Refer to Guide E 844 for the selection, irradiation, and quality control of neutron dosimeters.

Refer to Practice E 261 for a general discussion of the determination of fast-neutron fluence rate with threshold detectors.

Pure aluminum in the form of foil or wire is readily available and easily handled.

²⁴Na has a half-life of 14.951 h (1)³ and emits gamma rays with energies of 1.368.633 and 2.754028 MeV (2).

Fig. 1 shows a plot of cross section versus neutron energy for the fast-neutron reaction ²⁷Al(n,α)²⁴Na from the IRDF2002 dosimetry cross section library(3). This figure is for illustrative purposes only to indicate the range of response of the ²⁷Al(n,α) reaction. Refer to Guide E 1018 for descriptions of recommended tabulated dosimetry cross sections.

Two competing activities, ²⁸Al and ²⁷Mg, 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.

FIG. 1 ²⁷Al(n,α)²⁴Na Cross Section

1.1 This test method covers procedures measuring reaction rates by the activation reaction ²⁷Al(n,)²⁴Na.

1.2 This activation reaction is useful for measuring neutrons with energies above approximately 6.5 MeV and for irradiation times up to about 2 days (for longer irradiations, see Practice E 261).

1.3 With suitable techniques, fission-neutron fluence rates above 10⁶cm²s¹ can be determined.

1.4 Detailed procedures for other fast neutron detectors are referenced in Practice E 261.

This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.