The experimental delayed-neutron spectra of 25 precursors in fission have been described in terms of a series of fine structure
peaks superimposed on a gross structure consisting of 1–3 components corresponding to different wave-numbers. These precursors
are responsible for 85–87% of the delayed-neutron effect in nuclear fuel. By including also some precursors whose spectra
have been deduced by an extrapolation procedure the effective delayed-neutron energy distribution in nuclear fuel can be accurately
calculated. As a byproduct the applicability of some recent mass formulas in the region of very neutron-rich nuclei has been
tested. Systematic deviations have been found, which indicate the need of further investigations.
Analyses of uranium and thorium by delayed neutron counting are described.The experimental system comprises an automatic pneumatic transfer system associatedwith a device made of twelve BF 3 neutron counters. Using homogeneous preparedsolutions of the samples, the analyses were based on a triple cycle each including60-second irradiation followed by 1-second cooling and 60-second counting.In these conditions, the limit of detection of uranium is about 0.3 µgwith a precision of measurement better than 10%. The contributions of possibleperturbations from 17 O(n,p)17 N reactions, followed by simultaneous –disintegration and neutron emission and from (n) reactions, have been studied.
Delayed neutron activation analysis (DNAA) presents a fast, accurate, and reliable method for quantification of fissile material.
The method has relatively few sources of error and may be accomplished nondestructively. The need for a fast, accurate screening
of materials stems from the necessity to protect cleanroom facilities from widely varying fissile quantities in samples and
from desired gains in efficiency of mass spectrometric analysis by assisting in spike level selection and by removing from
the sample set those materials that are not of interest. During the last several years, many different materials have been
screened or analyzed in support of international safeguards, internal process control for actinide separations, and in uranium
contamination assessments. Swipes from a variety of sources have been analyzed, either before or after dissolution, and comparison
of the DNAA results to mass spectrometry results is generally favorable. A facility characterization of the High Flux Isotope
Reactor was performed using filter paper swipes to demonstrate the utility of the DNAA technique.
The cascade process of decay of most radionuclides with corpuscular and photon radiation (β-α, α-ψ, β-ψ, ψ-ψ, α-x, β-x) with
an average life-time of the intermediate states from 10−10 to some 10 sec, makes it possible to use the delayed coincidence method for selective analysis. Natural mixtures of radionuclides
were analyzed for isotopes214Bi(RaC),212Bi(ThC),219Rn(An) and220Rn(TN)with the aid of instruments including scintillation detectors and a multichannel time selector by using β-α and α-α
delayed coincidences, while isotopic ratio235U/235U in natural uranium was determined by using α-ψ coincidences. The instrument background did not exceed 1 pulse per hour per
coincidence channel. Subjected to analysis were rocks with Clarks of radioactive elements.
The predominant use of the nuclear track technique (NTT) in analytical chemistry has been to measure the prompt charged particle emission from neutron induced reactions with stable or fissile nuclides of selected elements. This work describes the use of the NTT for determining bismuth via delayed alpha particle emission from the decay of210P. This technique is sensitive and reliable since alpha track counting is highly efficient and can provide information, on elemental spatial distributions. Bismuth determinations in various materials by this technique appears possible to at least the 1.0 microgram per gram level.
Authors:J. Moon, S. Kim, Y. Chung, J. Lim, G. Ahn, and M. Koh
A delayed neutron counting system has been implemented at the HANARO research reactor in 2007. Thermal neutron flux measured
at the NAA #2 irradiation hole coupled to the delayed counting system, was higher than 3 × 1013 n cm−2 s−1. The delayed neutron counting system is composed of 18 3He detectors which are divided into three groups with six detectors and the collected signals of each group are processed
to a digital signal. The count numbers were measured with the uranium mass by using NIST SRMs under fixed analytical condition
and their correlation could be determined. Finally, delayed neutron activation analysis has been carried out for the determination
of uranium mass fraction in the collected environmental samples.
An automated delayed neutron counting (DNC) system has been developed at the Royal Military College of Canada (RMC) to enhance
nuclear forensics capabilities pertaining to special nuclear material analysis. The system utilises the SLOWPOKE-2 Facility
at RMC as a neutron source and 3He detectors. System control and data acquisition occur through a LabVIEW platform. The time dependent count rate of the delayed
neutron production has been examined for 235U, using certified reference materials. Experimental validation according to ISO 17025 protocols suggests typical errors and
precision of −3.6 and 3.1%, respectively, and a detection limit of 0.26 μg 235U.
In this paper some predictions about some delayed neutron precursor yields are presented. The predictions are applied for certain actinides with some special interest in the nuclear energy field. The predictions are based on correlations which might be related to the cluster structure of the nucleus.
The Eskiehir-Beylikahir district has the largest and richest thorium and rare earth elements deposits in Turkey. The uranium and thorium concentrations of samples taken from four different parts of this area have been determined by the delayed neutron counting technique. The results are compared with those of previous analyses by other techniques and found to be in good agreement.
A simple method for the determination of uranium and thorium by delayed neutron counting is described. One portion of the
sample is irradiated in a reactor and the delayed neutrons are counted. Another portion of the sample is mixed with B4 C powder absorbing the thermal neutrons, and irradiated in the same position. From those data, both uranium and thorium can
be calculated when a quantitative calibration has been made beforehand. The detection limits for the pure elements are 0.07
ppm for uranium and 2 ppm for thorium with the minimum analyzing time being 2 min. The accuracy of the method is investigated
by comparing results obtained by the method described here with results obtained by epithermal activation analysis.