(19)

(11)

EP 1 004 134 A1

(12)

(43) Date of publication: 31.05.2000 Bulletin 2000/22 (21) Application number: 98938821.0 (22) Date of filing: 14.08.1998

(51) International Patent Classification (IPC)7: H01J 9/12, H01J 43/22 (86) International application number: PCT/GB9802/447 (87) International publication number: WO 9909/577 (25.02.1999 Gazette 1999/08)

(84) Designated Contracting States: GB (30) Priority: 14.08.1997 GB 9717210 (71) Applicant: COUNCIL FOR THE CENTRAL LABORATORY OF THE RESEARCH COUNCILS Chilton Didcot,Oxfordshire OX11 0QX (GB)	(72) Inventors: GRAYER, Geoffrey, Howard Bright Walton,Newbury RG20 7BE (GB) HUQ, Syed, Ejazul Didcot OX11 8JR (GB) (74) Representative: Perkins, Sarah  Stevens, Hewlett & PerkinsHalton House20/23 Holborn London EC1N 2JD London EC1N 2JD (GB)