Implanted-fluorine depth profiles in silver gallium diselenide

Range distributions for fluorine ions in ¹⁹F⁺-implanted silver gallium diselenide (AgGaSe₂) in an energy range of 80–350 keV were measured by using the ¹⁹F(p, )¹⁶O resonant nuclear reaction at E_R=872.1 keV with width =4.2 keV. A proper convolution calculation method was used to extract the true distributions of fluorine from the experimental excitation-yield curves. The experimental range-distribution parameters, R_p and R_p, were compared with those obtained from Monte Carlo simulation codes. PACS 79.20.Rf; 66.30.Jt; 61.72.Ww     

Cross section and resonance strength measurements of 19F(p, αγ)16O at Ep= 200–800 keV

An excitation function of the ¹⁹F(p, αγ)¹⁶O reaction has been measured over the proton beam energy range E_p= 200–800 keV using a 4 π NaI summing spectrometer. A new resonance was found at E_R= 237 keV and its properties Γ_R, σ_R and ωγ have been extracted. The strengths of all resonances at E_p= 200–800 keV have been also extracted. The importance of the 1⁺ resonance at E_R= 11 keV is discussed and its width has been estimated taking into account interference effects with the strong 1⁺ resonance at E_R= 340 keV. The reaction rates have been calculated over a wide range of temperatures and compared with the rates of the (p, α₀) and (p, α_π) branches of the ¹⁹F(p, α)¹⁶O reaction. Received: 21 June 1999 / Revised version: 30 September 1999     

Study of range distribution parameters for bismuth-ion implantation in silver gallium diselenide

Range distributions for bismuth ions implanted in AgGaSe₂ in the energy range 80–300 keV were investigated by using 2.1-MeV He²⁺ Rutherford backscattering spectrometry (RBS). A convolution calculation method was used to extract the true distributions of bismuth from the measured RBS spectra. The range distribution parameters, R_p and ΔR_p, were obtained and compared with those obtained from Monte Carlo simulation. The experimental R_p values agree with the Monte Carlo simulation values very well, but the experimental ΔR_p values are systematically larger than those from the theoretical simulation. Received: 28 January 2002 / Accepted: 11 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-531/856-5167, E-mail: xdliu@sdu.edu.cn     

A new level at 192.5 keV in Ge

In the experiments on ⁷⁴Ge(d, pγ)⁷⁵Ge, a 52.5±0.1 keV γ-ray was found in ⁷⁵Ge with a half-life of 216±5 ns. From the analysis of the γ-ray spectra the conversion coefficient of the 52.5 keV γ-ray was determined. Then, a new level of is confirmed to exist at 192.5 keV. The reduced transition probabilities of the 52.5 keV transition are deduced to be (6.9^+5.6 _−2.1) × 10⁻⁵ for B(M1) and 31⁺³ ₋₂ for B(E2) in Weisskopf units.     

Nuclear orientation study of the decay of204BiFe

The decay of²⁰⁴Bi nuclei (I =6⁺, T_1/2=11·22 h) oriented in an iron host was investigated on the JINR low-temperature nuclear orientation facility SPIN. The orientation parameterB ₂=1·17 (6) was obtained from the analysis of six prominent E1 gamma-transitions. From the measured normalized intensities of the gamma-rays observed some 70 values of multipole mixing ratios for the gamma-transitions in²⁰⁴Pb nucleus were determined for the first time. The spins 6, 6, 5 and 4 could be uniquely assigned to the²⁰⁴Pb negative parity levels at 3891·5 keV, 3768·4 keV, 3301·5 keV and 2338·2 keV, respectively. The spin-parity assignments of the levels at 4183·8 keV, 4094·2 keV, 3782·0 keV, 2506·9 keV and 2065·1 keV were confirmed as 6^–, 6^–, 5^–, 5^– and 5⁺, respectively. For the level at 3105·1 keV spin-parity 5^– was suggested and spinparity 7^– of the level at 2696·4 keV was called in question. The possible placements of the gammatransitions 3 1351·7 keV and 1353·4 keV in the decay scheme is discussed. The reorientation parameters for the long-living levels at 2264·2 keV (T _1/2=0·45 s) and 1273·9 keV (T _1/2= =265 ns) were determined asG ₂=0·41 (14) andG ₂=0·60 (17), respectively. For the isomeric level at 2185·7 keV (T _1/2=67·2 min) the value ofG ₂=0·88 (49) was proposed.The authors would like to express their thanks to T. I. Kracíková and M. Trhlík for the valuable discussions in the course of the evaluation of the experimental data.     

