In-beam Measurements Research Articles

High spin states in 109Sn.

High spin states in $^{109}\mathrm{Sn}$ have been established up to 9.1 MeV in excitation energy and to a spin of 43/${2}^{\mathrm{\ensuremath{-}}}$\ensuremath{\Elzxh} with the reaction $^{94}\mathrm{Mo}$${(}^{19}$F,p3n${)}^{109}$Sn at a beam energy of 88 MeV. In-beam measurements involved \ensuremath{\gamma}-\ensuremath{\gamma} coincidences and directional correlation of oriented states. A negative-parity band consisting of stretched E2 transitions has been established. This band has been identified as the favored signature branch of the decoupled ${\mathrm{h}}_{11/2}$ neutron coupled to the deformed \ensuremath{\pi}(${\mathrm{g}}_{9/2}^{\mathrm{\ensuremath{-}}2}$\ensuremath{\bigotimes}${\mathrm{g}}_{7/2}^{2}$) core configuration. \textcopyright{} 1996 The American Physical Society.

Optimization of a Compton-suppression system by escape-peak ratio

Abstract A Compton-suppression system consisting of an HPGe central detector surrounded by eight BGO scintillators in an annular geometry was assembled. This system is dedicated to in-beam γ-ray measurements. The ratios of full-energy to single-escape peak and full-energy to double-escape peak, at γ-rays of 2754, 4443, and 6139 keV, were used to derived associated suppression factors in order to optimize detection conditions of the system. The suppression factors derived both from the escape peak ratios and the corresponding peak-to-Compton ratios of the γ-ray spectra are compared and discussed. This optimization technique may be of great significance for analyzing complicated spectra, where high-energy γ-rays are considered for analytical use.

New Isomeric States in 197Bi

The high-spin states in 197Bi have been studied with the 187Re(16O,6n) reaction at 16O energies from 85 to 105 MeV. In-beam measurements of γ-ray excitation functions, γ-γ-t coincidences and γ-ray angular distributions were carried out with six BGO(AC)HPGe detectors and one intrinsic Ge planar detector. Eleven new transitions and three new isomers were observed, and a level scheme for 197Bi was established. Some differences between the present work and the previous results were found.

Observation of isomeric states in197Bi

The high-spin states in197Bi have been studied with the187Re(16O, 6n)197Bi reaction at16O energies between 85 and 105 MeV. In-beam measurements ofγ-ray excitation functions,γ-γ-t coincidences and γray angular distributions were carried out with 6 BGO(AC) HPGe detectors and one intrinsic Ge planar detector. 11 new transitions and 3 new isomers at 2089, 2357 and 1968+Δ keV with t1/2 =19.3±4.9, 53.4±20.5 and 18.0±3.1 ns., respectively, were observed, and a level scheme is established. Some differences between the present work and the previous results were found.

Isomer-shift of interstitial and substitutional iron in silicon and germanium

We describe results from in-beam Mossbauer implantation measurements for57Fe inn-type Si, inp-type Si, and in Ge. Ab initio calculations for the contact densities from density functional theory in the local-density approximation are presented and their results are employed to locate the type of position of Fe in the lattice of the host. Thus the different spectral features corresponding to interstitial and substitutional Fe in Si and Ge are unambiguously identified.

High-spin states in 206Pb

Excited states in 206Pb have been populated in the 204Hg(α, 2n) reaction using a 35 MeV α-beam. In-beam measurements have been performed to obtain γ-ray angular distributions, time spectra and γγ-coincidences. The level scheme has been extended to a spin value of 16kh and an excitation energy of 6.8 MeV. The present measurements confirm the previously reported half-life of the 12 + state and identify nine new high-spin states above the 12 + isomer in 206Pb. The new high-spin states are expected to have a one-particle three-hole character and they are interpreted within the nuclear shell model using known two-hole and particle-hole states.

Level scheme and mixed-symmetry states of 134Ba from in-beam (n, n′γ) measurements

The decay properties of the existed states of 134Ba below 3 MeV have been studied with the (n, n′γ) reaction. From γ-ray excitation function and angular distribution measurements, several new levels, spin-parity values and multipole mixing ratios were obtained. Lifetimes were measured by the Doppler-shift attenuation method, and reduced transition probabilities were calculated for a number of levels using the proton-neutron interacting boson model. The 2029 and 2088 keV states appear to share the properties of the lowest mixed-symmetry 2 + state.

