In-beam γ-ray spectroscopy of 103Cd

Excited states of ¹⁰³Cd were studied in the reaction ⁵⁸Ni(⁵⁰Cr,4pn)¹⁰³Cd. The NORDBALL array with neutron and charged particle detectors was employed for the detection of γ rays and light evaporated particles. The level scheme of ¹⁰³Cd was significantly extended. A strong cascade of E2 transitions connecting negative parity states was found. Shell model calculations were performed and positive parity excited states were interpreted in terms of neutron-particle and proton-hole excitations with respect to the doubly magic N = Z = 50 core. The negative parity band was well reproduced by the total routhian surface calculations.     

In-beam γ-ray spectroscopy of 42Ca

High-spin states of the ⁴²Ca nucleus, populated in the 68 MeV ¹⁸O + ³⁰Si reaction, have been studied in a γ-γ-recoil coincidence experiment. The level scheme of ⁴²Ca has been extended up to 13.7 MeV. An elaborate decay pattern with various paths, together with high-quality DCO and polarization information assigns spins and parities for almost all observed levels. The sequence of non-yrast positive-parity states is discussed and compared with highly deformed bands in ³⁶Ar and ⁴⁰Ca. Received: 26 November 2002 / Accepted: 11 December 2002 / Published online: 18 February 2003 RID="a" ID="a"e-mail: Malgorzata.Lach@ifj.edu.pl RID="b" ID="b"Present address: TRIUMF, Vancouver, Canada. RID="†" ID="†"Deceased. Communicated by D. Schwalm     

In-beamγ-ray spectroscopy of the neutron deficient100Ag

The neutron deficient nucleus¹⁰⁰Ag, three proton holes below and three neutron particles above the N=Z=50 shell closure at¹⁰⁰Sn, has been identified and studied by in-beam spectroscopy. The reactions⁴⁶Ti(⁵⁸Ni,3pn) at 231 MeV and⁶⁴Zn(⁴⁰Ca,3pn) at 167 MeV of the respective⁵⁸Ni and⁴⁰Ca beams were used, and states up to 8.7 MeV excitation energy and spin I?20 were found in two mainγ-ray cascades forming band-like structures of even and odd parity. Large scale shell model calculations suggest predominantπg ₉ ^2/?3 ν(d_5/2,g_7/2)³ andπg ₉ ^2/?3 ν(d_5/2,g_7/2)²h_11/2 structures with maximum spins I ^π = 19⁺ and I ^π =22^?, respectively, for the two level sequences. The influence ofπp_1/2 vs.νh_11/2 excitations is discussed for low lying odd-parity levels.     

In-beam γ-ray Spectroscopy of Level Structure in ^134Ba

Excited states of ^134Ba, populated via the heavy-ion induced ^128Te(^10B, 1p3n)134Ba reaction at 46 MeV beam energy, have been studied to medium and high spins by in-beam γ-ray spectroscopy techniques. The experiment was performed at the tandem accelerator laboratory in the University of Tsukuba, Japan. The target is an isotopically enriched ^128Te metallic foil of 2.3mg/cm^2 thickness with a 3mg/cm^2 gold backing. Nine anti-Compton HPGe detectors were employed for the measurements of γ-γ-t coincidences. The level scheme of ^134Ba, deduced from this study, was shown in Fig.1.     

In-beam γ-spectroscopy with relativistic radioactive ion beams

This work demonstrates the feasibility of in-beam %-spectroscopy employing radioactive ion beam species at relativistic energies of E = 210 ~ 280 A · MeV. Neutron-rich nuclei below ⁴⁸Ca with neutron number between the two magic numbers 20 and 28 have been investigated. Using a Pb target, single step inelastic excitation originating mainly from Coulomb interaction takes place populating preferentially low-lying low-spin states and enabling the extraction of B(E2) values. On a C target, nucleon removal reactions are dominating and medium-spin states are populated thus offering spectroscopic information in neighboring nuclei. Cross sections of inelastic excitation are determined and compared to coupled-channels calculations. Two new states of the very neutron-rich nucleus ⁴⁴Ar at 1.78(8) MeV and 2.61(16) MeV are deduced from %-transitions.     

Probing the tilting mode in fission with γ-ray multiplicity techniques

The γ-ray multiplicities of the fragments from a number of ⁴He-induced fission reactions have been measured as a function of fragment emission angle. The value of M_γ is found to vary with angle in qualitative agreement with the predictions of statistical models of fission-fragment angular distributions. The observed variation is rather weak, on the order of 5%. The data are compared with several models. Calculations assuming a rigidly rotating, transition-state nucleus predict a much stronger angular dependence of the fragment spin than indicated by the data. The agreement is significantly improved if a fragment-spin enhancement effect is included in these calculations. The fragment spins are explored within the framework of the statistical scission model and the collective mode model. Both of these models predict large fragment spins and thus a relatively weak angular dependence of the total fragment spin. Neither model provides a completely satisfactory explanation of the data. Depending on the assumptions made in the calculations, the models either predict too strong an angular dependence of the total fragment spin or spins which seem incompatible with M_γ.     

