Mass recombinator for accelerator mass spectrometry

A mass recombinator comprising in combination a dipole magnet having a base line and having a field pattern substantially in accordance with the formula B=B.sub.0 (z/a).sup.n in which z is the distance from the base line, n=0.924 and B.sub.0 and a are other constants, a source of negative ions to be analyzed, means for accelerating negative ions from said source to substantially the same moderate kinetic energy as a beam, electrostatic means for focusing said negative-ion beam to a substantially parallel beam, and means for directing said parallel beam into said field pattern through said base line at an angle of about 47.7 degrees with respect to said base line, whereby said beam of negative ions is deflected in such a manner that it describes a loop of approximately 264.6 degrees forming a mass spectrum at a position inside the magnet after deflection of approximately 132.3 degrees and exits the field as a parallel beam substantially where it entered, independent of the mass of the ions, and means of blocking ions of certain mass numbers at the position of the mass spectrum and allowing others to pass, the passed ions being reassembled and exiting the magnet as a parallel beam substantially where it entered, independent of the mass numbers of the ions.