High-energy Neutron Source Research Articles

A High-Performance D-Lithium Neutron Source for Fusion Technology Testing: Accelerator Driver Design

Recent advances in high-current linear accelerator technology have considerably increased the attractiveness of a deuterium-lithium high-energy neutron source for fusion materials and technology testing. This paper describes a new Los Alamos conceptual design for a deuteron accelerator aimed at meeting near-term flux requirements of an International Fusion Materials Irradiation Facility. The lithium target, neutronics, and irradiation facilities are discussed in a companion paper1 at this conference. The new neutron-source driver concept is based on the idea of multiple accelerator modules, with each module consisting of two 125-mA, 175-MHz radiofrequency quadrupoles funneling 3-MeV cw deuteron beams into a 35-MeV, 250-mA, 350-MHz drift-tube linac.

Neutron-Induced Photon Production Cross Sections

A procedure for the determination of neutron-induced photon production cross sections is described, including corrections for the neutron-induced photon background and the unfolding of the gamma-ray spectra. As an example, data have been obtained for tantalum and beryllium with five bismuth germanate detectors and the high-energy white neutron source at the Los Alamos Meson Physics Facility. Calculations and measurements indicate that a beryllium sample may be used to simulate a neutron-induced photon background. Results for the Ta(n,chi..gamma..) reaction for neutron energies below E/sub n/ = 20 MeV are compared with previous measurements at the Oak Ridge Electron Linear Accelerator.

Beam-driven ultra-low-q torus for intense 14MeV neutron source.

This paper studies a conceptual design of a compact high-energy neutron source which might be considered for applications in the field of fusion-material researches. A possibility of a compact neutron source has been found by matching advantages of the ULQ equilibrium and the beam-driven (TCT) concept. The ULQ configuration, which is in the safety-factor <1 regime, permits a large plasma current, so that has a strong poloidal field that confines high energy beam particles injected to enhance the fusion reaction (TCT concept). The ULQ/TCT neutron source designed here has the following favorable characteristics. (1) Compact dimension is obtained. (Major radius= 2.5m, minor radius=0.4m, neutron wall loading=1.4MW/m2) (2) Small toroidal field (4.6T) is enough to carry large plasma current. (3) Small confinement time is enough to ignite the plasma. (4) The TCT D-beam produces the beam-driven plasma current that is strong enough to sustain the total equilibrium current.

Theoretical investigation of neutron scattering cross sections in Si and Ge.

The development of high-flux high-energy pulsed neutron sources makes it possible to study electronic transitions in solids which are in the electron-volt range. A theoretical study has been carried out to determine the feasibility of using such sources to obtain information about the band structure of semiconductors. Calculations of the inelastic neutron scattering cross sections for germanium and silicon based on an empirical pseudopotential description of the energy bands have been com- pleted. This study is an extension of previous work to more realistic (larger) momentum transfers. The calculated cross sections were found to be quite small for realistic experimental conditions. Measurement of these relatively small cross sections could, however, provide important information about the band structure of semiconductors which cannot be obtained from most other experimental techniques.

New neutron cross sections for fusion materials studies

Abstract Neutron cross sections are being developed for a variety of fusion-related applications including neutron dosimetry, fusion plasma diagnostics, the activation of very long-lived isotopes, and high-energy accelerator neutron sources.

Prediction of high-energy spin-wave excitation in iron.

Calculations have been made of inelastic neutron-scattering cross sections for ferromagnetic iron. Quite unexpectedly, a rich picture of high-energy collective excitations has emerged. In particular, ''optic'' spin-wave modes with energies ranging to about 750 meV are predicted. Thus, iron is an ideal candidate for a novel high-energy-transfer experiment on recently developed high-energy neutron sources.

Stratton Field, Texas Gulf Coast: A Successful Cased-Hole Re-Evaluation of an Old Field to Determine Remaining Reserves and to Increase Production Level

