Revision of the 21909 standard on passive personal neutron dosemeters.

Since 2012, International Standardization Organization TC85/SC2 Working Group 19 dealing with 'Individual monitoring for external radiations' has been conducting important work revising the 21909 standard on passive personal neutron dosemeters. A consensus in the community acted that the 2005 version(  1) needed to be revised for two main reasons: (1) to achieve a document applicable to all systems irrespectively to the considered techniques and (2) to reach harmonisation between performance tests and conditions of use at the workplaces. The document was completely rewritten to be binding enough to ensure that any neutron dosimetry system fulfilling the criteria would be reliable in most of the usual work situations, in terms of dose level, energy and direction distributions of the neutron fluence. This paper explains the reasons behind the revision and the new philosophy of the series published in 2021, so that Individual Monitoring Services may better understand how to apply the requirements in practice.