Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Aluminum

Importancia y uso:

5.1 Refer to Guide E844 for the selection, irradiation, and quality control of neutron dosimeters.

5.2 Refer to Practice E261 for a general discussion of the determination of fast-neutron fluence rate with threshold detectors.

5.3 Pure aluminum in the form of foil or wire is readily available and easily handled. ²⁷Al has an abundance of 100 % (1).3

5.4 ²⁴Na has a half-life of 14.958 (2)4 h (2) and emits gamma rays with energies of 1.368630 (5) and 2.754049 (13) MeV (2).

5.5 Fig. 1 shows a plot of the International Reactor Dosimetry and Fusion File (IRDFF-II) cross section (3, 4) versus neutron energy for the fast-neutron reaction ²⁷Al(n,α) ²⁴Na (3) along with a comparison to the current experimental database (5, 6). While the RRDF-2008 and IRDFF-1.05 cross sections extend from threshold up to 60 MeV, due to considerations of the available validation data, the energy region over which this standard recommends use of this cross section for reactor dosimetry applications only extends from threshold at ~4.25 MeV up to 20 MeV. This figure is for illustrative purposes and is used to indicate the range of response of the ²⁷Al(n,α) reaction. Refer to Guide E1018 for recommended sources for the tabulated dosimetry cross sections.

FIG. 1 ²⁷Al(n,α)²⁴Na Cross Section, from IRDFF-II Library, with EXFOR Experimental Data

5.6 Two competing activities, ²⁸Al (2.25 (2) minute half-life) and ²⁷Mg (9.458 (12) minute half-life), are formed in the reactions ²⁷Al(n,γ)²⁸Al and ²⁷Al(n,p)²⁷Mg, respectively, but these can be eliminated by waiting 2 h before counting.

Subcomité:

E10.05

Referida por:

E0720-23, E0721-22, E2005-21, E0798-24, E0261-16R21, E1005-21, E0944-19

Volúmen:

12.02

Número ICS:

17.240 (Radiation measurements), 27.120.30 (Fissile materials and nuclear fuel technology)

Palabras clave:

activation; activation reaction; aluminum; cross section; dosimetry; fast-neutron monitor; neutron metrology; pressure vessel surveillance; reaction rate;