Absorption line narrowing (A.L.N.) in a three-level system of neon under interaction with two quasi-resonant lasers

We report the observation of Absorption Line Narrowing (A.L.N.) in a Doppler-broadened three-level system of neon under interaction with two quasi-resonant single-mode lasers. The resonance signals are obtained with the laser beams propagating either in the same direction or in opposite direction. The resonance width is found to be smaller in the latter case. The isotopic shifts ²²Ne-²⁰Ne of the lines λ = 1.15μ, λ = 6096 Å and λ = 5945 Å have been measured using the A.L.N. method.     

Nuclear reactions of astrophysical interest with radioactive beams

The ARENAS³ facility, coupling the two cyclotrons of Louvain-la-Neuve, is intensively been used over the past years for cross-section measurements of nuclear reactions of astrophysical interest. We will describe the characteristics of the available beams and the experiments going on using these beams. The ¹⁹Ne(p,γ)²⁰Na reaction, of considerable importance for the reaction flow between the CNO and the NeNa mass region in high-temperature hydrogen burning conditions, will be discussed in particular. The proposed low-energy resonance at 0.447 MeV has been measured in inverse kinematics using novel activation techniques. An upper limit (90% C.L.) of 18 meV is obtained for the strength of this first particle-unbound state of ²⁰Na together with preliminary values for the strength of the higher excited states.     

Inelastic scattering of20Ne and12C on58Ni and the three-body continuum

Using beams of²⁰Ne at 291 and 392 MeV and¹²C at 300 MeV the inelastic excitation of collective modes in⁵⁸Ni has been studied with a Q3D magnetic spectrometer. In the analysis different contributions are unfolded from the spectra:1. single lines,2. the inelastic continuum,3. the three-body continuum, which mainly originates from one-nucleon pick-up to unbound states followed by the nucleon emission. Special care was taken to calculate the spectral shape and strength of this process. The population of unbound²¹Ne-states is measured in a neutron-²⁰Ne coincidence experiment. Coupled channel calculations have been performed to extract the deformation parameters for the inelastic states, including mutual excitation. For the giant quadrupole resonance 70 % of the energy weighted sum rule is found. The excitation of higher multipoles is calculated and extrapolated to higher incident energies (50 MeV/u). The importance of the in-elastic excitation as a “doorway process” to more complex interactions is discussed. It is found that especially the excitation of the projectile (²⁰Ne) takes a large fraction (20–50 %) of the incoming flux in the first step.     

16O(α,γ)20Ne反应的实验研究

讨论了目前16O(α ,γ) 2 0 Ne反应的实验研究工作 ,并对2 0 Na β+—→2 0 N →16O +α的β+ 缓发衰变α能谱的相对强度值同文献进行了比较 ,讨论了低能激发能级、共振强度及其对共振截面的贡献、S因子的理论研究.The experimental investigations of 16 O(α,γ) 20 Ne reaction is reviewed. The energy spectrum of β + delay α decay were measured through the 20 Naβ +-→ 20 Ne *→ 16 O+α process, and the relative densities of α decays are compared with the reference s results. The low excitation energy levels, resonance strength and its contribution to the resonance crosses section are also discussed. Finally, we have calculated the reaction rate of the direct capture reaction.......     

Study of nuclear reactions with radioactive 17F at HRIBF

Radioactive ¹⁷F beams were produced at the Holifield Radioactive Ion Beam Facility (HRIBF) using the Isotope Separator On-Line (ISOL) technique. Two of the experiments using accelerated ¹⁷F beams to study reaction mechanisms are presented: the simultaneous emission of two protons from a resonance in ¹⁸Ne and the breakup of ¹⁷F by ²⁰⁸Pb.     

Decay of a Resonance in 18Ne by the Simultaneous Emission of Two Protons

Radioactive ion beams of 17F were used to study several resonance states in 18Ne. Clear evidence for simultaneous two-proton emission from the 6.15 MeV state (Jpi = 1(-)) in 18Ne has been observed with the reaction 17F+1H. Because of limited angular coverage, the data did not differentiate between the two possible mechanisms of simultaneous decay, diproton (2He) emission or direct three-body decay. The two-proton partial width was found to be 21+/-3 eV assuming 2He emission and 57+/-6 eV assuming three-body decay. The total width of the 1(-) state was measured to be 50+/-5 keV. Several additional resonances that decay by single proton emission were also studied.     

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.     

Helium, neon and argon diffraction from Ru(0001)

We present an experimental and theoretical study of He, Ne and Ar diffraction from the Ru(0001) surface. Close-coupling calculations were performed to estimate the corrugation function and the potential well depth in the atom-surface interaction in all three cases. DFT (density functional theory) calculations, including van der Waals dispersion forces, were used to validate the close-coupling results and to further analyze the experimental results. Our DFT calculations indicate that, in the incident energy range 20-150?meV, anticorrugating effects are present in the case of He and Ar diffraction, whereas normal corrugation is observed with Ne beams.     

