ELECTRONIC AREA DETECTOR DATA REDUCTION SYSTEM AT THE SRS

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ELECTRONIC AREA DETECTOR DATA REDUCTION SYSTEM AT THE SRS

J. Campbell, D. Croft, J. Helliwell, P. Machin, M. Papiz, A. Thompson

To cite this version:

J. Campbell, D. Croft, J. Helliwell, P. Machin, M. Papiz, et al.. ELECTRONIC AREA DETECTOR

DATA REDUCTION SYSTEM AT THE SRS. Journal de Physique Colloques, 1986, 47 (C5), pp.C5-

109-C5-113. �10.1051/jphyscol:1986514�. �jpa-00225831�

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JOURNAL DE PHYSIQUE

Colloque C5, supplement au no 8, Tome 47, aoiit 1986

ELECTRONIC AREA DETECTOR DATA REDUCTION SYSTEM AT THE SRS

J.W. CAMPBELL, D. CROFT, J.R. HELLIWELL~

I ) ,

P. MACHIN, M.Z. PAPIZ and A.W. THOMPSON

SERC Daresbury Laboratory, GB-Warrington W A 4

4AD,

Great-Britain

Abstract

-

With t h e c u r r e n t d e t e c t o r and computer technology, d a t a c o l l e c t i o n a t synchrotron x-radiation sources poses s i p c i a l problems. Fast d a t a

c o l l e c t i o n r a t e s a r e e s s e n t i a l f o r k i n e t i c experiments a t roan temperatures.

I f maximum r e f l e c t i o n measuring r a t e s of lo2-lo3 r e f l e c t i o n s per second f o r monochromatic and l o 5 r e f l e c t i o n s per second with white beam a r e t o become

f e a s i b l e , some s i m p l i f i c a t i o n s a t d a t a c o l l e c t i o n time must be made, a t t h e expense of p o s s i b l e complications during d a t a reduction a t a l a t e r stage.

The main b e n e f i t of EAD's over film i s t h a t a 3 D p r o f i l e scan of each r e f l e c t i o n can maximise t h e peak-to-background r a t i o . The b e n e f i t s a r e even more marked on synchrotron sources since t h e i n t r i n s i c mosaicity of p r o t e i n c r y s t a l s can be small. With optimum collimation the angular spread of a r e f l e c t i o n can be reduced 5-fold over a conventional source, thus g i v i n g f u r t h e r improvement i n signal-to-noise.

Brief d e t a i l s a r e given of t h e EAD system (hardware and software) f o r p r o t e i n crystallography a t t h e SRS wiggler beam l i n e , based on a TV system f o r 0.5 (

A

$ 1.5

A.

I

-

INTRODUCTION

For many experiments

i n

p r o t e i n crystallography a t a synchrotron x-radiation source, f i l m

is

still t h e most e f f i c i e n t and r e l i a b l e data recording medium. Where photon count r a t e s a r e low, f o r instance in an anomalous dispersion experiment, weak scat- t e r i n g samples o r monochromatic time-resolved crystallography, t h e s e n s i t i v i t y of e l e c t r o n i c a r e a d e t e c t o r s (EAD) o f f e r s more e f f i c i e n t and accurate methods of d a t a c o l l e c t i o n . The main b e n e f i t s of EAD over film a r e improved counting s t a t i s t i c s and an on-line c o n t r o l of t h e experiment.

Computational and d e t e c t o r hardware problems a r e encountered when high x-ray f l u x e s a t t h e sample a r e combined with t h e kind of s e n s i t i v i t y a v a i l a b l e

i n

an EAD.

