The present status of core-collapse supernova models as well as the role played by neutrons and weak interaction processes are discussed. Special attention is given to the necessary microphysics input data and to possible observational tests. It is demonstrated that certain properties of neutron-rich matter are crucial for the dynamics of supernova explosions including, in particular, the nuclear equation of state. As far as neutrinos are concerned theoretical predictions and expectations are in fairly good agreement with the luminosity and average energy of neutrinos observed from SN 1987A, provided they signaled the formation of a neutron star. In addition, there are indirect ways to constrain the models, such as the optical light curves and nucleosynthesis predictions. They also are discussed.

Most naturally occurring elements were evidently synthesized in the interiors of stars, and, in particular, most of the heavy ones via neutron capture processes. We present here an introductory review on the stellar alchemy by neutrons. In due course, we attempt to cover the very basics through the latest developments of theoretical studies of the rapid (r-) process.

The excitations functions of the reactions ⁹Be((alpha) ,n)¹²C, ¹³C((alpha) ,n)¹⁶O, ¹⁷O((alpha) ,n)²⁰Ne, ¹⁸O((alpha) ,n)²¹Ne, ²¹Ne((alpha) ,n)²⁴Mg, ²²Ne((alpha) ,n)²⁵Mg, ²⁵Mg((alpha) ,n)²⁸Si and ²⁶Mg((alpha) ,n)²⁹Si have been measured at the 4 MV dynamitron accelerator in Stuttgart, Germany in the energy range of astrophysical interest, and from these S-factor- curves have been determined. Advanced techniques, especially with the windowless gastarget facility Rhinoceros have been applied. For neutron detection NE213 scintillation counters and a long counter like 4(pi) -detector have been used. A sensitivity limit in the range of 10^-10b to 10^-\11b was reached with these experiments. Using our new experimental results astrophysical reaction rates have been calculated for all reactions except the Mg-reactions. Analytic expressions have been fitted to all reaction rates.

Neutron capture nucleosynthesis during stellar helium burning (s-process) accounts for the production of about half of the elements heavier than iron. Since this process involves mostly stable nuclei along the stability valley, the related nuclear physics data can be determined in laboratory experiments. This allows a quantitative reproduction of the observed abundances. A particularly interesting feature of the s-process is the occurrence of the so-called branchings in the neutron capture chain. Whenever the reaction flow encounters an unstable isotope with a halflife similar to the neutron capture time, competition between (beta) -decay and neutron capture gives rise to such a branching. The resulting abundance pattern can be analyzed in terms of the stellar neutron flux. In some cases the branchings are even sensitive to the temperature and density in the stellar plasma. The current status of this important source of information on the late stages of stellar evolution is reviewed and compared to the yet uncertain stellar models.

From calculations of the r-process abundance pattern, constraints on stellar as well as nuclear parameters are deduced. Deviations between calculated and observed abundances are interpreted as hints to deficiencies in existing nuclear models. New structure effects related to the extreme neutron-excesses of the nuclei in the r-process path are discussed.

The (n,(gamma) )-cross sections for neutron-rich oxygen isotopes have been calculated in the direct capture model. The experimental data for ¹⁸O(n,(gamma) )¹⁹O can be reproduced using this model. Compared to previous work the cross section for ^{19- 21}O(n,(gamma) )^20-22O are enhanced considerably by factors between four and 300.

A new technique for measurements of total neutron cross sections is presented. This method has been applied to measurements of the excitation function for the ¹¹B + n system at E_n equals 7.2 - 8.5 MeV, in order to obtain the ⁸Li(n,(alpha) )¹¹B thermonuclear reaction rate.

The Weapons Neutron Research Facility (WNR) is an intense, high energy spallation source, driven by the LAMPF 800 MeV proton linac. We describe below some of the basic and applied research projects which are currently being worked on at this facility

An inexpensive spectrometer has been developed for the study of charged particle reactions induced by 22 MeV neutrons. The principal components of the spectrometer are three flat multiwire proportional counters which act as energy loss detectors and a curved plastic scintillator as an energy detector. This novel combination provides background suppression, particle identification, and energy resolution of < 0.7 MeV for 6 - 22 MeV protons and 8 - 20 MeV deuterons. The spectrometer allows the simultaneous accumulation of data over an angular range of 70 degree(s) with an angle resolution < 5 degree(s) (FWHM), and thus makes feasible angular distribution studies of (n,p) and (n,d) reactions on selected targets. The spectrometer has been recently extended for the study of reactions induced by 60 - 200 MeV neutrons.