Revisiting band structures in 118Xe nucleus via in-beam γ-ray spectroscopy

The neutron deficient Xe nuclei with A≈120 are predicted to have strong octupole correlation at low spins.In the present study,an attempt was made to improve upon the level scheme and also to examine the signatures of octupole correlation in ¹¹⁸Xe via high spin γ-ray spectroscopy.High spin states in ¹¹⁸Xe have been populated via the ⁹³Nb(²⁸Si,p2n)¹¹⁸Xe fusion-evaporation reaction at a beam energy of 115 MeV provided by the 15 UD pelletron ac...     

Photo-transmutation based on resonance γ-ray source

High intensity γ-ray source can be obtained through resonance reaction induced by protons. In this work, the possibility of using such high intensity MeV-range γ-ray source to transmute nuclear waste is investigated through Mont Carlo simulation.~(197) Au(γ, n)~(196)Au experiment is performed to obtain the transmutation rate and compared with the simulation result. If the current of the proton beam is 10 mA at the resonance energy of 441 keV, with the γ photons emitted from~7 Li(p, γ)~8 Be, then the corresponding transmutation yield for~(129)I in 2π direction can reach 9.4 × 10~9 per hour. The result is compared with that of LCS γ-ray source.     

In-beam M?ssbauer spectroscopy of 57 Mn implanted into lithium hydride

We measured the temperature dependence of ⁵⁷Fe M?ssbauer spectra obtained after ⁵⁷Mn implantation into polycrystalline LiH with an extremely low implantation dose. Density functional calculations suggested that the Fe atoms were predominantly implanted into both Li and H substitutional sites of the LiH crystal.     

On the origin of cosmic γ-ray bursts

As is well known, the distribution of the number of cosmic γ-ray bursts (CGBs) as a function of their duration has two maxima. In the present letter it is suggested that the longer-duration but less powerful CGBs arise when two neutron stars merge and a magnetic field is generated, as examined below, and the shorter-duration CGBs can arise as a result of collisions of a black hole either with a neutron star or another black hole. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 417–421 (10 October 1999)     

High energy γ-ray emission in heavy-ion collisions

We calculate double-differential cross sections for energetic photon production in intermediate energy nucleus-nucleus collisions. The production mechanism is assumed to be either that of collective bremsstrahlung or that of electromagnetic transitions between time-dependent single-particle states as emerging from a self-consistent treatment of the heavy-ion dynamics in the one-body limit (TDHF). Effects from residual nucleon-nucleon collisions on the collective current are further taken into account via a relaxation ansatz for the single-particle occupation numbers. The total yields for energetic photon production above 50 MeV in the simple limit considered indicate that up to 10% of the experimental cross sections can be attributed to collective bremsstrahlung and electromagnetic transitions.     

Pre-equilibrium γ-ray emission in dissipative heavy-ion collisions

-rays are measured in coincidence with the dissipative complex fragments from the³⁵Cl +⁶⁴Ni reaction at 7.7 A MeV. Theoretical -ray coincidence spectra are determined through a fitting procedure using the contribution of the excited fragment statistical -decay calculated by means of the CASCADE code. Whereas the expected statistical spectra fit very well the data in the energy regionE =2 to 8 MeV, above this energy another emission mechanism in addition to the statistical decay has to be considered in order to reproduce the experimental spectra. Simulations based on the Vlasov equation suggest that this emission could come from the decay of dipole strength excited in the intermediate dinuclear system.The authors are greatly indebted with A. Boiano, A. Buccheri, M. Cipriano, F. Pagano and R. Rocco for their assistance during the set up of the experimental apparatus. Dr. J. Girard and the technical staff of the CEA/DAPNIA-DPhN are acknowledged for the valuable operation of the accelerator.     

Laser wakefield electron acceleration for γ-ray radiography application

An electron beam is obtained using laser wakefield electron accelerator, and converted into a γ-ray source after undergoing bremsstrahlung radiation in a dense material. A quasi-monoenergetic structure is observed when the length of the plasma channel was modified. The structure has a 58-MeV peak energy, 15mrad (full-width at half-maximum) divergence angle, and 340-pC charge. The γ-ray source generated by this high-quality electron beam is brighter and has higher spatial and temporal resolutions than other conventional sources. A γ-ray radiography demonstrational experiment is performed. Pictures of a ball with different layers made of different materials are taken. The results show a clear structure and density resolution.     

