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No abstract available

[en] Two different technical solutions to the problem of generation of mono-energetic fast neutron beams on the gaseous targets are presented here. A simple and cost-effective design of a cooled windowed gas target system is described in the first part of this paper. It utilises a thin metallic foil window and circulating deuterium gas cooled down to 100 K. The ultimate beam handling capability of such target is determined by the properties of the window. Reliable performance of this gas target system was achieved at 1 bar of deuterium gas, when exposed to a 45 μA beam of 5 MeV deuterons, for periods in excess of 6 h. Cooling of the target gas resulted in increased fast neutron output and improved neutron to gamma-ray ratio. The second part of this paper discusses the design of a high pressure, windowless gas target for use with pulsed, low duty cycle accelerators. A rotating seal concept was applied to reduce the gas load in a differentially pumped system. This allows operation at 1.23 bar of deuterium gas pressure in the gas cell region. Such a gas target system is free from the limitations of the windowed target but special attention has to be paid to the heat dissipation capability of the beam dump, due to the use of a thin target. The rotating seal concept is particularly suitable for use with accelerators such as radio-frequency quadrupole (RFQ) linacs that operate with a very high peak current at low duty cycle. The performance of both target systems was comprehensively characterized using the time-of-flight (TOF) technique. This demonstrated that very good quality mono-energetic fast neutron beams were produced with the slow neutron and gamma-ray component below 10% of the total target output

[en] Full text: Successful application of neutron techniques in research, medicine and industry depends on the availability of suitable neutron sources. This is particularly important for techniques that require mono-energetic fast neutrons with well defined energy spread. There are a limited number of nuclear reactions available for neutron production and often the reaction yield is low, particularly for thin targets required for the production of mono-energetic neutron beams. Moreover, desired target materials are often in a gaseous form, such as the reactions D(d,n)³He and T(d,n)³He, requiring innovative design of targets, with sufficient target pressure and particle beam handling capability. Additional requirements, particularly important in industrial applications, and for research institutions with limited funds, are the cost effectiveness as well as small size, coupled with reliable and continuous operation of the system. Neutron sources based on high-power, compact radio-frequency quadrupole (RFQ) linacs can satisfy these criteria, if used with a suitable target system. This paper discusses the characteristics of a deuteron RFQ linear accelerator system coupled to a high pressure differentially pumped deuterium target. Such a source, provides in excess of 10¹⁰ mono- energetic neutrons per second with minimal slow neutron and gamma-ray contamination, and is utilised for a variety of applications in the field of mineral identification and materials diagnostics. There is also the possibility of utilising a proposed enhanced system for isotope production. The RFQ linear accelerator consists of: 1) Deuterium 25 keV ion source injector; 2) Two close-coupled RFQ resonators, each powered by an rf amplifier supplying up to 300 kW of peak power at 425 MHz; 3) High energy beam transport system consisting of a beam line, a toroid for beam current monitoring, two steering magnets and a quadrupole triplet for beam focusing. Basic technical specifications of the RFQ linac are presented elsewhere. In the case of an RFQ accelerator, operating in a pulsed bunched mode, a suitable shutter mechanism can be used to effectively isolate the gas target between beam pulses and thus considerably reduce the gas load on a differentially pumped system whilst still maintaining the target at pressures up to ∼1.2 bar. Such a system operating on a 2% duty cycle RFQ system has been implemented. To go to even higher gas pressure or higher accelerator duty cycle, further improvements to the gas target system, in the form of a plasma window, have been investigated and are being implemented. The RFQ linear accelerator presently utilised delivers a maximum average beam current of 100 μA of 3.6-4.9 MeV deuterons, dependent on the phase coupling between the two accelerating cavities. In a 30 mm long deuterium gas cell, operating at a pressure of 1.2 bar, the expected neutron emission is ∼10¹⁰s¹, into the full solid angle. A maximum neutron energy obtained in the reaction D(d,n)³He would be 8.1 MeV with the spread of ∼750 keV. kinematics, approximately 50% of the primary neutron beam is emitted into a 20 deg. forward cone. This translates to the expected neutron densities in excess of 10⁷ n.s^-1cm^-2 some 10-20 cm away from the gas cell. Beam quality is high, with the slow neutron and gamma-ray components below 10% of the total primary fast neutron beam. The fast neutron energy spread (and the total neutron output) can be tailored to a specific application by adjusting either the gas cell length or the target gas pressure. The robust design and reasonable cost make the described neutron source a very attractive choice for variety of applications, such as mineral identification, material diagnostics (complementing thermal neutron radiography), and isotope generation. These activities are currently being pursued at NECSA along with close collaboration with academic institutions and industry. (author)