We modify the standard statistical model for precompound reactions (exciton model) by taking into account the correlations between fluctuating S-matrix elements with different total spin values. While angle-integrated cross-sections are not affected by our modification, differential cross-sections become asymmetric about 90 degree(s) c.m. This asymmetry weakens with time and with increasing complexity of the decaying nuclear system, but need not disappear even for the compound (thermalized) system. We present a comparison with data on double differential cross-sections in ¹⁸⁴W(n,n') and ²⁰⁹Bi(n,n') inelastic scattering showing such an asymmetry.

Detection of outgoing neutrons after pion absorption on nuclei is discussed. The importance of good energy and position resolution together with the knowledge of integral and differential neutron detection efficiency in the range from 10 MeV to 300 MeV is emphasized. Light response coefficients recently obtained for typical organic scintillators are given and Monte Carlo codes for neutron detection efficiency calculations are reviewed. Detection characteristics for neutrons of the large area position-sensitive TOF detector and the 4(pi) detector LADS, both developed at PSI to study pion-nucleus absorption, are described for the cases of kinematically complete multi-particle final states.

A research program on optical potentials has been performed for a broad range of nuclei. The data were deduced from the simultaneous measurement of the angular distributions of analyzing power and differential cross section in a polarized neutron scattering experiment. For these experiments the facility Scorpion has been used, and it is briefly characterized. Some typical results are shown in this overview.

Nuclear power reactor safety in the United States is about to enter a new era -- an era of risk- based management and risk-based regulation. First, there was the age of `prescribed safety assessment,' during which a series of design-basis accidents in eight categories of severity, or classes, were postulated and analyzed. Toward the end of that era, it was recognized that `Class 9,' or `beyond design basis,' accidents would need special attention because of the potentially severe health and financial consequences of these accidents. The accident at Three Mile Island showed that sequences of low-consequence, high-frequency events and human errors can be much more risk dominant than the Class 9 accidents. A different form of safety assessment, PSA, emerged and began to gain ground against the deterministic safety establishment. Eventually, this led to the current regulatory requirements for individual plant examinations (IPEs). The IPEs can serve as a basis for risk-based regulation and management, a concept that may ultimately transform the U.S. regulatory process from its traditional deterministic foundations to a process predicated upon PSA. Beyond the possibility of a regulatory environment predicated upon PSA lies the possibility of using PSA as the foundation for managing daily nuclear power plant operations.

This paper provides a general description of the various Soviet-designed reactor types operating in the countries of the former Soviet Union (FSU) and Eastern and Central Europe and the various safety issues associated with each reactor type, in terms of their design and operation. It also provides a general safety assessment and the technical potential for safety improvement for each reactor type (including potential short-term and longer-term actions). Other issues discussed, including their effect on safety, include organizational problems, lack of well established regulatory organizations, and the changing socio-political and economic situation. The condition of the Chernobyl sarcophagus and safety concerns related to it are addressed. Finally, international efforts and programs underway, including those originating in the USA, to provide financial and technical assistance to secure safety improvements and encourage indigenous improvements are noted.

Accelerator based monoenergetic neutron sources are reviewed for neutron energies between 20 keV and 200 MeV. In particular the reactions ³H(p,n)³He, ⁷Li(p,n)⁷Be, ¹¹B(p,n)¹¹C, ²H(d,n)³He, ²H(t,n)⁴He, ³H(d,n)⁴He, ¹H(t,n)³He, ¹H(⁷Li,n)⁷Be, ¹H(¹¹B,n)¹¹C, ¹H(¹³C,n)¹³N, and ¹H(¹⁵N,n)¹⁵O are considered. Special emphasis is laid on new developments at low and high energies, on sources of kinematically collimated neutrons, and on intense monoenergetic sources.

While nuclear fission research reactors as sources of a high thermal flux have more or less reached their limits as imposed by power density in the core, accelerator based spallation neutron sources are still largely a matter of development. The low power facilities (less than 0.5 MW of beam power) built and operated so far have successfully demonstrated the potential of the technique and have triggered several proposals for new installations in the medium power range (0.5 to 5 MW). Most of these projects relate to pulsed neutron sources which have enhanced capabilities for many techniques of neutron scattering work but are less suitable for other applications which require a high time average flux as provided by cw-sources. In both cases there is a rather limited data base on the radiation effects and other parameters affecting the design and life time of their targets. At present, there is one new spallation neutron source under construction, SINQ in Switzerland. It is expected to deliver neutrons as of 1996 and, apart from neutron scattering experiments with thermal and cold neutrons, it will also provide isotope production and activation analysis capabilities as well as opportunities for target development work.

