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ASTM E705-13a
Standard Test Method for Measuring Reaction Rates by Radioactivation of Neptunium-237
5 стр.
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Разработчик:
Зарубежные/ASTM
ICS:
27.120.30 Fissile. Including raw materials / Делящиеся ядерные вещества. Включая сырье, 17.240 Radiation. Including dosimetry / Измерения параметров излучений
Сборник (ASTM):
12.02 Nuclear (II), Solar, and Geothermal Energy; Radiation Processing / Ядерная энергия (II), Солнечная, и Геотермическая Энергия; Радиационная обработка
Тематика:
Nuclear Technology
Описание
Значение и использование

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

5.2 237Np is available as metal foil, wire, or oxide powder. For further information, see Guide E844. It is usually encapsulated in a suitable container to prevent loss of, and contamination by, the  237Np and its fission products.4

5.3 One or more fission products can be assayed. Pertinent data for relevant fission products are given in Table 1 and Table 2.

5.3.1 137Cs-137mBa is chosen frequently for long irradiations. Radioactive products 134Cs and  136Cs may be present, which can interfere with the counting of the 0.662 MeV  137Cs-137mBa gamma ray (see Test Methods E320).

5.3.2 140Ba-140La is chosen frequently for short irradiations (see Test Method E393).

5.3.3 95Zr can be counted directly, following chemical separation, or with its daughter 95Nb, using a high-resolution gamma detector system.

5.3.4 144Ce is a high-yield fission product applicable to 2- to 3-year irradiations.

5.4 It is necessary to surround the 237Np monitor with a thermal neutron absorber to minimize fission product production from trace quantities of fissionable nuclides in the 237Np target and from  238Np and  238Pu from (n,γ) reactions in the   237Np material. Assay of  238Pu and   239Pu concentration is recommended when a significant contribution is expected.

5.4.1 Fission product production in a light-water reactor by neutron activation products  238Np and   238Pu has been calculated to be insignificant (1.2 %), compared to that from  237Np(n,f), for an irradiation period of 12 years at a fast neutron (E > 1 MeV) fluence rate of 1 × 1011 cm−2 ·s−1, provided the  237Np is shielded from thermal neutrons (see Fig. 2 of Guide E844).

5.4.2 Fission product production from photonuclear reactions, that is, (γ,f) reactions, while negligible near-power and research reactor cores, can be large for deep-water penetrations (1).5

5.5 Good agreement between neutron fluence measured by  237Np fission and the  54Fe(n,p) 54Mn reaction has been demonstrated (2). The reaction  237Np(n,f) F.P. is useful since it is responsive to a broader range of neutron energies than most threshold detectors.

5.6 The  237Np fission neutron spectrum-averaged cross section in several benchmark neutron fields are given in Table 3 of Practice E261. Sources for the latest recommended cross sections are given in Guide E1018. In the case of the  237Np(n,f)F.P. reaction, the recommended cross section source is the ENDF/B-VI cross section (MAT = 9346) revision 1 (3). Fig. 1 shows a plot of the recommended cross section versus neutron energy for the fast-neutron reaction   237Np(n,f)F.P.

Note 1—The data are taken from the Evaluated Nuclear Data file, ENDF/B-VI, rather than the later ENDF/B-VII. This is in accordance with Guide E1018 Guide for Application of ASTM Evaluated Cross Section Data File, 6.1. since the later ENDF/B-VII data files do not include covariance information. For more details see Section H of (10)
Область применения

1.1 This test method covers procedures for measuring reaction rates by assaying a fission product (F.P.) from the fission reaction  237Np(n,f)F.P.

1.2 The reaction is useful for measuring neutrons with energies from approximately 0.7 to 6 MeV and for irradiation times up to 30 to 40 years.

1.3 Equivalent fission neutron fluence rates as defined in Practice E261 can be determined.

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

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 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.

Ключевые слова:
fission dosimeter; fission product; fission reaction rates; Neptunium-237