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Spatial neutron flux distributions have been measured in large volumes (450 liters) of several gaseous media. Measurements were made in nearly pure CO2 having a σs/σc ratio of ∼1200 and in mixtures...

Circular polarization measurements of the γ-radiation from polarized neutron capture combined with γ-γ angular correlation measurements in the 39 K(n,γ) 40 K reaction lead to J π = 2 − assignments to the E x = 0.80, 2.05 and 2.42 MeV states of 40 K, and to spin restrictions for the states at E x = 2.10, 3.44 and 4.25 MeV. Multipole mixing ratios for the γ-rays which de-excite these levels have been determined.

Products from recoil phosphorus reactions with PH3 or PF3 exhibit no pressure dependence. In the PH3 system 1,3-butadiene was found to be an effective scavenger probably due to the stabilization of the CP bond in the scavenged adduct by conjugation. It has also been shown that the H-abstraction by recoil 32P atoms from PH3 is about 160 times more effective than the F-abstraction from PF3. The upper limit for the complete retention of bonds in PH3 after radiative neutron capture has been estimated as 4 per cent.

The reaction167Er(n, e)168Er has been measured with the beta spectrometer at the FRM reactor in Munich and a new multiwire detector. 101 Transitions between 1 and 6.7 MeV have been found. 63 Multipolarities could be determined. The spin and parity assignments in the level scheme of Michaeliset al. have been verified by this measurement. Seven new levels and two new rotational bands have been observed.

A method is described to measure neutron capture rates of materials in a cavity in the center of a fast reactor. The method is based on neutron transmission through a probe of the material to be investigated and can be used also in zero power facilities. Some measurements were done for U-235 and for U-238. On account of the special detector used, it is limited, however, to sufficiently hard neutron energy spectra.

The decay of75Ga has been investigated with Ge(Li) spectrometers. Energy and intensity determinations for 37 gamma rays have been performed. A level scheme for75Ge was deduced, where 31 gamma transitions could be placed. Beta branch intensities were estimated from the measured gamma intensities. Spin and parity assignments for most of the levels were made in agreement with reaction and neutron capture studies. Half life of75Ga was measured to be (130±6) sec and that of the 139.3 keV isomeric state in75Ge to be (47.7±0.5) sec.

The neutron capture cross sections for tantalum of technical quality are measured with the aid of a lead spectrometer in the energy range of 45 eV to approx. 50 keV. Furthermore the self-shielding factors as a function of the energy and the surface coverage are determined using tantalum foils of various thicknesses.

A technique for localization of the response function of a Ge(Li) pair spectrometer is presented. Its application to gamma-ray spectra following neutron capture for several nuclides has permitted the evaluation of a new method of spectral analysis. This method, based upon a statistical description of spectra, allows the extraction of estimates for the number of transitions per energy interval and the average intensity per transition. Through the development of a simple cascade model of the (n,γ) reaction it is shown that the spectral density can be related to the nuclear level density at the neutron binding energy and the nuclear temperature. Results are obtained with this approach and are found to be in good agreement with data obtained by traditional non-statistical means.

Neutron capture γ-rays from cobalt have been used to photoexcite nuclear levels in the 5–8 MeV region. The decay properties of the 7491 keV level in 55 Mn and the 6877 keV level in 142 Nd were studied in detail. Total and partial radiative widths of nuclear levels in several isotopes were determined using nuclear self-absorption, temperature variation, and absolute scattering cross section measurements. The total radiative widths were found to be of the same magnitude as those of unbound levels populated in neutron resonances. The spins and parities of some resonance levels were determined by carrying out angular distribution and polarization measurements, respectively.

The spectrum of neutrons produced by 740-MeV protons striking a thick uranium target has been calculated, and measurements of the low-energy part of the spectrum have been made at two angles to verify calculational procedures. About 25 neutrons are produced per proton. The most probable neutron energy is 0.5 MeV.

The phonon dispersion relation of CdTe at 300 \ifmmode^\circ\else\textdegree\fi{}K has been measured for the [100], [111], and [110] directions of propagation using neutron inelastic scattering. The CdTe single crystal was grown from the melt with Cd present as $^{114}\mathrm{Cd}$ to reduce the neutron absorption of the specimen. The results have been fitted to a 14-parameter shell model that represents both the neutron data and other measured properties well when the non-neutron data are included in the fit. The present results, along with earlier measurements on $\ensuremath{\alpha}\ensuremath{-}\mathrm{Sn}$ and InSb, complete the isoelectronic sequence $\ensuremath{\alpha}\ensuremath{-}\mathrm{Sn}\ensuremath{\rightarrow}\mathrm{InSb}\ensuremath{\rightarrow}\mathrm{CdTe}$. The systematic trends in the lattice dynamics of this series of semiconductors (which is characterized by increasing band gap and ionicity) are brought out by comparison of frequency distributions calculated from the shell-model fits.

The spectrum of γ-rays given off following radiative neutron capture in 60 Ni and Fe has been studied as a function of neutron energy. The RPI LINAC provided the pulsed neutron source and the neutron energy was determined by the time-of-flight method using a lithium-drifted germanium [Ge(Li)]detector. The intensities of prominent γ-rays in the capture spectra were measured as a function of neutron energy from thermal to low keV neutron energies and the partial capture cross sections for these prominent γ-rays were measured in the low eV to low keV neutron energy range.