Monochromatic d a t a c o l l e c t i o n r a t e s a t a synchrotron f a c i l i t y using an EAD can be

i n

t h e range 100-600 r e f l e c t i o n s per second which corresponds t o a d a t a s e t within 10 min. In p r a c t i c e t h e l i m i t a t i o n s of encoding t h e s i g n a l , reading out t h e d i g i - t i s e d image, p r e d i c t i n g r e f l e c t i o n p o s i t i o n s on t h e d e t e c t o r image and w r i t i n g t h e i n t e g r a t e d i n t e n s i t i e s t o a s t o r a g e medim can i n c r e a s e t h e d a t a c o l l e c t i o n times considerably. When hardware

i s

a l i m i t i n g f a c t o r t o t h e r a t e s of data c o l l e c t i o n , s u r p l u s x-ray f l u x can be s a c r i f i c e d to improve p r o t e i n c r y s t a l l i f e t i m e s , s p e c t r a l r e s o l u t i o n and

to

s t a b i l i s e t h e x-ray beam by reducing heat loading on o p t i c a l elements.

A number of EAD a r e being c d s s i o n e d a t t h e Daresbury SRS which could be used f o r t h e purpose of p r o t e i n crystallography.

lwa m u l t i - w i r e

proportional chambers, s u i t a b l e

for

t h e 7.2 experimental s t a t i o n on t h e bending magnet, where they would be (''present address : Department of Physics. University of York, Heslington. GB-York YO1 5DD. Great-Britain

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986514

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C5-110

JOURNAL DE PHYSIQUE

used a t wavelengths above

A

= 1.5 A, and a TV d e t e c t o r system based on t h e design of Arndt and Gilmore [1,2] a s manufactured by Enraf-Nonius. The TV d e t e c t o r system has been i n s t a l l e d on the wiggler beam l i n e ( s t a t i o n 9.6) and w i l l be used i n the wave- l e n g t h range 0.5

< A <

1.5

A.

The discussion here w i l l be l i m i t e d to t h e TV detec- t o r system, with an assessment of t h e problems and usefulness of running such a system a t a synchrotron f a c i l i t y .

I1

-

INSTRUMENTATION

The p r o t e i n crystallography s t a t i o n on t h e wiggler beam l i n e has a number of o p t i c a l elements ( f i g u r e 1 ) which provide a wide range of experimental conditions a t t h e sample [3]. A 0.5 nun v e r t i c a l x-ray source s i z e i s produced a t t h e sample with a 75 cm, c y l i n d r i c a l l y bent, Pt coated, fused quartz focussing mirror. A monochromator v e s s e l containin? a 200 nun t r i a n g u l a r bent h o r i z o n t a l l y d i s p e r s i n g monochromator

i s

used i n experiments where high f l u x e s a r e required; f o r instance a G e ( l l 1 ) monochromator

is

used under conditions of 2 GeV machine energy, 5 T wiggler magnetic f i e l d and 200 mA e l e c t r o n beam c u r r e n t t o produce a f l u x of 7 x 1011 photons s-I nme2 a t 0.1% bandwidth. Single-crystal S i ( l l 1 ) monochromators, of various oblique c u t s , a r e a v a i l a b l e f o r anomalous dispersion experiments with a 6A/k

>

3 x For r a p i d t u n a b i l i t y a Si(220) channel c u t monochromator follows t h e f i r s t monochromator ves- sel: with t h e mirror s e t t o r e f l e c t a p a r a l l e l beam a minimum 6A/A of 8 x 1 0 ' ~ can be achieved. Because t h e Pt mirror has been s e t to a 3 m a d tilt to r e j e c t

A <

0.5

A,

f o r t h e case of a S i ( l l 1 ) or G e ( l l 1 ) monochromator, a v e s s e l containing a

f l a t geld-coated mirror has been i n s t a l l e d a f t e r t h e monochromator v e s s e l to r e j e c t harmonics of fundamentals g r e a t e r than 1.5 A.

~ i g . 1

-

Scheme of beam o p t i c s . Mono1

i s

a 20 cm t r i a n g u l a r G e ( l l 1 ) o r S i ( l l 1 ) mono- chromato? Mono2

i s

a channel c u t Si(220) monochromator.

