Gas Ionization Chamber Research Articles

Projectile X-ray detection: application and limits

Projectile X-ray detection (PXD) has been studied to estimate the potential of this ion identification technique in accelerator mass spectrometry (AMS). Limits and possible applications of PXD are discussed and compared to standard isobar identification techniques with gas ionisation chambers. The isobar discrimination capability of a gas ionisation chamber depends on mass, nuclear charge and energy of the ions to be identified. At about 1.5 MeV/amu, suppression factors higher than 10 4 and efficiencies close to 1 have been achieved for ions of masses up to 40 amu. The isobar discrimination capability of PXD is nearly independent of the ion energy, and suppression factors of 10 to 100 are possible. The detection efficiency depends on the ion-target combination, the detector arrangement and the energy of the projectiles. Our results show, that PXD can compete only at lower energies or higher masses, for which gas counters give insufficient isobar discrimination. For the PXD method detection limits on the order of 10 −12 for 36 Cl Cl , 10 −8 for 59Ni Ni and 10 −7 for 126Sn Sn were reached.

Neutron spectrometry using a 3He gas ionization chamber

To deduce an accurate neutron spectrum with high energy resolution from the pulse height data of a 3He gas ionization chamber, the detector response functions are evaluated in the neutron energy range between 0.5 MeV and 6.0 MeV by adjusting the results of Monte Carlo calculation to the measured data with monoenergetic neutron sources. A spectral unfolding code suitable for this detector is also developed on the basis of the maximum likelihood combined with the maximum entropy method. The present system demonstrates an energy resolution of about 2% (FWHM) for incident neutrons around 3.0 MeV through precise measurement of an accelerator DD neutron source.

Accelerator SIMS for trace element detection

An accelerator mass spectrometer has been used to detect negative secondary ions sputtered from a target by a Cs ion beam. The negative ions are analysed by an electromagnetic mass spectrometer and then injected into a 6 MV EN-Tandem accelerator. At the high voltage terminal the ions are stripped in a thin carbon foil which guarantees the destruction of all molecular ions. At the high energy side of the accelerator, ions in the charge state 7+ with an energy of 40 MeV are selected by an electrostatic deflector and then momentum analysed by a magnetic spectrometer. Final detection of the ions is done with a gas ionisation chamber that measures dEdx and the total energy of the particles. The main advantage of this method over ordinary SIMS (secondary ion mass spectrometry) is the complete suppression of molecular interferences due to the stripping process and the possibility of isobar separation in the final detector. This allows for example the detection of Fe in Si which is made very difficult in ordinary SIMS because of the interference with the Si2 dimer. The sensitivity of the method has been tested on a series of silicon samples with known impurity concentrations of a selection of elements in a mass range between 27 and 121. Detection limits between 10−10 and 10−6 per silicon matrix atom are obtained with the present set-up. In all cases, the sensitivity is limited by contamination in the ion source which was not specially designed for this application. With a clean sputter ion source, detection limits between 10−9 and 10−13 seem possible for most elements that form negative ions. The possibility of scanning accelerator SIMS (or SuperSIMS) and applications will be discussed.

Charge collection and energy resolution studies in compressed xenon gas near its critical point

We have built a 4.5 l high purity Xe gas ionization chamber and operated it at pressures of up to 62 atm (1.4 g/cm 3) at room temperature. This thermodynamic regime in pure xenon has not previously been studied. Ionization from a 207Bi internal conversion electron source was drifted over distances of 2.7 and 5.0 cm in two separate gridded ionization chambers within the gas volume. We observed that there was less than 1% difference in the charge collected from these two detectors at the same electric field strength. Energy resolution measurements were performed over the range of xenon densities from 0.49 to 1.40 g/cm 3 at several electric field strengths. An electronic noise subtracted resolution of 16 keV FWHM was measured for the 976 keV 207Bi internal conversion line at an electric field strength of 1.3 kV/cm in compressed xenon gas near its critical density.

A new AMS beam line at the Erlangen tandem accelerator facility

An accelerator mass spectrometry beam line is presently being built up at the EN tandem accelerator in Erlangen. A new Cs sputter ion source is being developed, and mass separators on both the low- and high-energy sides of the tandem and an electrostatic sector field for charge-state selection have been installed. Optimization of the beam quality will be possible with a new emittance measuring device. The tandem is stabilized via a position-sensitive Faraday cup, which simultaneously measures the current of the abundant isotopes. The spectra of the rare-isotope ions are taken by differential energy loss measurements in a gas ionization chamber.