TheP +19Nes- wave resonant state in20Na at stellar energies

The first excited state above the p +¹⁹Ne threshold in²⁰Na has been identified at 2.637 MeV (± 15 keV) with J^π=0⁺ or 1⁺ from the²⁰Ne(³He, t)²⁰Na reaction, suggesting this state to be the s-wave resonance in the p +¹⁹Ne scattering at stellar energies.     

Experimental evidence of (2)He decay from (18)Ne excited states

Two-proton decay from (18)Ne excited states has been studied by complete kinematical reconstruction of the decay products. The (18)Ne nucleus has been produced as a radioactive beam by (20)Ne primary projectile fragmentation at 45 AMeV incident energy on a Be target. The (18)Ne at 33 AMeV incident energy has been excited via Coulomb excitation on a (nat)Pb target. The obtained results unambiguously show that the 6.15 MeV (18)Ne state two-proton decay proceeds through a (2)He diproton resonance (31%) and democratic or virtual sequential decay (69%). The quoted branching ratio has been deduced from relative angle and momentum correlations of the emitted proton pairs.     

20Ne(p,p0)20Ne and states of 21Na

Cross-section and analyzing power angular distributions have been measured for ²⁰Ne(p, p)²⁰Ne and ²⁰Ne(p, p₁)²⁰Ne¹(1.63 MeV) for proton energies between 3.7 and 7.9 MeV. The measurements were made in 25 keV intervals between 3.7 and 4.4 MeV, and in 10 keV intervals over most of the region between 4.4 and 7.9 MeV. A phase-shift analysis of the elastic-scattering data has yielded resonance parameters for thirty-three levels in ²¹Na in the excitation energy region 6.0–9.9 MeV. Some of the strong even-parity resonances can be understood within the framework of the Nilsson model or the shell model. These resonances are also predicted by a macroscopic coupled-channels calculation involving rotational excitation of the 2⁺ and 4⁺ states of ²⁰Ne.     

Giant resonance decays in 20Ne, 22Ne and interference effects with quasifree scattering processes

The charged particle (c) decay from excited states up to the giant quadrupole resonance (GQR) in ²⁰Ne has been studied in a kinematically complete ²⁰Ne(α, α′ c) coincident experiment at E_α = 155 MeV. Angular correlation functions and branching ratios are extracted for the α₀, α₁ and p₀ decay channels. The (α, α′ α₀) angular correlation functions are analysed in PWBA in terms of coherent interference with the quasifree scattering process leading to the same final states. Good fits to the data are achieved over a large range of excitation energies. Branching ratios have been extracted and compared to results of Hauser-Feshbach calculations. Above E_x = 12.5 MeV excitation energy a discrepancy was found between the experimentally observed α₀ branching ratios and the HF predictions. These results yield evidence for a direct α₀ decay mechanism of the split isoscalar giant quadrupole resonance in ²⁰Ne. Some results are presented also for a ²²Ne(α, α′ c) coincidence experiment. Qualitative comparison has been made between the general decay behaviour of the two Ne isotopes.     

HIRFL辐照终端照射野均匀度与离子通量的关系

采用固体核径迹探测器聚碳酸脂膜,测定了兰州重离子研究装置提供的55MeV/u40Ar和80MeV/u20Ne离子束经辐照终端束流均匀化扫描装置后照射野均匀度与离子通量之间的关系.结果表明:对于40Ar和20Ne离子束,离子通量小于1×106和2×107ions/cm2时,横向照射野均匀度缓Ne离子束照射慢增加;当离子通量分别介于1×106—1×107和2×107—1×108ions/cm2时,40Ar和20野均匀度逐渐增加;离子通量达到1×107和1×108ions/cm2时,40Ar和20Ne离子束照射野均匀度分别约为58%和61%.从而说明,辐照终端束流扫描装置对束流的均匀化程度目前并不能满足辐照生物效应、辐射育种和重离子治癌等研究工作的需要,须对其性能做进一步的提高. Using 55 MeV/u 40Ar and 80 MeV/u20Ne ion beams delivered by the Heavy Ion Research Facility at Lanzhou (HIRFL), the relationships between the irradiation homogeneities in irradiation fields generated by the beam scanning device located at the irradiation terminal of the HIRFL and ion fluence were measured respectively with 100 μm polycarbonate films by means of nuclear track detection. The results show that the homogeneity increases when the ion fluence are lower than ........     