Compact ion linacs based on the radio frequency quadrupole (RFQ) can provide a wide range of neutron energies and fluxes. High current capability and flexibility of accelerated particles and output energies make these modern commercial accelerators well suited for providing either low energy neutrons for activation analysis, radiography and materials research, or high energy neutrons for cancer therapy and physics research. A description of these new compact ion linacs and a discussion of present and future applications using commercially available systems are presented here.

A method to determine an effective energy for beams with energies less than 100 meV is proposed using measured transmittances for neutron beams with continuum spectra. Effective energies for unknown beams were determined from a ratio of effective total macroscopic cross section of Ti to that of Pb. The effective energies are calibrated using mean energies from known neutron spectra of a thermal-neutron and two cold-neutron beams generated from research reactors. Results are summarized in a table and maximum systematic uncertainties of effective energies are estimated to be 14% for thermal and 27% for cold neutron regions.

When the goal of recycling nuclear waste is applied to the nuclear electricity generation, it leads to the recycling of plutonium first, then of other heavy radioactive nuclides as minor actinides (M.A.), and of a few long lived fission products. It is shown that several ways to recycle plutonium are possible and that this recycling allows one to better manage minor actinides and residual uranium.

Being able to produce pulses of neutrons differentiates sealed tube neutron generators from isotopic sources and they've become absolutely essential for a number of measurements. We briefly review pulsed neutron measurements in oil well logging, mineral exploration, and process control, emphasizing the neutron burst timing requirements. We then discuss the neutron burst timing properties of two types of neutron generators. One, currently the standard version, has a cold cathode Penning ion source, and the other, recently introduced into commercial service, uses a thermionic ion source.

Characterization of sealed containers requires the use of many techniques. These techniques may be via active interrogation or, if the contents are radioactive, by a variety of passive techniques. One of the frequently used interrogative techniques is neutron interrogation, thermal or fast. The resultant detected radiation can be either neutrons or photons (gamma- rays). The use of neutrons is greatly influenced by the presence of moderators (mainly ¹H) and neutron absorbers (¹H, Cd, etc.). Complete characterization of such containers also requires the determination of substances (e.g., mercury) which do not produce neutrons as a result of neutron interrogation. To solve some of these characterization challenges a facility is required to study neutron capture leading to the production of more neutrons [i.e. (n,f)] or to other reactions such as (n,(gamma) ). Among the requirements of such a facility are good neutron conservation, efficient neutron moderation and long thermal neutron die-away time. Since one of the materials to be identified and quantified is ¹H the facility must not contain this nuclide if possible.

A new pulsed neutron generator system has been introduced. It is based on a sealed tube neutron generator using the deuterium-tritium fusion reaction. The new system incorporates latest technology features in its electronics, neutron head configuration, and computer control. These address common concerns about neutron generators such as economics, ease of use, and safety. The system is extremely flexible and adaptable to a very wide range of applications in the field of materials non-destructive analysis.

The 14 MeV neutron generator (FNG), in operation at the ENEA Energy Center of Frascati, Italy, is described. It produces up to 1 X 10¹¹ neutrons per second and consists essentially of a deuterium-ion accelerator, a beam transport system, and a target of titanium tritide, where neutrons are produced by the T(d,n)⁴He fusion reactions. An application of FNG in the context of research activity on controlled thermonuclear fusion research is also briefly described.

The Austrian Federal Government is promoting the installation of an international research center in Austria. The Austron project, supported by scientists throughout Europe, is likely to become this center. In December 1992 the Austrian Federal Government expressed its support for a proposal made by the Minister of Science and Research, E. Busek. This proposal stated that the Austrian government would be prepared to finance the Austron project by up to 1 billion Austrian schillings (about one third of the estimated construction costs) provided that partner countries assume the remaining costs.

The formation cross sections of tritium from oxygen have been measured in p-Li and p-Be neutron fields installed at the INS SF cyclotron in order to estimate the production of tritium in the cooling water of accelerators. Irradiations were performed with the semi-monoenergetic neutrons produced from the ⁷Li(p,n) reaction at proton energies (Ep) from 20 up to 40 MeV in 5 MeV steps and those from ⁹Be(p,n) in 2.5 MeV steps with proton intensities of 2 - 5 (mu) A, which yields from 10¹¹ to 10¹² n/cm² at the target position. The neutron energy spectra were determined by an NE-213 scintillator. The tritium produced in the water used as the oxygen target was extracted by a distillation method, and measured by a liquid scintillation counter. The excitation functions for ¹⁶O(n,t)¹⁴N reaction obtained by the p-Li and p-Be neutrons agreed well with each other within the experimental uncertainties.

