Extended Gas Target Research Articles

Measurement of radiative capture resonance energies with an extended gas target

The DRAGON facility for the study of radiative capture reactions has an extended gas target, surrounded by an array of BGO detectors. The distribution of detected gamma rays amongst the segmented array permits an estimate of the reaction position and consequently of the resonance energy. We report a study of the technique, using the 24Mg(p, γ)25Al reaction. Energy determination to better than 0.5% has been demonstrated.

First experiments with the polarized internal gas target at ANKE/COSY

A Polarized Internal gas Target (PIT) has been developed for the ANKE spectrometer at COSY. After its first installation at the ANKE target position in summer 2005, commissioning studies were carried out. In March 2006, first single polarization measurements with the polarized hydrogen beam from an Atomic Beam Source (ABS) were performed. The beam was injected into a storage cell made from aluminum foil. The data analysis showed that the events from the extended gas target can be clearly identified in the ANKE forward detection system. Using unpolarized nitrogen, the background from the cell walls could be determined as well. The thickness of the gas in the storage cell with the hydrogen atoms in hyperfinestate |1⟩ was measured as 2×1013 atoms/cm2. The ABS jet target thickness was 1.5×1011 atoms/cm2. In November 2006, the commissioning of a Silicon Tracking Telescope (STT) was successfully finished. In the following beam time in January 2007, a new storage cell from aluminum coated with teflon was used together with the STT. The Lamb-shift polarimeter (LSP) was mounted below the target chamber to allow for online tuning of the transition units and monitoring of the ABS jet polarization. A first double-polarized experiment was performed, the results will be presented.

Recoil separator ERNA: charge state distribution, target density, beam heating, and longitudinal acceptance☆

For improved cross section measurements of the reaction 12C(α,γ)16O in inverted kinematics, a recoil separator ERNA is developed at the 4 MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with high efficiency. The 16O recoils are produced by the 12C projectiles in a windowless 4He gas target. We report on the charge state distribution of the 16O recoils, the gas target density, the beam heating of the gas target, and the acceptance of the separator along the extended gas target.

Recoil separator ERNA: charge state distribution, target density, beam heating, and longitudinal acceptance

For improved cross section measurements of the reaction 12 C ( α , γ ) 16 O in inverted kinematics, a recoil separator ERNA is developed at the 4 MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with high efficiency. The 16O recoils are produced by the 12C projectiles in a windowless 4He gas target. We report on the charge state distribution of the 16O recoils, the gas target density, the beam heating of the gas target, and the acceptance of the separator along the extended gas target.

Testing the ISAC radioactive ion accelerator beam specifications using the H( 15N,αγ) 12C reaction

Important ion beam parameters like energy spread and stability of the new isotope separator and accelerator accelerator at TRIUMF were determined during the first beamtime with the detector of recoils and gammas of nuclear gas target and BGO array. For this purpose a variation of the nuclear resonance method, using a geometrical scan over the resonance as placed in an extended gas target cell, as well as time-of-flight correlations were employed.

Capture reactions at astrophysically relevant energies: extended gas target experiments and GEANT simulations

Abstract Several resonances of the capture reaction 20 Ne ( α , γ ) 24 Mg were measured using an extended windowless gas target system. Detailed GEANT simulations were performed to derive the strength and the total width of the resonances from the measured yield curve. The crucial experimental parameters, which are mainly the density profile in the gas target and the efficiency of the γ-ray detector, were analyzed by a comparison between the measured data and the corresponding simulation calculations. The excellent agreement between the experimental data and the simulations gives detailed insight into these parameters.

Target and detection techniques for the 13N(p, gamma )14O reaction using radioactive ion beams: 13C(p, gamma )14N reaction as a test case.

A feasibility study was undertaken for the measurement of the resonance at ${\mathit{E}}_{\mathit{r}}$=545 keV in the $^{13}\mathrm{N}$(p,\ensuremath{\gamma}${)}^{14}$O reaction, using intense radioactive ion beams. The analog resonance at ${\mathit{E}}_{\mathit{r}}$=512 keV in $^{12}\mathrm{C}$(p,\ensuremath{\gamma}${)}^{14}$N was chosen as a test case, leading to improved knowledge of the resonance parameters. Thin- and thick-target yields were obtained with $^{13}\mathrm{C}$ beams on an extended gas target and a polyethylene foil, respectively. In addition, thin and thick targets of enriched $^{13}\mathrm{C}$ were irradiated with proton beams. Normalization problems arising with mixed ion beams ${(}^{13}$N${/}^{13}$C) are discussed.

