Physical and chemical forms of radionuclides of 38S, 38Cl, 39Cl, and 82Br, produced at a high-energy proton accelerator facility

High-energy protons and neutrons produce various radionuclides in the air, mainly through the nuclear spallation of atmospheric elements. Air samples were collected from the EP-2 tunnel of the KEK 12 GeV proton synchrotron facility with a filter pack, which consisted of a membrane filter for aerosols, a Na₂CO₃-impregnated filter for acidic gases, and an activated carbon fiber filter for non-acidic gases. Sulfur-38 was found on the membrane and Na₂CO₃-impregnated filters, ³⁸Cl and ³⁹Cl were on the membrane, Na₂CO₃-impregnated, and ACF filters, and ⁸²Br was only on the ACF filter. The results on the relative abundances of aerosol and gaseous acidic components have indicated that ³⁸Cl produced by thermal neutron capture, which is the main reaction for ³⁸Cl production in the EP-2 tunnel air, are likely not to be present as aerosol or acidic gas. This was similar to the case of ⁸²Br produced by thermal neutron capture.     

Measurement of the production rates of <Superscript>36</Superscript>Cl from Cl,K, and Ca in concrete at the 500 MeV neutron irradiation facility at KENS

In order to estimate the total radioactivity induced in a concrete shield by thermal neutron-capture reactions at high-energy accelerator facilities, the observed activity of ³⁶Cl in the concrete is expected to serve as an indicator of the thermal neutron fluence. Since ³⁶Cl can also be produced from K and Ca by spallation reactions, we measured these production rates in order to clarify the contribution of each reaction. The Cl, K, and Ca targets were irradiated with neutrons having a maximum energy of 500 MeV. As a result, the production rates of ³⁶Cl from Cl were only two orders higher than those from K and Ca. It was found that the ³⁶Cl production ratios from Cl, K, and Ca were 6.7%, 6.8%, and 86.5%, respectively, and Ca was the main source of ³⁶Cl production.     

Monitoring of gamma emission and neutron transmission during boron neutron capture treatment delivery

The ability to map boron and hydrogen distributions in the body is paramount to the success of boron neutron capture therapy (BNCT). We investigated treatment-time quantitative mapping of these distributions by detecting (i) 0.48 MeV de-excitation photons from neutron capture by boron-10; (ii) 2.22 MeV photons from neutron capture by hydrogen; and (iii) transmitted neutrons. Monte Carlo simulations reported no detectable difference when ¹⁰B in tumour was varied from 0 to 50 ppm, and when the tumour size was varied from 0.0 to 9.5 cm³.     

Utilization of cyclotron produced fast neutrons in the activation analysis for oxygen

The possible application of cyclotron-produced fast neutrons to activation analysis for oxygen based on the¹⁶O(n, p)¹⁶N reaction has been investigated. Neutrons were produced by bombarding a thick beryllium target with 22 to 45 MeV deuterons. It was found that the sensitivity increases rapidly with the energy of the deuterons. Using 45 MeV deuterons and a 10 μA beam current a sensitivity of about 20 counts per 1 μg oxigen could be achieved, enabling the determination of less than 1 μg oxigen. In a direct comparison it was experimentally established that the sensitivity for cyclotron-produced neutrons assuming a deuteron beam of about 10 μA, is up to two orders of magnitude higher than that achievable for 14 MeV neutrons with a flux of about 10¹⁰ n/s. The interference of fluorine is at about the same level for both the cyclotron-produced and 14 MeV neutrons. Using cyclotron-produced fast neutrons in the investigated energy range, sodium and magnesium can also interfere, but only to a very much lower extent.     

Performance comparison of 2.8 MeV and <Superscript>241</Superscript>Am-Be neutrons based moisture measurement setups

Performance of a ²⁴¹Am-Be neutron source-based and 2.8 MeV neutrons-based moisture measurement setups have been compared using Monte Carlo simulation. In the setup fast neutrons transmitted through the sample were detected by a fast neutron detector, which was placed behind a massive long double truncated collimator. The setup geometry was optimized to detect maximum effect of 1–7 wt.% moisture on the neutron intensity transmitted through the sample. The yield of neutrons transmitted through concrete, coal, wood and soil samples containing 1–7 wt.% moisture was calculated for 2.8 MeV neutrons and neutrons from an ²⁴¹Am-Be source. The slopes of the fast neutron intensities transmitted through the samples vs. their moisture contents are very sensitive to the neutron energy and the sample composition. Higher slopes have been observed for the samples with larger bulk density. The slopes of fast neutron yield show dependence on the incident neutron energy. Larger slopes have been observed for neutrons with samller energy. Due to the overall large slopes of the transmitted intensity data of the samples for 2.8 MeV neutrons, it is expected to achieve better sensitivity in moisture measurements for a 2.8 MeV neutrons based moisture setup.     

