Γ-ray Branching Research Articles

Spectroscopy of 155Gd following Coulomb excitation: Signature-independent M1 properties and evidence for octupole correlations

The spectroscopy of 155Gd has been studied following Coulomb excitation. Gyromagnetic ratios were measured in the 3 2 − [521] ground-state band by the transient field technique and the identification of states up to spin 23 2 − in the ground-state band was confirmed by γ-γ coincidence measurements. Level lifetimes were deduced from Doppler broadened lineshapes; γ-ray branching intensities and multipolarity mixing ratios were determined from particle-γ-ray angular correlations. The population of a positive parity band (mainly 3 2 + [651] ) by E3 Coulomb excitation from the ground-state band provides evidence of octupole correlations. Particle-rotor model calculations were performed for the negative parity states. The spectroscopy is best described when the Coriolis interactions are attenuated by ≈50%.

Nuclear Data Sheets for A = 151

Abstract:Nuclear spectroscopic information for known nuclides of mass number 151 (Cs, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) with Z=55, 58 to 71 and N=96, 93 to 80 have been evaluated and presented together with adopted energies and Jπ of levels in these nuclei. No excited state data are yet available for151Cs,151Ce, and151Lu. The existence of151Cs is reported from mass separation of products from U(p,X) reaction but there is no information about its half-life.In151Tb and151Dy, Several excited superdeformed bands have been reported, in addition to the yrast superdeformed band. This evaluation represents a revision of earlier (88Si15) Nuclear Data Sheets for A = 151.Cutoff Date:Literature available up to January 15, 1997 has been consulted.General Policies and Organization of Material:See the January issue of Nuclear Data Sheets.Acknowledgments:The evaluator thanks M. J. Martin at Oak Ridge National Laboratory for a detailed and constructive review of the mass chain, especially, concerning adopted γ-ray branching ratios.General Comments:The statistical analysis of γ-ray data and deduced level schemes is carried out through computer codes available at Isotopes Project, Berkeley and Nuclear Data Center, Brookhaven. The methodology and procedures for some of these codes are described by 86BrZQ and 86Br21. A general 3% uncertainty is assumed is quoted theoretical internal conversion coefficients taken mainly from 68Ha53. The values of μ and Q are from compilation by 89Ra17, when available.

Structure of 72As nucleus

Abstract γ-ray, internal conversion electron and γγ-coincidence spectra of the 72Ge(p,nγ) 72As reaction were measured with Ge(HP) γ and superconducting magnetic lens plus Si(Li) electron spectrometers at eight bombarding proton energies between 5.75 and 6.51 MeV. Energies and relative intensities of 123 (among them 58 new) 72As γ-rays, as well as 51 (including 38 new) internal conversion coefficients have been determined. A more complete level scheme, γ-ray branching ratios, level spin and parity values have been deduced. The energy spectra and electromagnetic properties were calculated using the interacting boson-fermion-fermion model. The calculations reasonably well describe the level spectra and electromagnetic properties of 72As nucleus.

The 108,110,112Ru isotopes in the generalized collective model

Abstract Very recently two groups reported on the measurement of excitation energies and γ-ray branching ratios for the very neutron-rich 108,110,112 Ru isotopes. The experimental data were analyzed using the rigid triaxial rotor and the rotation-vibration models resulting in basically different conclusions about the essential physics of these nuclei. In order to try to resolve this matter we applied the generalized collective model to these isotopes: Our results are compared systematically to the available experimental data and to calculations within the two aforementioned models.

Comptonization as Blazar High Energy Emission

We explain the overall continuous Grazar (Gamma Ray Blazar) spectrum from the synchrotron turnover to the EGRET GeV detections by means of Comptonization in the parsec scale jet's substructures.While making use of the constraints on the synchrotron spectrum and other measurable quantities, no exotic particle acceleration is needed to achieve the high energy output.We show, that the “Lighthouse Model” of blobs of relativistic electrons, travelling with the jet plasma at relativistic speeds, produce both, correct timescales and shapes for the lightcurve, and correct ratios and slopes of the synchrotron, X-ray and γ-ray branches.

