. The long period is 290

a .

The

corresponding contour plot is shown k l m .

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Fig. 7

-

Contour plots obtain& during the heating of a 50 pm thick or-polypropylene foil f r m 133% close to the melting pint. Every plot corresponds to 128 accumulated frames.

/I/ Synchrotron Radiation in Polymer Science Elsnff, G., Riekel, C., and Zachmann, H. G., "~dvances in Polymer science", Kausch, H., Ed., Springer Verlag, Heidelberg ( 1 985)

I T / Prieske, W. D. Ph-D thesis, University of Hamburg (1985)

/3/ Prieske, W. D., Riekel, C., Koch, M.H.J., Zachmann, H. G., Nucl. Instr. and Methods 208, p. 435 (1 983)

J4/ Abrahamsson, S., Acta Cryst. A28, p. 248 (1972)

/5/ Amdt, U. W., Gilmore, D. J., Mv. Electronics and Electron ~hys. 40B, 913 (1975)

/6/ Hashizume, H., Kohra, K., Cquro, Y., J. Appl. Cryst. 8, p. 249 (1975) /7/ Reynolds,G. T,, Milch, J. R., and Gruner, S. M., IEEE Trans. Nucl. Sci.

NS-24, P. MI (1977)

/8/ Kalata, K., IEEE Trans. Nucl. Sci. NS-28, p. 852 (1 981 )

/9/ Milch, J. R. ,IEEE Trans. Nucl. Sci. NS-26, p. 338 (1 979) /lo/ Hartmann, W., BMFT, Forschungsbericht &rz 1979, Nr. Kt0668

/I 1 / mffrey, M., Bilderback, D. H., Nucl. Instr. and Methods. ,208 p.495 (1 983) 1121 Rust, H.P.,Krahl, D.,Herm,K. H., J. Phys. E: Sci.Instrum.,Vol.l7 (1984) 1131 Koch, M.H.J., Bendall, P.J., Dainton, D.M., Golding, F.R. McLaughlin, S.M.,

Manual EM3LHH-VOO2-V2.2. EMBL Outstatim Hamburg (1985) Am-

We wish to thank M.H.J. Kcch for his support in using the program "KOW4.U".

Helpful discussions with K. Bartels, H. Bartunik, W. Prieske and Prof. H.G.

Zacham are acknailedgd.

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