In-beam magnetization measurements of thin Fe foils and simultaneous observation of the transient magnetic field at Pd ions

The well established phenomenon of heavy ion beam induced attenuations of transient magnetic fields (TF) was studied by measuring the in-beam magnetization of bombarded Fe foils employing the magneto-optical Kerr-effect. Whereas the macroscopic magnetization did not show any deterioration, the simultaneously measured TF of recoiling108Pd(2+) ions was found to be substantially attenuated.

The level structure of 87Nb

The level structure of 87Nb has been studied through β-decay of 87Mo activity produced by the 58Ni(32S, 2pn) reaction and through in-beam γ-ray measurements in the 58Ni(32S, 3pγ)87 Nb reaction. In the β-decay study, the decay scheme of 87Mo is constructed firstly from γ-ray energies, intensities of γ-rays and conversion electrons, and γ-, βγ- and γ(ce)-coincidence relations. Spins and parities of the low-lying statesof 87Nb and 87Zr were also investigated. In the in-beam study, intensities, coincidence relations and angular distributions of γ-rays were measured in coincidence with charged particles evaporated from the compound nuclei. Then high-spin states of Jπ ⩽ (33+2) in 87Nb were established in this study. Systematic behavior in the level structures of N = 46 isotones, and the comparison between those of 85Y and 87Nb, are discussed.

In-beam study of the level structure of 122Te

The level structure of 122Te has been studied using the 120Sn(α, 2n) reaction at beam energies of 18 and 24 MeV. Standard in-beam γ-ray spectroscopy measurements of excitation functions, γγ-coincidences, and γ-ray angular distributions were performed. A level scheme up to 3995 keV in excitation was constructed and spin-parity values up to 12 + were assigned to almost all of the states. The identification of several new levels and the first in-beam observation of the excited 0 + state at 1357.4 keV are discussed. The low-lying excitations are examined in the context of coexisting structures of collective, single-particle, and particle-hole intruder excitations.

The high-spin structure of 202Po and 204Po and systematical features of the even polonium isotopes

The high-spin structure of 202,204Po was studied using the 196,198Pt(12C, 6n) and 204Pb(α, 4n) reactions at a beam energy of 100 and 52-54 MeV, respectively. In-beam conversion electron and γ-ray spectroscopy measurements including γγ(t) coincidence, γ(t) and angular distributions were performed. The level scheme of 202Po was extended to spin 21 h and the excitation energy 5.5 MeV while levels in 204Po were observed at 5.9 MeV with a spin of 20 h. The previously observed isomeres in 202Po and 204Po were confirmed and in addition to these a Jπ = 13− level with the half-life 9(3) ns was observed in 204Po at 3387.3 keV. The expected configuration of this state is πh9/22 ⊗ vf5/2-1 i13/2-1. A shell-model description of the observed excited states is given.

In-beam quadrupole interaction measurements by level mixing resonance

A new method to measure the quadrupole interaction of in-beam produced isomeric nuclear states is proposed. A simplified version of the theory, adapted to the particular experimental configuration of an in-beam experiment is described.

Residence sites of19F implants in carbon allotropes

Abstract The (p,p') reaction with a pulsed proton beam has been used in in-beam TDPAD measurements to excite and recoil implant 19F ions into various carbon allotropes (single and polycrystalline graphite and vitreous and colloidal carbon). Spin rotation R(t) spectra generated from delayed time spectra of the 19F 197 keV gamma ray show that the implants take up two characteristic residence sites in the host samples. One site is sharply defined (low spread δ), and has a quadrupole coupling frequency of vq = 57 MHz; the other, of lower vq , is more diffuse (large δ). The parameters of the electric field gradients at the two implant sites in the carbon allotropes are compared with similar measurements on 19F in diamond, Si and Ge hosts, and in several F-C compounds.

Low-spin and isomeric states in 198Pb

Low- and medium-spin states in 198Pb are studied using the reaction 198(3He, 3n) at laboratory energy 27.5 MeV. The in-beam measurements comprise γ-ray singles, γ-RF timing, γ-ray angular distributions and γ-γ coincidences. Seven new levels are located and assigned spins and parities. The previously reported lifetimes are unambiguously assigned: T1/2(5−) = 50.4 ± 0.5 ns, T1/2(7−) = 4.19 ± 0.10 μs and T1/2(9−) = 240 ± 15 ns. The corresponding transition rates B(λ) are deduced. The new non-yrast levels are compared to the existing systematics. A tentative excited (collective) band structure is proposed and compared to a similar one in 196Pb. Systematic trends in E1, E2 and E3 transition rates in light Pb isotopes are discussed.

