Gas Target Cell Research Articles

Design and test of a beam profile monitoring device for low intensity radioactive beams

Development efforts have gone into the construction and performance testing of a device that can be used to provide snap shot images of the beam profile. It is intended to function even at very low ion intensities, such as those expected from a rare-isotope accelerator. Intensity profiles and emittance analysis are among the most critical tools used for optimizing beam transport through accelerators. This article describes the design and performance of a beam image monitor. The device is sensitive at a wide dynamic range which spans from ∼102 to ∼1012 pps. With the advent of double-plane slits or a pepper pot plate, this system can be used to scan transverse emittance profiles in both the x–x′ and y–y′ phase space planes, simultaneously. Conventional diagnostic devices used for heavy ion accelerators generally require at least 109 pps intensity to carry out similar diagnostics, which is not practical when considering beams with very low intensities, such as rare isotope beams. Furthermore, the detection system used here can be used for a wide range of incident ion velocities. Compared with solid-state detectors and scintillators that are inserted directly into the beam, this type of detection system is less susceptible to beam induced damage resulting in longer lifetimes and less maintenance. The test was done using single charge state Kr beams at energies ranging from 3.6 to 18 keV/u. The device’s sensitivity was monitored for intensities below 1012 pps and an emittance scan was recorded and analyzed. The spatial resolution was characterized by comparing the emittance profile with that obtained by a wire scanning device which had better resolution but was sensitive only to intensities above 1011 pps. Recently, the device has been used to aid in the transport of ∼6 MeV/u radioactive beams, such as F17, produced by pickup reactions with a gas cell target at the ATLAS accelerator facility.

Excitation function and thick target yield of the 40Ar(α,p) 43K reaction: Production of 43K

The excitation function of the 40Ar(α,p) 43K nuclear reaction has been measured via the activation technique using stacked gas cell targets. Absolute cross section values were deducted from the experimental data and were compared with theoretical predictions calculated by means of the STAPRE code. Thick target yields of 43K were calculated from the experimental data. A target system working in static (batch) or in recirculating gas flow mode has been developed to produce 43K.

Fabrication and Testing of Gas Filled Targets for Large Scale Plasma Experiments on Nova1

An experimental campaign on the Nova laser was started in July 1993 to study one st of target conditions for the point design of the National Ignition Facility (NIF). The targets were specified to investigate the current NIF target conditions--a plasma of {approximately}3 keV electron temperature and an electron density of {approximately}1.0 E + 21 cm{sup {minus}3}. A gas cell target design was chosen to confine as gas of {approximately}0.01 cm{sup 3} in volume at {approximately} 1 atmosphere. This paper will describe the major steps and processes necessary in the fabrication, testing and delivery of these targets for shots on the Nova Laser at LLNL.

A high-brightness source for polarized atomic hydrogen and deuterium

An atomic beam source for polarized hydrogen and deuterium is described. The source, which will be used to supply atoms to a polarized gas target cell for internal-target experiments in storage rings, was designed to optimize the flux of polarized atoms into a 1 cm diameter 13 cm long tube placed 26 cm from the end of the last magnet. High-field permanent magnet sixpoles with a tapered bore are employed. Studies of gas scattering and dissociator output were combined with ray tracing calculations of atomic trajectories to find an optimum source design. The beam is cooled by thermal accomodation to an aluminum dissociator nozzle at 84 K. The beam intensity which passes through the 1 cm diameter, 13 cm long tube is (6.7 ± 0.1) × 10 16 atoms/s. The total hydrogen beam intensity is 8.6 × 10 16 atoms/s in two hyperfine spin states. The measured beam profile and intensity agree with calculations to within 10%.

Physical parameters at the internal target positions for experiments in COSY-Jülich

COSY-Jülich provides a number of regions, where experiments can be carried out using the internal beam in the storage ring mode. At the internal target positions fiber targets, ribbon targets, gas-jet or cluster targets and polarized atomic beam or gas cell targets can be installed. The size of the effective target spot and the minimum distance between the nozzle and catcher of a gas jet target depend on the beta functions at the target position and on the acceptance of the ring. These quantities will be discussed together with the figure of merit for each target position, including positions where use can be made of a standard COSY dipole as spectrometer. Experiments planned as internal experiments in COSY will be briefly mentioned.

