γ-ray emission probabilities of Os

Precise measurements of disintegration rates by using a 4πβ-γ coincidence apparatus have resulted in improved certainties of the principal γ-ray emission probabilities of ¹⁹³Os. Most of the uncertainties are less than 1%, whereas the uncertainties of emission probabilities evaluated in the Nuclear Data Sheets (83 (1998) 921) are more than 6%. The precision is improved for the β-ray branching ratio for direct transition to the ground state and the value is larger than the evaluated value by about 6%.     

An accurate redetermination of the Sn binding energy

The energy of well-known strong γ line from ¹⁹⁸Au, the “gold standard”, has been modified in the light of new adjustments in the fundamental constants and the value of 411.80176(12) keV was determined, which is 0.29 eV lower than the latest 1999 value. An energy calibration procedure for determining the neutron binding energy, B_n, from complicated (n, γ) spectra has been developed. A mathematically simple minimization function consisting only of terms having as parameters the coefficients of the energy calibration curve (polynomial) is used. A priori information about the relationships among the energies of different peaks on the spectrum is taken into account by a Monte-Carlo simulation. The procedure was used in obtaining B_n for ¹¹⁸Sn. The γ-ray spectrum from thermal neutron radiative capture by ¹¹⁷Sn has been measured on the IBR-2 pulsed reactor. γ-rays were detected by a 72 cm³ HPGe detector. For a better determination of B_n it was important to determine B_n for ⁶⁴Cu. This value was obtained from two γ-spectra. One spectrum was measured on the IBR-2 by the same detector. The other spectrum was measured with a pair spectrometer at the Brookhaven High Flux Beam Reactor. From these two spectra, B_n for ⁶⁴Cu was determined to be equal to 7915.52(8) keV. This result essentially differs from the previous value of 7915.96(11) keV. The mean value of the two most precise results of the B_n for ¹¹⁸Sn, was determined to be 9326.35(9) keV. The B_n for ⁵⁷Fe was determined to be 7646.08(9) keV.     

A detector for filtering γ-ray spectra from weak fusion–evaporation reactions out of strong background and for Doppler correction: The recoil filter detector, RFD

A detector has been designed and built to assist in-beam γ-ray spectroscopy with fusion–evaporation reactions. It measures with high efficiency the evaporation residues that recoil out of a thin target into the angular interval from 1.8° to 9.0° at an adjustable distance of 1000–1350 mm from a target, in coincidence with γ-rays detected in a Ge-detector array. This permits filtering of such γ-rays out of a much stronger background of other reaction products and scattered beam. Evaporation residues are identified by their time-of-flight and the pulse height using a pulsed beam. The velocity vector of the γ-emitting recoil is also measured in the event-by-event mode, facilitating to correct the registered γ-ray energy for the Doppler shift, with the resulting significant improvement of the energy resolution. The heavy-ion detection scheme uses emission of secondary electrons caused by the recoiling ions when hitting a thin foil. These electrons are then electrostatically accelerated and focused onto a small scintillator that measures the summed electron energy, which is proportional to the number of electrons. The detector is able to operate at high frequency of the order of 1 MHz and detect very heavy nuclei with as low kinetic energy as 5 MeV. The paper describes the properties of the detector and gives examples of measurements with the OSIRIS, GAREL+ and EUROBALL IV γ-ray spectrometers. The usefulness of the technique for spectroscopic investigations of nuclei with a continuous beam is also discussed.     