Structure of 74As from the (p,nγ) reaction and interpretation within IBFFM

Abstract γ-ray, internal conversion electron, and γ-coincidence spectra of the 74Ge(p,nγ)74As reaction were measured with Ge(HP) γ-ray and superconducting magnetic lens plus Si(Li) electron spectrometers at five bombarding proton energies between 3.6 and 4.7 MeV. Energies and relative intensities of 171 (among them > 105 new) 74As γ-rays, as well as 65 (including 51 new) internal conversion coefficients have been determined. A more complete level scheme, γ-ray branching ratios, level spin and parity values have been deduced. The scheme contains 52 levels, from which 18 are new. The energy spectra and electromagnetic properties were calculated using the interacting boson-fermion-fermion model. The calculations reasonably well describe the level spectra and electromagnetic properties of 72Ge, 73As, 73Ge and 74As nuclei.

Structure of the 70As nucleus

γ-ray, γγ-coincidence, internal conversion electron and γ-ray angular distribution spectra of the 70Ge(p,nγ) 70As reaction were measured with Ge(HP) γ and superconducting magnetic lens plus Si(Li) electron spectrometers at eight bombarding proton energies between 7.59 and 8.7 MeV. Energies and relative intensities of 113 (among them 60 new) 70As γ rays, as well as 29 new internal conversion coefficients were determined. The proposed level scheme contains 16 new levels. γ-ray branching and mixing ratios, level spin and parity values have been deduced. The spins and parities have been determined on the basis of decay properties of levels, internal conversion coefficients, Hauser-Feshbach analysis of reaction cross sections, γ-ray angular distribution and other data. The energy spectra and electromagnetic moments were calculated in the framework of the interacting boson-fermion-fermion/truncated quadrupole phonon model for odd-odd nuclei and reasonable agreement has been obtained between the experimental and theoretical results.

Measurement of Pu γ-ray intensities between 148 and 161 keV

Utilizing Pu isotopic standards characterized by the Institute for Nuclear Materials and Measurement (IRMM), New Brunswick Laboratory (NBL) measured the γ-ray branching ratios of the 148.567-keV 241Pu, the 152.72-keV 238Pu, the 159.995-keV 241Pu and the 160.28-keV 240Pu γ-rays. The study reported here includes the measurement of four IRMM standards, utilizing three different detectors for a total of 16 spectra, finding branching ratios of (1.863 ± 0.008) × 10 −6, (9.230 ± 0.068) × 10 −6, (6.321 ± 0.040) × 10 −8 and (4.065 ± 0.017) × 10 −6, γ/disintegration, respectively.

The role of triaxiality in the ground states of even-even neutron-rich Ru isotopes

Partial decay schemes for the very neutron-rich nuclei 108,110,112Ru and 114Ru, about which nothing was previously known, have been determined from the study of prompt, triple-γ coincidences in 248Cm fission fragments. Levels with probable spin up to 10ħ have been observed and γ-ray branching ratios obtained. Ratios of reduced electric quadrupole transition probabilities obtained from the branching ratios are in good agreement with predictions of a simple model of a rigid triaxial rotor.

Low-spin states of 66Zn excited in the decay

Abstract Gamma-rays from the 66 Ga (β + + e) 66 Zn decay have been investigated with a Ge(Li) spectrometer in a Compton-suppression shield. In preceding work the energies of 34 strong lines had been obtained with very high precision. By internal calibration the energies of many other lines observed in the present work, and thus of most excitation energies, could also be measured with good accuracy. The 141 observed transitions have been placed in a 66 Zn level scheme containing 33 states. Additional new information has been obtained on γ-ray branching ratios, log ft values, spins and parities.

Structure of 66Ga from (p, nγ) reaction

γ-ray, γγ-coincidence, and internal conversion electron spectra were measured with Ge(HP), as well as superconducting and traditional magnetic lens plus Si(Li) electron spectrometers at different bombarding proton energies between 6.5 and 7.1 MeV. Energies and relative intensities of 131 (among them 52 new) 66Ga γ-rays have been determined. Internal conversion coefficients of 33 transitions were measured for the first time. A more complete level scheme with new levels, γ-ray branching ratios, level spin and parity values has been deduced. The energy spectrum and electromagnetic properties were calculated on the basis of an interacting boson-fermion-fermion/truncated quadrupole phonon model for odd-odd nuclei. The model calculations reasonably describe the level spectra and electromagnetic properties of 64Zn, 65Ga, 65Zn and 66Ga nuclei with consistent parametrization.

