Model independent Jπ assignments in 38Ar from γ-ray experiments in heavy-ion induced reactions

High-spin states of ³⁸Ar and ³⁵Cl have been investigated with the ²⁴Mg(¹⁶O, 2pγ)³⁸Ar and ²⁴Mg(¹⁶O, pαγ)³⁵Cl reactions at beam energies of 38 and 45 MeV. The experiments consisted of γ-γ coincidence, angular distribution and linear polarization measurements. A high-resolution large volume Ge(Li)-NaI(Tl) Compton-suppression spectrometer and a three-Ge(Li) Compton polarimeter were used. The analysis of the data, without assumptions about the reaction mechanism for the formation of the levels under study, is discussed. Unambiguous spin-parity assignments of J^π = 6⁺, 8⁺, and limitations of (5, 6, 7) and (7, 8⁺, 9) for the ³⁸Ar levels at E_x = 6408.3±0.2, 7609.3±0.3, 8012.9±0.3 and 10173.8±0.4 keV, respectively, are obtained. They are compared with results of shell-model calculations. Mixing ratios and spin-alignment attenuation factors for several transitions and levels in ³⁸Ar and ³⁵Cl are reported.     

Hyperfeinstrukturuntersuchungen mit einem sphärischen Fabry-Perot-Interferometer mit internem Absorptionsatomstrahl im Tm I- und Eu I-Spektrum

A spherical Fabry-Perot spectrometer with an absorbing atomic beam passing the interior of the interferometer is described. By use of the internal beam it is possible to reduce the amount of material needed for the atomic beam source to a few milligrams per hour. The set-up is especially suitable for hyperfine structure and isotope shift investigations. For the photoelectric recording of the signal the geometrical distance between the spherical mirrors was changed using the piezoelectric effect. In order to reduce the influence of the intensity distribution of the light sourceI ₀(λ) the ratio [I ₀(λ)-I(λ)]/I ₀(λ) was measured, whereI ₀(λ)=I ₀(λ) exp (—V·k(λ)·d) is the observed intensity with absorbing atoms between the mirrors, andV the increase of the absorption signal due to the multiple reflections of the light through the atomic beam (V≈75). For an accurate and easy evaluation of the data this ratio was measured by a digital voltmeter and punched into paper tape. The small line width of the absorption profile obtained in the experiments with Tm and Eu enabled us to measure hyperfine distances of the order of 5 · 10^?3 cm^?1 to 20 · 10^?3 cm^?1 with an error not exceeding 0.1 · 10^?3 cm^?1 in some cases. From the measurements theA-factors for five levels of the configurations 4f ¹³6s 6p and 4f ¹²5d 6s ² in Tm I and theA- andB-factors of the stable Eu isotopes of the 4f ⁷ 6s 6p y ⁸ P _5/2level in Eu I were determined.     

Observation of a new α-ray emitter:168W

Alpha-decay of¹⁶⁸W was identified in¹³⁶Ba(³⁶Ar, 4n) and¹⁴¹Pr(³²S, p4n) reactions. The α-ray energy was measured to be 4399 (12) keV. Using the intensity ratio of the simultaneously detected α-and 178.5 keV γ-rays, I_α/I_γ=4.1(6)·10^?5 the α-branching is discussed.     

Effective moment of inertia in132Ce,134Nd and136Nd

The effective moment of inertiaI _eff ⁽²⁾ of¹³²Ce,¹³⁴Nd and¹³⁶Nd produced in⁴⁰Ar induced reactions has been deduced from continuumγ-ray spectra measured by sum spectrometer methods. Results concerning the deformation of these nuclei are obtained by comparison of the experimental data and calculations in the frame of a cranking Nilsson — Strutinsky model.     