Thermal neutron cross-section and resonance integral for Dy(n,γ)Dy reaction

The thermal neutron cross-section (σ₀) and the resonance integral (I₀) of the reaction ¹⁶⁴Dy(n,γ)¹⁶⁵Dy were measured by the activation method, using ⁵⁵Mn(n,γ)⁵⁵Mn monitor reaction as a single comparator. The diluted MnO₂ and Dy₂O₃ powder samples within and without a cylindrical Cd shield case were irradiated in an isotropic neutron field obtained from the ²⁴¹Am–Be neutron sources, moderated with paraffin wax. The γ-ray spectra from the irradiated samples were measured by high-resolution γ-ray spectrometry with a calibrated n-type Ge detector. The necessary correction factors for γ-ray attenuation, thermal neutron and resonance neutron self-shielding effects and epithermal neutron spectrum shape factor () were taken into account in the determinations. The thermal neutron cross-section for ¹⁶⁴Dy(n,γ)¹⁶⁵Dy reaction studied has been determined to be 2672±104 b at 0.025 eV. This result has been obtained relative to the reference thermal neutron cross-section value of 13.3±0.1 b for the ⁵⁵Mn(n,γ)⁵⁶Mn reaction. For the thermal neutron cross-section, most of the experimental data and evaluated one in ENDF/B-VI, in general, are in good agreement with the present result. The resonance integral has also been measured relative to the reference value of 14.0±0.3 b for the ⁵⁵Mn(n,γ)⁵⁶Mn monitor reaction using a 1/E¹⁺ epithermal neutron spectrum of the ²⁴¹Am–Be neutron source. By defining Cd cut-off energy 0.55 eV, the resonance integral obtained was 527±89 b. The existing experimental and evaluated data for the resonance integral are distributed from 335 to 820 b. The present resonance integral value agrees with some previously reported values, 520 b by Holden, 505 b by Simonits et al. and 575±100 b by Heft, within the limits of error.     

Detection of γ-rays with a 3.5 l liquid xenon ionization chamber triggered by the primary scintillation light

A gridded ionization chamber with a drift length of 4.5 cm and a total volume of 3.5 l, was operated with high-purity liquid xenon and extensively tested with γ-rays from ¹³⁷Cs, ²²Na and ⁶⁰Co radioactive sources. An electron lifetime in excess of 1 ms was inferred from two independent measurements. The electric field dependence of the collected charge and energy resolution was studied in the range 0.1–4 kV/cm, for different γ-ray energies. With an electric field of 4 kV/cm, the spectral performance of the detector is consistent with an energy resolution of 5.9% at 1 MeV, scaling with energy as E^−0.5. The chamber was also used to detect the primary scintillation light produced by γ-ray interactions in liquid xenon. The light signal was successfully used to trigger the acquisition of the charge signal with a FADC readout. A trigger efficiency of 85% was measured at 662 keV.     

Studies of weak capture-γ-ray resonances via coincidence techniques

A method for measuring weak capture-γ-ray resonances via γγ-coincidence counting techniques is described. The coincidence apparatus consisted of a large-volume germanium detector and an annular NaI(Tl) crystal. The setup was tested by measuring the weak E_R=227 keV resonance in ²⁶Mg(p,γ)²⁷Al. Absolute germanium and NaI(Tl) counting efficiencies for a range of γ-ray energies and for different detector–target geometries are presented. Studies of the γ-ray background in our spectra are described. Compared to previous work, our method improves the detection sensitivity for weak capture-γ-ray resonances by a factor of ≈100. The usefulness of the present technique for investigations of interest to nuclear astrophysics is discussed.     

富集10B的Ce:Li6Lu(10BO3)3晶体生长及其闪烁性能

为了提高中子探测效率, 以富集¹⁰B的H₃¹⁰BO₃为原料, 通过提拉法生长了富集¹⁰B的Ce:Li₆Lu(¹⁰BO₃)₃晶体。X射线激发发射光谱测试表明: 其发光峰位于360~480 nm, 属于Ce³⁺离子典型的5d - 4f跃迁发光, 其闪烁发光效率为BGO晶体的3.9倍。在350 nm紫外光和¹³⁷Cs所发出的662 keV的γ射线激发下测得的衰减时间分别为21.0 ns 和31.7 ns, 在¹³⁷Cs辐射源激发下所测得的相对光输出是CsI(Tl)晶体的20%, 能量分辨率为9.7%。在慢化²⁵²Cf中子源激发下可以观测到明显的中子全能峰, 其能量分辨率为33%。上述研究结果表明, Ce:Li₆Lu(¹⁰BO₃)₃晶体具有较高的闪烁效率、快的衰减时间和良好的中子探测效率, 是一种具有应用前景的中子探测用闪烁晶体。     

γ-ray energies for calibration from the decay of Tb, Hf + Lu, and Am

The energies of a few γ-rays from 23 to 125 keV from the decay of the radioisotopes ¹⁶¹Tb, ¹⁷²Hf+ ¹⁷²Lu, and ²⁴¹Am have been determined. These energies were obtained from measurements of differences in the energies of closely spaced lines. The statistical components of the uncertainties of these energy differences range from 0.1 to 1.9 eV. Since it is a long-lived nuclide, these results should make ¹⁷²Hf, which has γ-rays from 23 to 125 keV, a useful energy calibration source. For ²⁴¹Am, our value of 59.5412(2) for this widely used line differs from the previously accepted value of 59.537(1) keV.     

