Thermal Neutron Absorption Cross Sections of Boron and Gold

Abstract

The cross sections of boron and gold, which are widely used as standards for slow neutron measurements, have been determined as functions of wavelength. Total cross sections were measured in the wavelength range 1.5-10A with the Brookhaven slow chopper, the long wavelengths being used to minimize the effects of scattering. The absorption cross section of boron of "normal" isotopic constitution is 749±4 barns at 2200 m/sec (1.80A); the variation of cross section with boron source is expected to be only about 1 percent. The measurement of the gold cross section is complicated by the deviation from 1/v resulting from a nearby resonance and by grain orientation effects in the scattering. The 2200-m/sec value, resulting from measurements at long wavelength together with a small correction for the 4.9-ev resonance, is 98.7±0.6 barns.

Thermal stability and high-temperature behavior of the natural borate colemanite: An aggregate in radiation-shielding concretes

“…The need to protect workers and public exposed to radiation emitted, for example, by nuclear reactors for energy production or by neutron facilities for scientific research or medical applications requires the development and the production of suitable materials able to shield from harmful radiations. In this light, 10 B (which accounts for approximately the 20% of natural boron [1]) emerges as an interesting isotope for its elevated ability to absorb thermal neutrons due to its high cross section for 10 B(n,α) 7 Li reaction (3840 barns [2,3]). Consequently, neutrons reaction with 10 B suppresses escaping radiations and generates alpha particles (easily absorbable by few μm of material) and 7 Li, a stable isotope.…”

Absolute calibration of the NBS standard thermal neutron density

“…From the diboran e a sample of boric-acid solu tion was prepared for comparison with a solution of the standard boric oxide of the Argonne National Laboratory by the da nger-coefficient method in the Argonne low-energy pile. The boron cross section of this standard has been accur ately measured as 755 ± 3 barns [6] and verified by the Brookhaven National Laboratory's r esult of 753 ±3 [7]. The Argonne comp ariso n gave a value of 746 ± 7 barns for the NBS boron.…”

Precision neutron total cross section measurements on gold and cobalt in the 40 ?eV-5 meV range

“…The wavelength calibration was mostly done with Bragg cutoffs observed on polycrystalline samples in transmission. As discussed by Gould et al [4] and Carter et al [9], the accuracy of this calibration procedure is practically limited by the wavelength resolution of the spectrometer. Resolutions A2/2 of 2-4% were used in [4,9] and the systematic uncertainty of the wavelength scale was estimated to be 0.2-0.3 %.…”

“…As discussed by Gould et al [4] and Carter et al [9], the accuracy of this calibration procedure is practically limited by the wavelength resolution of the spectrometer. Resolutions A2/2 of 2-4% were used in [4,9] and the systematic uncertainty of the wavelength scale was estimated to be 0.2-0.3 %. No details about resolution were given by Als-Nielsen and Dietrich [6], but a 0.2% overall accuracy and a 0.06 % wavelength uncertainty were claimed.…”

“…In the previous experiments on gold, which were performed with crystal spectrometers [4,6] and the time-of-flight method [5,9], the principal sources of error were the wavelength measurement and statistics. The wavelength calibration was mostly done with Bragg cutoffs observed on polycrystalline samples in transmission.…”