The idea of adjustment of cross section data by the least squares method to fit calculated integral data to measured values was first proposed in 1964 at the Geneva Conference. The proposal encountered severe criticism from a number of influential scientists, and international opinion has since been sharply divided on whether or not the method should be accepted. Meanwhile, much effort has been directed by others favoring the method toward improving the method, and toward offering convincing answers to each criticism. The results of these efforts were presented at the Tokyo Symposium in 1973, in the form of an improved method of the least squares adjustment. This paper reviews these past developments and discusses the remaining topics concerning the adjustment.

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Activation cross sections for the (n, p) and (n, α) reactions of Nd, Sm, Yb and Lu have been measured at 14.6 MeV by using a Ge(Li) y-ray detector. The following cross sections (in millibarns) have been obtained : ¹⁵⁰Sm(n, p)¹⁵⁰Pm, 7.19±1.01 ; ¹⁷³Yb(n, p)¹⁷³Tm, 13.5±2.8 ; ¹⁷⁵Lu(n, p)¹⁷⁵Yb, 18.5±2.2 ; ¹⁴⁶Nd(n, α)¹⁴³Ce, 4.42±0.47 ; ¹⁵²Sm(n, α)¹⁴⁹Nd, 2.81±0.42 ; ¹⁷⁴Yb(n, α)¹⁷¹Er, 1.22±0.23 and ¹⁷⁶Lu(n, a)¹⁷³Tm, 2.30±0.57. The results are compared with predictions based on the evaporation, the pre-equilibrium and other models. The present experimental (n, p) cross sections agree fairly well with the pre-equilibrium model predictions. A comparison made between the experimental (n, α) cross sections and the predictions of the pre-equilibrium model suggests the existence of a mechanism of preequilibrium emission in the (n, α) reaction in this mass region.

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Two-dimensional current distribution in two regions-resistive electrode and plasma-are studied to optimize the shape of the resistive electrode in the MHD generator. Numerical computations are made for an example of potassium-seeded argon in non-equilibrium. As a first step, the performance is analyzed on an electrode of rectangular shape, and calculations performed more quantitatively than in the previous work by Maxwell et al. reveal that better uniformity is obtained for the current distribution along the electrode surface by increasing the thickness and resistivity of the electrode. The uniformity is found to improve also when the load current is increased.
To diminish the power loss produced in the resistive layer, the electrode shape is optimized by eliminating from the rectangular resistive electrode the portion that produces the power loss. The electrode thus optimized in shape has an effective internal resistance that is independent of the value of the resistivity of the resistive layer. Consequently, in the optimized electrode, the power loss is independent of the uniformity of current distribution along the electrode surface, whereas it depends on the uniformity when a rectangular-shaped electrode is used.

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A simple method is derived to improve the accuracy of the predicted neutron flux in and around control rods by coarse mesh difference diffusion scheme in fast reactor criticality calculations. In a two-region slab lattice, a simple polynomial function is used to approximate the flux in the integral transport model, and the coefficients in the polynomial are determined by the variational method, From this approximate transport solution, the terms of net current into the control rods are corrected in the difference diffusion scheme before treatment by iteration in the criticality calculation. The results represent an appreciable improvement over those obtained with the conventional diffusion scheme, without any increase of computer time in the iteration. This improvement is confirmed in comparison with the results obtained with the usual fine mesh transport scheme as the standard reference.

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The time-dependent energy spectra of neutrons have been measured in a small 30×30×30 cm³ graphite assembly by means of the linac-chopper method, with a view to establishing experimental evidence that there is no asymptotic spectrum in such a small assembly, and in order to study the non-asymptotic behavior of neutrons.
The arrangement of a polyethylene pre-moderator adjacent to the assembly made the measurements possible with the improvement obtained thereby of the neutron counting statistics. It was indicated from calculation that the presence of the premoderator had little effect--at least above the Bragg cut-off energy--on the evolution in time of the energy spectra of neutrons in the graphite assembly.
The experimental results indicated very probable disappearance of asymptotic spectra, and revealed significant enhancement of trapping at Bragg energies with the lapse of time. This is consistent with the results of pulsed neutron experiments in small assemblies conducted by Takahashi et al., and falls in line with de Saussure's approximation.
The spectra in the graphite assembly showed significant space dependence, the spectra becoming harder with increasing distance from the pre-moderator. This hardening may be attributed to the relatively faster propagation of higher energy neutrons.

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The band structure of metallic Th and NaCl-type ThX (X=C, N, P, S) compounds were calculated by tight-binding method, with the parametrization improvement. Values of two-center parameters chosen so as to fit the result for Th given by Gupta & Loucks were found to be very close to two-center integrals with a suitable integration range. Applying this method for evaluating parameters, the band structures for ThX compounds were also computed. Population analysis to determine the electron populations in each orbital based on the results obtained by the method indicated that for all compounds calculated the occupied states consist mainly of a type bonding between metalloid p and Th d_r as well as r bonding between p and Th d_g.

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In sodium pool burning occurring in the case of an LMFBR accident, some radioiodine in the sodium coolant may be transported into the gas phase and act in common with sodium oxide aerosol. If some iodine is converted to volatile compounds, the radioactivity may remain for many hours in the gas phase of the reactor containment. The present work was carried out in an attempt to throw more light on these circumstances.
Reactor-grade sodium with sodium iodide tagged with ¹³¹I in an amount of about 1 ppm was burned by heating in a closed vessel containing, air. Most of the iodine released into the gas phase took the form of aerosol, but some amount remained in vaporous state. It was determined by Maypacks and radio-gaschromatography that the volatile radioiodine compounds were of organic form. The proportion of organic iodide referred to total airborne iodine in the present experiments falls within the experimental data on what will be formed in a loss of coolant accident involving a light water reactor. It is concluded that volatile iodine formation would present similar aspects under accidental conditions affecting both LWR and FBR, though the mechanisms governing the two cases would be different.

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