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Abstract: For our research in precision Penning trap
mass spectrometry
(PTMS), we are making several changes to improve the accuracy and
flexibility of our measurements. We have tested a special gas-fed
Penning ion source, and are assembling an ion-beam tube for
loading a variety of ions into a coaxial double Penning trap
arrangement. The upper Penning trap will be used to store ions and
prepare them for measurement in the lower, precision
trap.
This double-trap system will allow us to load single
ions-of-interest in a reliable and flexible manner. At our present
level of accuracy, (˜10 ppt), we are concerned with
minimizing frequency shifts due to any (weakly coupled) unwanted
ions, and also the disturbances caused by our current in-trap
ionization procedure. The new apparatus should allow quick
interrogation of different ions, reducing other sources of
uncertainty. We will first measure the mass ratio of
3H+
and 3He+, giving the quantity
m(3H) -
m(3He), with less than 0.1 eV uncertainty. A more precise value of this mass difference should aide future direct neutrino
mass measurements (KATRIN[1]) which analyze the energy
spectrum from the beta-decay of tritium.
Abstract: Using a Penning trap mass spectrometer (PTMS), the atomic mass of 4He has been found to be 4 002 603 254.153(64) nu (an uncertainty of 16 ppt). This number agrees well with the previous two best measurements of the 4He mass[1,2] . In addition to giving a precise atomic mass of the α-particle, 4He can now be used as a convenient reference ion by less precise mass spectrometers. For this measurement, the cyclotron frequencies of 12C6+ and 4He2+ ions were compared, using a Penning ion trap with an extremely stable (less than 2 ppt/h of drift) magnetic field. While many aspects of our experiment have been previously described (as for the recent 16O result, at 10 ppt unceratinty[3]), we will present several techniques and changes to the apparatus that have improved the accuracy of our machine by about an order of magnitude in recent years.