Analysis of interface states and series resistance at MIS structure irradiated under Co γ-rays

In this research, we investigated the effect of ⁶⁰Co γ-ray exposure on the electrical properties of Au/SnO₂/n-Si (MIS) structures using current–voltage (I–V) measurements. The fabricated devices were exposed to γ-ray doses ranging from 0 to 300 kGy at a dose rate of 2.12 kGy h⁻¹ in water at room temperature. The density of interface states N_ss as a function of E_c–E_ss is deduced from the forward bias I–V data for each dose by taking into account the bias dependence effective barrier height and series resistance of device at room temperature. Experimental results show that the γ-irradiation gives rise to an increase in the zero bias barrier height Φ_BO, as the ideality factor n and N_ss decrease with increasing radiation dose. In addition, the values of series resistance were determined using Cheung's method. The R_s increases with increasing radiation dose. The results show that the main effect of the radiation is the generation of interface states with energy level within the forbidden band gap at the insulator/semiconductor interface.     

Color centers and charge state recharge in γ-irradiated Yb:YAP

Gamma-ray irradiation induced color centers and charge state recharge of impurity and doped ion in 10 at.% Yb:YAP have been studied. The change in the additional absorption (AA) spectra is mainly related to the charge exchange of the impurity Fe²⁺, Fe³⁺ and Yb³⁺ ions. Two impurity color center bands at 255 and 313 nm were attributed to Fe³⁺ and Fe²⁺ ions, respectively. The broad AA band centered at 385 nm may be associated with the cation vacancies and F-type center. The transition Yb³⁺ → Yb²⁺ takes place in the process of γ-irradiation. Oxygen annealing and γ-ray irradiation lead to an opposite effect on the absorption properties of the Yb:YAP crystal. In the air annealing process, the transition Fe²⁺ → Fe³⁺ and Yb²⁺ → Yb³⁺ take place and the color centers responsible for the 385 nm band was destroyed.     

A method for decomposition of hexachlorobenzene by gamma-alumina

A method of decomposing hexachlorobenzene (HCB) by γ-alumina was investigated at low temperature of 300 °C. It was found that HCB was rather quickly decomposed under such a condition. Decomposition efficiency (DE) increases with increasing the surface area of γ-alumina. Pretreated γ-alumina has a better performance for the decomposition reaction. A high decomposition efficiency within the short reactive time of 60 min was achieved to be 94.2%, which was obtained by preheating γ-alumina with the surface area of 220 m² g⁻¹ at 450 °C for 2 h. High surface area and appropriate pretreatment temperature probably provide more reactive sites such as the isolated OH groups and Al³⁺ sites surrounded by O²⁻ sites. These sites may induce the decomposition of HCB via a main ring-cracking process. The present study, hopefully, holds the promise for the eliminating of HCB contained hazardous materials in industrial application.     

Pyroelectric properties of BST/PLT composite thick films with addition of xPbO–(1 − x)B2O3 glass