The Enraf-Nonius TV diffractometer

is

mounted on a motorised experimental car- r i a g e to f a c i l i t a t e alignment to t h e x-ray beam. The 20 arm, on which t h e d e t e c t o r

i s

mounted, swings i n t h e v e r t i c a l plane. The p r o t e i n c r y s t a l

is

mounted on a Kappa g o n i o s t a t with a h o r i z o n t a l w axis. The d e t e c t o r has an a c t i v e area of 64 x 48 nun2.

A 6-bit ADC r e g i s t e r

i s

read i n t o a 512 x 512 16-bit deep mass s t o r e every 40 m s . The gain of t h e image i n t e n s i f i e r p l u s camera can be v a r i e d through a range of 1:250. A MICROVAX-I computer runs t h e c r y s t a l l o g r a p h i c software. A t t h e p r e s e n t time t h e primary x-ray beam decay

i s

monitored from a V/F converter and PDP-11/23 computer v i a CAMAC. In t h e f u t u r e CAMAC

w i l l

be connected d i r e c t l y

to

t h e MICROVAX-I computer. Data a r e t r a n s f e r r e d w e r ETEERNET o r on magnetic tape to a VAX-11/750 where t h e raw data a r e reduced and merged.

111

-

^SOFTWARE

The d a t a c o l l e c t i o n software package MADNES (J. Pflugrath and A. Messerschmidt, t h i s meeting) was used. This program

suite

measures small r o t a t i o n images of d a t a ,

re-

duces them to indexed three-dimensional ( 3 ~ ) r e f l e c t i o n p r o f i l e s and o p t i o n a l l y in- t e g r a t e s t h e i n t e n s i t i e s within t h e p r o f i l e s . The 3D p r o f i l e s were modified by cor- r e c t i n g each 4 r o t a t i o n s l o t within t h e p r o f i l e f o r primary beam decay.

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Time (s)

Time ( s )

Fig.?

-

^Intensity^versustime measurements from the ion chamber. (a) Full time s c a l e of the experiment. fb) Expanded view o f the f i r s t 550 s.

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25-1 12

JOURNAL DE PHYSIQUE

The i n t e g r a t e d i n t e n s i t i e s were merged and Rs ^{' S}c a l c u l a t e d by a modified ver- s i o n of t h e r o t a t i o n f i l m merging program A G R O V A ~ w r i t t e n by P h i l Evans (MRC, Cambridge).

IV

-

EXPERIMENTAL

The d e t e c t o r hardware and software wereevaluated by c o l l e c t i n g d a t a of pea l e c t i n during ' s i n g l e bunch' running of t h e SRS. The machine running conditions were:

2 GeV energy, wiggler magnetic f i e l d of

5

T and a beam c u r r e n t a t i n j e c t i o n of 20

a,

decaying to 7 mA by t h e end of t h e experiment. The primary x-ray beam was monitored with

an

a i r gap i o n chamber placed a f t e r t h e collimator. The readings

from t h e chamber i n t e g r a t e d a t 1

s

i n t e r v a l s , were w r i t t e n through CAMAC and

an

LSI-11/23 onto a Winchester disk. These i n t e n s i t y readings were used t o c o r r e c t t h e c r y s t a l l o g r a p h i c d a t a f o r beam i n t e n s i t y f l u c t u a t i o n s . lbnochromatic r a d i a t i o n was produced f r a u a S i ( l l 1 ) monochromator of oblique c u t , 6.75O. The wavelength of r a d i a t i o n was 0.884

A

and t h e c o r r e l a t e d s p e c t r a l d i s p e r s i o n (Gh/h)COR = -2 X 10'~.

The divergences of t h e beam i n t h e h o r i z o n t a l and t h e v e r t i c a l d i r e c t i o n s were O.lSO and 0.013O, respectively. The p r o t e i n c r y s t a l used to c o l l e c t data was spg. P212121, c e l l dimensions

5

= 50.8 8,

2

= 61.4

8

and

5

= 136.4

A.