Measurement of the cross section 22Ne(p,n)22Na.

The first cross-section measurements for the reaction $^{22}\mathrm{Ne}$(p,n${)}^{22}$Na were performed at several proton energies from threshold to 18 MeV. A gas cell target containing natural Ne gas was irradiated on the beam line of a cyclotron. The yield of $^{22}\mathrm{Na}$(${T}_{1/2}$=2.6 yr) was subsequently determined by counting gamma rays with a Ge detector. Several systematic corrections associated with the counting geometry and beam heating of the gas during bombardment were applied.

Design and calibration of an x-ray polarimeter for ion-atom collision studies

The design and calibration of a system for the measurement of the polarization of X-rays from ion-atom collisions in a gas target cell is described. The performance of the system was tested by measuring the polarization of the KL 1 satellite lines of Al induced by 5.5 MeV He ion impact.

Production of High-Q Ions by Laser Bombardment Method

The expanding plasma produced when an intense pulse of laser radiation is focused in vacuum onto a solid target has been used as a source of highly stripped ions for collision cross-section measurements. Usable fluxes of carbon nuclei at energies of a few hundred eV/charge have been obtained by irradiation of graphite with pulses of CO2 laser radiation at a focused power density of 3 × 1010 W/cm2. Bombardment of aluminum and iron targets at comparable power levels have yielded ions of maximum charges of 9 and 16 respectively. A time-of-flight apparatus has been constructed to utilize the laser source for measurement of electron capture cross sections for highly stripped ions in gases at energies in the few hundred eV/charge range. Apertures collimate an ion beam from the plasma blowoff, and an electrostatic analyzer selects ions from the expanding plasma which have the same energy per charge. The beam is directed through a gas target cell, charge analyzed once more by deceleration, and detected by a channel plate electron multiplier used in a current amplification mode. Electron capture cross sections have been measured for C+q ions, q = 3, 4, 5 in H2 at energies ranging from 150-1160 eV/charge. Preliminary data have been obtained for carbon ions in atomic hydrogen, and similar measurements are planned for O+q and Fe+q ions.

A gas cell target for studying fusion and damped collisions of light nuclei

A compact gas cell target for studying fusion and damped collisions of light nuclei has been constructed. The specifications, geometry and other features of the target are described. Typical experimental results obtained with the gas target are presented.

Ar40(p,d)Ar39reaction atEp=35MeV

The $^{40}\mathrm{Ar}(p,d)^{39}\mathrm{Ar}$ reaction has been studied at a bombarding energy of 35 MeV. A thin planar gas cell target allowed an energy resolution of 30 keV to be achieved. Excitation energies of levels in $^{39}\mathrm{Ar}$ up to 5.6 MeV were obtained, angular distributions being taken from 6\ifmmode^\circ\else\textdegree\fi{} to 40\ifmmode^\circ\else\textdegree\fi{} (laboratory). Distorted-wave Born approximation fits were made to the observed angular distributions of the stronger states and spectroscopic factors extracted. The results are compared with previous experiments and to shell-model calculations. The data support the contention that much of the antianalog state strength is contained in the 3.379 MeV state.NUCLEAR REACTIONS $^{40}\mathrm{Ar}(p,d)$, ${E}_{p}=35$ MeV, $\ensuremath{\Delta}E=30$ keV, measured $\ensuremath{\sigma}({E}_{d},\ensuremath{\theta})$; DWBA analysis, deduced $l$ values and spectroscopic factors. Planar gas cell target.

