The 55Fe half-life measured with a pressurised proportional counter

S Pommé; H Stroh; R Van Ammel

doi:10.1016/j.apradiso.2019.01.008

The ⁵⁵Fe half-life measured with a pressurised proportional counter

Appl Radiat Isot. 2019 Jun:148:27-34. doi: 10.1016/j.apradiso.2019.01.008. Epub 2019 Jan 29.

Authors

S Pommé¹, H Stroh², R Van Ammel²

Affiliations

¹ European Commission, Joint Research Centre (JRC), Directorate for Nuclear Safety and Security, Retieseweg 111, B-2440, Geel, Belgium. Electronic address: stefaan.pomme@ec.europa.eu.
² European Commission, Joint Research Centre (JRC), Directorate for Nuclear Safety and Security, Retieseweg 111, B-2440, Geel, Belgium.

PMID: 30917331
DOI: 10.1016/j.apradiso.2019.01.008

Abstract

The half-life of ⁵⁵Fe has been measured accurately by following the decay curve of three sources with a large pressurised proportional counter. An argon(90%)-methane(10%) mixture was used as counter gas, at atmospheric pressure (∼1 × 10⁵ Pa) and at enhanced pressures of 5 × 10⁵ Pa and 8 × 10⁵ Pa (for 1 source), respectively. The first measurements were performed in 2001, but the experiment was executed more systematically between 2005 and 2018, covering a period of about 5 half-lives. The residuals from an exponential decay curve were of the order of 0.1% to 0.2% at 1 × 10⁵ Pa, and 0.03% at 5 × 10⁵ Pa and 8 × 10⁵ Pa. The gain of stability with increased gas pressure was due to asymptotically reaching the maximum counting efficiency, resulting in lower sensitivity to pressure variations. The deduced half-life value of T_1/2(⁵⁵Fe) = 1006.70 (15) d or 2.7563 (4) a is more accurate than other data in literature, which are mutually discrepant. It is consistent with previous measurements at JRC with an X-ray defined solid angle counter.

Keywords: Calibration; Clearance; Decay constant; Decommissioning; Discrepancy; Half-life.