The Self-Consistent Charge Method: A Numerical Approach to Radiation-Induced Charge Transport Phenomena

Reconsidering the numerous conceptions as they have been developed in atomic physics (self-consistent field), heat and charge transport theory (carrier-enhanced and radiation-induced conductivity) and many other related fields for iteratively solving the corresponding integro-differential equation systems we come now to propose a new approach to the subject addressed in the title. This method has been implemented in a FORTRAN code, allowing for a self-consistent solution of kinetic equations on a quite broad scale. However, in treating a particular problem (irradiated semiconductor, ionisation gas detectoed etc.) it appears recommendable to employ a confined specialized version. Model calculations of a (a.c. or d.c. driven) gas ionisation chamber have been carried out to demonstrate the systematizing potential of the present approach.

Isotopic identification of energetic heavy nuclei using [formula omitted] vs total energy in a high pressure gas ionization detector

We have developed a high pressure (3–10 atm) segmented-anode gas ionization chamber and have investigated the capabilities of this type of instrument for identifying energetic heavy nuclei. For individual nuclei which stop in the active volume of the detector, we use one or more measurements of the particle's energy loss ( ΔE) and its residual energy ( E′) to derive its charge and mass. Experiments using accelerator beams have yielded unambiguous charge identification over the range of elements studied (up to Z = 26), and mass resolutions from σ M ⋍ 0.08 amu (Z = 6) to σ M ⋍ 0.35 amu (Z = 26) . The energy loss measurements provided by the segmented anode are supplemented by two-dimensional measurements of particle track coordinates made using a combination of drift time and charge division in a set of single-wire proportional counters. These tracking detectors provide a position resolution ≲ 0.6 mm for each coordinate, and make possible the path length corrections needed to study isotropic particle distributions such as those encountered in the cosmic radiation.

Data acquisition for the HILI detector

A large acceptance, multisegmented detector system capable of the simultaneous detection of heavy ions and light ions (HILI) has been constructed. The heavy ions are detected with a segmented gas-ionization chamber and a multiwire proportional counter, while the light ions are detected with a 192-element plastic 'phoswich' hodoscope. Processing the large number of signals is accomplished through a combination of CAMAC and FASTBUS modules and preprocessors and a host minicomputer. Details of the data acquisition system and the reasons for adopting a dual-standard system are discussed. A technique for processing signals from an individual hodoscope detector is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New far UV detector calibration facility at the National Bureau of Standards

A description is given of a new facility, located at the NBS (Gaithersburg) Synchrotron Ultraviolet Radiation Facility (SURF-II), in which the absolute calibration of working standard detectors for the 5-50-nm spectral region, and the subsequent calibration of outgoing transfer standard detectors is performed. A dual toroidal grating monochromator, with diffraction gratings optimized for 3-13 and 12-52 nm, disperses synchrotron radiation from the electron storage ring into tandem experimental chambers in which a rare gas ionization chamber determines the absolute magnitude of the incident radiant flux and hence the efficiency of the photoemissive photodiodes.

A UHV-compatible ΔE− E gas telescope for depth profiling and surface analysis of light elements

We have developed a compact ΔE− E gas telescope that can easily be incorporated into a standard ultrahigh vacuum ion scattering chamber. If energetic, heavy ions are available as a primary beam, the gas telescope can be used to detect light elastic recoils scattered from the surface region of a sample. The detector consists of a gas ionization chamber in front of a surface-barrier detector. The energy loss signal in the gas ( ΔE) is taken in coincidence with the energy signal in the surface-barrier detector ( E) to identify both the atomic number and the total energy of the elastic recoil. The design parameters of the detector have been chosen to allow detection of elements from H to O with good depth resolution ( < 100 Å) and submonolayer sensitivity. The mass resolution is adequate to easily separate all elements from H to O.

Spectral energy measurements in a fast neutron therapy field

Various basic physical parameters are needed to convert a specific dosimeter reading in air to tissue kerma or to absorbed dose in a phantom. In a neutron radiation field, spectral information is required for the evaluation of these parameters. Using NE213 liquid scintiillator as a proton recoil spectrometer, neutron spectra were measured in the collimated d(16)+ Be beam of the Pretoria fast neutron therapy facility. The neutron events wer eidentified by means of pulse shape discrimination and a well established computer code employed to unfold the acquired pulse height data. The analysed neutron spectrum was used to compute the neutron kerma ratio ( K t/ K m) N and the ratio of the average energies W N/ W c required to create an ion pair in an A-150/TE gas ionization chamber. The determined values concur with published data from other centres with similar neutron beams. The mean neutron energy E n of the therapy beam was also calculated from the spectral distribution.

A gas ionization chamber for on-line heavy ion identification

A gas ionization chamber is described for on-line identification of products from nuclear reactions. The chamber can work with two different anodes: the resistor type or the split type. Response of the device, proved experimentally, enables fast identification of Z values subtending some defined region. Possible modifications of the detector are discussed. The concept of extending the Z value flexibility of the system is proposed.