The use of the absolute radiometric techniques for the E. C. bulk shield experiment at the 14 MeV Frascati Neutron Generator (FNG) is reported. In this application, the activity level, in some cases, results too low to be measured at the Frascati counting station. In these cases the radiometric measurements are performed using the low background HPGe detectors located at the underground laboratory of Gran Sasso d'Italia. The use of these detectors enhances the FNG capability of performing bulk shield benchmark experiments allowing the measurements of very low activation levels.

Recent developments in accelerator technology enable high current proton or deuteron beams production up to several milliamps, providing attractive sources for high neutron yield production. Be(p,n), Be(d,n) and ²³⁸U(X,n) reactions are discussed to produce high energy and thermal neutron yields. A 140 MeV, 2.5 mA extracted beam cyclotron is also proposed to feed a spallation neutron source, generating thermal neutron fluxes similar in intensity to those produced by nuclear reactors.

The concept of the MOL cavity fission spectrum standard neutron field is highlighted. Two applications to neutron dosimetry are treated: (1) Neutron flux determination by distinct fission fragment absolute radiometric measurements on fission foils. (2) Neutron flux determination by detection of the delayed neutrons emitted by a fissile sample. For both applications the measuring technique, the calibration procedure, the application domain, the advantages of the method, as well as the restrictions in absolute neutron flux determination are considered.

In the electron linear accelerators used for radiotherapy by high energy electrons or gamma rays, there is a non negligible production of neutrons by photodisintegration or electrodisintegration reactions on the high Z components of the head machine (target, flattening filter, collimators). At the Experimental Physics Department of Torino University, Torino, Italy an experimental and theoretical evaluation has been performed on the undesired neutron production in the MD Class Mevatron Siemens accelerator used at the Radiotherapy Department of S. Giovanni Battista A.S. Hospital for cancer therapy by a 15 MV gamma ray beam. A simulation of the total process has been carried out, using EGS4 MonteCarlo computer code for the evaluation of photoneutron spectra and MCNP code for the neutron transport in the patient's body. The geometrical description both of the accelerator head in EGS4 and of the anthropomorphous phantom in MCNP have been highly optimized. Experimental measurements have been carried out by bubble detectors BD 100R appropriately allocated inside a new phantom in polyetylene and plexiglass, especially designed for this purpose.

Following a brief review of neutron spectrometers used for measurements around nuclear installations, and of the results obtained to date with these devices, the reasons for performing spectrometry measurements are outlined. The implications of measured spectral shapes for neutron dosimetry are then discussed.

Neutron kerma factors can be determined by measuring the cross sections, angular distributions, and charged-particle emission spectra from (n,z) reactions where z stands for the light charged particles, namely protons, deuterons, tritons, ³He, or (alpha) -particles, and combining these data with information on the heavy nuclear recoils. This approach is compared with other approaches of determining kerma factors. Data are given near 14 MeV for materials from carbon to niobium.

This paper presents the development of a new dose equivalent counter for neutron area monitoring. In order to improve the responses of neutron survey meters, a multi-element proportional counter has been designed using the general Monte Carlo code MCNP. The manufacture and calibration of a prototype have been undertaken. Recent measurements have shown that the new detector is capable of producing promising response in terms of the required neutron energy dependence and in providing a counter with reduced weight. A successful solution has been found to the challenge arising following the publication ICRP 60 (1991), whose recommendations lead to a drastic reduction in annual radiation dose limits.

Single event upsets (SEUs) can deposit sufficient electrical charge on integrated circuit nodes to initiate logic state reversal without causing any permanent changes in the device. A hardware system employing dynamic random access memories (dRAMs) is being designed and constructed with a view to using it in neutron detection. Having initially proved that dRAMs can be used as heavy charged particle detectors, it was thought that these devices can be made sensitive to neutrons by adding a foil to convert the thermal neutrons to charged particles by making use of the (n,(alpha) ) reaction. A model has been developed to examine the use of possible converters with respect to soft error (SE) generation including those factors that determine the optimum thickness and the efficiency of such a detector.

