Pressure Ionization Chamber Research Articles

An ionization chamber for coincidence experiments in a search for double beta positron decay and electron positron conversion of 78Kr

A search for double positron decay and electron capture with positron emission in the transition 78 Kr(0 gs +) → 78Se(0 gs +) has been carried out by using a high pressure ionization chamber surrounded by a set of NaI detectors. Coincidences between the emitted positron(s) and the two (four) consequent annihilation gammas have been looked for as signature(s) of the process(es). The ionization chamber of krypton gas (enriched up to 94.08% in the 78 isotope) registers the positron energy, whereas the set of sodium iodide scintillators searches for the annihilation gamma rays. The features and performances of the experimental device are presented and the results obtained for the half-life limits of the processes investigated are reported.

Long-Term Tracer Study at Los Alamos, New Mexico. Part I: Wind, Turbulence, and Tracer Patterns

An array of three portable, pressurized ionization chambers (PICs) measured external radiation levels during 1986 and 1987 caused by radionuclides emitted from a 30-m stack of the Los Alamos Meson Physics Facility (LAMPF). Three PICs were located from 700 to 900 m north to northeast of the release stack, across a 120-m-deep canyon, and at the closest off-site location. Four additional PICs were deployed during 1987 at various sites and directions, at distances varying from 550 to 2700 m downwind of the stack. Winds were measured near the source and 700 m downwind, across a deep canyon. Analysis of monitoring data confirmed that a predominant mountain-valley wind up the Rio Grande Valley during the evening and early morning transported the emissions to the north-northeast and northeast of LAMPF, causing the highest external atmospheric radiation levels there. Daytime winds are southerly and southeasterly, transporting more radionuclides to the north and northwest. Because of increased turbulence, external radiation levels were generally lower during the day.

A pressurized ion chamber monitoring system for environmental radiation measurements utilizing a wide-range temperature-compensated electrometer

The performance of a complete pressurized ion chamber (PIC) radiation monitoring system is described. The design incorporates an improved temperature-compensated electrometer which is stable to /spl plusmn/3/spl middot/10/sup -16/ A over the environmental range of temperature (-40 to +40/spl deg/C). Using a single 10/sup -11//spl Omega/ feed-back resistor, the electrometer accurately measures currents over a range from 3/spl middot/10/sup -15/ A to 3/spl middot/10/sup -11/ A. While retaining the sensitivity of the original PIC system (the instrument responds readily to small background fluctuations on the order of 0.1 /spl mu/R h/sup -1/), the new system measures radiation levels up to the point where the collection efficiency of the ion chamber begins to drop off, typically /spl sim/27 pA at 1 mRh/sup -1/. A data recorder and system controller was designed using the Tattletale Model 4A computer. Digital data is stored on removable solid-state, credit-card style memory cards. >

Results of a search for double positron decay and electron-positron conversion of 78Kr.

The results of a search for the 2[beta][sup +] and [ital K][beta][sup +] decay modes of [sup 78]Kr, in a coincidence experiment using a high pressure ionization chamber of enriched [sup 78]Kr inside an array of sodium iodine scintillators, are presented. After 4434 h of counting time, the half-life lower limits obtained are [ital T][sub 1/2]([ital K][beta][sup +])[sub 0[nu]][ge]5.1[times]10[sup 21] yr and [ital T][sub 1/2](2[beta][sup +])[sub 0[nu]+2[nu]][ge]2.0[times]10[sup 21] yr at 68% C.L.

Results of a search for double positron decay and electron-positron conversion of 78Kr

The results of a search for the 2β + and Kβ + decay modes of 78Kr, in a coincidence experiment using a high pressure ionization chamber of enriched 78Kr inside an enceinte of sodium iodine scintillators, are presented. After 4434 hours of counting time, the half-life lower limits obtained are T 1 2 ( Kβ +) 0τ ≥ 5.8×10 21 y and T 1 2 (2β +) 0τ+2τ ≥ 2.0×10 21 y at 68% C.L.

Determination of Restricted LET Distribution for Mixed (n,gamma) Radiation Fields by High Pressure Ionisation Chamber

Abstract A novel method is presented for the determination of the energy loss distribution in the nanometric region from the initial recombination of ions in high pressure ionisation chambers. Low resolution distributions can be obtained by comparison of saturation curves for mixed and reference gamma radiations. The method was tested using two different ionisation chambers in field of 241Am-Be, 238Pu-Be and 252Cf neutron sources. Both the gamma component of the absorbed dose and the quality factor calculated from the obtained energy loss distributions agree with the values measured by other methods.