Electron fluence perturbation by gap-shaped and by cylindrical gas-filled ionization chambers with axes normal to the beam

Abstract For electron beam absorbed dose measurements using gas-ionization chamber, a perturbation correction factor has been defined to correct for the disturbance of the fluence. For a gap-shaped cavity, a revised perturbation factor is derived. The range of validity of the calculations is extended over that of a previous study. The direct calculations for cylindrical cavities are very difficult. Instead, the form of the cylinder is approximated by a square parallelepiped. Comparison with Monte Carlo calculations showed good agreement.

Quasielastic transfer reactions induced byFe56onNi58,Ni64, andSn122

Differential cross sections sigma(Z,A,E,theta) for the quasielastic projectilelike reaction products from the bombardment of /sup 56/Fe on /sup 58,64/Ni and /sup 122/Sn at 5.9 and 8.5 MeV/nucleon have been measured with a channel-plate time-of-flight telescope followed by a ..delta..E-E gas-ionization chamber. Angular intervals of 10/sup 0/--15/sup 0/ centered at the grazing angles were covered. The differential cross sections for one-proton transfer with Q values near zero were analyzed using the distorted-wave Born approximation, which can account for the shape of the angular distributions and, to better than a factor of 5, for the absolute cross sections. At Q values more negative than -10 MeV the measured angular distributions begin to deviate from the distorted-wave Born approximation predictions. Substructures were observed in the energy spectra near Q = -25 MeV. A model for unfolding the effects of particle evaporation from the reaction products is developed. It is shown that, within the limitations of the model, the observed substructures cannot be accounted for by evaporation effects alone but must be present in the primary energy spectra. Finally the optimum Q values are analyzed with a one-body dissipation model. The model is reasonably successful if the concept of a local Fermi momentum ismore » introduced.« less

Particle identification through the measurement of the Bragg curve centroid

A new method of particle identification of heavy ions through the measurement of the Bragg curve centroid and particle energy has been developed using a gas ionization chamber with a resistive anode layer. Z-resolutions comparable to the conventional ΔE-E counter telescope could be rather easily attained.

A ΔE-E telescope with very large solid angle

We have developed a charged particle telescope primarily for heavy ions with several new features. A very compact gas ionization chamber with axial charge collection and without a Frisch grid is used as a ΔE coungter. The E counter consists of a 50 mm × 16 mm multi-detector array fabricated on a single silicon wafer. The entire device is operated at −30°C to reduce the leakage current in the solid state detector and to eliminate the need for a gas flow system. At a distance of 50 mm from the target this detector subtends a solid angle of 300 msr and an angular range of 53°.

Environmental Gamma-Ray Measurement Methods for French Nuclear Installation Impact Studies

Due to the development of the nuclear industry and current concern for the environment, studies need to be carried out on the impact of new nuclear power plants. One of the elements of this impact is external irradiation, which should be measured before installations are put into operation. Four measurement devices are compared: a scintillometer using a composite crystal, which takes into account the photon ionization power as a function of the energy (SCINTOMAT 6134 BEFIC); a tissue equivalent ionization chamber with magnesium fluoride polyethylene walls (CET 72 SAPHYMO-SRAT); a big ionization chamber filled with air at atmospheric pressure (CD 43 ALCATEL); and a pressurized gas ionization chamber made of a 25.4-cm-diam sphere containing argon at a 25-atm pressure STP (RSS 111 Reuter Stokes). For purposes of environmental measurements, the most important criteria of comparison are sensivity, relative fluctuation, and velocity of response, so that low dose rates can be measured when the device is set up in a truck moving at low speed for regional mapping. The comparison shows that the pressurized gas ionization chamber comes the closest to meeting the required conditions.

Ion chambers for fluorescence and laboratory EXAFS detection

It is possible to design gas ionization chambers with a noise equivalence of 10 3 photons/s for 10 keV X-radiation. With such a low noise level, ion detectors can be used for laboratory EXAFS facilities and fluorescence detectors at national synchrotron facilities where the detected signal is above 10 3 photons/s. In such use the ion chambers are limited by statistical noise and produce as good a signal to noise as counting detectors. The advantages of ion chambers are simplicity, high linearity at high counting rates and large detecting area.

A cryogenic ionization chamber for high-resolution fission cross-section measurements

This paper describes a multiple-plate gas ionization chamber designed for cross-section measurements of neutron-induced fission in strongly radioactive nuclei. The requirements of high resolution are discussed, in particular the need for cooling the sample to reduce Doppler broadening, and the selection of the gas mixtures that will enable fast counting at a low temperature. The observed gain in resolution with cooled samples is in good agreement with theoretical predictions.

Particle Detection Systems

A brief review is given of the most common nuclear particle detectors such as the gas ionization chamber, the surface barrier detector, and scintillation detectors. Some combinations of detectors are discussed with particular emphasis on heavy-ion spectroscopy. Magnetic (momentum) spectrographs and one example of a proposed energy-mass spectrograph complete the list. Some possible future trends are indicated.