The r o t a t i o n a x i s was

b

and t h e $ = O 0 p o s i t i o n was defined by t h e

5

a x i s a n t i p a r a l l e l to t h e x-ray beam. Images w e r e c o l l e c t e d a t O.1° i n t e r v a l s with i n t e g r a t i o n times of 30

s.

A n e l e c t r o n i c background image was measured a t t h e s t a r t of data c o l l e c t i o n and was s u b t r a c t e d f r a u a l l subsequent d a t a images. Corrections f o r non-uniform d e t e c t o r response were made during the experiment from a p i x e l look-up t a b l e . The look-up t a b l e was gener- a t e d by i l l u m i n a t i n g t h e d e t e c t o r with a uniform plane wave of x-radiation f r a u

an

uncollimated Cu Ka s e a l e d x-ray source. A t o t a l of 3.3- of data were c o l l e c t e d within a time of 80 min.

V

-

DISCUSSION

The r e s u l t s of d a t a c o l l e c t i o n

are

shown

i n

t a b l e s 1 and 2. The d e v i a t i o n of inten- s i t i e s on symmetry r e l a t e d r e f l e c t i o n s

i s

5.8%. This

is

of t h e same order of magni- tude a s t h e d e v i a t i o n s i n t h e ion chamber readings ( f i g u r e 2) used

t o

c o r r e c t t h e Table 1

-

^R by r e s o l u t i o n bins.

SYm Table 2

-

^RsP i n i n t e n s i t y ranges(a).

a m i n ( ~ ) ( a )

Rsym ( b ) < 1 , ( ~ ) N ( d ) <I> R~~ N

(")4nin(~)

minimum Bragg plane of t h e range.

( C ) < I > mean i n t e n s i t y .

(a),

number of r e f l e c t i o n s . where Ii.(h) a r e t h e

set

of equiva-

l e n t r e f l e c t i o n s of i n d i c e s h and mean i n t e n s i t y < I ( h ) > .

-

T o t a l 456 0.058 542 ( a ) average number of r e f l e c t i o n s

g r e a t e r than 30

i s

98%.

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d a t a f o r f l u c t u a t i o n s i n t h e primary beam. The a i r gap ion chamber used i n t h i s experiment

i s

i n e f f i c i e n t and i s influenced by t h e f l u c t u a t i o n s i n t h e environment.

A b e t t e r way of measuring the primary beam i n t e n s i t y would be with a sealed Xe/A gas f i l l e d ion chamber. A s e r i o u s problem in t h i s experiment was t h e beam movement ob- served over a period of 2500

s.

Although t h i s was corrected f o r , with a primary beam monitor, it was an undesirable f e a t u r e of t h e experiment which it would be b e t t e r t o eliminate i n t h e f u t u r e . It is believed t h a t t h e problem l i e s i n t h e beam l i n e o p t i c s and a p o s s i b l e s o l u t i o n would be t o move away £ran single-crystal/mirror focusing o p t i c s t o a system of a l a r g e v e r t i c a l s i z e p a r a l l e l beam i n c i d e n t on an Si(220) channel c u t monochromator.

The r e s u l t s suggest t h a t u s e f u l d a t a can be c o l l e c t e d on t h e TV d e t e c t o r a t t h e SRS. However, u l t i m a t e accuracy of data may not be achieved without a s t a b l e x-ray beam and an e f f e c t i v e means of monitoring and c o n t r o l l i n g it.

REFERENCES

t11 Arndt, U.W. and Gilmore, D.J., J. Appl. Crystallogr.,

12

(1979) 1.

t21 Arndt, U.W. and Thomas, D.J., Nucl. I n s t r m . Meth.,

201

(1982) 21-6.

[3] Helliwell, J.R., Papiz, M., Moore, P.R. and Thompson, A.W., Acta Crystallogr.

Suppl.,

A40

(1984) C-394.