Accurate normalized differential cross-sections for elastic electron scattering from H2 and N2 are reported. These measurements are obtained using the relative flow method with helium as the standard (calibrating) gas, except that a thin aperture source of gas is used, which obviates the need to know the gas kinetic molecular diameters of either the calibration gas (He) or the unknown gas (H2 or N2) whose differential cross-sections need to be determined. Our present measurements are found to be in very good agreement with past differential elastic electron scattering measurements using the relative flow with tube collimating sources and independently vindicate the application of the conventional relative flow method for ‘hard-sphere’ gases. They also resolve some observed differences between the differential cross-sections in the low incident energy region. They also provide a good test of our relative flow method for two well-known targets.

The first key comparison in microwave frequencies within the SIM (Sistema Interamericano de Metrología) region has been carried out. The measurands were the S-parameters of 50 ohm coaxial devices with Type-N connectors and were measured at 2 GHz, 9 GHz and 18 GHz. SIM.EM.RF-K5b.CL was the identification assigned and it was based on a parent CCEM key comparison named CCEM.RF-K5b.CL. For this reason, the measurements standards and their nominal values were selected accordingly, i.e. two one-port devices (a matched and a mismatched load) to cover low and high reflection coefficients and two attenuators (3dB and 20 dB) to cover low and high transmission coefficients. This key comparison has met the need for ensuring traceability in high-frequency measurements across America by linking SIM's results to CCEM. Six NMIs have participated in this comparison which was piloted by the Instituto Nacional de Tecnología Industrial (Argentina). A linking method of multivariate values was proposed and implemented in order to allow the linking of 2-dimensional results. KEY WORDS FOR SEARCH Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).