ASTM E496-09
Standard Test Method for Measuring Neutron Fluence and Average Energy from 3H(d,n)4He Neutron Generators by Radioactivation Techniques 1
- Standard No.
- ASTM E496-09
- Release Date
- 2009
- Published By
- American Society for Testing and Materials (ASTM)
- Status
- Replace By
- ASTM E496-14
- Latest
- ASTM E496-14(2022)
- Scope
Refer to Practice E 261
for a general discussion of the measurement of fast-neutron fluence rates with threshold detectors. Refer to Test Method E 265
for a general discussion of the measurement of fast-neutron fluence rates by radioactivation of sulfur-32. Reactions used for the activity measurements can be chosen to provide a convenient means for determining the absolute fluence rates of 14-MeV neutrons obtained with 3H(d,n)4He neutron generators over a range of irradiation times from seconds to approximately 100 days. High purity threshold sensors referenced in this test method are readily available.
The neutron-energy spectrum must be known in order to measure fast-neutron fluence using a single threshold detector. Neutrons produced by bombarding a tritiated target with deuterons are commonly referred to as 14-MeV neutrons; however, they can have a range of energies depending on: (1) the angle of neutron emission with respect to the deuteron beam, (2) the kinetic energy of the deuterons, and (3) the target thickness. In most available neutron generators of the Cockroft-Walton type, a thick target is used to obtain high-neutron yields. As deuterons penetrate through the surface and move into the bulk of the thick target, they lose energy, and interactions occurring deeper within the target produce neutrons with correspondingly lower energy.
Wide variations in neutron energy are not generally encountered in commercially available neutron generators of the Cockroft-Walton type. Figs. 1 and 2 (1) show the variation of the zero degree 3H(d,n)4He neutron production cross section with energy, and clearly indicate that maximum neutron yield is obtained with deuterons having energies near the 107 keV resonance. Since most generators are designed for high yield, the deuteron energy is typically about 200 keV, giving a range of neutron energies from approximately 14 to 15 MeV. The differential center-of-mass cross section is typically parameterized as a summation of Legendre polynomials. Figs. 3 and 4 (1,2) show how the neutron yield varies with the emission angle in the laboratory system. The insert in Fig. 4 shows how the magnitude, A1, of the P1(θ) term, and hence the asymmetry in the differential cross section grows with increasing energy of the incident deuteron. The nonrelativistic kinematics (valid for Ed < 20 MeV) for the 3H(d,n)4He reaction show that:
where: En = the neutron energy in MeV, Ed = the incident deuteron energy in MeV, and θ = the neutron emission angle with respect to the incident deuteron in the laboratory system. Fig. 5 (2) shows how the neutron energy depends upon the angle of scattering in the laboratory coordinate system when the incident deuteron has an energy of 150 keV and is incident on a thick and a thin tritiated target. For thick targets, the inci.........
ASTM E496-09 history
- 2022 ASTM E496-14(2022) Standard Test Method for Measuring Neutron Fluence and Average Energy from 3H(d,n)4He Neutron Generators by Radioactivation Techniques
- 2014 ASTM E496-14e1 Standard Test Method for Measuring Neutron Fluence and Average Energy from?3H40;d,n41; 4He Neutron Generators by Radioactivation Techniques
- 2014 ASTM E496-14 Standard Test Method for Measuring Neutron Fluence and Average Energy from?3H40;d,n41; 4He Neutron Generators by Radioactivation Techniques
- 2009 ASTM E496-09 Standard Test Method for Measuring Neutron Fluence and Average Energy from 3H(d,n)4He Neutron Generators by Radioactivation Techniques 1
- 2002 ASTM E496-02 Standard Test Method for Measuring Neutron Fluence and Average Energy from 3H(d,n)4He Neutron Generators by Radioactivation Techniques 1
- 1996 ASTM E496-96 Standard Test Method for Measuring Neutron Fluence Rate and Average Energy From Neutron Generators by Radioactivation Techniques