In boron neutron capture therapy (BNCT) the absorbed dose consists of the contribution of many radiation components, and its spatial distribution is highly nonuniform. Three- dimensional dose determinations are therefore to be done, and the utilized dosimeters have to perturb the radiation field as little as possible. Thermoluminescent dosimeters (TLDs) are widely utilized for mapping the radiation field. But TLDs with high sensitivity for thermal neutrons have shown an irreversible damage from such neutrons producing an alteration in the response. A tissue equivalent phantom dosimeter is proposed allowing a 3-D determination of absorbed dose by an NMR imaging of the phantom.

The neutron profile monitor diagnostic at JET consists of two neutron cameras viewing 19 different chords of the plasma through 10 horizontal and 9 vertical collimators. At the end of each collimator, a detector system using liquid scintillators records the neutrons coming from the subtended solid angle. To obtain absolute measurements of the plasma neutron emission, the system has to be calibrated taking into account the neutron transport in the materials constituting the profile monitors. The Monte Carlo code MCNP has been employed to simulate the transport through the cameras, to calculate the corrections to the simple optical model, due to transmission, cross talk, scattering and absorption of neutrons. The result of the simulation has led to correction factors that, depending on the position and the width of the channel considered and on the neutron source energy (2.45 or 14 MeV), can be as large as 20% in a diagnostic which is now calibrated to a few percent.

We have developed a high resolution thermal neutron imaging detector, combining a composite solid neutron convertor and a low-pressure gaseous avalanche electron multiplier. Neutron-induced charged particles from a primary convertor element induce multiple low- energy secondary electrons from a second electron-emissive film. These are multiplied in the gas upon their emission. A localization resolution of the order of 0.5 mm (FWHM) was measured with detectors equipped with Gd and Li convertors coated with thin CsI films. These detectors are characterized by good imaging properties (also in divergent neutron beams), fast time resolution, low sensitivity to gamma background, and the capability of operating at very high neutron flux. Possible applications are discussed.

A brief review is given of position-sensitive detector systems for thermal neutron imaging, highlighting novel techniques and the goal of sub-mm spatial resolution. The links between position-sensitive neutron detection and soft x-ray imaging are emphasized.

Thermal and cold neutron probes provide researchers in such fields as materials science, physics, chemistry, and biology information that often can be obtained by no other means. The main focus of this paper is on recent studies at NIST which illustrate how thermal and cold neutrons are utilized for materials research.

This paper outlines some on-line and off-line applications of small accelerator and isotope neutron sources in materials research. The following topics are discussed: determinations of average activating flux and flux density spectra of neutrons inside and outside of bulk samples, activation and prompt radiation analysis of various materials, pulsed neutron methods in elemental analysis, and fast neutron irradiation effects in solids.

Experiments designed to select the most appropriate target material for generating a particular radioactive ion beam (RIB) are in progress at the Oak Ridge National Laboratory. They are important to the future success of the Holifield Radioactive Ion Beam Facility (HRIBF). The 25-MV HHIRF tandem accelerator is used to implant stable complements of interesting radioactive elements into refractory targets mounted in a high-temperature FEBIAD ion source which is `on-line' at the UNISOR facility. The intensity versus time of implanted species, which diffuse from the high-temperature target material (approximately equals 1700 degree(s)C) and are ionized in the FEBIAD ion source, is used to determine release times for a particular projectile/target material combination. From such release data, diffusion coefficients can be derived by fitting the theoretical results obtained by computational solution of Fick's second equation to experimental data. The diffusion coefficient can be used subsequently to predict the release properties of the particular element from the same material in other target geometries and at other temperatures, provided that the activation energy is also known. Diffusion coefficients for Cl implanted into and diffused from CeS and Zr₅Si₃ and As, Br, and Se implanted into and diffused from Zr₅Ge₃ have been derived from the resulting intensity versus time profiles. Brief descriptions of the experimental apparatus and procedures utilized in the present experiments and plans for future related experiments are also presented.

High-resolution neutron diffraction has become a powerful method to determine strains caused by residual stresses in polycrystalline materials on a microstructural scale, measuring distorted lattice plane distances to within an accuracy of better than 0.5 X 10^-4. The method implies very good knowledge of the equivalent undistorted (stress-free) lattice parameters in order to avoid systematic errors. Lattice parameters can also be affected by material composition, so that one can arrive at false values even under stress-free conditions. This has led the authors to use neutrons to measure both lattice distances by neutron time-of- flight (TOF) and chemical composition by prompt-gamma analysis non-destructively at the same time. Aluminum-copper alloys with copper contents between 0.08 and 4.98 weight% have been investigated as model substances, because the aluminum lattice contracts with increasing copper solute.