Summary Recompletion decisions at Stratton field historically have been complicated by the presence of many thin sand lenses of widely varying pay quality. The advent of a cased-hole formation evaluation tool-the dual detector pulsed neutron log (DDPN)-has simplified matters greatly by revealing current, detailed information about reservoir rock properties and fluid saturations. By using 4 years of recompletion data, DDPN log characteristics and log derived parameters have been identified and used successfully to distinguish between gas-, oil-, and water-bearing zones, to predict when fracture stimulations will be required to produce at commercial gas rates, to tify depleted gas zones, and to rank potential recompletion zones according to their respective absolute open-flow potentials (OFP's). potentials (OFP's). Introduction Stratton-Agua Dulce field, discovered in the late 1930's, is a gulf coast field located about 45 miles [72 km] west of Corpus Christi, TX (see Fig. 1). Production is from the Frio and upper Vicksburg formations (Oligocene shaley sands), with the typical wellbore penetrating more than 25 reservoirs scattered throughout a 3,000-ft [914-m] interval (see Fig. 2 for a type log). The reservoirs are relatively thin sand lenses, ranging from 5 to 20 ft [1.5 to 6.1 m] gross interval. The areal extent of these resvoirs is limited by both the many down-to-the-coast faults in the area and reservoir pinchouts attributed to sand depositional environments. Thus recompletion attempts have been complicated not only by the sheer number of reservoirs, but by the complex geology of the area. It is quite common that recompletion attempts reveal a sand that is wet, depleted, or tight but productive in an ediate offset well. Likewise, sands known to be wet or depleted in some wells often are found to be commercial in offset recompletion attempts. With the increase in hydrocarbon value since 1978, recompletion econonmics have improved vastly and created a need for a tool to help identify the best possible zone remaining in the wellbore. The original suite of openhole logs (for all the older wells this consisted of simply an electric log) was not found to be useful since production from a given reservoir in offset wells could raise a water table into the prospective zone or pressure deplete it. Migration of gas between zones behind pipe also has been found to occur. The tool with the highest degree of success in recompletion attempts is the DDPN. Specifically designed to be run in a cased hole, it consists of a high-energy neutron source and two detectors in a logging sonde. The DDPN had been accepted in areas of the Texas gulf coast with highly saline water before 1978; however, the lower Stratton water salinities (15,000 ppm total Cl ) had delayed use of the log in Stratton. After some experimentation it was determined that indeed the DDPN could be used in Stratton since, although not fully understood, the DDPN routinely recorded capture cross-section values (E) in the range of 24 to 30 c.u. for Stratton's wet, shaly Frio sandstones. Equivalent to a much larger indicated water salinity (50, OW to 80, OW ppm total Cl ), this allowed the required resolution to discriminate between hydrocarbonand water-bearing sands. Additionally, the newer generation of DDPN equipment offered both porosity indicators and gas detection. The DDPN, therefore, was selected for cased-hole recompletion analysis and subsequently assisted in both selection of recompletion zones and updating the condition of producing reservoirs. Theoretical calculations based on DDPN tool responses are used to calculate rock porosities and fluid saturations of behind-pipe zones. Schlumberger's experiences with recompletion results since 1978 have determined certain log characteristics and log-derived parameters useful as guidelines to predict the parameters useful as guidelines to predict the commercial potential of a candidate recompletion zone in Stratton field. They used a (effective porosity times water saturation) product of 10% or less as indicative of a commercial hydrocarbon zone. This paper refines the service company pay cutoff by establishing correlations between actual recompletion attempt results at Stratton and the corresponding DDPN curve readings. Over the last 4 years, we ran 27 DDPN logs in Stratton field (see Fig. 3) and attempted a total of 76 recompletions across the logged intervals. JPT p. 105

The development of small specimen mechanical test techniques

The current program plan for the development of materials for fusion reactors requires testing candidate materials in both fission reactors and high energy neutron sources. Because of the volume limitations of available facilities, both current and near term, and because of the relatively large number of materials and test conditions that will need to be explored, it is essential that test techniques be developed to extract mechanical property information from small volume specimens. A variety of such test techniques are under development at the University of California, Santa Barbara. These include instrumented microhardness, bulge, shear punch, indentation creep and load relaxation and miniaturized fracture tests for obtaining strength, ductility, time-dependent flow, and fracture behavior information on specimens as small as TEM discs.