[en] The overall technical status of the Lund nuclear microprobe is presented. Several parts of the instrument have been replaced by newly developed systems. In this paper the main emphasis is directed to a newly installed, versatile specimen chamber. The special characteristics are: very quick opening and sample-changing procedures, many samples of varying sizes can be housed simultaneously and several detector systems can be used. (orig.)

[en] The importance of statistical evaluation of multielemental data is illustrated using the data collected in a macro- and micro-PIXE analysis of human brain tumours. By employing a multivariate statistical classification methodology (SIMCA) it was shown that the total information collected from each specimen separates three types of tissue: High malignant, less malignant and normal brain tissue. This makes a classification of a given specimen possible based on the elemental concentrations. Partial least squares regression (PLS), a multivariate regression method, made it possible to study the relative importance of the examined nine trace elements, the dry/wet weight ratio and the age of the patient in predicting the survival time after operation for patients with the high malignant form, astrocytomas grade III-IV. The elemental maps from a microprobe analysis were also subjected to multivariate analysis. This showed that the six elements sorted into maps could be presented in three maps containing all the relevant information. The intensity in these maps is proportional to the value (score) of the actual pixel along the calculated principal components. (orig.)

[en] The grid-shadow technique has proved to be an important tool for the characterization of the quadrupole lenses used for focusing the ion beam in nuclear microprobes. A technique is described which can identify and distinguish between beam aberrations, seen in the grid-shadow patterns, caused by parasitic multipoles in the lenses from those caused by stray external fields. Also presented is an on-line method to correct for the internal parasitic fields in the lenses by observing the grid-shadow patterns, thereby improving the spatial resolution in the nuclear microprobe. (orig.)

[en] Nuclear microprobe analysis was applied to the study of elemental distribution in brains sections of patients with a diagnosis of Alzheimer's disease. Stained and nonstained cryosections were studied. The work carried out shows that serious elemental losses follow the sample staining procedure. Major losses occurred in a simple rinse of the tissue section, probably reducing most of the in-vivo gradients, which show that generally very little information can be gained from stained sections. However, in many cases stained sections are compulsory because of the requirement to recognize the area which is to be studied. All the elemental maps obtained for the neurofibrillary deposits indicate a localized concentration for Si and probably also Al, associated with the senile plaque core. Neither of these elements were found in the staining solutions used. The validity of the results is discussed as well as the possible link of Al and/or Si in the development of Alzheimer's desease. (orig.)

[en] A review of recent advances in high-energy ion beam analysis at the Lund Institute of Technology is presented. A nonvacuum specimen chamber allows chemical speciation using a combination of ion beam analysis and controlled heating. The development of a new versatile scanning proton microbeam based on a new dedicated accelerator, an achromatic triplet lens and an advanced specimen chamber is outlined together with the performance of a microVAX-II/VMEbus-based data acquisition system. (orig.)

[en] Low energy accelerator-based neutron sources have promising potential for use in a clinical treatment of cancer with boron neutron capture therapy (BNCT) and boron neutron capture synovectomy (BNCS). Such sources often utilise a thick target Be(p,n) reaction using incident proton energies from several hundred keV to 1-2 MeV above the reaction threshold of 2.06 MeV. The resulting neutron and gamma-ray beams require considerable moderation and filtration in order to obtain thermal and epithermal neutron fluxes for therapy. The detailed knowledge of neutron and gamma-ray spectra, yield and angular distribution are necessary in order to design effective moderators and filters to be used for the treatment. Thick and thin beryllium target neutron and gamma spectra have been investigated in detail using the time-of-flight (TOF) technique, for incident proton energies from above threshold to 4 MeV. The results show characteristics of neutron and gamma-ray production of importance for the application of this neutron source for BNCT and BNCS. (orig.)