The role of the reflection phase in the determination of the scattering-length density profile in neutron specular reflection is emphasized. Various schemes for obtaining information on this phase as input to the solution of the inverse scattering problem are discussed. The possible effects of the finite thickness of the substrate on the measurements are considered.

For many years a research program on lithium metazirconate has been underway in the framework between ENEA and the Department of Applied Chemistry and Science of Materials (Bologna University). This research is aimed to verify the possibility of using such material as a breeder in future nuclear fusion reactors. The research program includes studies on nuclear properties and experimental work on the development of fabrication methods and the characterization of sintered samples, with the aim to verify that lithium metazirconate has the nuclear, physical, chemical, and mechanical properties able to satisfy the requested performance in the blanket of a fusion reactor. The metazirconate is developed as an alternative to other breeding materials, such as (gamma) -aluminate and silicates. One of the most interesting properties of the zirconate, as compared to the other candidate materials, regards its better behavior in releasing tritium; this very favorable characteristic is the main incentive for strengthening the research. In the choice of a breeding material, it is necessary to take into account all relevant characteristics, also including nuclear properties. The paper describes the results obtained experimentally and by calculation on the main physical and nuclear properties of lithium metazirconate.

This paper provides the highlights of the role risk assessment plays in the United States technology program for nonintrusive inspection of cargo containers for illicit drugs. The Counterdrug Technology Assessment Center is coordinating the national effort to develop prototype technologies for an advanced generation, nonintrusive cargo inspection system. In the future, the U.S. Customs Service could configure advanced technologies for finding not only drugs and other contraband hidden in cargo, but for a wide variety of commodities for customs duty verification purposes. The overall nonintrusive inspection system is envisioned to consist primarily of two classes of subsystems: (1) shipment document examination subsystems to prescreen exporter and importer documents; and (2) chemical and physics-based subsystems to detect and characterize illicit substances. The document examination subsystems would use software algorithms, artificial intelligence, and neural net technology to perform an initial prescreening of the information on the shipping manifest for suspicious patterns. This would be accomplished by creating a `profile' from the shipping information and matching it to trends known to be used by traffickers. The chemical and physics-based subsystems would apply nuclear physics, x-ray, gas chromatography and spectrometry technologies to locate and identify contraband in containers and other conveyances without the need for manual searches. The approach taken includes using technology testbeds to assist in evaluating technology prototypes and testing system concepts in a fully instrumented but realistic operational environment. This approach coupled with a substance signature phenomenology program to characterize those detectable elements of benign, as well as target substances lends itself particularly well to the topics of risk assessment and elemental characterization of substances. A technology testbed established in Tacoma, Washington provides a national facility for testing and evaluating existing and emerging prototype systems in an operational environment. The results of initial tests using the advanced x-ray subsystem installed at the testbed are given in this paper. A description of typical cargo contents and those characteristics applicable to nuclear interrogation techniques are provided in the appendix.

Three techniques are described and compared in this brief review of neutron based technologies for the detection of contraband in cargo containers. These nuclear techniques can be used for explosives detection (physical and airline security), narcotics interdiction and manifest verification (Customs), detection of biological, chemical and nuclear weapons (arms control and non-proliferation) and radwaste remediation and pollution control.

A least-squares algorithm developed for analysis of fast-neutron transmission data resulting from non-destructive interrogation of sealed luggage and containers is subjected to a probabilistic interpretation. The approach is to convert knowledge of uncertainties in the derived areal elemental densities, as provided by this algorithm, into probability information that can be used to judge whether an interrogated object is either benign or potentially contains an illicit substance that should be investigated further. Two approaches are considered in this paper. One involves integration of a normalized probability density function associated with the least-squares solution. The other tests this solution against a hypothesis that the interrogated object indeed contains illicit material. This is accomplished by an application of the F-distribution from statistics. These two methods of data interpretation are applied to specific sets of neutron transmission results produced by Monte Carlo simulation.

A project of a transportable neutron system has been designed for nondestructive detection of weapon materials such as chemical agents or explosives. The system combines imaging and identifying techniques, and uses a sealed tube neutron generator GENIE 46. The neutron emitting module is embedded in a moderator/collimator. The resulting mixed 14 MeV and thermal neutron beam allows the user to perform neutron radiography and gamma-ray spectroscopy. Substances to be detected are imaged in a first step and then identified by comparing relative spectral line intensities with those of reference materials. The moderator provides a first level protection against radiation to the operators. This project includes only industrial sub assemblies, transportable by truck to be used in open area.

