Spallation Neutron Production Research Articles

The study of spallation reactions, neutron production, and transport in a thick lead target and a uranium blanket during 1.5 GeV proton irradiation

The Neutron Activation Analysis Method was used to study neutron field in a setup consisting of a thick lead target and a natural uranium blanket. This setup was exposed to 1.5 GeV proton beam from the Nuclotron accelerator. By means of gamma-ray spectroscopic measurements we determined the yields of various nuclear reactions induced in the radio-chemical sensors. The data obtained were then compared with the results of a MCNPX simulation.

Spatial distribution of moderated neutrons along a Pb target irradiated by high-energy protons

High-energy protons in the range of 0.5–7.4 GeV have irradiated an extended Pb target covered with a paraffin moderator. The moderator was used in order to shift the hard Pb spallation neutron spectrum to lower energies and to increase the transmutation efficiency via ( n, γ) reactions. Neutron distributions along and inside the paraffin moderator were measured. An analysis of the experimental results was performed based on particle production by high-energy interactions with heavy targets and neutron spectrum shifting by the paraffin. Conclusions about the spallation neutron production in the target and moderation through the paraffin are presented. The study of the total neutron fluence on the moderator surface as a function of the proton beam energy shows that neutron cost is improved up to 1 GeV. For higher proton beam energies it remains constant with a tendency to decline.

Neutron Production in Semiprototypic Target Assemblies for Accelerator Transmutation Technology

Integral neutron production was measured by the manganese-activation technique, on targets semiprototypic of spallation-neutron-driven transmutation systems, after irradiation by 400-MeV to 2.0-GeV protons. The purpose of these experiments was to provide data to benchmark nuclear transport codes for targets irradiated by protons in this energy range, as well as to evaluate design options to maximize the production of spallation neutrons in various targets under consideration. These computer codes are used to design accelerator systems that will utilize spallation neutrons for the generation of tritium, transmutation of nuclear waste, production of radioisotopes, and other scientific investigations. Some of the targets used in this investigation were semiprototypic of the proposed Accelerator Production of Tritium target. Other targets were included to provide data to test the computational models in the codes. Total neutron production is the main factor that determines the economics of transmutation for a particular accelerator design. Comparisons of the data reported here with calculations from computer simulations show agreement to within 15% over the entire energy region for most of the targets.

On the use of lead/tin alloys as target material for the production of spallation neutrons

We have examined the suitability of lead (Pb)/tin (Sn) alloys with atomic ratios between 4:1 and 12:1 for use as a spallation target material for the PSI spallation ultracold neutron source. The measured corrosion rate with distilled water, R c < 6 × 10 - 5 cm / year , is more than a factor of 80, less than for normal Pb; this corrosion rate is satisfactory. Microscopic investigations of the surface after the exposure to water revealed no visual changes. Small angle neutron scattering showed that the alloy is mechanically stable under thermal cycling. An experimental simulation of a water-cooled spallation neutron target made of Pb/Sn pebbles with a filling factor of 60% was investigated; the pulsed proton beam was simulated using hot and cold water in the target ‘cooling’ circuit. With realistic operational parameters for the cooling circuit, serious deformation of the PbSn pebbles occurred which finally blocked the cooling circuit. The Pb/Sn alloys solve the corrosion problem but its mechanical properties are inadequate leading to too short a lifetime to be practical in the PSI spallation source.

Spallation neutron production by 0.8, 1.2, and 1.6 GeV protons on various targets

Spallation neutron production in proton induced reactions on Al, Fe, Zr, W, Pb and Th targets at 1.2 GeV and on Fe and Pb at 0.8, and 1.6 GeV measured at the SATURNE accelerator in Saclay is reported. The experimental double-differential cross-sections are compared with calculations performed with different intra-nuclear cascade models implemented in high energy transport codes. The broad angular coverage also allowed the determination of average neutron multiplicities above 2 MeV. Deficiencies in some of the models commonly used for applications are pointed out.

Spallation neutron production and the current intra-nuclear cascade and transport codes

A recent renascent interest in energetic proton-induced production of neutrons originates largely from the inception of projects for target stations of intense spallation neutron sources, like the planned European Spallation Source (ESS), accelerator-driven nuclear reactors, nuclear waste transmutation, and also from the application for radioactive beams. In the framework of such a neutron production, of major importance is the search for ways for the most efficient conversion of the primary beam energy into neutron production. Although the issue has been quite successfully addressed experimentally by varying the incident proton energy for various target materials and by covering a huge collection of different target geometries --providing an exhaustive matrix of benchmark data-- the ultimate challenge is to increase the predictive power of transport codes currently on the market. To scrutinize these codes, calculations of reaction cross-sections, hadronic interaction lengths, average neutron multiplicities, neutron multiplicity and energy distributions, and the development of hadronic showers are confronted with recent experimental data of the NESSI collaboration. Program packages like HERMES, LCS or MCNPX master the prevision of reaction cross-sections, hadronic interaction lengths, averaged neutron multiplicities and neutron multiplicity distributions in thick and thin targets for a wide spectrum of incident proton energies, geometrical shapes and materials of the target generally within less than 10% deviation, while production cross-section measurements for light charged particles on thin targets point out that appreciable distinctions exist within these models.

