Ray Angular Distributions Research Articles

宇宙線角度分布測定装置―大型構造物の非破壊検査を目的とした開発

As muons which are a major component of cosmic rays at the ground level have strong penetrating ability, they are possibly utilized as a radiation source for non-destructive inspection of large materials or geological survey.To examine the feasibilities of them, we developed a cosmic ray measuring system using the coincidence counting method with two largearea plastic scintillators. After some fundamental tests, cosmic ray angular distribution (for zenith angle) measurement was made in an underground tunnel. The data obtained well represented the topography above the tunnel.

Reaction 52Cr(p, gamma )53Mn from 1.38 to 1.66 MeV.

The reaction $^{52}\mathrm{Cr}$(p,\ensuremath{\gamma}${)}^{53}$Mn has been studied in the proton energy range 1.38--1.66 MeV (7.91${\mathit{E}}_{\mathit{x}}$8.19 MeV). Spectra and \ensuremath{\gamma}-ray angular distributions at 16 of the 33 resonances provide ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$ assignments and \ensuremath{\gamma} decay schemes for these and many of the bound states. Eight fragments of the isobaric analog of the $^{53}\mathrm{C}$ 5/${2}^{\mathrm{\ensuremath{-}}}$ 1.006-MeV state were found near ${\mathit{E}}_{\mathit{x}}$=8.05 MeV. Isobaric analog state centroids and widths are presented for the strong \ensuremath{\gamma}-decay channels and are related to the structure of the parent state.

Nuclear deformation in excited Pb isotopes from giant dipole gamma -ray-fission angular correlations.

Angular correlations between {gamma} rays and fission fragments were measured in the reaction {sup 19}F+{sup 181}Ta at 105 and 141 MeV bombarding energy. These correlations are used to extract the probability of giant dipole resonance {gamma}-ray emission relative to the spin axis of the compound system which gives direct information about the projection quantum numbers of the split giant dipole resonance components in a deformed nucleus. Large anisotropies observed in the {gamma}-ray energy region of the compound nucleus giant dipole resonance demonstrate unambiguously a deformed shape of the {sup 200}Pb compound system at excitation energies of 69.5 and 102.4 MeV. The singles and fission-coincidence {gamma}-ray spectra are fitted consistently in terms of the statistical {gamma}-ray decay of the compound system and excited fission fragments. The giant dipole resonance parameters of these fits are then used to compute the {gamma}-ray angular distribution with respect to the compound nucleus spin axis for prolate and oblate shapes. At 69.5 MeV the {gamma}-ray anisotropy relative to the compound nucleus spin axis is well described by a prolate shape with a deformation {beta}=0.43 in general agreement with theoretical predictions of a superdeformed shape in {sup 200}Pb. However, the large observed deformation survives to much highermore » temperatures than predicted. At 102.4 MeV the data require a reduction of the fission probability in the very early decay steps of the compound system. At this excitation energy the extraction of the shape of the {sup 200}Pb nucleus is ambiguous, allowing both a collective prolate as well as a noncollective oblate shape.« less

Three- and five-quasiparticle high-spin states inNd143

The level structure of {sup 143}Nd has been studied via the {sup 130}Te({sup 18}O,5{ital n}) reaction. A level spectrum up to 5.3 MeV in excitation energy has been constructed from {gamma}-{gamma} coincidence spectra and {gamma}-ray angular distributions. In addition to the single particle 1.228 MeV (13/2){sup +} state, others states arising from three- and five-quasiparticle configurations are identified, and spins and parities are suggested for these states.

Structure of the N=Z+1 nucleus 69Se.

Charged-particle-\ensuremath{\gamma} and charged-particle-neutron-\ensuremath{\gamma} coincidences have been used to identify in-beam \ensuremath{\gamma}-ray transitions in $^{69}\mathrm{Se}$ produced in the reaction $^{40}\mathrm{Ca}$${(}^{32}$S,2pn${)}^{69}$Se. Charged-particle-\ensuremath{\gamma}-\ensuremath{\gamma} coincidences, neutron-\ensuremath{\gamma}-\ensuremath{\gamma} coincidences, and neutron-gated \ensuremath{\gamma}-ray angular distributions were used to deduce the level scheme. A long-lived isomer attributed to the ${g}_{9/2}$ state was found; its half-life was measured with charged-particle-\ensuremath{\gamma} timing as 1023\ifmmode\pm\else\textpm\fi{}110 ns. The presence of strong \ensuremath{\Delta}J=1 and \ensuremath{\Delta}J=2 transitions in the band built on the \ensuremath{\nu}${g}_{9/2}$ neutron single-particle state and the measured sign of the E2/M1 mixing ratio for the ${(11/2}^{+}$\ensuremath{\rightarrow}${(9/2}^{+}$ transition are consistent with a theoretically predicted oblate shape for this nucleus.