Cross-sections of 14 MeV neutron reactions producing short-lived nuclides

The cross-sections for the production of the short-lived nuclides:^26mAl,^197mAu,^136mBa,^79mBr,^139mCe,³⁴Cl,^167mEr,^114m3In,^114m2In,^38mK,^38mCl,²⁶Na,²⁰F,¹⁹²Re,^207mPb,^203mPb,^46mSc,^183mW,^90mZr obtained from (n, 2n), (n, n′), (n, alpha), (n,p) reactions using 14 MeV neutrons, were evaluated by the activation method. The experimental results of this work were compared with those obtained by other authors.     

Design of aerosol sampler to remove radon and thoron progeny interference from aerosol samples for nuclear explosion monitoring

A Nuclear Explosion Monitoring Inertial Impactor (NEMII) system was developed to physically separate naturally occurring radionuclides from those produced in nuclear weapons explosions. Studies show that aerosols containing natural activity have an aerodynamic diameter in the range of 0.1–1.0 μm. It has been established that atmospheric nuclear explosions produce radioactive aerosols with aerodynamic diameters <0.1 μm and surface explosion produce a bimodal distribution of radioactive particles with aerodynamic diameters both >1.0 μm and <0.1 μm. A high volume (66 m³ h⁻¹) impactor was designed to separate the particles into three size distributions: aerosols with aerodynamic diameters >1.0 μm, between 0.1 and 1.0 μm, and smaller than 0.1 μm. Calculations based on previous work for high-volume impactors were completed to obtain the impactor geometry that yields the desired cutoff values. The components of the aerosol impactor were manufactured or obtained and then assembled. In addition, a submicrometer aerosol generation system was assembled to benchmark the NEMII system against a commercial Micro-Orifice Uniform-Deposit Impactor (MOUDI). The MOUDI was also used to verify the naturally occurring radioactivity distribution using ²¹²Pb gamma spectra.     

Production of monoenergetic MeV-range neutrons by <Superscript>3</Superscript>H(p,n)<Superscript>3</Superscript>He reaction

Monochromatic MeV-energy neutron source for secondary reaction was developed utilizing tritium embedded titanium (Ti-³H) thin film via ³H(p,n)³He reaction. We have measured the neutron energies and the energy spread by resonance reactions of ¹²C(n,tot) and ²⁸Si(n,tot). The available energy was within the range from 0.6 to 2.6 MeV. Energy spread was 1.6% at energy of 2.077 MeV. The flux in the beam direction was determined to be 3.76·10⁷ n/s/sr by irradiating ¹⁹⁷Au by about 2 MeV neutrons. This source was shown to be useful for measurements of nuclear data by measuring the total cross sections of neutrons on Fe and comparing these data to the data of ENDF-6.     

Resonance activation analysis of iodine

Resonance neutron activation and gamma-ray spectrometry were used to determine traces of iodine in biological materials. The method developed is purely instrumental and fairly rapid. The major interfering activities of²⁴Na,³⁸Cl,³⁶Mn and⁸²Br were significantly reduced by irradiating the samples inside a shield of Cd, NaCl, MnBr₂ and MnO₂. Neutrons with energies close to the resonances of Na, Cl, Mn and Br were absorbed in the shield and did not activate the sample while neutrons with energies close to the resonances of iodine were not absorbed appreciably. Thus the activity of¹²⁸I was enhanced relative to the interfering activities. The 442 keV gamma of¹²⁸I (T=25 min) was measured using a high-resolution Ge(Li) detector and a multichannel analyzer. Sensitivity of 0.05 ppm was obtained.     

Aerosol-size distribution of radon daughter218Po in the accelerator tunnel air

Aerosol-size distributions of²¹⁸Po were determined for the accelerator tunnel air sampled during machine operation and for the basement air of a concrete building, where the number and the size distribution of non-radioactive aerosols are greatly different from each other. The²¹⁸Po distributions depended very much on the size distributions of ambient non-radioactive aerosols, and could be well explained by an attachment model of²¹⁸Po to ambient non-radioactive aerosols.     

Formation and internal energy distribution of the CH(A2Δ) radical by electron-impact dissociation of methyl halides

The dissociative excitation of CH₃X (X = Cl, Br, I) producing CH(A²Δ) is investigated by low-energy electron impact. The onsets of the CH(AX) emission from CH₃Cl, CH₃Br and CH₃I are 11.8 ± 0.3, 11.4 ± 0.3 and 11.2 ± 0.3 eV, respectively. It can be concluded that CH₃X → CH(A) + H₂(X) + X (X = Cl, Br, I) is the predominant process for formation of CH(A) near its onset. The internal energy distributions of CH(A) evaluated by means of a simulation analysis of the CH(AX) band are nearly independent of the impact energy for impinging electrons above 19 eV.     