Fast-neutron interrogation techniques are of interest for detecting illicit substances such as explosives and drugs because of their ability to identify light elements such as carbon, nitrogen, and oxygen, which are the primary constituents of these materials. Two particular techniques, fast-neutron transmission spectroscopy and pulsed fast-neutron analysis, are discussed. Examples of modeling studies are provided which illustrate the applications of these two techniques.

The application of on-line analysis techniques in the mineral industry allows rapid and accurate analyses to be provided in real time for improved control of processes. The Commonwealth Scientific and Industrial Research Organization (CSIRO) Division of Mineral and Process Engineering has developed a number of on-line analysis systems based on neutron techniques for use in the Australian minerals industry. This paper describes the development of neutron-induced gamma-ray techniques in two different industrial applications, namely, the on-line analysis of low rank coal and the on-line measurement of pre-reduction degree in iron ores.

The interest in bauxite as a major source of alumina results in a strong demand for on-line instrumentation suitable for sorting, blending, and processing operations at the bauxite mine and for monitoring instrumentation in the Bayer process. The results of laboratory experiments based on neutron interactions with bauxite are described. The technique was chosen in order to overcome the problem of spatial heterogeneity in bulk mineral analysis. The evaluated elements contributed to approximately 99.5% of the sample weight. In addition, the measurements provide valuable information on physical parameters such as density, hygrometry, and material flow. Using a pulsed generator, the analysis system offers potential for on-line measurements (borehole logging or conveyor belt). An overall description of the experimental set-up is given. The experimental data include measurements of natural radioactivity, delayed radioactivity induced by activation, and prompt gamma rays following neutron reaction. In situ applications of neutron interactions provide continuous analysis and produce results which are more statistically significant. The key factors contributing to advances in industrial applications are the development of high count rate gamma spectroscopy and computational tools to design measurement systems and interpret their results.

The lineshape of a neutron spectrometer consisting of a single deuterated anthracene scintillation crystal has been investigated as a function of neutron energy from 7 - 30 MeV. The spectrometer has been used to study backscattering of 14 MeV neutrons by samples containing carbon, nitrogen, and oxygen. The results indicate that it should be possible to analyze bulk samples for these elements by means of this technique.

New developments in instrumentation for, and methodology of, Instrumental Neutron Activation Analysis (INAA) may lead to new niches for this method of elemental analysis. This paper describes the possibilities of advanced detectors, automated irradiation and counting stations, and very large sample analysis. An overview is given of some typical new fields of application.

Reference materials (RMs) and certified reference materials (CRMs) are an important tool in achieving measurement compatibility. One of the possible approaches in producing such materials is organization of world-wide interlaboratory comparisons. The sequence of actions that have to be taken in order to prepare and certify a reference material for multielement inorganic trace analysis is described and discussed. The significance of careful supervision by the person responsible for all the steps starting from choice of the material and sampling, through various stages of preparation down to analysis, evaluation of results, and final assigning of `recommended' (certified) and `information' values is emphasized. The significance of using the proper method of data evaluation and proven criteria for assigning `recommended' (certified) values is discussed in detail. It is shown on several examples that neutron activation analysis (NAA) plays a very important and sometimes unique role in the homogeneity checking and certification of reference materials. Some approaches enabling independent validation of the `recommended' or `information' values assigned in the process of certification are demonstrated.

A case history of the calibration of neutron porosity tools is given in the paper. The calibration of neutron porosity tools is one of the most difficult, complicated, and time consuming tasks in the well logging operations in geophysics. A semi empirical approach to this problem is given in the paper. It is based on the correlation of the tool readings observed in known environments with the apparent neutron parameters sensed by the tools. The apparent neutron parameters are functions of the true neutron parameters of geological formations and of the borehole material, borehole diameter, and the tool position inside the borehole. The true integral neutron transport parameters are obtained by the multigroup diffusion approximation for slowing down of neutrons and by one thermal neutron group for the diffusion. In the latter, the effective neutron temperature is taken into account. The problem of the thermal neutron absorption cross section of rocks is discussed in detail from the point of view of its importance for the well logging results and for the experimental techniques being used.