Gamma-ray spectroscopy of Cr

A study of low-lying states in the self-conjugate nucleus ⁴⁸Cr has been performed with the reaction ⁴⁰Ca(¹⁰B, pnγ)⁴⁸Cr. Several techniques of γ-ray spectroscopy have been used: activity measurements, γ-ray angular distributions, γ-γ coincidences, p-n-γ triple coincidences, and recoil-distance lifetime measurements. The following level energies, spin-parity assignments, and lifetimes have been found: 752.4±0.5 keV, 2₁⁺, τ_m = 9.7±2.6 ps; 1858.7±0.7 keV, 4₁⁺, τ_m = 1.5_−0.5^+2.0 ps; 3532.7±1.2 keV, (6₁⁺); 4064.3±1.3 keV, ( 4), τ_m < 60 ps. The 2₁⁺ state in ⁴⁸Cr is found to have the lowest excitation energy and highest E2 transition strength (33±9 W.u.) among the 2₁⁺ states of even nuclei in the 1f shell.     

E2 polarization charge in Sn

The nucleus ¹⁰²Sn, which is the lightest Sn isotope with known excited states, was investigated with the ⁵⁰Cr(⁵⁸Ni,α2n) reaction using delayed in-beam γ-ray and conversion-electron spectroscopy. The experimental setup was designed to study the decay of μs-long isomeric states by placing γ-ray and electron detectors behind the focal plane of the Fragment Mass Analyzer at the Argonne National Laboratory. A 44 keV conversion-electron line corresponding to the (6⁺)→(4⁺) transition in ¹⁰²Sn was identified and a half-life of 0.62^+0.43_−0.19 μs was measured for the (6⁺) state. From the available experimental information neutron effective charges from 1.6 to 2.3 e were deduced, based on the comparison with different shell-model calculations.     

An investigation of range distribution parameters of implanted 19F ions in Au,Ag and Cu noble metals

Depth profiles of fluorine implanted in gold, silver and copper metal have been accurately measured using the ¹⁹F(p,αγ)¹⁶O resonance nuclear reaction at E_R = 872.1 keV. A proper deconvolution calculation method was used to extract the depth profile of fluorine from the experimental excitation yield curves. The range parameters, R_p, ΔR_p, and SK obtained in this work were compared with the theoretical calculations. The comparison shows that for all materials studied here the experimental R_p values are in good agreement with the results obtained by the TRIM96 code, while the experimental range stragglings, ΔR_p, are systematically larger than the TRIM simulation results.     

() reaction studies of Dy and Hf

Angular distributions for the ¹⁶³Dy(t,p) and ¹⁷⁷Hf(t,p) reactions were measured using 17 MeV tritons from the McMaster University Tandem Van de Graaff accelerator. Reaction products were analyzed with a magnetic spectrograph and detected with photographic emulsions. Favored L=0 transitions confirmed assignments of the 5/2⁻[523] band in ¹⁶⁵Dy and 7/2⁻[514] band in ¹⁷⁹Hf. Additional L=0 transitions in each nuclide identified previously unknown 5/2⁻ levels in ¹⁶⁵Dy and 7/2⁻ ones in ¹⁷⁹Hf. Overall trends of L=0 strengths support the existence of subshell closures at neutron numbers 98 and 108. On the basis of a relatively strong L=2 transition, the K^π=11/2⁻ γ-vibration based on the 7/2⁻[514] state is identified at 1689 keV in ¹⁷⁹Hf, about 440 keV above its previously-assigned K^π=3/2⁻ partner.     

The K<Superscript>-</Superscript>α scattering length and the reaction dd↦αK<Superscript>+</Superscript>K<Superscript>-</Superscript>

We present predictions for the K^-α scattering length obtained within the framework of the multiple-scattering approach. Evaluating the pole position of the K^-α scattering amplitude within the zero-range approximation, we find a loosely bound K^-α state with a binding energy of E_R = - 2,..., - 7 MeV and a width Γ_R = 11,..., 18 MeV. We propose to measure the K^-α scattering length through the final-state interaction between the α and K^--meson produced in the reaction dd↦αK⁺K^-. It is found that the K^-α invariant-mass distribution from this reaction at energies near the threshold provides a new tool to determine the s-wave K^-α scattering length.     