Two-center effects in electron emission inHe2+3-He andH+-He collisions at intermediate energies

We present measurements of doubly differential cross sections (DDCS) with respect to energy and angle for electron emission produced when 100- and 50-keV/u $^{3}\mathrm{He}^{2+}$ and ${\mathrm{H}}^{+}$ collide with He. An electron spectrometer designed for this purpose enables us to measure electron distributions which, even at small emission angles, do not present appreciable deformations of the measured distributions by extended gas target effects. Using the ratio of the emissions obtained with $^{3}\mathrm{He}^{2+}$ and ${\mathrm{H}}^{+}$, we study the dependence of the DDCS on the projectile charge. We confirm a saturation of this emission ratio that increases with increasing angle. Furthermore, we report a sudden enhancement of the emission ratio that is found at and above the electron capture to the continuum peak. These observations are in basic but not quantitative agreement with calculations performed using a model that incorporates the continuum distorted wave and eikonal initial state and that approximately accounts for a two-center interaction of the active electron.

Absolute cross section of the3He(?,?)7Be reaction

The absolute cross section σ(E) of the3He(α, γ)7Be reaction has been measured fromE c.m. =195 to 686 keV. The studies employed both a supersonic jet gas target and an extended gas target, and were carried out by the observation of the prompt capture γ-ray transitions as well as the7Be residual nuclei. The absolute cross sections deduced from the capture γ-rays are in good agreement with most previous work and remove a discrepancy with other earlier work. In comparison, the σ(E) values obtained from the7Be residual nuclei are systematically higher, suggesting a small production of additional7Be by contaminant reactions.

The4He(12C, ?)16O reaction at stellar energies

The capture reaction4He(12C, γ)16O (Ec.m.= 1.34–3.38 MeV) as well as the elastic scattering process4He(12C,12C)4He (Ec.m.=1.44–3.38 MeV) have been investigated with the use of an intense12C beam and a windowless and4He recirculating gas target system. The measurements involved two large NaI(T1) crystals in close geometry to an extended gas target, whereby angle-integrated γ-ray yields were obtained. A large area plastic detector was used for the suppression of time-independent background. A search for cascade γ-ray transitions was carried out by coincidence techniques. The measurement of absolute cross sections is also reported. Theoretical fits of the excitation function for the groundstate γ-ray transition requireE1 as well asE2 capture amplitudes, which are of equal importance at stellar energies. This result increases significantly the stellar burning rate of4He(12C, γ)16O and leads to16O as the dominant product at the end of helium burning in massive stars. The observed capture yield to the 6.92 MeV state is dominated by the direct capture mechanism and plays a small role at stellar energies.

The influence of intense ion beams on gas target densities

The geometrical location of a narrow resonance within an extended gas target moves along the beam axis as the beam energy is varied. This location changes however for a constant gas target pressure, if the ion beam intensity is varied. It is also found, that - for a constant ion beam current - the expected location differs from that observed as the gas pressure is increased. It is concluded, that the gas target densities along the beam axis depend on both the energy loss per unit length and the ion beam current, i.e. the dissipated power in the gas. This dissipated power increases in turn the temperature of the target gas. Effects greater than 10% are seen for dissipated powers greater than 20 mW/mm. The effects have been studied at the E p = 278 keV resonance of the 14N(p, γ) 15 O reaction.

Geometric penumbra calculations for a gas target neutron source.

A computational approach is used to investigate the geometric effects of an extended gas target neutron source on the penumbra characteristics of a collimated 14 MeV neutron beam for radiotherapy. It was found that for a cylindrical gas target, 50 cm long, 2 cm in diameter, and operated at 10 torr of 8T gas, the geometric penumbra is superior to that of a 2 cm diameter flat target at a comparable SSD.