The mass and low-lying levels of 40Cl

The mass excess of the T_z = 3 nucleus ⁴⁰Cl has been determined using the ⁴⁰Ar(⁷Li, ⁷Be)⁴⁰Cl reaction. A value ?27.527 ± 0.035 MeV was obtained. A number of excited states of ⁴⁰Cl were a1so observed. In addition, the ⁴⁰Ar(¹¹B, ¹¹C)⁴⁰Cl and ⁴⁰Ar(¹¹B, ¹³N)³⁸S reactions were investigated. Excited states of ³⁸S were observed at 1.28 ± 0.04 and 3.38 ± 0.10 MeV.     

Investigation of the fragmentation of 20Ne and 40Ar ions at the COMBAS setup

Properties of the COMBAS fragment separator are compared with respective properties of similar setups. Results of experiments aimed at obtaining products of one-proton-stripping reactions induced by a beam of ⁴⁰Ar ions with an energy of 35 MeV/A and two-neutron-stripping reactions induced by a beam of ²⁰Ne ions with an energy of 52 MeV/A are presented. A high resolution of the fragment separator in obtaining secondary neutron-rich ³⁹Cl and neutron-deficient ¹⁸Ne ion beams is demonstrated.     

Widths of the 7.74 MeV analogue state in39K

The³⁸Ar(p, p)³⁸Ar and³⁸Ar(p, γ)³⁹K reactions have been investigated in the analogue resonance region at E_p=1.39 MeV. For the 7.74 MeV state of³⁹K branching ratios, unique spin and parity, \(J^\pi = \tfrac{3}{2} - \) , proton and total width, Γ_p=Γ=1.1±0.2 keV, have been determined.     

TheN=47 shell model nucleus90Tc

Lifetimes of high spin states in the nucleus⁹⁰Tc have been measured via the fusion evaporation reactions⁵⁸Ni(³⁶Ar,3pn)⁹⁰Tc at 140 MeV and⁵⁸Ni(³⁵Cl,2pn)⁹⁰Tc at 120 MeV beam energy. The OSIRIS spectrometer as well as a new neutron-γ-coincidence setup were used to measure lifetimes in the 10^?12-10^?9 s range by the recoil distance Doppler-shift method. By means ofγ-multiplicity and neutron-gated spectra fifteen lifetimes wered-educed. The experimental branching ratios and transition probabilities are compared to predictions of shell model calculations in a restricted π(p_1/2), π(g_9/2), ν(p_1/2), and ν(g_9/2) configuration space. In most cases the agreement with the calculations using the Gross-Frenkel parameters is striking but the results for several yrare states very sensitively depend on the residual interaction used.     

The influence of incidence angle on disorder production in Cl and Ar ion implanted Si

Abstract

Cl and Ar ions have been implanted, at 30 keV and at various incidence angles, into Si substrates maintained at room temperature during implantation. Implantation induced Si disorder was measured using RBS channelling. The effects upon disorder of various incidence angles were studied over a fluence range of 10¹²-6·10¹⁵ ions·cm^?2

The results show that, at low fluences Cl and Ar ion implantations generate a bimodal disorder-depth profile, whilst at higher fluences measurements of amorphised layer thickness as a function of ion incidence angle allow values of the standard deviation of the disorder profile parallel and transverse to the ion beam direction for each ion to be obtained with good agreement to theoretical predictions. The disorder-fluence behaviour under these conditions is ion species independent.     

ISOL beams of hafnium isotopes and isomers

The production of ISOL beams of hafnium is described. Radioactive Hf isotopes were produced at ISOLDE by 1.4 GeV proton-induced spallation in Ta and W foils. Chemical evaporation in form of HfF₄ and mass separation in the molecular sideband HfF₃⁺ after electron impact ionization provided intense and pure beams. Beams of ^158-185Hf and short-lived isomers down to 1.1 s ^177mHf were observed, but the method could be extended to reach even more exotic isotopes: down to about ¹⁵⁴Hf (N=82) on the neutron-deficient side and up to neutron-rich ¹⁸⁸Hf.     