Isoscalar quadrupole strength in Ca from the (p,p′α0) reaction at Ep = 100 MeV

The ⁴⁰Ca(p,p′ α) reaction has been studied at an incident proton energy E_p = 99.5 MeV for proton laboratory scattering angles Θ_p^lab = 17°, 23° and 27°. Emission of α particles coincident with the scattered proton has been measured for an angular range Θ_α 0° − 180° relative to the recoil axis. A multipole decomposition for the α₀-decay channel to the ³⁶Ar ground state has been performed from the angular-correlation functions. The energy distribution of the dominating E2 strength deduced in the excitation energy range E_x = 11–21 MeV agrees reasonably well with the results from electron and α-induced α₀-decay investigations. The exhaustion of the E2 energy-weighted sum rule in this channel up to an energy of 17 MeV is 16.1(4.0)%, in accord with the study of the (α, α′ α₀) reaction. However, this value is twice what is found in the (e,e′ α₀) experiment in the same energy region. Thus, the puzzling discrepancy in the E2 strengths derived from electromagnetic and hadronic probes remains unsolved.     

Interpretation of experimental data near λ-transition point in liquid helium

The recently published experimental data for specific heat C_p of liquid helium in zero gravity conditions very close to the λ–transition have been discussed. We have shown that these data allow different interpretations. They can be well interpreted within the perturbative RG approach and within our recently developed theory, as well. Allowing the logarithmic correction, the corresponding fits lie almost on top of each other over the whole range of the reduced temperatures t (for bin averaged data) 6.3 ×10^-10 < t < 8.8 ×10^-3. However, the plot of the effective exponent α _eff(t) suggests that the behaviour of C_p, probably, changes very close to T_λ. To clarify this question, we need more accurate data for t<10^-7. In addition, we show that the experimental data for superfluid fraction of liquid helium close to T_λ within t ∈[3 ×10^-7;10^-4] can be better fit by our exponents ν=9/13 ≃0.6923, Δ=5/13 ≃0.3846 than by the RG exponents ν≃0.6705 and Δ≃0.5. The latter ones are preferable to fit the whole measured range t ∈[3 ×10^-7;10^-2] where, however, remarkable systematic deviations appear. Our estimated value 0.694 ±0.017 of the asymptotic exponent ν well agrees with the theoretical prediction ν=9/13.     

The sub-micrometer thickness n-InSb/i-GaAs epilayers for magnetoresistor applications at room temperatures of operation

Magnetotransport at fields up to 500 mT and LF-noise characteristics are reported for miniature magnetoresistors with ferrite concentrators based on Sn-doped n-InSb/i-GaAs heterostructures grown by MBE. The thickness of the InSb epilayers lie in the range 0.55–1.5 μm giving room temperature mobilities of 2.5–5.5 m² V⁻¹ s⁻¹ with carrier densities of (0.5–1.5)×10¹⁷ cm⁻³. The room temperature magnetoresistance (MR) for our two terminal devices could be as high as 115% at 50 mT which is comparable to the extraordinary MR (ExMR) recently reported in microscopic composite van der Pauw disks four terminal devices [Science 289 (2000) 1530]. In addition, a high signal-to-noise ratio and a good temperature stability of R(B)/R₀=0.5–0.83% K⁻¹ was observed for B<60 mT (below the saturation field B_sat for ferrite). Device resistance stability R₀(T) was equal to 0.27–0.66% K⁻¹ in zero field with a nominal device resistance R₀=197–224 Ω for DC currents in the range I=0.01–1.0 mA. The minimum detectable magnetic field is estimated from the reduced differential MR (∂R/∂B)/R=2000% T⁻¹ at B=31 mT and normalised 1/f current noise power spectral density measured at the same field. The resolution limit B_min=2.6 nT at 10² Hz and B_min=0.82 nT at 10³ Hz. These resolution limits are seven times better than those recently reported for the same material n-InSb/i-GaAs and ferrite fabricated Hall sensors [Magnetotransport and Raman characterization of n-InSb/i-GaAs epilayers, for Hall sensors applications over extremely wide ranges of temperature and magnetic field, Proceedings NGS 10, IPAP Conference Series 2, IPAP, Tokyo, 2001, pp. 151–154].     

The measurement of R2, and R2′ in HIV-infected patients using the prime sequence as a measure of brain iron deposition

Brain iron deposition was assessed at 1.5 T in the caudate nucleus, globus pallidus and frontal and parietooccipital white matter in 28 human immunodeficiency virus (HIV)-infected patients and 15 control subjects with a new Partially Refocussed Interleaved Multi-Echo sequence by measuring 1/T₂, 1/T₂^* and 1/T2′ (i.e., R₂, and R₂′). There were significant differences in the R₂ and of the caudate nucleus (p < 0.0001 and p < 0.05) and the R₂, and R₂′ of the globus pallidus (p < 0.001, p < 0.005 and p < 0.05) in HIV-infected patients compared to control subjects. There was a trend for higher values of R₂, and R₂′ in the globus pallidus and caudate nucleus in HIV-infected patients with later stage HIV disease. These results suggest that there is greater iron deposition in the basal ganglia of HIV-infected patients compared with control subjects, with a predilection for the globus pallidus. The relationship between iron deposition in the brain and various parameters of severity of HIV infection remains uncertain.     