Two-photon optical free induction decay measurement by broad-band excitation in undirectional beams

Measurement of two-photon linewidths by broad-band excitation is reported, for the first time in unidirectionally propagating beams. Free induction decay measurement is used in order to determine the pressure broadening coefficients for the 3s–5s transition of Na for collisions with He and Ne. At high He, Ne concentration the Doppler effect and the collisions of other types of atoms are eliminated.     

A study of three-nucleon transfer reactions on 17O

The reactions ¹⁷O(¹¹B, ⁸Li)²⁰Ne, ¹⁷O(¹²C, ⁹Be)²⁰Ne and ¹⁷O(¹³C, ¹⁰B)²⁰F have been studied using beams of 115 MeV ¹¹B and ¹²C and 105 MeV ¹³C incident on a gas target. Shell-model calculations have been performed for ²⁰Ne and ²⁰F, for comparison with the experimental data. It is found that the data can be interpreted using the shell model spectroscopic factors and a semi-classical reaction theory. We justify the use of the latter by applying it to the cases of three-nucleon transfer on ¹⁶O. Spin assignments are suggested for previously unidentified states in ²⁰F.     

A new kinetic description of the complex optical behavior in photochromic polymer films

Kinetics of photoinduced birefringence in precolored spirooxazine-doped polymer films pumped with He–Ne laser beams of various powers was investigated in detail. An improved model, elucidating a competition between photo-orientation and photo-isomerization, was precisely presented. Kinetic parameters determined by fitting to the experimental data were analyzed. As He–Ne laser intensity is increased, the thermal rate constants for isomerization and randomization increase in linear and exponential fashions, respectively. Taking these factors into account, the Thermal Effect Model was more suitable for describing the experiment than the Constant Model, indicating that thermal effect of He–Ne laser plays a key role in decreasing the saturated birefringence. According to the Thermal Effect Model, the highest value of the saturated birefringence was obtained at the He–Ne laser power of 6.5 mW in our experiment.     

Production of copper vapor in a pulsed hollow cathode discharge

Spectral emission from a pulsed Cu hollow cathode was investigated in relation to discharge current to gain information on the density of the sputtered Cu vapor and on the persistence time of the metastable and ground-state atoms. The cathode was excited with 250 μsec discharge pulses at current densities up to 1 A/cm², using He, Ne and Ar as buffer gases. The intensities of the emitted Cu I lines were found to depend strongly on the simmer current. In atmospheres of Ne or Ar, the intensities of the resonance lines exhibited characteristic maxima during the initial 20 μsec of the discharge pulses. The density of the sputtered Cu atoms was determined by absorption measurements using a second Cu hollow cathode as alight source.     

Search for high excitation energy structures in the 20Ne + 208Pb system at EA = 30 MeV

The inelastic scattering of 600 MeV ²⁰Ne from ²⁰⁸Pb has been reinvestigated. Cross sections for giant resonance excitation have been extracted and analysed in terms of DWBA. No evidence has been found for higher excitation energy structures.     

Power resonances in a Raman gas laser

The observation of a new type of resonance due to double-quantum transitions in the standing-wave field of a Raman gas laser is reported. A resonance dip with a width equal to that of the optically forbidden transition was experimentally detected in the output-vs-timing curve of a Raman Ne laser (λ=1.15 m) upon pumping by radiation of a He−Ne laser at 1.52 m. The theory presented shows that the resonance arises in the third order of perturbation theory when in resonant SRS the line is inhomogeneously broadened. The resonance can be considered as resulting from the overlap of dips in the velocity distribution of the nonlinear polarization induced by the standing laser wave.     

A detailed study of the 12C + 16O fusion reaction at Ecm = 19 to 24 MeV

Excitation functions of evaporation residues following the ¹²C + ¹⁶O reaction are investigated at E_cm = 19 to 24 MeV. At the resonances which have been previously identified in the ¹²C(¹⁶O, ⁸Be)²⁰Ne two-body channel, an order of magnitude larger resonance cross section is observed in the fusion channel than that in the two-body one and is shared among a few evaporation residues (²⁰Ne, ²³Na and ²⁴Mg). Here the resonance cross section is defined as the resonance part of the cross section on a resonance in an excitation function. It is found that for each resonance the relative intensity of the resonance cross sections of these residues is fairly well explained by assuming that they are coming from the decay of a compound nuclear resonance. It indiates that these intermediate resonances have a large probability to proceed to the formation of a more complicated configuration prior to its decay into exit channels. However, the resonant enhancement in the fusion channel is found to be weak at three energies (E_cm = 19.7, 22.0 and 22.6 MeV), where prominent resonant structures have been observed in inelastic channels. These distinct situations may be attributed to the magnitude of level density of the compound nucleus.