Measurements of the radiative widths of the first T = 1, 2 + state of 20Ne and their relationship to analog β-decays

The radiative widths for decays of the 20Ne T = 1, 2 + (10.27 MeV) state were measured by resonance α-capture in the reaction 16O(α, γ) 20Ne. A special windowless gas-cell target yielded a low-background spectrum enabling six γ-branches to be observed with a Ge(Li) detector. The six branches correspond to decays from the 10.27 MeV level to the following levels: 2 +(7.83 MeV), 2 +(7.42 MeV), 3 −(5.62 MeV), 2 −(4.97 MeV), 2 +(1.63 MeV) and 0 +(g.s.). The branching ratios and radiative widths Γ γ to these levels are: 7.83 MeV [(0.22 ± 0.06)%, 0.008 ± 0.002 eV], 7.42 MeV [(6.9 ± 0.4)%, 0.31 ± 0.04 eV], 5.62 MeV [(2.1 ± 0.2)%, 0.097 ± 0.014 eV], 4.97 MeV [(1.3 ± 0.1)%, 0.060 ± 0.008 eV], 1.63 MeV [(88.9 ± 0.5)%, 4.08 ± 0.43 eV] and 0.0 MeV [(0.64 ± 0.14)%, 0.029 ± 0.008 eV]. The radiative widths to the 1.63 MeV and 7.42 MeV levels are used to determine the CVC predictions of the weak magnetism form factors and their effects on certain β-decay observables are evaluated.

Analysing power in neutron-proton and neutron-deuteron scattering at 14 MeV

Analysing power data in n-p and n-d elastic scattering at 14 MeV were deduced from asymmetry measurements using a polarized neutron beam arrangement consisting of a gas target cell, a neutron collimator and a spin processing solenoid. The incident neutron beam was produced by the reaction 2 H( d), n) 3 He at θ lab = 30° . The neutron polarization was P = (42.9 ±0.9)%. Liquid scintillators of C 6H 6 and C 6D 6 were used as scattering targets. Eight neutron detectors allowed the simultaneous measurement of the asymmetry at different angles. The n-p analysing power data were used to perform new phase-shift analyses, including all available n-p scattering data in this energy region. The results for the n-p analysing power at 14.5 MeV were found to be slightly different from the predictions of the Livermore (LRL X) as well as from those of the Yale (Y IV) phase-shift sets. The results for the n-d analysing power at 14.3 MeV show no significant difference to the p-d data at this energy. Three-particle calculations from Dolescball and from Benayoun et al. give reasonable agreement with the experimental data although there are still some minor deviations.

An electroformed gas target for electron scattering

This paper describes an electroformed gas target cell of 15 cm 3 volume and operating at 20 atm.

Correction of differential cross sections for finite angular resolution

The angular resolution of a differential scattering apparatus of the common type is investigated. The primary and scattered beam are each assumed to be non-parallel and collimated by two arbitrary rectangular apertures. A function eta ( theta , Theta ) describing the acceptance of the apparatus for particles scattered at laboratory angle theta is derived, which connects the directly measurable angular distribution dN/d Theta with the differential cross section sigma ( theta ). The two cases of a gas cell target and a locally defined target such as an atomic or molecular beam are both treated.

A low-volume, high-pressure gas target for use in electron-scattering experiments

A thin-window, low-volume, high-pressure gas-target cell suitable for use in high-resolution electron-scattering investigations is described. Details of the design and construction as well as the results of several tests are discussed.

Gas target for production of monoenergetic neutrons

A new design of gas target cell is described for neutron production. Results are given on effects attributed to diffusion of tritium gas from the cell into the window material.

Gas target cell for a precision scattering chamber

A gas target cell with demountable cylindrical windows has been developed for use with the Florida State University 45.7 cm (18″) scattering chamber. Designed for maximum experimental flexibility, this cell allows observation throughout an angular range from 20° to 170°. Several interchangeable gas handling plugs, one of which incorporates a Ti getter pump within the cell interior, are described. A 16 detector array permits the simultaneous acquisition of 16 excitation functions or the efficient measurement of detailed angular distributions by angular displacement of the detector ring. This cell has been used at a gas pressure of 35 Torr for measurements of cross sections for elastic scattering of alpha particles by 20Ne and 36Ar in the energy range from 10 to 14 MeV.