Successful Application of Carbon/Oxygen Logging to Coalbed Exploration

Summary Two primary objectives of TRW's involvement as integrating contractor for the U.S. DOE's Methane Recovery from Coalbeds Project (MRCP) are (1) to demonstrate that this unconventional methane resource can be characterized and (2) to select target sites with the greatest production potential. It was contemplated that the wireline carbon/oxygen (C/O) logging tool could help the project's activities meet these objectives. A study using the C/O tool was initiated in the Arkoma basin at the Barringer Well 1–11 located in the Kiowa syncline, Pittsburg County, OK. Several nearby wells are producing methane commercially from strata that are associated with these coalbeds. The C/O log has shown that the various coalbeds in the Barringer well can be delineated. C/O ratio measurements have proved a valuable means of determining the presence of coal behind casing. Results from the Barringer well study indicate that this tool can identify and locate coal behind casing for possible recompletion and production of associated coalbed methane. Comparative data based on previous logging programs for the uncased Barringer Well 1–11 and laboratory studies on the coal are presented. Introduction The Arkoma basin contains extensive bituminous coal reserves. Accurate coalbed correlation and coalbed thickness are essential prerequisites to the determination of coal resources and reserves, especially those beds that are particularly gassy. The coals in the basin are generally considered moderately to highly gassy (appx. 200 to greater than 500 cu ft/ton). A range in coalbed methane contents is to be established for each bed and is used in conjunction with the verified coalbed reserves to provide an estimate of the volume of methane in place. Mustang Production Co. of Oklahoma City completed a successful coalbed characterization field test using the C/O tool during Jan. 1980. The cased test well. Barringer 1–11, is located in the Kiowa syncline (west central part of the Arkoma basin), Pittsburg County, OK (Fig. 1). This well penetrates about 18 possible coalbeds of Desmoinesian age (Pennsylvanian) over a 4.635-ft interval (Table 1). Several offset wells are producing methane commercially from strata associated with coalbeds in the Kiowa syncline. The objectives of this field test were to demonstrate that coalbeds can be (1) identified and located behind casing, (2) distinguished from gas-producing zones. and (3) shown to contain gas. Examples of the C/O tool response to coal are presented. Discussion of the field test includes a description of completed MRCP activities in the Arkoma basin, the resulting MRCP well test data, the C/O log field test configuration, and the test description. Comparison of the C/O results were made with openhole log information. Results have shown that the C/O logging tool successfully delineated the various coalbeds in the Barringer well. Application of the C/O log includes:identification of coalbeds behind casing,differentiation of coalbeds from gas zones,location of thin coalbeds on the order of 1 ft thick, anddetermination of coal quality. C/O Tool Response to Coal The C/O log utilizes a high-energy pulsed neutron source that produces 14-MeV neutrons by the deuterium/tritium reaction. Under high-energy neutron irradiation, elements emit gamma rays with specific energy levels. JPT P. 421^

Multi-element analysis of coal during borehole logging by measurement of prompt γ-rays from thermal neutron capture

The performance of borehold logging equipment is described which is based on a 252Cf neutron source and measurement of the spectra of thermal neutron capture γ-rays from most of the important elements in coal. It is shown that although a high statistical counting accuracy can be obtained for several elements in a measuring period of about 5 min, the derived concentrations are limited by the low capture cross-section of carbon. It is concluded that it is strongly preferable to employ a high energy neutron source, such as 241Am-Be, so as to include oxygen in the analysis and to obtain a higher precision of measurement for all the other elements.

Microhardness tests for high energy neutron source experiments

In a development effort to extract mechanical property information from miniature specimens, standard diamond pyramid microhardness (DPH) tests have been conducted at Hanford Engineering Development Laboratory (HEDL) on specimens irradiated in the rotating target neutron target neutron source (RTNS-II); and techniques to extend the information available from microhardness tests have been developed at the University of California, Santa Barbara (UCSB). In tests at HEDL, radiation hardening has only been observed in pure metals irradiated to neutron fluences less than 4 × 10 21 n/m 2. In copper, specifically, a proprotional increase in the DPH with neutron fluence has been observed, and this microhardness increase has been correlated with an increase in the 0.2 percent offset yield strength. At UCSB it has been found that hardness and microhardness data obtained with spherical indenters can be used to determine the true stress-true plastic strain relationship of the test material; moreover, it has been found that features of the indentation lip geometry can be used to characterize localized flow phenomena like Lüders strain in steel. Consequently, microhardness test techniques appear attractive for small specimen test applications.

Hydrogen bonding and hydrogen motion in some alkali metal dicarboxylates studied using incoherent inelastic neutron scattering spectroscopy

Incoherent inelastic neutron scattering spectra of MH(CO 2CX 3) 2, M  Na, K; X  F, Cl are presented for energy transfers in the range 350 → 2000 cm −1. Despite the complexity of these salts the observation of those normal modes of vibration which involve motion of the hydrogen atom is relatively simple. This is primarily due to the sensitivity of incoherent neutron scattering spectroscopy to the motion of hydrogen atoms and to the availability of an intense source of high energy neutrons. In the case of KH(CO 2CF 3) 2 we were able to determine which of the two previously published assignment schemes, based on optical data, for the vibrations of the hydrogen bond is the correct one. Several different methods of predicting the intensities of neutron scattering bands were tried and the results compared with the observed values.

Summary of high energy neutron sources and their characteristics

The neutron sources presently in use in clinical neutron therapy and several proposed are reviwed as to their engineering problems and dose distribution characteristics. For the deuteron on beryllium sources presently being used in neutron therapy the following observations are made: • source reliability to date has been quite acceptable; • skin sparing obtained increases with increasing deuteron energy, 16 MeV d +, Be gives a dose buildup similar to 137Cs and that for 30 MeV d +, Be is similar to 60Co; • depth dose increases with increasing deuteron energy with the 30 MeV d +, Be depth dose distribution similar to that for 60Co. The use of protons on beryllium results in dose distributions which agree well with those of the d +, Be source for equivalent energies. The only major difference is a lower neutron yield for the p +, Be reaction which requires target power loadings five to six times as great for a given dose rate. Comparable data for the d +, T sources are presented and the target power dissipation problems which have plagued this design for a number of years are discussed. Data are presented supporting the contention that in phantom scattering for neutron therapy sources is large enough to warrant accepting a total dose shield leakage value of 1% as opposed to the 0.1% for photon sources.

