TY - ICOMM AU - C O'Brien AU - D Burns AU - C Kessler C1 - http://iopscience.iop.org C2 - http://iopscience.iop.org DA - 2012-03-23 LA - en PB - http://iopscience.iop.org PY - 2012 TI - Key Comparison BIPM.RI(I)-K2 of the air-kerma standards of the NIST, USA and the BIPM in low-energy x-rays ER -