Gas-filled magnet detection system

Department of Nuclear Physics and Accelerator Applications

The group has continued to develop AMS measurements using our gas-filled magnet (GFM) system, with the type of ions measured in this device now including 26Al and 53Mn, along with 32Si. The GFM allows ions of AMS interest to be separated from their much more abundant stable isobars (26Mg, 53Cr and 32S).

The gas-filled magnet detection system consists of an Enge Split-Pole magnetic spectrograph coupled to a position sensitive multi-anode gas ionisation detector (see upper figure). Ions travelling in a magnetic field region, which is filled with nitrogen gas at an appropriate pressure, do so with a circular trajectory with a singular average-charge state. This average charge state is proportional to the Z of the ion, thus giving rise to a physical separation between ions of differing Z at the exit of the magnet (see lower figure).

The ability to detect 26Al in a GFM by suppressing the 26Mg isobar enables AMS of 26Al to be performed with the Al- beam instead of the traditional method, injection of AlO-. The advantage of this is that the Al- beam is up to twenty times more prolific than AlO-, thus superior counting statistics can be obtained for the equivalent measuring time. This should lead to 26Al to Al ratios with statistics near those obtained for 10Be.

The AMS of 53Mn is being pursued with the hope that isotope could be used as a new cosmogenic nuclide for erosion-rate applications. Its long half-life, at 3.7 Ma, means it should be suitable for examining landscape processes at the timescale of the order of 1 Ma. In situ, 53Mn is produced by cosmic rays (mainly spallation) on Fe. Thus the 53Mn may be useful in ancient landscapes were only Fe-bearing rocks remain after all other minerals have weathered away.

Fifield, Keith  profile

Updated:  26 March 2023/ Responsible Officer:  Director, RSPhys/ Page Contact:  Physics Webmaster