Electron multiplier as a detector for soft x rays from synchrotron and laser plasma sources

ABSTRACT An Electron-Tubes-LTD 129EM electron multiplier tube has been modified to act as a detector of soft x-rays. The first dynodewas coated with lOOnm ofCsl and the assembly was mounted in a small vacuum chamber with lOOnm thick silicon nitrideentrance window. Initial tests show the detector is linear up to an input flux of-IMHz on a synchrotron source and has provedeffective in providing pulse height discrimination when used on a pulsed laser plasma source.Keywords: detector, soft x-rays, microscopy, electron, multiplier, synchrotron, laser-plasma 1. INTRODUCTION X-rays are typically detected by interactions that produce charged particles which are collected and their number amplified toform an electronic signal. Ideally, the interaction ofthe x-ray photon with the sensitive volume ofthe detector will produce manycharged particles resulting in an electronic signal which is considerably greater than the electronic noise in the system. Soft x-rayshave energies in the range 200 to 700eV and will generally produce a small number of charged particles. Where small numbers ofphotons are involved (as is often the case in soft x-ray microscopy), the detector will typically need an intrinsic amplificationprocess in order to produce an electronic signal of sufficient magnitude.Here we introduce a modified electron multiplier tube as a detector for both photon counting and pulse height analysisapplications in x-ray microscopy. Initial tests on synchrotron and laser plasma sources indicate that the prototype has some pulse-height non-linearity, but is both useful and competitive with existing scanning soft x-ray microscope detectors.