Explosive hydrogen burning of 35Cl

Proton threshold states in 36Ar have been studied via the reactions 35Cl( 3He, d) 36Ar, 32S( 6Li, d) 36Ar, 32S(α, γ) 36Ar, 35Cl(p, γ) 36Ar and 35Cl(p, α) 32S to investigate their influence on a possible SC1 reaction cycle in explosive hydrogen burning. Three new states in 36Ar have been observed in the ( 3He, d) reaction at E x = 8806, 8887 and 8923 keV. Deuteron angular distributions were measured for 14 states near the 35Cl+p threshold and were analyzed with DWBA calculations. Values of transferred orbital angular momenta, spectroscopic factors and proton partial widths were determined. Gamma-ray spectra have been measured at ten (p, γ) resonances. Three new resonances were observed at E R = 311, 416 and 627 keV, corresponding to 36Ar states at E x = 8806, 8909 and 9117 keV, respectively. Excitation and resonance energies, γ-ray branching ratios and resonance strengths are presented. The astrophysical implications of our results for explosive hydrogen burning of 35Cl are discussed.

The shell model for T = 0 and T = 1 states in the middle of the sd shell

Spectroscopic properties of several hundreds of T = 0 and T = 1 states of A = 28 and 30 nuclei have been compared with the results of a shell-model calculation (untruncated sd shell). For A = 28 the calculation also includes γ-ray branching and mixing ratios, lifetimes, spectroscopic factors, proton widths and log ft values for the 28P(β +) 28Si decay. Uncertainties in spin, parity and isospin determinations have been resolved and parent-analogue relations have been established. Errors have been spotted in the analysis and evaluation of experimental data. A clear indication has been found of intruder states in 28Si and 30P. The present work has provided a good idea as to the reliability of the shell model in the middle of the sd shell. With previous results for A = 26 taken along one arrives at an average error of 145 keV in the theoretical energies. The averaged absolute spread in the ratio of theoretical over experimental strengths amounts to a factor 1.9 for isoscalar E2 transitions, and to a factor 2.3 for isovector Ml transitions.

Structure of the 68Ga nucleus from (α, nγ) reaction

Single-γ, γγ-coincidence and internal-conversion electron spectra of the 65Cu(α, nγ) 68Ga reaction were measured with Ge(HP) γ-ray and superconducting magnetic lens plus Si(Li) electron spectrometers at 14.5 MeV α-particle energy. The energies and relative intensities of 98 γ-transitions have been measured. Internal-conversion coefficients were determined for 19 transitions. A more complete level scheme with many new levels, γ-ray branching ratios, level spin and parity values have been deduced. The energy spectrum and electromagnetic moments were calculated on the basis of the interacting boson-fermion-fermion/truncated quadrupole phonon model for odd-odd nuclei (IBFFM/OTQM).

Low-background measurement of fast neutrons by means of Ge detectors

Abstract A low-background high-resolution Ge detector surrounded by neutron scatterers is shown to be used as a low-background neutron counter for fast (1–5 MeV) neutrons. The neutron flux and the energy are obtained by measuring yields of the γ-rays following inelastic scattering of fast neutrons by nuclei in the scatterer and the γ-ray branching ratios, respectively. Detection efficiencies, including solid angles, are ϵn = 10−3−10−4, and the minimum neutron flux (sensitivity) to be detected is Sn = 2.5−5 × 10−3 (3−6 × 10−4) neutrons per second for one week (year) of measurements.

Energy levels of A = 21–44 nuclei (VII)

The experimentally determined properties of A = 21–44 nuclides are complied and evaluated with special emphasis on nuclear spectroscopy. Separate tables for each of the nuclides reviewed present the available information about the following properties (in this order): • - excitation energies E x, • - γ-ray branching ratios b( γ), • - γ-ray mixing ratios σ, • - lifetimes γ m or widths Λ, • - neutron, proton, or α-particle resonances, • - partial widths, • - single-nucleon transfer reactions, • - beta-decay, • - arguments for spin and parity ( J π ) and isospin ( T) assignments. For each nuclide a master table summarizing the “best” or adopted values for E x, J π ; T and τ m or Λ precedes the auxiliary tables listed above. The review of each A-chain concludes with a discussion of isospin multiplets. Figures are presented of the level schemes of all nuclei and, for each A-chain, an overview of the relative energies of the ground states and lowest analogue states of all nuclei in the chain.