A review of nuclear data for fast neutron activation analysis in different applications has been performed involving isotopic and accelerator induced neutron sources. This review concerns those nuclear data bases and specific handbooks and initiatives completed, underway or planned, according to the advice of the International Nuclear Data Committee in accordance to the international effort coordinated by the IAEA with particular regard to the standards. Specific discussion is devoted to nuclear data requirements for the purposes of the present topic. Main topics on nuclear data evaluation and the corresponding model calculations are reviewed with regard to the activities and results of the ENEA Nuclear Data Program.

Neutron activation analysis was used to determine microelements in Romanian fossil bones and a correlation was found between some elements and ¹⁴C estimated age of the bones. Fluorine and manganese content in the bone structure increases with the time elapsed, during the fossilization. Uranium, sodium, scandium, iron and zinc have also been determined in fossil bones but a relation with the increasing antiquity of the fossil has not been observed. Measurable concentrations of some elements together with known environmental conditions provide a relative tool of dating of bones beyond 70,000 years radiocarbon limit.

The role of neutrons in the management of cancer has a long history. However, it is only in recent years that neutrons are beginning to find an accepted place as an efficacious radiation modality. Fast neutron therapy is already well established for the treatment of certain cancers, and clinical trials are ongoing. Californium neutron sources are being used in brachytherapy. Boron neutron capture therapy has been well tested with thermal neutrons and epithermal neutron dose escalation studies are about to commence in the USA and Europe. Possibilities of neutron induced auger electron therapy are also discussed. With respect to chemotherapy, prompt neutron capture analysis is being used to study the dose optimization of chemotherapy in the management of breast cancer. The rationales behind these applications of neutrons in the management of cancer are examined.

The final goal of any radiotherapy project is to expose the tumor as the target to a lethal dose of ionizing radiation, sparing thereby the surrounding healthy tissues to a maximum extent. Precise treatment is nevertheless essential for cure, since the danger exists that the tumor might re-establish itself if every cancer cell is not destroyed. The conventional therapy treatments existing to date, e.g., surgery, radiation therapy, and chemotherapy, have been successful in curing some kinds of cancers, but still there are many exceptions. In the following, the progress of a promising therapy tool, called the boron neutron capture therapy (BNCT), which has made its dynamic evolution in recent years, is briefly described. The approach towards clinical trials with BNCT is described in detail.

Non-invasive in vivo elemental analysis is a technique used to assess human body composition which is indicative of nutritional status and health condition. The in vivo measurement of the body's major elements is used for a variety of medical studies requiring the determination of the body's compartments (protein, fat, water, bone). Whole body gamma-ray counters, consisting of Nal(Tl) crystal detectors in a shielded room, are used for measuring in vivo the body's Ca, Cl, Na and P by delayed neutron activation analysis. Thermal neutrons from a moderated ²³⁸Pu-Be source are used for the measurement of total body nitrogen (and thus protein) and chlorine at low radiation exposure (0.80 mSv). The resulting high energy prompt gamma-rays from nitrogen (10.83 MeV) and chlorine (6.11 MeV) are detected simultaneously with the irradiation. Body fat (the main energy store) and fat distribution (which relates to risk for cardiovascular disease) are measured by detecting C and O in vivo through fast neutron inelastic scattering. A small sealed D-T neutron generator is used for the pulsed (4 - 8 KHz) production of fast neutrons. Carbon and oxygen are detected by counting the 4.44 and 6.13 MeV gamma-rays resulting from the inelastic scattering of the fast neutrons from the ¹²C and ¹⁶O nuclei, respectively. One use of this method is the systematic study of the mechanisms driving the age-associated depletion of the metabolizing, oxygen-consuming cellular compartment of the body. The understanding of this catabolism may suggest ways to maintain lean tissue and thus to preserve quality of life for the very old.

The production of radioisotopes by fast neutron reactions may be especially useful in lieu of the recent problems with reactor production in the U.S. Some of the fast neutron (n,2n) nuclear reactions are quite large and may be used to produce radioisotopes with little additional radioactive waste. For example, ^99mTc, which is used for more than 80% of the diagnostic imaging in nuclear medicine, is generated from ⁹⁹Mo. The ¹⁰⁰Mo (n,2n) ⁹⁹Mo reaction has a cross section of 1400 mb for 14 MeV neutrons and is a good candidate for ⁹⁹Mo production.

A simple fast method for determination of the isotopic ratio, using a neutron source with intensity 5 X 10⁴ n/s, is described. Gas detectors filled with ³He are used. The accuracy of the method is in the order of 0.4% or less.