Properties Of Nuclear Levels Research Articles

Prospects for nuclear physics with lasers

The development of high intensity lasers has opened up new opportunities for nuclear physics studies in extreme conditions which cannot be reached with conventional particle accelerators. A laser is a unique tool to produce plasma and very high fluxes of photon and particle beams in very short duration pulses. Both aspects are of great interest for fundamental nuclear physics studies. In plasma the electron–ions collisions may modify atomic and nuclear level properties. This is of prime importance for the population of isomeric states and the issue of energy storage in nuclei. Nuclear properties in the presence of very high electromagnetic fields, nuclear reaction rates or properties in hot and dense plasmas are new domains of investigation. Our group has launched an experimental program to evaluate the possibilities for such nuclear physics studies at high intensity laser facilities. This program and its first results are presented.

Breakout from the hot-CNO cycle via the 18Ne(α, p)21Na reaction

A detailed presentation is given of estimating uncertainties in thermonuclear reaction rates for stellar nucleosynthesis involving narrow resonances, starting from random errors in measured or calculated resonance and nuclear level properties. Special attention is given to statistical matters such as probability distributions, error propagation, and correlations between errors. Interpretation of resulting uncertainties in reaction rates and the distinction between symmetric and asymmetric errors are also discussed. Computing reaction rate uncertainties is described. We give examples from explosive nucleosynthesis by hydrogen burning on light nuclei.

Error analysis for resonant thermonuclear reaction rates

A detailed presentation is given of estimating uncertainties in thermonuclear reaction rates for stellar nucleosynthesis involving narrow resonances, starting from random errors in measured or calculated resonance and nuclear level properties. Special attention is given to statistical matters such as probability distributions, error propagation, and correlations between errors. Interpretation of resulting uncertainties in reaction rates and the distinction between symmetric and asymmetric errors are also discussed. Computing reaction rate uncertainties is described. We give examples from explosive nucleosynthesis by hydrogen burning on light nuclei.

Magnetic spectrometer Grand Raiden

A high-resolution magnetic spectrometer called “Grand Raiden” is operated at the RCNP ring cyclotron facility in Osaka for nuclear physics studies at intermediate energies. This magnetic spectrometer has excellent ion-optical properties. In the design of the spectrometer, the second-order dispersion matching condition has been taken into account, and almost all the aberration terms such as (x|θ 3), (x|θφ 2), (x|θ 2δ) and ( x| θδ 2) in a third-order matrix calculation are optimized. A large magnetic rigidity of the spectrometer ( K = 1400 MeV) gives a great advantage to measure the charge-exchange ( 3He, t) reactions at 450 MeV. The ability of the high-resolution measurement has been demonstrated. Various coincidence measurements are performed to study the nuclear structures of highly excited states through decay properties of nuclear levels following nuclear reactions at intermediate energies.

Chaotic behavior of nuclear spectra

Bohigas, Giannoni and Schmit conjectured that quantum analogs of classically chaotic systems have level statistics which are consistent with the Gaussian orthogonal ensemble (GOE) of random matrix theory. This suggests that the fluctuation properties of nuclear levels may be used as a signature for chaos or regularity. Resonance data are known to display the long and short range order predicted by GOE. In one nucleus, 26Al, all levels are known from the ground state to the resonance region. This provides the first experimental test of the behavior of fluctuation properties as a function of symmetry breaking — in this case, isospin. In addition there are many nuclides where level schemes are complete over a more limited range of energies and spins. Our analysis of a large data set (~ 160 sequences in 60 nuclides) reveals a strong dependence on the mass number A.

Nuclear spectroscopy

Nuclear spectroscopy can be defined as the study of how nuclei absorb and emit energy. It is particularly concerned with the properties of individual levels such as energy, angular momentum (spin), isospin (the embodiment of the basic equivalence of neutrons and protons), magnetic and electric moments and transition rates and so forth. Our knowledge of these properties has increased rapidly and dramatically since 1945. This nearly exponential advance has occurred because of tremendous technical advances in equipment, in experimental methods, and in analyzing experimental data. Figure 1 shows one example of the sort of spectrometers available to nuclear physicists today. The use of the computer in analysis has been especially important in the last 15 years. In this article we will try to convey a feeling for the diversity and sophistication of present‐day nuclear spectroscopy; we will concentrate on those areas where in recent years the most progress has been made in our understanding of the properties of nuclear levels.

Systematics of nuclear level properties in the lead region

This survey of the lead region is an extension of our “Survey of Nuclear Structure Systematics for A ≥ 229” (72ElSc) published previously. The mass range covered is primarily A = 190 through A = 221. The emphases are on properties of low-lying states, their shell-model configurations, and their decay modes. A comprehensive systematics of α-decay hindrance factors is presented; for β − decay, only transitions between pure single-particle states are included in the log ft systematics. For IT decays the important case of M4 transitions is presented. Magnetic dipole moments are tabulated and the additivity relation is examined. The starting point of the present survey was the Evaluated Nuclear Structure Data File (ENSDF) (see the Cumulated Index to A-Chains on page iii of this issue for references to the individual mass chains). Most changes and updates of this file, made in the course of preparing the present survey, are mentioned in the text. We refer the reader to Nuclear Data Sheets for information on high-lying states, spectroscopic factors, documentation of the data, and other topics not treated in this survey.

