Significant progress has been made in support of the International Avogadro Coordination project (IAC). Our new Sartorius CCL 1007 balance has been commissioned and is in almost constant operation. This balance, which incorporates BIPM technology under a licensing agreement, operates in vacuum, air or other non-reactive gases. Ultimately it will be used to calibrate a 1 kg silicon sphere in vacuum with respect to a 1 kg prototype maintained in ambient air. The transfer is made through a special set of artefacts designed and manufactured at the BIPM. The BIPM has already supplied an additional set of these artefacts to one NMI and will fulfill orders from three additional NMIs in the near future.
The requirements for mass metrology within the IAC are in many important ways similar to those of watt balance experiments. We recognize the need to coordinate such activities within the BIPM, as well as throughout the world. For this reason we suggested that the CCM create two Task Groups (TG) within the CCM Working Group on Mass Standards. One TG will coordinate work on the transfer of the mass unit from air to vacuum conditions, as well as the maintenance of mass standards under vacuum or well defined atmospheres. The second TG will assist the BIPM in a re-examination of the uncertainty chain leading to the international prototype of the kilogram. We consider both TGs to be essential preparative steps to any of the proposed redefinitions of the kilogram. The CCM implemented our suggestions at its last meeting, in March 2007.
We continue our core activity, which is the calibration of national prototypes for Member States and the calibration of 1 kg standards in stainless steel for NMIs of Member States. Demand for these services was below the average, but not unusual for a one-year period. The calibration service successfully passed an external peer-review, as required by our Quality Management System. As part of the review, the following measurement capabilities were audited: comparison weighing, volume determination, determination of the magnetic properties of mass standards, location of the centre of gravity of mass standards. These services also provide an essential infrastructure for the IAC and watt balance projects. Two examples of support are: volume calibration of the special artefacts mentioned in the first paragraph, which is essential to their use; internal calibrations of submultiples of the kilogram, which was exploited to characterize the linearity of the Sartorius balance.
Finally, we have maintained our contact with the LISA team of the European Space Agency (ESA). This year, the BIPM determined the magnetic susceptibilities of three test masses that are being characterized for the LISA test package.
Summary