The Ba_xSr_1−xTiO₃ (BST)/Pb_1−xLa_xTiO₃ (PLT) composite thick films (20 μm) with 12 mol% amount of xPbO–(1 − x)B₂O₃ glass additives (x = 0.2, 0.35, 0.5, 0.65 and 0.8) have been prepared by screen-printing the paste onto the alumina substrates with silver bottom electrode. X-ray diffraction (XRD), scanning electron microscope (SEM) and an impedance analyzer and an electrometer were used to analyze the phase structures, morphologies and dielectric and pyroelectric properties of the composite thick films, respectively. The wetting and infiltration of the liquid phase on the particles results in the densification of the composite thick films sintered at 750 °C. Nice porous structure formed in the composite thick films with xPbO–(1 − x)B₂O₃ glass as the PbO content (x) is 0.5 ≥ x ≥ 0.35, while dense structure formed in these thick films as the PbO content (x) is 0.8 ≥ x ≥ 0.65. The volatilization of the PbO in PLT and the interdiffusion between the PLT and the glass lead to the reduction of the c-axis of the PLT phase. The operating temperature range of our composite thick films is 0–200 °C. At room temperature (20 °C), the BST/PLT composite thick films with 0.35PbO–0.65B₂O₃ glass additives provided low heat capacity and good pyroelectric figure-of-merit because of their porous structure. The pyroelectric coefficient and figure-of-merit F_D are 364 μC/(m² K) and 14.3 μPa^−1/2, respectively. These good pyroelectric properties as well as being able to produce low-cost devices make this kind of thick films a promising candidate for high-performance pyroelectric applications.     

Effects of palladium on the thermal behavior of the γ1-phase of the Ag-Sn-Cu dental amalgam

Effects of the addition of 1 weight percent (w/o) palladium on the thermal behavior of a lathe-cut type of high copper amalgam (13 w/o copper) were studied. Two identical alloys, with and without 1 w/o palladium were fabricated. X-ray diffraction studies of these amalgams have revealed the elimination of the γ₂-phase by palladium addition. DSC thermograms of non-palladium-containing alloy indicated the existence of two γ₁-phases, one with the transition temperature at 88 °C and the other at 109 °C. Aging for 18 months at 37 °C cannot eliminate the presence of the γ₁-phase which has a low transition temperature. The addition of 1 w/o palladium into amalgam produced a more thermally stable amalgam.     

Excited levels in Po and Pb fed by β-decays of Bi (T1/2 = 45.6 min) and Tl (T1/2 = 2.2 min)

The γ-decay of radiochemically separated ²¹³Bi sources (T_1/2 = 45.6 min), in equilibrium with ²⁰⁹Tl (T_1/2 = 2.2 min) and ²¹³Po (T_1/2 = 4.2 μs), has been reinvestigated using coaxial HPGe detectors, a LEPS detector and the γ-γ coincidence method. The energies and intensities of 20 γ-lines were measured, of which 11 are reported for the first time. Of the ten γ-rays attributed to ²¹³Bi β-decay, five are new. All of them were interpreted in a ²¹³Po level scheme using γ-γ coincidence data. New levels at 292.8, 1003.6 and 1119.5 keV are proposed in ²¹³Po. In the ²⁰⁹Tl β-decay, five γ-lines were measured, two of which are new. On the basis of γ-γ coincidence, we suggest that two new levels of 3069.6 and 3388.9 keV are fed into the ²⁰⁹Pb magic nucleus.     

Sintering behavior and microwave dielectric properties of Bi3(Nb1−xTax)O7 solid solutions

Solid solutions of Bi₃(Nb_1−xTa_x)O₇ (x = 0.0, 0.3, 0.7, 1) were synthesized using solid state reaction method and their microwave dielectric properties were first reported. Pure phase of fluorite-type could be obtained after calcined at 700 °C (2 h)⁻¹ between 0 ≤ x ≤ 1 and Bi₃(Nb_1−xTa_x)O₇ ceramics could be well densified below 990 °C. As x increased from 0.0 to 1.0, saturated density of Bi₃(Nb_1−xTa_x)O₇ ceramics increased from 8.2 to 9.1 g cm⁻³, microwave permittivity decreased from 95 to 65 while Q_f values increasing from 230 to 560 GHz. Substitution of Ta for Nb modified temperature coefficient of resonant frequency τ_f from −113 ppm °C⁻¹ of Bi₃NbO₇ to −70 ppm °C⁻¹ of Bi₃TaO₇. Microwave permittivity, Q_f values and τ_f values were found to correlate strongly with the structure parameters of fluorite solid solutions and the correlation between them was discussed in detail. Considering the low densified temperature and good microwave dielectric proprieties, solid solutions of Bi₃(Nb_1−xTa_x)O₇ ceramics could be a good candidate for low temperature co-fired ceramics application.     