Electromagnetic transition probabilities in the natural-parity rotational band of 173Yb.

The ground-state rotational band of $^{173}\mathrm{Yb}$ has been investigated through multiple Coulomb excitation with a beam of 250-MeV $^{58}\mathrm{Ni}$. \ensuremath{\gamma}-ray branchings and E2/M1 mixing ratios were determined up to the ${(23/2}^{\mathrm{\ensuremath{-}}}$ state by measurements of \ensuremath{\gamma}-ray angular distributions and \ensuremath{\gamma}-\ensuremath{\gamma} angular correlations. Nuclear lifetimes of levels up to I=(25/2 have been measured using the Doppler-shift recoil-distance method. No significant signature dependence was observed for \ensuremath{\Delta}I=1 M1 and E2 transition probabilities. The data are analyzed in terms of the rotating shell model and the differences between spin-up and spin-down orbitals are discussed.

G factors near the first backbend in 82Sr and 84Sr

The transient-field technique has been used to measure g factors of excited states in 82Sr and 84Sr populated in the reactions 12C(72, 74Ge, 2n) at 215 MeV. The nuclei recoiled through a 6 mu m iron foil and the nuclear precessions were deduced from the rotations of the gamma -ray angular distributions observed by four Ge(Li) detectors. The feeding time to discrete states in the vicinity of the first backbend, determined by lineshape analysis of some of the gamma -ray transitions was sufficiently short to allow g-factor determinations for these states. Large positive g factors of the 82+ and 102+ states in both 82Sr and 84Sr indicate proton g9/2 quasiparticle alignment. The lifetime of the 81+ state in 82Sr was measured as tau m=1.1(2) ps.

Low-Lying Excited States in213Rn and215Ra

Gamma rays from low-lying levels in 213 Rn and 215 Ra have been studied following the 208 Pb( 9 Be, 4n) 213 Rn and 206 Pb( 12 C, 3n) 215 Ra reactions. Spins and parities were determined by means of the measurements of γ ray angular distributions, linear polarizations and lifetimes. Enhanced E3 transitions have been observed between the ground and the first excited state. The enhancements were as high as 38±5 for 213 Rn and 34±2 for 215 Ra in Weisskopf unit. The enhancement is qualitatively explained by the particle-vibration coupling model. Cascade E3 transitions have been observed in both nuclei. The role of the two-phonon octupole vibration has been examined in relation to these cascade E3 transitions.

Yrast states of217Fr and the onset of static intrinsic reflection asymmetric shapes in the light actinide region

Yrast states in 217Fr have been populated by bombardment of a 210Pb radioactive target with 11B ions at energies in the range 52-68 MeV. Measurements of gamma -ray excitation functions, gamma -ray angular distributions and gamma - gamma coincidences were made. The proposed level spectrum exhibits at medium angular momenta alternating positive and negative parity levels strongly coupled by E1 transitions. A survey of the neighbouring nuclei leads to the conclusion that in the actinide region 217Fr and 217Ra are the lightest nuclei presenting properties which are generally related to static intrinsic reflection asymmetric shapes.

Low- and high-spin excited states in 139Pr.