Annealing of γ-ray irradiated lithium compensated p-type silicon

Abstract

Annealing behavior of electrical properties and photoluminescence spectra both at 77 °K in electron-irradiated melt-grown n-GaAs were investigated. Defects electrically active in the Hall mobility and carrier removal anneal through two stages centered at 250° and 460 °K. From the temperature dependence of carrier concentration the existence of a defect level located near 0.15 eV below the conduction band is supposed. Several emission bands are resolved at 1.51, 1.47, 1.415, 1.305 and ～1.2 eV in photoluminescence experiments. Electron irradiation (1.5–2.0 MeV) causes a remarkable decrease in emission intensity of 1.51 and ～1.2 eV bands. Recovery of emission intensity occurs remarkably when samples are annealed to 520 °K which would correspond to the 460 °K annealing stage for carrier concentration and Hall mobility. The 250 °K annealing stage is not observed in photoluminescence experiments. The 1.415 eV peak appears clearly after irradiation and grows remarkably with the 520 °K annealing, especially in Si-doped samples, resulting in large reverse annealing. This band is tentatively speculated to be a complex of Si on As site with As vacancy. Moreover, in samples doped with Te a new emission band at 1.305 eV (9500 Å) is observed after 470°–620 °K annealing.     

Tachyonic γ-ray bursts generated by nonlocal plasma currents

The dispersion relations of superluminal wave propagation in electron plasmas are derived, and the tachyonic energy flux, the velocity of energy transport, and the relaxation time asymptotics of the conductivity are studied. The formalism is based on Maxwell-type equations for Proca fields with negative mass-square in dispersive and dissipative media. Specifically, superluminal radiation fields generated by the ultra-relativistic electronic source plasma of γ-ray bursts (GRBs) are investigated. The radiation field is coupled to the shock-heated electron gas by a frequency-dependent fine-structure constant. The varying coupling constant generates long-range dispersion in the charge and current densities. At high energy, the coupling strength approaches a finite limit, so that the Proca field becomes minimally coupled to the electron current. The tachyonic fine-structure constant scales with the frequency-dependent superluminal velocity of the radiated modes. This scaling is manifested in the tachyonic flux densities of the GRB plasma, so that the scaling exponent can be extracted from spectral maps in the soft γ-ray band. To this end, tachyonic spectral fits of GRB 930506, GRB 950425, and GRB 910503 are performed. The scaling amplitude of the fine-structure constant is inferred from the burst duration. The transversal and longitudinal tachyonic luminosity of the source plasma is calculated in the high-temperature regime. Estimates of the plasma temperature and the internal energy of the ultra-relativistic electron gas are obtained.     

Radio waves and γ-ray emission from astrophysical sources

A mechanism of X- and γ-ray emission by relativistic electrons at interaction with astrophysical objects (maser clouds) is considered and the contribution of this mechanism to the formation of a continuous spectrum and its correlation with radio-wave radiation are investigated. The radiation yield upon deexcitation of a quantum system by an electron exceeds that of “conventional” (i.e., without a change in the quantum-system state) bremsstrahlung at small nuclear charges (Z < 10) and may be about 8% of the total γ-ray intensity. It is shown that in the direction in which the γ-ray intensity increases, one should observe radio waves corresponding to a particular maser source.     

The collective Lamb shift in nuclear γ-ray superradiance

The electromagnetic transitions of M?ssbauer nuclei provide almost ideal two-level systems to transfer quantum optical concepts into the regime of hard x-rays. If many identical atoms collectively interact with a resonant radiation field, one observes (quantum) optical properties that are strongly different from those of a single atom. The most prominent effect is the broadening of the resonance line known as collective enhancement, resulting from multiple scattering of real photons within the atomic ensemble. On the other hand, the exchange of virtual photons within the ensemble leads to a tiny energy shift of the resonance line, the collective Lamb shift, that remained experimentally elusive for a long time after its prediction. Here we illustrate how highly brilliant synchrotron radiation allows one to prepare superradiant states of excited M?ssbauer nuclei, an important condition for observation of the collective Lamb shift.     

Surface modification of UHMWPE with γ-ray radiation for improving interfacial bonding strength with bone cement (II)

The surface of ultra high molecular weight polyethylene (UHMWPE) was exposed to γ-ray for improving bonding strength to polymethylmethacrylate (PMMA) bone cement. Two types of irradiation methods, pre-irradiation and syn-irradiation, were engaged in this study. The intensity of irradiation was 5–30 kGy for pre-irradiation, and 1–3 kGy for syn-irradiation. The grafting process was performed in a glass ampule filled with methanol, MMA monomer (60 v%), FeSO₄ · 7H₂O (1.5 × 10⁻⁴ M) and H₂SO₄ (0.1 M). The graft rate of each specimen was measured with time variation. The grafting effect of the acrylates on to the UHMWPE surface was investigated by mechanical test for bonding strength. Pre-irradiation method showed thinner coverage PMMA graft on the surface of the UHMWPE and higher bonding strength than syn-irradiation method. The interfacial bonding strength between UHMWPE and PMMA bone cement was considerably improved by γ-ray irradiation method. For medical application, the pre-irradiation method might be recommended, because the PMMA could be grafted as optimized thickness to the UHMWPE surface.