Further observations on the variation with dielectric constant and thickness of the reflectance and phase change on reflection of films

Studies of the behaviour with ₁, ₂ and film thickness of the optical functions reflectance (R) and phase change on reflection (Φ_r) have previously been made for both very thin and very thick films. Abelès [J. Opt. Soc. Amer. 47 (1957) 473] has formulated equations for very thin films where functions of ₁ and ₂ are the coefficients of a power series of the optical thickness, x(2πd/λ) up to x², whilst in the case of very thick films (solids) the relationships between ₁ and ₂ can be represented in polar coordinates L and α by ₁=L cos α, ₂=L sin α where L_R=2y²₀W²(1+cos α−1/W²) [W=(1+R)/(1−R)] and L_Φr=2(y₀/ tan Φ_r)²(1−cos α+tan ² Φ_r) [Ward, Opt. and Laser Tech. 27 (1995) 125]. The present study is concerned with films of intermediate optical thicknesses (1.0<2πd/λ<solid) and has revealed that the polar-type relationships previously noted for solid materials are augmented by secondary structures of maxima and minima whose position and amplitude can be predicted by adapting the exact equations for R and Φ_r.     

A methodology to optimize the quantification of sp carbon fraction from K edge EELS spectra

A methodology is presented to select a consistent method, using electron energy loss spectroscopy (EELS), to extract the fraction of sp²-bonded carbon atoms in carbonaceous materials. According to this methodology, a reliable method has to conjointly fulfill two criteria. The first one consists in verifying, on a perfect graphite sample, that the experimental evolution of R = I_π*/(I_π* + I_σ*)-ratios is in good agreement with the one theoretically predicted as a function of experimental settings. The second criterion consists in measuring sp² fractions in amorphous carbon samples with a minimum of fluctuation. We test three commonly used R-extraction techniques, and we show that they exhibit some failures. We thus implement a more accurate R-extraction process that accounts for the predicted graphite R-evolution and exhibits a low intrinsic 4%-noise, as determined from the sp² fraction fluctuation. Moreover, we check the transferability of our method on a wide range of EELS spectra, acquired with different experimental resolutions on samples exhibiting various sp² contents.     

The gamma decay of analogue states in61Cu

Resonances in the reaction⁶⁰Ni(p, γ)⁶¹Cu have been studied in the proton energy rangesE _p=1840–1880 keV and 2220–2300 keV. Decay schemes and branching ratios have been determined for a number of resonances, three of which are identified as analogue fragments of the 283 keV (1/2^?) and 656 keV (3/2^?) states in⁶¹Ni. The split analogue components of the 283 keV state atE _x≈6.6 MeV are seen to decay significantly to a group of states in the region of excitation 3–4 MeV. Gamma ray angular distributions yield the following resonance spins:E _p=2248 keV,J=3/2;E _p=2263 keV,J=5/2. Also, the⁶¹Cu ground stateβ ⁺ decay to parent levels in⁶¹Ni has been compared to the respective analogue stateM1 gamma decay to the⁶¹Cu ground state.     

Experimental search for solar axions

A new technique has been used to search for solar axions using a single crystal germanium detector. It exploits the coherent conversion of axions into photons when their angle of incidence satisfies a Bragg condition with a crystalline plane. The analysis of approximately 1.94 kg.yr of data from the 1 kg DEMOS detector in Sierra Grande, Argentina, yields a new laboratory bound on axion-photon coupling of g_αγγ < 2.7 × 10⁻⁹GeV⁻¹, independent of axion mass up to 1 keV.     

Angular distribution measurements of gamma-rays from the22Ne(p, γ)23Na reaction

Angular distribution measurements of gamma-rays from the²²Ne(p, γ)²³Na reaction on theE _p =897, 1006, 1091 and 1278 keV resonances have been made. Spin and parity assignments for several bound states are presented together with multipole mixing ratios for transitions from resonance and bound states. The level at 6617 keV (7/2⁺) is proposed to be a member of the rotational band based on the Nilsson orbit 5(K ^π=5/2⁺).     

Al Chemical Shielding Anisotropy

Accurate values for the²⁷Al chemical shielding anisotropy (CSA) are reported for sapphire (α-Al₂O₃). The values (δ_σ= −17.3 ± 0.6 ppm, η_σ= 0.03 ± 0.06) are obtained from single-crystal²⁷Al NMR and appear to be the first convincing determination of an²⁷Al CSA.