The level structure of the N=80 nucleus $^{139}\mathrm{Pr}$ has been studied in-beam by the $^{140}\mathrm{Ce}$(p,2n\ensuremath{\gamma}${)}^{139}$Pr reaction using a 25-MeV p beam and by the $^{139}\mathrm{La}$(\ensuremath{\alpha},4n\ensuremath{\gamma}${)}^{139}$Pr reaction using a 47-MeV \ensuremath{\alpha} beam. \ensuremath{\gamma}-ray singles, \ensuremath{\gamma}-\ensuremath{\gamma} coincidence (prompt and delayed), and \ensuremath{\gamma}-ray angular distribution experiments were performed. We have assigned 41 \ensuremath{\gamma} rays deexciting 24 states in $^{139}\mathrm{Pr}$ from the (p,2n\ensuremath{\gamma}) reaction and 43 \ensuremath{\gamma} rays deexciting 31 (generally higher-spin) states from the (\ensuremath{\alpha},4n\ensuremath{\gamma}) reaction, for a total of 43 different states. These in-beam experiments, taken together with results from $^{139}\mathrm{Nd}^{\mathrm{m}+\mathrm{g}}$ decay and the $^{141}\mathrm{Pr}$(p,t${)}^{139}$Pr reaction, allowed ${J}^{\ensuremath{\pi}}$ assignments to be made for most of the states and allowed us to deduce the intrinsic configurations for many of them. These are discussed in terms of single-quasiparticle shell-model states and triaxial weak-coupled collective states and are compared with systematics for this nuclear region.

111Cd from the (3He,2n gamma ) reaction and a rotational interpretation.

The structure of $^{111}\mathrm{Cd}$ was studied using the $^{110}\mathrm{Pd}$${(}^{3}$He,2n\ensuremath{\gamma}${)\mathrm{}}^{111}$Cd reaction, which populated a number of new nonyrast states. The experiments included \ensuremath{\gamma}-ray excitation functions, \ensuremath{\gamma}-ray angular distributions, and \ensuremath{\gamma}-\ensuremath{\gamma} coincidences. Even though $^{111}\mathrm{Cd}$ is only two protons away from the closed Z=50 shell, there is evidence that it is slightly deformed. A symmetric particle-plus-rotor model has been used to interpret the results, and shows that rotational features are present.

High spin states in 52Cr

High spin states in the two nuclei $^{52}\mathrm{Cr}$ and $^{52}\mathrm{Mn}$, with ${J}^{\ensuremath{\pi}}$\ensuremath{\le}${11}^{+}$, have been studied via the reactions $^{51}\mathrm{V}$(\ensuremath{\alpha},p2n\ensuremath{\gamma}) and $^{51}\mathrm{V}$(\ensuremath{\alpha},3n\ensuremath{\gamma}), respectively, by in-beam \ensuremath{\gamma}-ray spectroscopy. Measurements of lifetimes of excited states by the Doppler shift attenuation and recoil distance techniques, \ensuremath{\gamma}-ray angular distributions, excitation functions, and \ensuremath{\gamma}\ensuremath{\gamma} coincidence, have been carried out in both the nuclei. New results obtained in $^{52}\mathrm{Cr}$ are the mean lifetime values of ${0.35}_{\mathrm{\ensuremath{-}}0.13}^{+0.25}$, ${0.23}_{\mathrm{\ensuremath{-}}0.11}^{+0.22}$, and <2.0 ps for the three highest observed states 8216.0 (${11}^{+}$), 7237.1 (${10}^{+}$), and 6453.4 keV (${9}^{+}$), and multipole mixing ratios ${\mathrm{\ensuremath{-}}0.10}_{\mathrm{\ensuremath{-}}0.05}^{+0.08}$, ${0.06}_{\mathrm{\ensuremath{-}}0.03}^{+0.05}$, and ${\mathrm{\ensuremath{-}}0.22}_{\mathrm{\ensuremath{-}}0.15}^{+0.08}$ for the 978.9, 784.7, and 629.1 keV \ensuremath{\gamma} rays depopulating these states, respectively. In $^{52}\mathrm{Mn}$, the lifetime of the 4163.4 keV (${10}^{+}$) state, hitherto unreported, has been measured to be ${0.20}_{\mathrm{\ensuremath{-}}0.16}^{+0.35}$ ps.Lifetimes of two other states in $^{52}\mathrm{Mn}$, at 870.1 (${7}^{+}$) and 2907.9 keV (${9}^{+}$), for which only the upper limits were known previously, have been measured in this work and are found to be ${0.07}_{\mathrm{\ensuremath{-}}0.04}^{+0.08}$ and 0.12\ifmmode\pm\else\textpm\fi{}0.08 ps, respectively. A comparison of the present experimental results on level lifetimes, multipole mixing ratios, and transition probabilities with the available theoretical calculations shows that most of the levels in $^{52}\mathrm{Cr}$ with excitation energies greater than 3.4 MeV are almost pure 1p5h states, while the lower lying states have a predominantly 0p4h configuration, with \ensuremath{\sim}20% 1p5h admixture. The observed M1 and E2 transition strengths between the high spin states in $^{52}\mathrm{Mn}$ favor interpretation of these states as having predominantly (${f}_{7/2}$${)}^{n}$ configuration and provide evidence for the existence of collective features in this nucleus.

