Precision measurement of half-life and specific activity of 236U

Methods for primary standardization of activity

“…Alpha-particle counting at a defined low solid angle is amongst the most accurate primary standardization methods for alpha-emitting radionuclides, with attainable accuracies around 0.1% [88][89][90][91]. It has been applied in various standardization exercises [17,92,93], but also in the frame of half-life determinations of long-lived radionuclides [94][95][96][97][98][99][100]. A special application is the standardization of radon gas that is condensed on a cold circular disc [56,101,102].…”

The uncertainty of counting at a defined solid angle

“…The uncertainty of counting at a defined solid angle by several institutes, including IRMM (formerly CBNM) [8,9], LRL [10], NIST [11], ANL [12], CIEMAT [13,14], LNE-LNHB [15,16] and PTB [17]. New set-ups have recently been constructed in TAEK (Turkey) and NPL (UK), inspired by the IRMM model.…”

“…IRMM uses a segmented design with source chamber, distance tube and diaphragm fitting together on smoothly connecting flanges. The distance between diaphragm and a reference plate in the source holder can be measured directly or calculated from the sum of the heights of the individual components with an accuracy of about (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) µm. The distance seems unaffected by vacuum pumping.…”

“…One can also use approximating formulas [12,29] (which are fairly accurate for a < R D ) to estimate the uncertainty propagation due to a displacement a of a source from its theoretical position: (13) in which D is defined as…”

“…Before exact solutions were available, approximating equations were used. For small sources, there are relatively simple approximations by Jaffey et al [12,29]:…”