Investigation of CdTex and Cd1-xZnxTe Schottky Barrier Diode Structure Based γ-Ray Detectors

Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe) based detectors have been developed for hard X-ray and γ -ray detection. These semiconducting materials have high resistivity because of the wide bandgap and also have high photon absorption efficiency because of the large atomic number (Z_Cd = 48, Z_Te = 52). CdTe and CdZnTe substrates (7 mm × 9 mm × 0.5 mm) with different stoichiometry were taken for the fabrication of γ-ray detectors. The substrate was prepared by polishing the bulk crystals grown by the rotational Bridgman method. Crystals with maximum electrical resistivity were grown in this way. For fabrication of Schottky barrier diode structures, the Schottky contacts were made by electroless deposition for gold (Au) and thermal evaporation for Indium (In). The Au/CdTe/In and Au/CdZnTe/In Schottky barrier diodes were linked to the charge sensitive preamplifier by gold wires. Then, I-V measurement and detector efficiency like charge collection performance with energy resolutions were analyzed at room temperature by using ⁵⁷Co and ¹³⁷Cs gamma sources. The good energy resolutions of ⁵⁷Co (122 KeV) and ¹³⁷Cs (662 KeV) sources are obtained for both CdTe and CdZnTe diode detectors.     

A Fourier-based algorithm for modelling aberrations in HETE-2''s imaging system

The High-Energy Transient Explorer, launched in October 2000, is a satellite experiment dedicated to the study of γ-ray bursts in a very wide energy range from soft X-ray to γ-ray wavelengths. The intermediate X-ray range (2–30 keV) is covered by the Wide-field X-ray Monitor (WXM), a coded aperture imager. In this article, an algorithm for reconstructing the positions of γ-ray bursts is described, which is capable of correcting systematic aberrations to approximately 1′ throughout the field of view. Functionality and performance of this algorithm have been validated using data from Monte-Carlo simulations as well as from astrometric observations of the X-ray source Scorpius X-1.     

Structural properties of swift heavy ion beam irradiated Fe/Si bilayers

The Fe/Si multilayers were prepared by electron beam evaporation in a cryo-pumped vacuum deposition system. Ag⁺ and Au⁺ ions of 100 MeV at two different fluencies such as 1 × 10¹² ions/cm² and 1 × 10¹³ ions/cm² at a pressure of 10^− 7 torr were used to irradiate the Fe/Si samples. The irradiated samples were analyzed by High-Resolution XRD and it reveals that the irradiated films are having polycrystalline nature and it confirms the formation of the β-FeSi₂. The structural parameters such as crystallite size (D), strain (ε) and dislocation density (δ) have been evaluated from the XRD spectrum. The role of the substrates and the influence of swift heavy ions on the formation of β-FeSi₂ have been discussed in this paper.     

TRASMA, a detector for γ-charged particle coincidences

An apparatus for detecting light and heavy fragments, in coincidence with γ-rays is described. Its use is foreseen for studying heavy ion complete and incomplete fusion reactions at low and intermediate energy.

The ΔE-E and TOF techniques are used for charged particle identification at small angles using a combination of Si strip detectors and CsI(Tl) crystals. The γ-ray detection is performed by using a coverage of 9 clusters, each consisting of 7 BaF₂ crystals, similar to the TAPS configuration, resulting in a large solid angle and a high granularity. We report on recent results about the charged particle discrimination and the time and energy resolution for the whole detector. Initial tests were performed using ¹²C, ¹⁹F and ²⁸Si beams accelerated by the 15 MV tandem of the Laboratorio Nazionale del Sud in Catania.     

Sensitive method for the determination of F attached to aerosol particles in a PET centre

A new grab sampling method has been developed for the measurement of ¹⁸F attached to aerosol particles. It is based on direct β-counting of filtered aerosol sample over successive time intervals by an end-window Geiger–Müller counter. The effect of the progeny of radon and thoron on the β-counting rate is separated by analysing the decay curve. The defined solid angle absolute counting was used to evaluate the efficiencies for ¹⁸F and for the progeny of radon and thoron one by one. Absolute activity concentration of ¹⁸F can be determined with less than 10% systematic error. Glass-fibre filter and high sampling flow rate are applied, leading to a detection limit for ¹⁸F of less than 1 Bq m⁻³. The method was tested under different circumstances in the PET centre of University of Debrecen, Hungary.