Determination of Restricted LET Distribution for Mixed (n,gamma) Radiation Fields by High Pressure Ionisation Chamber

Determination of Restricted LET Distribution for Mixed (n,gamma) Radiation Fields by High Pressure Ionisation Chamber

The Assessment of External Photon Dose Rate in the Vicinity of Nuclear Power Stations: An Intercomparison of Different Monitoring Systems

Four environmental dose rate instruments having different detectors, a high pressure ionisation chamber, a Geiger-Müller counter, a proportional counter and scintillation counter, were used to make continuous measurements over a four month period of the air kerma rate at a location close to a nuclear power station. The responses of each of these detectors to the natural radiation and to the radiation from the power station are given. Estimations by three of the dose rate instruments of the air kerma from all the radiation components are intercompared with the results from three different types of thermoluminescence dosemeter. The results clearly demonstrate that accurate estimations of doses in the environment arising from a nuclear facility can only be obtained if the responses of the detectors used to the different radiation components at that location are accurately evaluated. By correcting the measured air kerma values by the accurately determined detector responses the standard deviation, expressed as a percentage of the mean value of the total air kerma for the instruments and the TLDs, was reduced from 20% to 5%.

Final dt sticking? s using the ?survived moun method?

A new direct measurement of the final dt sticking probability ωs using a special data analysis called the “survived muon method” is presented. The data were obtained at PSI using a high pressure ionization chamber with H/D/T gas mixtures. The method can provide information on final sticking dμt → μα+n independent of theoretical models of stripping and initial sticking. It was found:ω s=(0.57±0.07±0.02)%. The experiment and the analysis method are discussed in detail.

In-situ gamma-ray site characterization of the Tatum Salt Dome Test Site in Lamar County, Mississippi.

Field surveys of gamma-ray emitting nuclides and soil core sampling were conducted at 12 sites on the Tatum Salt Dome Test Site and surrounding control areas to determine exposure rates from surficial radioactivity. 137Cs was the only man-made radionuclide detected and was most abundant at three off-site locations on cultivated lawns. 137Cs inventories at all of the on-site survey locations were lower than expected, given the high annual precipitation in the area. The vertical distributions were more extended than those reported for undisturbed sites. Pressurized ion chamber measurements indicated no significant differences in exposure rates on and off the test site.

High pressure ionization chamber designed to search for 2β decay of 136Xe

The construction of a high pressure ionization chamber operating with Xe is given. Its volume is 3.66 1. Operational features obtained during irradiation by an external source of γ-quanta at a Xe pressure of up to 30 bar are presented. At an energy level of E γ = 1.836 MeV the energy resolution was 2.6% (FWHM).

The standardization and decay scheme of rhenium-186

Rhenium-186 has been standardized for activity by the CIEMAT/NIST method of 4πβ liquid-scintillation efficiency tracing with tritium, with an uncertainty (equivalent to 1 SD) of 1.61%. Half-life measurements with a pressurized ionization chamber give a T 1 2 = 89.25 ± 0.07 h . Photon emission rates were measured with semiconductor detectors, and the probability of emission of the principal γ-ray at 137 keV was found to be P 7 = 0.0945 ± 0.0016.

Microdosimetric Characterisation of Radiation Fields with a High Pressure Ionisation Chamber: A Comparison with the Low Pressure Proportional Counter

Abstract The application is described of a tissue-equivalent (TE) high pressure ionisation chamber that permits evaluation of the mean quality factor in mixed neutron-gamma radiation fields and compares the data obtained with those acquired with a TE proportional counter (Rossi counter). Irradiations are produced by a research fission reactor. The radiation spectrum composition is modified by moderating the beam by various heavy water (D2O) or lead thicknesses and by inserting boral shutters in the neutron beam. Thus, radiation fields with most of the radiation dose originating from thermal neutrons or fast neutrons are obtained, with associated gamma ray absorbed doses ranging from 35% to 90%. The mean quality factors derived are in agreement (±10%) for situations where most of the radiation dose is due to fast neutrons. When most of the delivered dose is due to thermal or intermediate neutrons, the Rossi counter systematically predicts smaller (30 to 40%) quality factors than the high pressure TE chamber, this observation being confirmed on theoretical grounds, as most of the neutrons interacting with the Rossi counter do not cross the counter at these energies (i.e. they are 'stoppers'). The practical advantages and disadvantages of using either instrument in a particular situation are discussed.

Microdosimetric Characterisation of Radiation Fields with a High Pressure Ionisation Chamber: A Comparison with the Low Pressure Proportional Counter

Microdosimetric Characterisation of Radiation Fields with a High Pressure Ionisation Chamber: A Comparison with the Low Pressure Proportional Counter

Results of the experiment on the search for double beta decay of 136Xe, 134Xe and 124Xe

The limits on different 2ß − -decay modes of 136Xe and 134Xe and also 2ß + -and Kß + -decay modes of 124Xe are obtained using a high pressure ionization chamber. In particular, for the 2ß(2ν)-decay of 136Xe it is found that T 1 2 >8.4 × 10 19 yr .