Differential elastic and quenching cross sections for Ar*(3P) and CO2(X1 ∑ g +)

The energy dependence of the differential scattering of metastable Ar*(³P) by ground-state CO₂(X¹ ∑ _g ⁺) has been studied at relative kinetic energies from 58 to 126 meV over an angular range of 5–160° c.m. using crossed molecular beams. The position and curvature of rainbow maxima, which are observed at each energy, are used to obtain parameters for a Lennard-Jones (12, 6) spherically symmetric potential. The position of the minimum, r _m = 5·02 ± 0·65 Å, is identical to that for K + CO₂ and the well depth, ε = 16·3 ± 0·8 meV, is about 10 per cent greater. The scattered intensity shows a distinct fall-off on the dark side of the rainbow compared to that expected for elastically scattered Ar*. This depletion, caused primarily by the quenching of Ar*, is analysed in terms of the optical-shadow model to determine the energy dependence of the observed quenching cross section, which is predicted to have a maximum of 67 Ų at 193 meV.     

Emission Spectroscopic Investigation of the Decomposition of CCl4 in Plasma Etching Processes

The CCl₄ plasma decomposition and the etching of SiO₂ and Al by the CCl₄ plasma is investigated with the aid of emission intensity Iλ of such species as Cl₂, CCl, Cl and CO, which are influenced systematically by the etching process. A time independent electron density (n_e ≈ 2 · 10⁸ ?1 · 10¹⁰ cm^?3, dependent on plasma conditions) is measured by microwave diagnostics. The ratio Iλ/n_e and Iλ/I_reference' resp. (I_reference = I_Helium) is a relative measure of concentrations. The ratio I_cl2/I_ccl is very sensitive against CCl₄-decomposition and etching processes of SiO₂ and Al. Its changes during the etching process of SiO₂ and Al in a CCl₄ plasma are investigated.     

Formation of high-energy electron beams in gases of different densities

An investigation was made of the formation of beams of fast electrons in different gases at pressures of from 0.01 to 100 kPa. Plots were made of the dependences of the electron beam currents I_e on the gas pressure p for different electric field strengths E. The dependences I_e=f(p) for air were found to intersect the similar dependences for other gases (helium, nitrogen, neon, and argon) at a pressure of p=10.6 kPa and for E=2.3·10⁵ V·cm^–1. This fact is explained by the influence of the oxygen ions and atoms on the electron beam formation process. Another experimental result, the appearance of a minimum in the dependences I_e=f(p) for all gases, is explained by defocusing of the electron beam, the appearance of a reverse current, and magnetic neutralization of the beam. Electron beams were obtained having a pulse duration of 15–20 nsec and a current of 10⁵-10⁶ A/m² per unit cathode area.Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 67–70, June, 1993.     

Der Faraday-Effekt an amorphen Selenschichten

Cl^38m was produced by neutron activation of chlorine containing samples in a pneumatic irradiation facility. The decay of the Cl³⁸-isomer was investigated by various scintillation spectrometer technics. The half-life and the internal conversion coefficient α of the 0.66 MeV isomeric transition was found to beT _1/2=0.74±0.03 sec and α=(5.0±1.2)×10^?4. These data suggest aM-3 transition between an isomeric state with the spinI=5^? and the ground-state of Cl-38 (I=2^?).     

A facility for production and utilization of radioactive beams

A radioactive ion beam facility, GIRAFFE, has been built at the CIAE HI-13 Tandem accelerator. The facility makes use of the inverse kinematics. A D-Q-Q type magnetic separation and focusing system was used in the beam line. This simple device is expected to yield some radioactive ion beams(A<20) near the β-stability line with the acceptable intensities(10⁵–10⁶ pps). The ion beams of ⁷Be, ¹¹C and ¹⁷F were delivered, and the ⁷Be beam was applied for two experiments.     