Properties of nuclear levels photoexcited by neutron-capture γ-rays of Ti and Cu

Neutron capture γ-rays of Ti and Cu have been used to photoexcite nuclear levels in the 5–8 MeV region in various nuclei. The spins, parities, and radiative widths of resonance levels in 65Cu, 100Mo, 118Sn, 126Te, 130Te, 186W and 209Bi, were measured. The spins of the resonance levels were obtained by angular distribution measurements, and the parities by polarization measurements. The radiative widths 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 neutron resonances, after applying a correction allowing for different excitation energies. Some E2 M1 mixing ratios of high energy transitions were obtained; the E2 widths were found to be of the same magnitude as those obtained in (n, γ) experiments.

Properties of nuclear levels excited by neutron capture γ-rays from cobalt

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 55Mn and the 6877 keV level in 142Nd 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.

Nuclear Reaction Studies of 151Sm

Properties of nuclear levels in 151Sm have been studied by measuring angular distributions for the 152Sm(d,t)151Sm reaction and spectra at several angles for the 152Sm(3He,α)151Sm and 150Sm(d,p)151Sm reactions. The reaction products were analyzed with a magnetic spectrograph and detected with photographic emulsions. Transfer l values were deduced from the (d,t) angular distributions and from the ratios of (3He,α) and (d,t) cross sections. The (d,t), (d,p), and (3He,α) reactions on targets of 151Sm were also studied in order to learn more about the wave function of the 151Sm ground state. The low-lying positive parity levels can be described by the Nilsson model with Coriolis and ΔN = 2 interactions included. However, the properties of the low energy negative parity states could not be explained as easily. No mixture of Nilsson states was found which could simultaneously explain the single neutron transfer intensities and the Coulomb excitation probabilities from previous measurements.

Nuclear spectroscopy of neutron-deficient La, Dy and Er activities

A large accumulation of conversion-electron data has made it feasible to study the properties of nuclear levels in the rare-earth region of neutron numbers 88 to 94. The first experimental level scheme for 153Tb ( N = 88) is constructed; 84 transitions originate from 21 states excited below 1 MeV. The conversion spectrum of 155Tb is augmented from 40 to 120 transitions below 1.1 MeV energy. Multipole orders are deduced for 55 of the 96 transitions placed between 28 levels in 155Tb. Rotational parameters and γ-ray branching ratios are evaluated for 155Tb. Levels in the 0.5 to 1 MeV region are interpreted as β- and γ-vibrations of the 3 2 + [411] state, and a single-particle 1 2 + [411] band. Our data on 158Ho consists of 41 transitions, of which 30 are new, and almost all of the transition intensity is accounted for in the level spectrum. Neutron orbital 3 2 − [521] is found to be common to each of four low-lying intrinsic configurations in doubly odd 158Ho. The order of odd-proton orbitals coupled to 3 2 − [521] corresponds to that of single-particle states observed in neighboring 159Ho. Eighty conversion-electron transitions are observed below 1 MeV in 161Ho, a six-fold increase over preceding studies. Using photon intensities from independent research, multipole orders are deduced for most of the transitions de-exciting 18 nuclear levels in 161Ho. More evidence is presented on decay spectra of 131, 132mLa, including transition multipolarity assignments.

Nuclear data for A = 206 isobars

Nuclear data relating to nuclear isobars with A = 206 are presented. When new data with better accuracy are available, older data are often not quoted but only referred to. Similarly, only the latest data from an author are quoted when the measurement has been reported several times. From the cumulative data presented, conclusions about level energies, spins and parities are derived. Decay schemes, γ-ray properties and other properties of nuclear levels are also presented, whenever pertinent data are available. The schematic relation of isobars of A = 206 is presented in Drawing 1 as a summary of the entire chain. Since very good theoretical calculations are now available for two-hole states in A = 206 nuclei, these theoretical results are presented in Drawing 2 together with the adopted level schemes for 206Tl (1 proton — 1 neutron hole) and 206Pb (2 neutron holes). For 206Hg no experimental data are available. For Z ⩾ 83 no results of theoretical calculations are presented. The only available calculation for 206Bi is suspect because of problems revealed in a similar calculation for 208Bi. A number of serious gaps in the available data are exposed, and attention is drawn to the possible experiments. These are:

Nuclear data sheets for A = 53

Experimental data pertaining to the nuclear level properties of 53V, 53Cr, 53Mn, and 53Fe are compiled, and a set of adopted level properties is presented for each nucleus. The quantity and variety of available information is found to be very impressive, particularly for 53Cr and 53Mn. The few instances in which there is disagreement between two or more measurements are brought to the users' attention. For the 121 reported levels below 4 MeV of excitation in these four nuclei, only 22 spins (including ground states) and 5 half-lives (excluding ground states) have been determined. Thus, in spite of the wealth of experimental data, the need for further study is indicated since the paucity of spin and lifetime measurements remains an obstacle to thorough theoretical study. The adopted level and decay properties are based on data received before January 1970. Data received during January 1970 have been ‘Added in Proof.’

