Standard Test Method for Measuring Fast-Neutron Reaction Rates By Radioactivation of Titanium

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 Titanium has good physical strength, is easily fabricated, has excellent corrosion resistance, has a melting temperature of 1668 °C, and can be obtained with satisfactory purity.

5.4 ⁴⁶Sc has a half-life of 83.787 (16)4 days (2). The ⁴⁶Sc decay emits a 0.889271 (2) MeV gamma 99.98374 (35) % of the time and a second gamma with an energy of 1.120537 (3) MeV 99.97 (2) % of the time.

5.5 The recommended “representative isotopic abundances” for natural titanium (3) are:

8.25 (3) % ⁴⁶Ti

7.44 (2) % ⁴⁷Ti

73.72 (2) % ⁴⁸Ti

5.41 (2) % ⁴⁹Ti

5.18 (2) % ⁵⁰Ti

5.6 The radioactive products of the neutron reactions ⁴⁷Ti(n,p)⁴⁷Sc (τ_1/2 = 3.3485 (9) d) (2) and ⁴⁸Ti(n,p)⁴⁸Sc (τ_1/2 = 43.67 h), (3) might interfere with the analysis of ⁴⁶Sc.

5.7 Contaminant activities (for example, ⁶⁵Zn and ¹⁸²Ta) might interfere with the analysis of ⁴⁶Sc. See 7.1.2 and 7.1.3 for more details on the ¹⁸²Ta and ⁶⁵Zn interference.

5.8 ⁴⁶Ti and ⁴⁶Sc have cross sections for thermal neutrons of 0.59 ± 0.18 and 8.0 ± 1.0 barns, respectively (4); therefore, when an irradiation exceeds a thermal-neutron fluence greater than about 2 × 10²¹ cm^–2, provisions should be made to either use a thermal-neutron shield to prevent burn-up of ⁴⁶Sc or measure the thermal-neutron fluence rate and calculate the burn-up.

5.9 Fig. 1 shows a plot of the International Reactor Dosimetry and Fusion File, IRDFF-II cross section (5) versus neutron energy for the fast-neutron reactions of titanium which produce ⁴⁶Sc (that is, ^natTi(n,X)⁴⁶Sc). Included in the plot is the ⁴⁶Ti(n,p) reaction and the ⁴⁷Ti(n,np:d) contributions to the ⁴⁶Sc production, normalized per ^natTi atom with the individual isotopic contributions weighted using the natural abundances (3). This figure is for illustrative purposes only and should be used to indicate the range of response of the ^natTi(n,X)⁴⁶Sc reaction. Refer to Guide E1018 for descriptions of recommended tabulated dosimetry cross sections. Fig. 2 compares the cross section for the ⁴⁶Ti(n,p)⁴⁶Sc reaction to the current experimental database (6, 7). Fig. 3 compares the cross section for the ⁴⁷Ti(n,np:d) reaction to the current experimental database (6, 7).

FIG. 1 SAND-II 640-Group Histogram Representation of the ^natTi(n,X)⁴⁶Sc Cross Section (Normalized per Elemental Ti Atom Using Natural Abundance Data), Represented By the Sum of the ^natTi(n,p)⁴⁶Sc, ^natTi(n,np)⁴⁶Sc, and ^natTi(n,d)⁴⁶Sc Cross Section Components

FIG. 2 ⁴⁶Ti(n,p)⁴⁶Sc Cross Section (Normalized per Isotopic ⁴⁶Ti Atom), from IRDFF-II, with EXFOR Experimental Data

FIG. 3 ⁴⁷Ti(n,np:d)⁴⁶Sc Cross Section (Normalized per Isotopic ⁴⁷Ti Atom), from IRDFF-II, with EXFOR Experimental Data

Subcomité:

E10.05

Referida por:

E0721-22, E2005-21, E1854-19, 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 reaction; cross section; dosimetry; nuclear metrology; pressure vessel surveillance; reaction rate; titanium;