A high pressure ionization chamber to observe ββ-decay in 136Xe

The energy resolution of liquid ionization detectors is limited by the initial recombination of ions and electrons formed by δ-electrons along the ionization track. We have constructed a high pressure ionization chamber in which the recombination problem has been overcome by reducing the density of the medium. Energy resolution is 2% at 1 MeV in argon at 108 atm and a drift field of 0.7 kV/cm and 5% in xenon at 30 atm. We measure the pressure-dependent effects of electronegative impurities. We will use this detector to do a ββ-decay experiment in 136Xe.

Determination of the Recombination Index of Quality for Neutrons and Charged Particles Employing High Pressure Ionisation Chambers

Abstract The concept of the recombination index of quality (RIQ) is based on the degree of initial recombination and was introduced to provide a measurable quantity of radiation quality. The RIQR values can be determined employing a high pressure ionisation chamber operated under saturation conditions and at a suitable collecting potential, UR. Experiments were performed with various types of radiation including monoenergetic neutrons with energies of 0.9, 2.1, 5.5 and 14 MeV, polyenergetic neutrons (Pu-Be and 252Cf with different filters), high energy protons and alpha particles from natural uranium. To obtain RIQ values for neutrons alone, the photon component of the total absorbed dose was determined using the twin chamber technique and the photon component was subtracted from the total RIQ. It is shown that RIQ4 values can estimate with good accuracy the quality factor values (ICRP 1973). RIQ1 (or RIQ0.5/1 determined from measurements at saturation and two voltages) can be used for estimation of QF values recently proposed by ICRU. The expected independence of RIQ4 on filling gas pressure was confirmed experimentally for a Pu-Be source.

Distribution of Gamma and Cosmic Ray Exposure Rates in a 12-Storied Concrete Building

General patterns of the ? and cosmic ray exposure rate distribution inside a 12-storied concrete building were obtained through simultaneous measurements using an intrinsic germanium spectrometer, NaI(Tl) scintillation detectors and a high pressure ionisation chamber. In general, the horizontal ? exposure rate increased with distance from a window, then became constant at the interior of a room. The cosmic ray exposure rate decreased with increasing distance from a window, then became constant within the room. The vertical profile of the cosmic ray exposure rate indicated a marked change between the roof and the upper floors because of the filtering out of the soft electromagnetic component of the cosmic ray flux, then decreased slowly with depth in the building. Gamma exposure rates varied from floor to floor and from room to room because of varying wall compositions. The representativeness of a measured value with regard to these observed patterns is also discussed.

Part III preliminary surveillance of prospective site — Environmental considerations —

The environmental issues in the R-project are mainly considered from radiological safety point of view. Supposing a new experimental site for the program to be constructed in Toki Area, land and water surveys have been made since 1982 on the background radiation levels and radioactive material concentrations. Results of in-situ observations using instruments of various types are given and compared, such as TLD's (exposed for every three months), a pressurized ionization chamber, a NaI(Tl) detector in DBM mode, and a portable Ge detector. Also shown are the data from laboratory analyses of sampled materials in α- and γ-spectrometries, and neutron activation method. Tritium concentrations in river water samples have been quarterly measured with a liquid scintillation counter. These kinds of data will further be compiled to define the regional characteristics of the site environments. In relating to the expected radiation yields in the R-project, the importance of monitoring methods effective to pulsed radiation components is particularly emphasized. Possible use of ionization chamber and TLD's for this purpose is discussed in some detail with the preliminary application to the existing tokamak experiments on JIPP T-IIU.

Part III. Preliminary surveillance of prospective site — environmental considerations —

The environmental issues in the R-project are mainly considered from radiological safety point of view. Supposing a new experimental site for the program to be constructed in Toki Area, land and water surveys have been made since 1982 on the background radiation levels and radioactive material concentrations. Results of in-situ observations using instruments of various types are given and compared, such as TLD's (exposed for every three months), a pressurized ionization chamber, a NaI(Tl) detector in DBM mode, and a portable Ge detector. Also shown are the data from laboratory analyses of sampled materials in α- and γ-spectrometries, and neutron activation method. Tritium concentrations in river water samples have been quarterly measured with a liquid scintillation counter. These kinds of data will further be compiled to define the regional characteristics of the site environments. In relating to the expected radiation yields in the R-project, the importance of monitoring methods effective to pulsed radiation components is particularly emphasized. Possible use of ionization chamber and TLD's for this purpose is discussed in some detail with the preliminary application to the existing tokamak experiments on JIPP T-IIU.