Level structure of 140Nd.

The structure of $^{140}\mathrm{Nd}$ has been studied via the $^{126}\mathrm{Te}$${(}^{18}$O,4n${)}^{140}$Nd and $^{128}\mathrm{Te}$${(}^{16}$O,4n${)}^{140}$Nd reactions at beam energies from 64 to 76 MeV and 72 to 76 MeV, respectively. In beam \ensuremath{\gamma}-ray spectroscopy techniques, including \ensuremath{\gamma}-ray excitation functions, \ensuremath{\gamma}-\ensuremath{\gamma} coincidences, and \ensuremath{\gamma}-ray angular distribution measurements, were used to construct a level scheme up to J=17 at an excitation energy of 6411 keV. Definite parity assignments were made up to the ${11}^{+}$ state. Two-particle configurations were calculated with a shell model and a modified surface delta interaction.

111Ag utilizing the (3He, pn gamma ) reaction: A rotational nucleus with intermediate deformation.

The structure of $^{111}\mathrm{Ag}$ was studied using the $^{110}\mathrm{Pd}$${(}^{3}$He, pn\ensuremath{\gamma}) $^{111}\mathrm{Ag}$ reaction, which has populated an essentially complete set of low-energy states. The proton exit channel was isolated from competing reaction channels by operating \ensuremath{\gamma}-ray detectors in coincidence with a large-solid-angle proton detector. The experiments included \ensuremath{\gamma}-ray excitation functions, \ensuremath{\gamma}-ray angular distributions, and \ensuremath{\gamma}-\ensuremath{\gamma} coincidences. Four rotational bands have been identified. A symmetric particle-rotor model has been used to interpret these bands, and the model has identified other rotational features as well. A tentative interpretation of several nonrotational states is presented, suggesting that the mixing between rotational and nonrotational states is minimal.

G-Factor of the first 2+ state in theN=82 nucleus138Ba

The 21+ level of138Ba has been Coulomb excited with a 105 MeV32S beam. The precession of the gamma ray angular distribution induced by the transient magnetic field when traversing a 2.14 mg/cm2 iron foil, has been measured to be 15.6(1.7) mr. A value of g(138Ba 21+)=0.72(11) was obtained assuming for the transient field strength the Chalk River calibration. The field parametrization has been checked using the first 2+ state in150Sm as probe. Theg value obtained is sensibly lower than predicted by large scale shell model calculations in a proton subspace. Theg-factor of the first 2+ state in148Sm has been remeasured yieldingg(148Sm 21+)=0.246(22).

Near-yrast discrete line -ray spectroscopy of159Er and160Er to I or 40

High-spin states in 159Er and 160Er have been populated using the 116Cd+48Ca reaction at a 48Ca bombarding energy of 210 MeV. Gamma rays were detected in an array (TESSA2) of six escape suppressed germanium spectrometers and a 50 element BGO multiplicity and summed energy detector. Decay scheme and angular correlation data for these nuclei were deduced from the gamma - gamma -BGO coincidence data. In 159Er the yrast band has been identified up to Ipi =89/2+ and three side bands have been observed to 69/2-(77/2-), 43/2+ and 51/2-(59/2-). In 160Er the lowest energy positive-parity band has been observed up to 38+(40+) and the two lowest energy negative-parity side bands up to 40-(44-) and 39-(41-). The ground state level sequence has been observed up to (28+). The spin and parity of the low-lying states (I<20h(cross)) in the bands observed in 160Er were established by measuring gamma -ray angular distributions and internal conversion coefficients following the 148Nd(16O, 4n) reaction at a beam energy of 80 MeV. The band structures can be understood in terms of aligning quasiparticles using the cranked shell model. The alignment of the first pair of h11/2 protons is observed in the three lowest energy bands in each nucleus. The increase in crossing frequency of this alignment with neutron number is further evidence for the increase in deformation for the light Er isotopes. Evidence is presented for the competition of favoured single-particle configurations with the collective structures at the highest spins.