Identification and structure of high spin particle-hole states in89Mo

Particle-γ andγ-coincidences of the reaction⁵⁸Ni(³⁶Ar, 4pn)⁸⁹Mo have been used to gain more information about high spin states in⁸⁹Mo and to establish the yrast sequence up to 7.6 MeV excitation energy and probable spin 37/2 ?. Spins and parities were assigned on the basis of DCO-ratios measured with the OSIRIS spectrometer and a large volume Ge detector placed at 162° to the beam. Furthermore, aγ-ray angular distribution experiment was carried out using the reaction⁵⁸Ni(³⁵Cl, 3pn)⁸⁹Mo. As in the neighboring isotopes⁸⁸Mo and⁹⁰Mo, the positive-parity high-spin states can be grouped into shell model multiplets characterized by increasing seniorities of proton particles and neutron holes in the 1g_9/2 shell. The negative-parity states can be explained with one nucleon moving in thep _1/2 orbit. The energies and wave functions of these states have been deduced by means of the shell model code RITSSCHIL. The 2584 keV (21/2⁺) is an isomeric state the mean life of which has been estimated from delayedγγ-coincidences.     

Intermolecular potential for Ar+D2O from differential cross sections

Differential cross sections for the scattering of D₂O (velocity selected beam) by Ar (nozzle beam) were measured at kinetic energies, ē, of 13·5 × 10^-14 erg? and 17·0 × 10^-14 erg by the crossed molecular beam technique. The distributions were compared with differential cross sections calculated from Lennard-Jones (12, 6) and Kihara-Stockmayer trial potentials to determine the potential parameters.     

Heavy ion beam polarization produced by the multi-tilted-foil interaction

Nuclear polarization of the 7/2^? ground-state of⁵¹V was produced via the Multi-Tilted-Foil (MTF) interaction with a V beam. The induced polarization was determined by measuring the left-right asymmetry of Coulomb excited⁵¹V nuclei and, for a⁵¹V beam at E=100 MeV, was measured to beP _I =0.012(2). The nuclear polarization was also induced atE=50 MeV and, after further acceleration, determined at E=195 MeV to be P_I=0.010(1). These experiments demonstrate the feasibility of polarizing a great variety of heavy-ion beams at arbitrary velocities with subsequent acceleration and passage through magnetic beam-optics elements. Such polarization, albeit small, can be utilized for the determination of electromagnetic moments of exotic beams and separated reaction products.     

High-intensity Si cluster ion emission from a silicon target bombarded with large Ar cluster ions

Secondary ions emitted from Si targets were measured with a quadrupole mass spectrometer under large Ar cluster and monomer ion bombardment. Incident ion beams with energies from 7.5 to 25 keV were used and the mean size of the Ar cluster ion was about 1000 atoms/cluster. Si_n⁺ ions with n values up to n = 8 were detected under Ar cluster ion bombardment, whereas Si cluster ions were scarcely detected under Ar monomer ion bombardment. These cluster ion yields showed the power law dependence on the cluster size.     

High-spin yrast levels of 38Ar

High-spin states of ³⁸Ar have been studied with the ³⁵Cl(α, pγ)³⁸Ar reaction at E_α = 18 MeV and with the ²⁴Mg(¹⁶O, 2pγ)³⁸Ar reaction at $\text{E(}{}^{16}\text{O}\text{) = 38}\text{and}\text{45}\text{MeV}$. The ³⁸Ar level scheme is obtained with the former reaction from a proton-γ coincidence measurement. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization experiments have been performed with a Ge(Li)-Na(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{= 7}{}^{\mathrm{?}}\text{, 7}{}^{\mathrm{+}}\text{, 8}{}^{\mathrm{+}}\text{, 7}{}^{\mathrm{?}}\text{, 9}{}^{\mathrm{?}}\text{and}\text{11}{}^{\mathrm{?}}$to the ³⁸Ar levels at E_x = 7.51, 8.08, 8.57, 8.97, 10.17 and 11.61 MeV, respectively, are obtained. The 8.57 MeV, 8⁺ level has a mean life below 0.8 ps. Excitation energies, branching ratios, multipole mixing ratios and transition strengths are reported. The experimental results are compared with shell-model calculations.