Spectroscopic information on 24Mg and 28Si from proton capture

Abstract Gamma-ray spectra with good statistics have been measured at three 23Na(p, γ)24Mg and five 27Al(p, γ)28Si resonances. The Ex = 9.30 MeV level of 24Mg is proved to be a triplet, and those at 9.53 and 10.66 MeV of 24Mg and at 10.67 MeV of 28Si are found to be doublets. Substantial improvements over previous work are obtained in the γ-ray branchings of the resonances and bound states, in excitation energies, and in lifetimes of 28Si levels (from observed Doppler shifts). The new information has led to new Jπ; T assignments (or restrictions) for 16 levels of 24Mg and 16 of 28Si. A shell-model calculation has helped to clarify the level schemes of both nuclei, in particular with regard to the T = 1 states. New information has also been obtained on levels close above the α-particle binding energy, which are important in nucleosynthesis.

Low-spin states of 23Na investigated with the reaction 22Ne(p, γ) 23Na

The 22Ne(p, γ) 23Na reaction has been studied with a Compton-suppression -γ-ray spectrometer at selected resonances in the range E p=0.6–1.8 MeV. The measurements of the decay schemes of these resonances also provide detailed information on the γ-ray branchings of many bound states. The excitation energies of about sixty levels deduced from these data have a precision which is typically an order of magnitude better than those reported from previous experiments. The reaction Q-value is found to be Q=8794.26±0.17 keV. Angular-distribution measurements, frequently combined with application of the RUL's to the decay data, yield the unique spin and parity assignments J π= 5 2 + , 3 2 +, 7 2 +, 3 2 −, 7 2 −~, 5 2 −, 3 2 +, 5 2 −, 3 2 |, 5 2 and 3 2 , to the bound states at E x = 5.74, 5.77, 5.93, 5.96, 6.04, 6.19, 6.74, 6.82, 6.95, 7.88 and 8.42 MeV, respectively. For several other bound states the possible spins have been restricted. The same data also yield multipolarity mixing ratios for many transitions, and lifetimes (or upper limits) for a few of the states involved. The presently available extensive data are compared with the results of shell-model calculations performed for the A=19−23 mass region in several configuration spaces. Both positive- and negative-parity states are considered.

Spins, parities and isospins of 26Al levels: Shell-model aspects

Abstract Two preceding papers on the 25 Mg(p , γ) 26 Al reaction have presented information on the energies, γ-ray branchings, lifetimes and resonance partial widths of 26Al states in the Ex = 0−9.1 MeV region. These data (combined with information from other reactions) provide new Jπ; T assignments to 127 levels (of which 111 assignments are unambiguous), as discussed in the present paper. The states obtained from a shell-model calculation in the untruncated sd-shell are found to correspond one-to-one with the 30 lowest T = 1 and the 42 lowest T = 0 even-parity states; for many higher T = 0 states the correspondence could also be established. An extensive comparison has been made of experimental and calculated γ-ray strengths. On the average E2IS strengths are calculated correctly, whereas M1IV strengths are high by a factor 1.85. For many levels the decay strengths are in excellent agreement, whereas the poor agreement for some pairs of neighbouring levels with the same Jπ; T value could be ascribed to a poor description of the configuration mixing. In some cases the strength comparison has helped to establish the correspondence between calculated and experimental states. A comparison has also been made between T = 1 levels of 26Al and 26Mg. For one (out of 44) 26Al states the 26Mg parent is unknown, whereas for one 26Mg level the analogue in 26 Al has not been identified.

Energy levels of 37K

Abstract Angular distributions have been measured for six 36 Ar(p, γ ) 37 K resonances in the E p = 0.9−3.0 MeV energy region. These experiments yield spin- and parity assignments to seven excited states of 37 K, γ-ray branching ratios for each state, together with the multipolarity mixing ratios of most transitions. Lifetimes have been deduced from the same data with the DSA method. Excitation energies have been determined with a precision up to 20 eV. A resonance- and excitation-energy measurement at the E p = 918keV resonance yields a 36 Ar(p, γ ) 37 K Q -value of Q = 1857.57 ± 0.09 keV. The 36 Ar(p, p 1 γ ) yield curve, measured in the E p = 2.6–3.3 MeV region, yields additional information on resonance and excitation energies of 37 K states with a typical precision of 0.6 keV. The new data on 37 K levels allow a detailed comparison of the level schemes of the mirror nuclei 37 Ar and 37 K. The present experimental data agree quite well with the results of previous shell-model calculations.