Yrast states of 216Rn and the extent of a region of possible static intrinsic reflection asymmetry.

We report the results of a study of the yrast excitation spectrum for $^{216}\mathrm{Rn}$ via the $^{208}\mathrm{Pb}$${(}^{14}$C,\ensuremath{\alpha}2n${)}^{216}$Rn reaction. Measurements of \ensuremath{\gamma}-\ensuremath{\gamma} coincidences, \ensuremath{\gamma}-ray angular distributions, and \ensuremath{\gamma}-x-ray coincidences were made. We propose a level spectrum up to ${J}^{\ensuremath{\pi}}$${=(10}^{+}$) which does not exhibit the alternating parity structure observed in several isotopes of radium and thorium. From an examination of information on $^{216}\mathrm{Rn}$ and the neighboring nuclei, we can tentatively determine that the radon isotopes of masses 216 to 222 and the N=128 isotones $^{216}\mathrm{Ra}$ and $^{218}\mathrm{Th}$ define a lower mass boundary of a region beyond which static intrinsic reflection asymmetric shapes may exist in the nuclear ground states.

Signature dependence observed for M1 transitions between rotational levels based on an f7/2 single-particle state in 163Dy.

The ground-state rotational band in $^{163}\mathrm{Dy}$ has been investigated through multiple Coulomb excitation with beams of 160-MeV $^{35}\mathrm{Cl}$ and 250-MeV $^{58}\mathrm{Ni}$. Excited states up to ${(27/2)}^{\mathrm{\ensuremath{-}}}$ were established by measuring \ensuremath{\gamma}-\ensuremath{\gamma} coincidences and \ensuremath{\gamma}-ray angular distributions. Nuclear lifetimes for levels up to spin (23/2) have been determined by analysis of Doppler broadened \ensuremath{\gamma}-ray lineshapes. Considerable signature dependence was observed in M1 transition probabilities.

Levels in 99Ru populated by the (3He,2n gamma ) reaction: Complete particle-core multiplets.

The energy-level structure of $^{99}\mathrm{Ru}$ was studied using the $^{98}\mathrm{Mo}$${(}^{3}$He, 2n\ensuremath{\gamma}${)}^{99}$Ru reaction at a bombarding energy of 13 MeV, in an attempt to populate an extensive set of non-yrast states. The experiments included \ensuremath{\gamma}-ray excitation functions, \ensuremath{\gamma}-\ensuremath{\gamma} coincidence measurements, \ensuremath{\gamma}-ray angular distributions, and \ensuremath{\gamma}-ray linear polarization measurements. A large number of non-yrast states were observed, with angular momenta ranging from (1/2) to (17/2). The comparison of experimental energies and electromagnetic transition properties to the predictions of a particle-rotor model is presented. This interpretation suggests that several complete particle-core multiplets have been populated. The population of non-yrast states is attributable to the properties of the reaction rather than any details of the nuclear structure involved.

Simplex splitting in the light actinides.

The structure of the nucleus $^{219}\mathrm{Ac}$(Z=89,N=130) has been studied via the $^{209}\mathrm{Bi}$${(}^{13}$C,3n${)}^{219}$Ac reaction. In-beam \ensuremath{\gamma}-ray spectroscopic techniques, including \ensuremath{\gamma}-ray and \ensuremath{\alpha}-particle excitation functions, \ensuremath{\alpha}-\ensuremath{\gamma} coincidence, \ensuremath{\gamma}-\ensuremath{\gamma} coincidence, and \ensuremath{\gamma}-ray angular distribution measurements were used in the construction of a level scheme up to a spin of J=(31/2)\ensuremath{\Elzxh} at an excitation energy of 2245 keV. A total of five bands have been constructed and a series of parity doublets has been observed. For four of the bands the states have been labeled in terms of the simplex quantum number, which should be an appropriate quantum number even for octupole deformed nuclei. However, considerable simplex splitting is observed. The level scheme of $^{219}\mathrm{Ac}$ indicates that the nucleus lies in the boundary region between the single-particle shell structure seen in the nuclei immediately surrounding $^{208}\mathrm{Pb}$ and the collective rotational structure prevalent in the heavier actinides. However, no detailed model predictions are, as yet, available to describe the observed structure, which may require quadrupole, octupole, and nonaxial degrees of freedom.