A search for non-statistical effects in the resonance neutron capture γ-ray spectra of Au, Sb, I and Tb is made through observation of the correlation between neutron and partial radiation widths, and through detection of intermediate structure in the intensity of high energy γ-rays, when plotted as a function of the neutron resonance energy. The integrated intensity method, which is used in the present measurements, is shown to be attractive for a faster mapping of width correlations. A high correlation of 0.96 for Tb and the zero values for Au and I are in agreement with the doorway state hypothesis of Lane. The 159 Tb data show non-statistical behaviour, indicating the existence of a narrow intermediate structure with a width of about 40 eV, together with a high value for the correlation coefficient. No evidence for such structure is found in the earlier measurements of similar type on 115 In and 187 Re when the recently established run statistic is applied to the data. From several experimental facts it is concluded that the neutron capture decay process in Au is in complete agreement with the statistical model, in contrast to the earlier 2p-1h doorway hypothesis for this nucleus.

The conditions are examined under which the spin of low-lying levels may be deduced from a comparison of the probabilities of populating such levels with γ-cascades starting from neutron capture states with different spins. To test this spin-assignment method low-energy γ-ray spectra from neutron capture in single resonances of 105 Pd and 177 Hf have been measured, and the relative intensities of γ-transitions from low-excitation levels have been determined. For each level the ratio between its populations from two different initial spin states is obtained and is found to provide a firm indication of the level spin. The experimental values of the population ratios are compared with the values obtained by a general formula based on simple statistical assumptions and by more realistic Monte Carlo calculations of the γ-cascade. The perspectives of the method are discussed.

The objective of this paper is to discuss the technological motivations for gas cooling of nuclear power reactors, as there are: (1) pure single-phase operation; (2) low neutron absorption and moderation; (3) chemical and radioactive inertness in the case of helium; (4) transparency; (5) total coolant loss impossible — only depressurization; and (6) low total stored energy. The present discussion is primarily in the context of the needs of the fast breeder reactor. More generally, it is pointed out that gas cooling allows full utilization of the most modern steam plant development, with substantial advantages both to plant cost and efficiency. It also makes feasible the intergral PCRV type of construction. The prospect of future combination with the gas turbine offers a unique field for future reduction of plant cost.

The decay of81As was investigated with Ge(Li) spectrometers. Accurate energy and intensity determinations for 29 gamma rays have been performed, from which a level scheme was deduced for81Se. Beta component intensities were obtained from the measured gamma intensities. Spin and parity assignments for most of the levels were made in agreement with the reaction and neutron capture studies. The half life of81As is measured to be (35.8±1.6) sec.

P-wave neutron strength functions of 21 nuclei, in the rare-earth and deformed region 138

An experimental study is described which could provide a method for the non-destructive assay of the fissile content in depleted fuel elements of power reactors. The basis of the method is a comparison of pulsed prompt neutron responses of the unknown fuel element with responses of known standards. The method has been tested on non-irradiated BR2 fuel elements simulating two types of examination: 1. (a) determination of the remaining 235 U-content and of the associated boron content (residual burnable poison); 2. (b) classification of poisoned CERMET-elements with respect to increasing burn-up, without discrimination of uranium and poison effects. An installation is described which should allow determination of burn-up values up to 50 per cent within reasonable measuring times and with acceptable accuracy.

$\ensuremath{\gamma}$ rays following neutron capture in natural germanium have been studied up to ${E}_{n}\ensuremath{\approx}500$ eV with the fast chopper at the Brookhaven high flux beam reactor. Up to this energy only resonances in $^{73}\mathrm{Ge}$ contribute. From the high-energy $\ensuremath{\gamma}$ rays observed, levels in $^{74}\mathrm{Ge}$ are identified to an excitation energy of about 3 MeV. From the low-energy $\ensuremath{\gamma}$ rays depopulating the $^{74}\mathrm{Ge}$ levels, spin assignments for several $^{73}\mathrm{Ge}$ resonances are made; namely 102 eV, ${J}^{\ensuremath{\pi}}={4}^{+}$; 204 eV, ${J}^{\ensuremath{\pi}}={5}^{+}$; and 224 eV, ${J}^{\ensuremath{\pi}}={4}^{+}$. The results of the resonance capture experiments are compared to previous "average-resonance" and thermal-capture work, and in general are found to be in good agreement. Average radiative strengths for $M1$ and $E2$ transitions are calculated and compared to model estimates.

Thermonuclear neutron-capture approaches to heavy transuranium element synthesis are investigated. Certain feature of capture experiments using thermonuclear macro-explosives are re-analyzed in view of recent results of nuclear shell-structure theory and theoretical developments in laser-energized fusion micro-explosions. The micro-explosion conditions for prompt multiple neutron capture are estimated for the simplest moderation techniques. We speculate on some practical neutor-capture paths to the superheavy island, especially a hybrid approach, using both macro-and micro-explosion events.

The results of a high sensitivity study of the 203Tl(n,γ)204Tl reaction are reported. Attention was focussed upon the detection of low intensity components and the establishment of the absolute intensity for the observed transitions. A technique for deconvolving the spectrum was employed which allows one to transform each spectral component into a simple Gaussian response and to thereby obtain a true representation of the gross spectral shape. The marked deviation of the spectrum from that expected using a simple statistical model is clearly revealed. The neutron separation energy was found to be 6655.8 ± 0.3 keV for 204Tl and 6503.4 ± 0.4 keV for 206Tl.