Systematics of electric-dipole transitions

The aim of the present paper is a systematical analysis of average radiative properties of nuclear levels lying near the nuclear binding energy. Theoretical estimates of electric-dipole radiative widths as well as of elastic-scattering cross-sections are presented. All the calculations have carried out by an extrapolation of theE1 giant resonance at lower energies, following a procedure suggested by Axel. A quantitative agreement with experiment has been obtained in most cases. We can thus confirm that, at least away from closed shells, Axel’s extrapolation procedure allows us to reproduce the systematical trend ofE1 radiative widths below the giant resonance; large shell effects are conversely evident near magic nucleon numbers.

Properties of nuclear levels in a number of even-mass nuclei (184≦ A ≦ 192)

A large accumulation of internal conversion-electron data has made it possible to study the properties of high-energy nuclear levels in the transition region of mass numbers 184 to 192. Reasonably detailed level schemes have been constructed from these measurements leading to the following even nuclei: Re 184m→W 184, Ir 186→Os 186, Ir 188→Os 188, Ir 190→Os 190 and Ir 192→Os 192. Parameters relevant to rotational configurations and branching ratios of the de-exciting transitions are evaluated. The low-energy spectra, with their associated vibrational and rotational modes of excitation, have been confirmed and extended. Triple isomerism was observed in Ir 190 including isomeric transitions of M3 (26 keV) and M4 (148 keV) character. The metastable state of Re 184 is partially de-excited by an 83 keV isomeric transition of M4 multipolarity.

Properties of Nuclear Levels in a Number of Odd-ANuclei (151≤A≤191)

In order to obtain more evidence on the systematic behavior of nuclear energy levels in the deformed region, a number of neutron-deficient odd-mass activities were studied with internal conversion electron spectrographs. Some scintillation counter measurements were made. Level schemes are postulated for decays leading to the following odd-neutron nuclei: ${\mathrm{Pm}}^{151}$ \ensuremath{\rightarrow} ${\mathrm{Sm}}^{151}$, ${\mathrm{Tb}}^{151}$ \ensuremath{\rightarrow} ${\mathrm{Gd}}^{151}$, ${\mathrm{Tb}}^{153}$ \ensuremath{\rightarrow} ${\mathrm{Gd}}^{153}$, ${\mathrm{Tb}}^{155}$ \ensuremath{\rightarrow} ${\mathrm{Gd}}^{155}$, ${\mathrm{Eu}}^{157}$ \ensuremath{\rightarrow} ${\mathrm{Gd}}^{157}$, ${\mathrm{Tm}}^{163}$ \ensuremath{\rightarrow} ${\mathrm{Er}}^{163}$, ${\mathrm{Tm}}^{165}$ \ensuremath{\rightarrow} ${\mathrm{Er}}^{165}$, ${\mathrm{Ho}}^{167}$ \ensuremath{\rightarrow} ${\mathrm{Er}}^{167}$, ${\mathrm{Re}}^{183}$ \ensuremath{\rightarrow} ${\mathrm{W}}^{183}$, ${\mathrm{Ir}}^{185}$ \ensuremath{\rightarrow} ${\mathrm{Os}}^{185}$, ${\mathrm{Ir}}^{187}$ \ensuremath{\rightarrow} ${\mathrm{Os}}^{187}$, and ${\mathrm{Ir}}^{189}$ \ensuremath{\rightarrow} ${\mathrm{Os}}^{189}$. As a corollary, data are presented for the odd-proton nuclei populated in the decays of ${\mathrm{Pt}}^{189}$ \ensuremath{\rightarrow} ${\mathrm{Ir}}^{189}$ and ${\mathrm{Pt}}^{191}$ \ensuremath{\rightarrow} ${\mathrm{Ir}}^{191}$. The proposed states are described using the Mottelson and Nilsson predictions. Some conclusions may be drawn concerning such properties of these orbitals as moments of inertia, $\frac{M1}{E2}$ mixing ratios, and positions of the intrinsic excitations. Ratios of gamma-ray transition probabilities from the various states are given. Previously published studies of odd-$A$ nuclei in the region of odd-$N$ numbers 99-107 are incorporated in the energy-level systematics.

Inelastic Scattering of High Energy Nucleons by Nuclei and Impulse Approximation

Inelastic scattering of high energy nucleons by nuclei is an important tool to investigate properties of nuclear levels. It is shown that a test regarding the impulse approximation can be performed. The inelastic scattering of 182 Mev protons by C/sup 12/ with energy losses of 4.43, 7.66, and 9.63 Mev is investigated. (W.D.M.)