Compton-suppression spectrometer for in-beam coincidence measurements and proposal for a detector configuration consisting of systems with a large solid angle

A γ-γ coincidence apparatus consisting of a Compton-suppression spectrometer with a large solid angle of 54 msr and a single Ge detector is described, and examples of experimental results obtained in in-beam spectroscopy of heavy-ion induced reactions are presented. Furthermore, a γ-γ coincidence Compton-suppression spectrometer consisting of three veto systems for three Ge-detectors is described. By using one integrated Compton-suppression shield consisting of a NaI(Tl) detector optimally divided into four parts for the Ge detectors, an extraordinarily large solid angle of 100 msr is obtained for each of Compton-suppression spectrometer. At the same time the total solid angle of the NaI(Tl) veto shield is minimized, which is the central problem when measuring γ cascades of high multiplicity.

A setup for spectrometry of high-energy conversion electrons

A conversion-electron spectrometer for in-beam measurements of up to 7–8 MeV electrons is described. The setup consists of a Siegbahn-Slätis type intermediate-image magnetic electron transporter combined with a cooled silicon or germanium detector.

In-beam investigations and structure studies of multiparticle excitations in the N = 82, 83 nuclei 138,139Ba

Abstract Excited states of 138Ba populated via the 136Xe(gas)(α, 2n) reaction have been studied by in-beam measurements of γγ-coincidences, excitation functions, angular distributions and the linear polarization of the γ-radiation as well as the γ-ray time distributions relative to the beam pulses and the Doppler shift of the γ-ray energy. The level scheme of 138138Ba could be extended by 10 new levels with spin values up to 12ħ and excitation energies up to 4864 keV. For the 71+, 81+, 101+ and 91− levels subnanosecond lifetimes have been determined, while for 5 further states upper limits of their lifetimes could be derived. Additionally, 4 new levels of 139Ba have been established which were populated via the (α, n) reaction channel. Among them the level at Ex = 1977 keV was found to be isomeric. The experimental data on excitation energies and electromagnetic properties of even-parity 138Ba levels are compared with predictions of the spherical shell model. Odd-parity states of 138Ba and 139Ba are interpreted in terms of a particle-core coupling approach which describes the coupling of one 1 h 11 2 proton and one 2 f 7 2 neutron, respectively, to π = + 1 shell-model states of the corresponding (A − 1) core nuclei. A rather good agreement between experiment and theory can be stated.

In-beam measurements of nuclear moments

Nuclear moments contribute valuable information to nuclear structure studies of nuclei under extreme conditions, such as nuclei at high angular momentum or far from stability. While the magnetic moment is sensitive to the nature of the participating nucleons (neutron or proton) the quadrupole moment is a direct measure for nuclear deformation.

The effect of iron on the radiation induced conductivity in gamma- and electron-irradiated MgO

Abstract In-beam measurements of the radiation induced conductivity in MgO have enabled one to separate the intrinsic from the impurity induced conductivity. The intrinsic conductivity varies directly with dose rate from < 103 to 109 rad h−1. The impurity sensitive conductivity is related to the iron content through the induced electron trapping centres.

Fission and particle evaporation following stopped-negative-pion absorption in 209Bi

Fission and particle evaporation following stopped- π − absorption were measured for 209Bi. The fission probability per captured π − was obtained as W f = (3.01 ± 0.34) × 10 −3 from the number of fission tracks observed in the mica track detector and that of π − stopped in the Bi target. The latter was derived from the observed absolute intensities of pionic Bi X-rays. The isotopic yield distributions for the ( π −, xn) and ( π −, pxn) reactions were also determined by in-beam and activation γ-ray measurements. From the analysis of the fission probability and the product-yield distribution, it was concluded that the thermally equilibrated nuclear states have a wide energy distribution and rather low excitation energies (∼50 MeV) compared to the initially involved energy of 140 MeV. A model was proposed for the formation and decay of 209Bi nuclei excited by the capture of the stopped π −. The model well reproduces the experimental results.