Review of liquid metal corrosion issues for potential containment materials for liquid lead and lead–bismuth eutectic spallation targets as a neutron source

Lead (Pb) and lead–bismuth eutectic (44Pb–56Bi) have been the two primary candidate liquid metal target materials for the production of spallation neutrons. Selection of a container material for the liquid metal target will greatly affect the lifetime and safety of the target subsystem. For the liquid lead target, niobium–1 wt% zirconium (Nb–1Zr) is a candidate containment material for liquid lead, but its poor oxidation resistance has been a major concern. In this paper, the oxidation rate of Nb–1Zr was studied based on the calculations of thickness loss resulting from oxidation. According to these calculations, it appeared that uncoated Nb–1Zr may be used for a 1-year operation at 900°C at P O 2 =1×10 –6 Torr, but the same material may not be used in argon with 5-ppm oxygen. Coating technologies to reduce the oxidation of Nb–1Zr are reviewed, as are other candidate refractory metals such as molybdenum, tantalum, and tungsten. For the liquid lead–bismuth eutectic target, three candidate containment materials are suggested, based on a literature survey of the materials’ compatibility and proton irradiation tests: Croloy 2-1/4, modified 9Cr–1Mo, and 12Cr–1Mo (HT-9) steel. These materials seem to be used only if the lead–bismuth is thoroughly deoxidized and treated with zirconium and magnesium.

Spallation Neutron Production by 0.8, 1.2, and 1.6 GeV Protons on Pb Targets

Spallation neutron production in proton induced reactions on Pb targets at 0.8, 1.2, and 1.6 GeV has been measured at the SATURNE accelerator. Double-differential cross sections were obtained over a broad angular range from which averaged neutron multiplicities per reaction were inferred for energies above 2 MeV. The results are compared with calculations performed with a high energy transport code including two different intranuclear cascade (INC) models: it is shown that the Cugnon INC model gives a better agreement with the data than the Bertini one, mainly because of improved nucleon-nucleon cross sections and Pauli blocking treatment. © 1999 The American Physical Society.

Biomedical Program for the Converted 200-MeV Synchrocyclotron at the Gustaf Werner Institute

Between 1956 and 1977, the former synchrocyclotron in Uppsala was used for biological experiments and clinical tests with 185-MeV protons. Therapeutic irradiations have been performed since 1957 by cross-firing with pencil beams through small intracranial structures for the treatment of Parkinsonism and intractable pain and with the spread-out Bragg peak for the treatment of large malignant tumors. Radiological and radiophysical aspects of the use of charged-particle beams were studied in detail. The former accelerator is now being converted to a sector-focusing, frequency-modulated cyclotron, SFSC-200, to permit acceleration of protons up to 200 MeV and other light ions to corresponding energies. Production of spallation neutrons and radionuclides for biomedical uses is expected to start this year. Experiments with charged-particle beams will begin in 1986. This paper presents a discussion of accelerator developments for planned experimental and clinical programs.

The Spallator and APEX Nuclear Fuel Cycle a New Option for Nuclear Power

A new nuclear fuel cycle is described which provides a long term supply of nuclear fuel for the thermal LWR nuclear power reactors and eliminates the need for long-term storage of radioactive waste. Fissile fuel is produced by the Spallator which depends on the production of spallation neutrons by the interaction of high energy (1 to 2 GeV) protons on a heavy metal target. The neutrons are absorbed in a surrounding natural uranium or thorium blanket in which fissile Pu-239 or U-233 is produced. Advances in linear accelerator technology makes it possible to design and construct a high beam current continuous wave proton linac for production purposes. The target is similar to a sub-critical reactor and produces heat which is converted to electricity for supplying the linac. The Spallator is a self-sufficient fuel producer, which can compete with the fast breeder. The APEX fuel cycle depends on recycling the transuranics and long-lived fission products while extracting the stable and short-lived fission products when reprocessing the fuel. Transmutation and decay within the fuel cycle and decay of the short-lived fission products external to the fuel cycle eliminates the need for long-term geological age storage of fission product waste.

Pulsed spallation neutron sources for slow neutron scattering

The role of pulsed spallation neutron sources for slow neutron spectroscopy is sketched. Various methods of neutron production, and some aspects of the spallation neutron production process are outlined. Accelerators for pulsed spallation neutron sources are discussed. Materials and coolants for neutron-producing targets and moderators are surveyed. The performance of moderators and the effects of varying size, composition, and temperature are summarized. Expressions for estimating moderator performance are given. The effect of moderator-reflectors, which enhance the slow neutron beam current at low energies, are examined. The ZING-P prototype pulsed neutron source and the proposed Intense Pulsed Neutron Source are described. Pulsed spallation sources are a new generation of sources for slow neutron spectroscopy which offer an order of magnitude improvements over currently available thermal neutron flux and several orders of magnitude greater epithermal flux.