Activation cross section measurements of 16O(n,t) above 18.1?MeV up to 33.1?MeV

We have measured the cross sections of the ¹⁶O(n,t) reactions above 18.1 up to 33.1 MeV in an neutron activation method. H₂O (water) as an ¹⁶O target was irradiated with semi-monoenergetic neutrons generated from the ⁹Be(p,n)⁹B reaction with 25–35 MeV protons. The neutron flux was obtained with the aid of previous study by Uwamino et al. (Nucl Instr Methods A 271:546, 1988). The tritium activities were measured by using the liquid scintillation counting (LSC) method. The present value for the cross section of ¹⁶O(n,t) reaction agrees with previous values measured by using the same LSC method at similar neutron energy ranging from 18.1 up to 33.1 MeV.     

Quantitative secondary ion mass spectrometry depth profiling of surface layers of cubic silver halide microcrystals

The present article describes depth-profiling studies on populations of cubic silver halide microcrystals (typical size between 400 and 600 nm). These crystals consist of mixed halides (Cl, Br, I) and are characterized by internal halide distributions such as core-shell structures. Determination of the spatial distribution of the different halides in the microcrystals offers valuable information for the optimization of the crystal design of new photographic materials. The first part describes the calibration of the sputtered depth, which is more complicated than in the one-dimensional case of flat surfaces. In a second part, three different quantification methods [halide intensity ratios, XCs₂⁺ detection (X=halide) and the infinite velocity method] are used to determine the mean composition of the surface layer as a function of sputtered depth in the silver halide crystals. Although particles of submicrometer size are obviously not the ideal samples for depth profiling, a good correlation with values obtained by scanning electron microscopy energy dispersive X-ray microanalysis and wavelength dispersive X-ray fluorescence bulk analysis could be achieved.     

Evolution of anthropogenic aerosols in the coastal town of Salina Cruz,Mexico: part III size-segregated elemental composition analysed by total-reflection X-ray fluorescence spectrometry

Heavy metals in various size modes of the atmospheric aerosol are a concern for human health. Their and other elements’ concentrations are indicative for anthropogenic and natural aerosol sources. Si, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Hg, and Pb were determined as a complementary contribution to a study on aerosol cycling during the wet season, June 2004, in a humid, subtropical climate, i.e. in the city of Salina Cruz, situated on the Pacific coast of the Isthmus of Tehuantepec (16.2°N, 95.2°W), Mexico. For mass (gravimetry) and elemental analyses, particles were collected by a Berner low-pressure round nozzle cascade impactor using four stages corresponding to 0.1–0.25, 0.25–1.0, 1.0–4.0, and 4–16?µm of aerodynamic particle size. The impaction plates were modified such that approx. 1/6 consisted of a plastic support (Persplex®) for total reflection X-ray fluorescence spectrometry (TXRF). The elements’ total content was determined by TXRF without any further sample pretreatment. Limits of quantification (LOQ) for elemental content in individual impactor stages corresponded to 25–60?ng?m^?3 for Si; 0.8–4?ng?m^?3 for Cl, K, Ca, Ti, and V; 3–20?pg?m^?3 for Cr, Mn, Fe, Cu, Ni, and Zn; and 7–50?pg?m^?3 for As, Se, Br, Rb, Sr, Hg, and Pb. In some samples, however, high blank values for the supports gave an LOQ?=?6–19?ng?m^?3 for Cl; 3--7?ng?m^?3 for Ca; 3–7?ng?m^?3 for Fe, Ni, Cu, and Zn; and 60–70?ng?m^?3 for Pb. The influence of local natural, industrial, and vehicle traffic sources for heavy-metal mobilization was obvious. Heavy-metal abundances did not coincide with regionally distributed pollutants. V and Ni were found at particularly elevated levels advected with the sea breeze, which points to ships as sources. Br and Pb were found at particularly low levels. The concentrations of Br, Rb, Sr, and Pb were found below LOQ at least in some, As, Co, Se, and Hg in all of the samples. The elements’ characteristic differences in mass size distributions were obvious despite the coarse size resolution. During the cycling of air masses from land to sea and back again, enrichment of super-micrometre particles in the near ground aerosol was observed under dry weather conditions. Rain preferentially removed the large particles with which heavy metals have been associated.     

