ASTM E266

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. Scope

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.

2. Referenced Documents

E1005 Test Method for Application and Analysis of Radiometric Monitors for Reactor Vessel Surveillance, E 706(IIIA)
E1018 Guide for Application of ASTM Evaluated Cross Section Data File, Matrix E 706 (IIB)
E170 Terminology Relating to Radiation Measurements and Dosimetry
E181 Test Methods for Detector Calibration and Analysis of Radionuclides
E261 Practice for Determining Neutron Fluence, Fluence Rate, and Spectra by Radioactivation Techniques
E844 Guide for Sensor Set Design and Irradiation for Reactor Surveillance, E 706(IIC)
E944 Guide for Application of Neutron Spectrum Adjustment Methods in Reactor Surveillance, E 706 (IIA)

Index Terms

activation; activation reaction; aluminum; cross section; dosimetry; fast-neutron monitor; neutron metrology; pressure vessel surveillance; reaction rate; ICS Number Code 17.240; 27.120.30

Citing ASTM Standards

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