High-pressure gas target for the production of intense fast-neutron beams

A high-pressure, liquid-nitrogen cooled gas target is described which is suitable as an intense high-energy neutron source using the 2H(d, n) reaction. Details of the design and construction are given and the performance of the target with respect to gas pressure, beam intensity, and gas density is discussed and illustrated. Measured neutron spectra and intensities agree with predictions.

OER reduction with high-energy nuetrons

We recently reported that neutrons produced by 80 MeV deuterons bombarding a thick beryllium target have an OER = 1·3 ± 0·2 measured with Vicia seedlings (Harrison et al., 1975). This study has been extended to include additional measurements with other high-energy neutron sources (Table I). The mean neutron energies were obtained from time-of-flight energy spectra; these spectra and other physical and dosimetric data will appear elsewhere (Harrison et al., 1976).

Neutron scattering by polaritons: Mechanical excitation of the polariton

The displacement-displacement correlation function in the case of an isotropic ionic crystal with several optic branches has been calculated to determine the inelastic-scattering neutron cross section. We have examined the feasibility of an experiment to measure the dispersion curves and the density of states of the polar modes. The infrared electromagnetic field outside the crystal associated with the polariton excitation has been considered and found directly related to the polariton density of states. Though relevant information can be gained by this kind of experiment, its feasibility seems to be subordinate to the planned fulfilment of the high-energy pulsed neutron sources.

The Inelastic Scattering of 15-Mev Neutrons by Lead, Iron, and Aluminum

A tritium-zirconium target bombarded by 1.0-Mev deuterons from the Rockefeller electrostatic generator was used as a source of high energy (\ensuremath{\sim}15-Mev) neutrons. This source was surrounded by lead, iron, and aluminum scatterers with dimensions of approximately one mean free path for inelastic scattering. The resulting neutron spectra were measured by means of proton recoils in photographic emulsions. An exposure without scatterer permitted an evaluation of the upper limit for the neutron background. The spectra indicate that most of the neutrons are inelastically scattered to energies below 3 Mev in the case of the lead and iron scatterers and to below 5 Mev with the aluminum scatterer. The data can be represented by a curve of the form (const $E{e}^{\ensuremath{-}\frac{E}{T}}$) as predicted by the Weisskopf statistical theory. The values obtained for the nuclear temperatures, $T$, are 0.7, 0.6, and 1.1 Mev for lead, iron, and aluminum, respectively. The fact that the measured temperatures for iron and lead are approximately the same supports the hypothesis that lead nuclei have a closed shell structure and therefore have properties similar to much lighter nuclei.

Total cross-section of hydrogen and carbon for 153-MeV. neutrons.

WE have used the 110-in. Harwell cyclotron1 as a source of high-energy neutrons for total cross-section measurements in good geometry. An internal beryllium target 8.9 mm. thick was bombarded by about 1 µ amp. of 171-MeV. protons, and neutrons emerging near the forward direction were collimated by a series of 5-cm. diameter holes through three concrete screening walls. A polythene disk 19 mm. thick and 6.3 cm. in diameter was set up in the beam at a distance of 16 metres from the target. Protons ejected from the disk at an angle of 10° to the forward direction were detected by a triple-coincidence proportional counter telescope. Carbon absorbers placed between the counters in the telescope ensured that only protons with an energy greater than 141 MeV. were counted. This placed a lower limit of 145 MeV. on the energy of the neutrons detected, while an upper limit of 169 MeV. was set by the energy of the primary protons in the cyclotron. In a subsidiary experiment, the high-energy part of the neutron-energy spectrum was investigated by varying the amount of carbon absorber in the telescope. The results showed that the effective mean energy of the neutrons during the total cross-section work was 153 MeV.

The Scattering of Neutrons of Energy between 12.0 Mev and 13.0 Mev by Protons

The angular distribution of the recoil protons projected during the scattering of neutrons by protons has been investigated in a methane-filled, high pressure cloud chamber. A deuterium gas target bombarded with 10 Mev deuterons provided the high energy neutron source. The spectrum of the neutrons from this source, which entered the cloud chamber through a collimator, was surveyed and showed a group of high energy neutrons superimposed on a continuous background. Examination of the data with rigorous selection criteria to determine those recoils projected by the scattering of neutrons between 12.0 Mev and 13.0 Mev yielded a total of 1573 recoil protons. The azimuthal and recoil angle distributions of these protons have been analyzed. A ratio of the differential cross sections for neutron scattering in the backward direction to scattering in a direction perpendicular to that of the incident neutron beam, of unity (spherically symmetric scattering) or slightly greater than unity can be consistent with these data.