ASTM E523-11

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

Refer to Practice E261 for a general discussion of the measurement of fast neutron fluence rate with threshold detectors. The general shape of the ⁶³Cu(n,α)⁶⁰Co cross section is also shown in Fig. 1 (3, 4) along with a comparison to the current experimental databse (5). This figure is for illustrative purposes only to indicate the range of response of the ⁶³Cu(n,α) reaction. Refer to Guide E1018 for descriptions of recommended tabulated dosimetry cross sections.

Note 1—The cross section appropriate for use under this standard is ENDF/B-VI release 8 library since it contains a covariance matrix. The ENDF/B-VII library has been released, but it does not contain a covariance matrix for this reaction. For dosimetry applications, an uncertainty metric expressed as a covariance matrix is required. See Guide E1018.

The chief advantages of copper for measuring fast-neutron fluence rate are that it has good strength, is easily fabricated, has excellent corrosion resistance, has a melting temperature of 1083°C, and can be obtained pure. The half-life of ⁶⁰Co is long and its decay scheme is simple and well known.

The disadvantages of copper for measuring fast neutron fluence rate are the high reaction apparent threshold of 5 MeV, the possible interference from cobalt impurity (>1 μg/g), the reported possible thermal component of the (n,α) reaction, and the possibly significant cross sections for thermal neutrons for ⁶³Cu and ⁶⁰Co (that is 4.50 and 2.0 barns, respectively),(6) which will require burnout corrections at high fluences.

1.1 This test method covers procedures for measuring reaction rates by the activation reaction ⁶³Cu(n,α)⁶⁰Co. The cross section for ⁶⁰Co produced in this reaction increases rapidly with neutrons having energies greater than about 5 MeV. ⁶⁰Co decays with a half-life of 1925.27 days (±0.29 days)(1) and emits two gamma rays having energies of 1.1732278 and 1.332492 MeV (1). The isotopic content of natural copper is 69.17 % ⁶³Cu and 30.83 % ⁶⁵Cu (2). The neutron reaction,
⁶³Cu(n,γ)⁶⁴Cu, produces a radioactive product that emits gamma rays which might interfere with the counting of the
⁶⁰Co gamma rays.

1.2 With suitable techniques, fission-neutron fluence rates above 10⁹ cm⁻²·s⁻¹ can be determined. The ⁶³Cu(n,α)⁶⁰Co reaction can be used to determine fast-neutron fluences for irradiation times up to about 15 years (for longer irradiations, see Practice E261).

1.3 Detailed procedures for other fast-neutron detectors are referenced in Practice E261.

1.4 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.