Physical quantification of the biological effectiveness of ionizing radiations

The role, and limitations, of the fundamental physical quantities used in our current system of dosimetry for the protection of individuals against the hazardous effects of ionizing radiation is discussed briefly. A major limitation is the inability to correlate biological data, in a unified way, as a function of linear energy transfer with the consequent necessity for quality factors. From consideration of the various interaction processes undergone by charged particles in the equilibrium slowing down spectra generated by the incident radiation field, it is shown that good correlation of biological effects, for all radiation types, can be achieved in terms of linear primary ionization. The implication is that delta-ray effects play at most a very minor role, at moderate fluences, and that, consequently, the absorbed dose is an unsuitable parameter for describing radiation effects. Structure in the radiosensitive targets is observed to have a critical dimension of about 2 nm. It occurs only when double-stranded DNA is present and the magnitude of the inactivation probability is consistent with double-stranded breaks being the significant lesion. Calculation is made of the yield of lesions as a function of the mean free path for primary ionization. Differential spectra of radiation quality are obtained for monoenergetic electrons (0.2 keV to 30 MeV); for characteristic X-rays from carbon, aluminium, neon, potassium, copper, silver, and tungsten; for 50 kV X-rays, 250 kV X-rays, ²⁴¹Am, ¹³⁷Cs, and ⁶⁰Co gamma rays; and for neutrons with energies between 0.1 and 50 MeV. Damage by electrons is shown to be predominant at the ends of their tracks between 50 and 200 eV, whereas this is not so for the proton recoil spectrum generated by neutrons above 1 MeV. Proposals are made for a unified system of dosimetry that is independent of radiation type and that obviates the need for quality factors. The method is thought to be of general applicability to irradiations by nuclides incorporated into mammalian cells, by ingested emitters, and by external sources.     

A study of measured neutron elastic differential neutron cross sections for 23Na

Elastic neutron scattering angular distributions from ²³Na have been measured for incident neutron energies between 1.0 and 4.0 MeV at the University of Kentucky Accelerator Laboratory using neutron time-of-flight techniques for the scattered neutrons. This is an energy region in which existing data are very sparse. Measurements are compared with the predictions of the light particle-induced reaction code TALYS. The calculations reproduce forward angle scattering but have difficulty with relative minima in the differential cross section and large-angle scattering.     

Adsorption of actinides by chelating agents containing benzene rings, fixed on charcoal

The Sun emits about 3^.10^{43 1}H per year in the solar wind (SW). Solar luminosity and the outflow of SW-protons come from the collapsed supernova core, a neutron star (NS), on which the Sun formed. The universal cradle of the nuclides indicates that the energy of each neutron in the Sun"s central NS exceeds that of a free neutron by »10–22 MeV. Solar luminosity and SW-protons are generated by a series of reactions: (a) escape of neutrons from the central NS, (b) decay of free neutrons or their capture by heavier nuclides, (c) fusion and upward migration of H⁺ through material that accreted on the NS, and (d) escape of H⁺ in the SW.     

Estimation of the possibilities of a neutron generator-based source of thermalized neutrons for activation analysis

Characteristics of a source of thermal neutrons based on an evacuated NG-400 neutron generator with the maximum flux (Φ_f) 2 × 10¹¹ neutron/s for 14 MeV neutrons and 2 × 10⁹ neutrons/s for 3 meV neutrons have been investigated. The possibilities of its application for neutron activation analysis have been estimated. The distribution, composition, and density (φ_T) values of the thermal neutron flux have been measured in the inner cavity of the moderator using activation detectors. φ_T was 2 × 10⁸ and 2 × 10⁶ neutrons/cm² s for thermalized neutrons with energies of 14 and 3 MeV, respectively. The possibilities of the apparatus have been estimated theoretically and experimentally for the cases of thermalized neutrons of 14 MeV and 3 MeV.     

Characteristics study on suspended fine particles in aqueous phenol solution formed by electron beam irradiations

The suspended fine particles formed in aqueous phenol solution under high-dose irradiation were studied using the MeV electron beam and ⁶⁰Co γ-ray irradiations. The fine particle's size was 100–800 nm in diameter and became bigger at higher and lower dose rates. The distributions of the particle size became narrower for irradiation at higher dose rate. The fine particles were regarded to consist of molecules of about 1.9×10² molecular weight.     

Extraction chromatographic separation of carrier-free Tb and Pm generated in (p,xn)-type nuclear reactions

The nuclear reactions of (p, xn)-type, E_p=100–120 MeV, on Gd and Nd have been used to produce highly radioactive preparations of Tb and Pm enriched with neutron-deficient isotopes. Under comparable conditions the yields of practically all isotopes are considerably higher than in Tb and Gd spallation reactions at E_p=660 MeV. The radioactivity of screened¹⁵⁴Tb and¹⁵⁶Tb isotopes has been increased more than 40 times. Tb and Pm were separated from gram amounts of the target-elements by the extraction chromatography technique with undiluted di-(2-ethylhexyl) phosphoric acid as stationary phase. The radiochemical method developed was also applied to separate the radiochemically pure preparation of¹⁶¹Tb from Gd oxide irradiated with thermal neutrons.