Nuclear Instruments and Methods in Physics Research A 536 (2005) 235–243 Polarized gas targets Frank Rathmann Institut fu ¨ r Kernphysik, Forschungszentrum Ju ¨ lich, 52425 Ju ¨ lich, Germany Available online 11 September 2004 Abstract Polarized internal gas targets are operated at various electron and proton machines reaching luminosities of 10 31 and 10 29 cm 2 s 1 ; respectively. The present paper focuses on experimental aspects, such as the design and construction of storage cells, and different methods employed for polarimetry. r 2004 Elsevier B.V. All rights reserved. PACS: 29.25.P; 07.60.F; 07.77; 67.65; 31.30.G; 24.70; 25.10 Keywords: Polarized targets; Polarimeters; Spin-polarized hydrogen and deuterium 1. Introduction Storage cells to enhance the target thickness provided by a source of polarized atoms have already been conceived some 30 years ago [1]. An application of this technique to nuclear and particle physics became possible only through the advent of storage rings. 1 The stored beam passes through the internal target about a million times per second and thus compensates the low target thickness. In order to obtain higher target thicknesses compared to a free beam of polarized atoms, the dwell time of atoms in the vicinity of the stored beam must be increased. For that purpose, an open-ended T-shaped storage cell is inserted into the ring through which the stored beam passes and into which the atomic beam is injected. Thereby the luminosity can be raised by about two orders of magnitude. Polarized internal targets nowadays provide densities up to a few times 10 14 atoms=cm 2 : The achieved nuclear vector or tensor polarizations are close to the theoretical maximum. 2. Milestones The suggestion by Haeberli to use a storage cell to enhance the available target thickness produced by an atomic beam source (ABS) in 1966 was motivated by the successful application of a storage container in the hydrogen maser [3]. The proof of principle, carried out by the Wisconsin ARTICLE IN PRESS www.elsevier.com/locate/nima 0168-9002/$-see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.08.078 E-mail address: f.rathmann@fz-juelich.de (F. Rathmann). 1 For a recent review on polarized gas targets, see Ref. [2].