Possibilities of using hafnium neutron filters for reactor NAA with fast neutrons

The possibilities of using hafnium irradiation filters for reactor fast neutron activation analysis have been evaluated. The filter characteristics of hafnium for this application are discussed and compared with some traditional filter materials. The main advantage for hafnium is its ability to remove a great portion of the slowing down neutrons, which may enhance the sensitivity of determination via threshold reactions.     

Determination of oxygen with reactor neutrons

Oxygen in silicon was determined by the secondary nuclear reactions of⁶Li(n, α)T and¹⁶O(t, n)¹⁸F. Lithium fluoride was deposited in vacuum on fused quartz, covered with the sample and irradiated in a nuclear reactor. The depth profiles of¹⁸F in fused quartz and in silicon were observed, and enough depth to eliminate surface oxygen was estimated. On the basis of these results, oxygen was determined by the average cross-section method. Oxygen concentration in CZ silicon with various growing condition was 5–26 ppm and was consistent with those determined by the infrared absorption method. The detection limit of oxygen in silicon is 5 ppm.     

Radiation damage in InGaAs photodiodes by 1 MeV fast neutrons

Irradiation damage in In_0.53Ga_0.47As p-i-n photodiodes by 1 MeV fast neutrons has been studied as a function of fluence for the first time, and the results are discussed in this paper. The degradation of the electrical and optical performance of diodes increases with increasing fluence. The induced lattice defects in the In_0.53Ga_0.47As epitaxial layers and the InP substrate are studied by Deep Level Transient Spectroscopy (DLTS) methods. In the In_0.53Ga_0.47As epitaxial layers, hole and electron capture levels are induced by irradiation. The influence of the type of radiation source on the device degradation is then discussed by comparison to 1 MeV electrons with respect to the numbers of knock-on atoms and the nonionizing energy loss (NIEL). The radiation source dependence of performance degradation is attributed to the difference of mass between the two irradiating particles and the probability of nuclear collision for the formation of lattice defects.     

An approximate simple formula for the shielding effect of the cadmium jacket designed for the use of fast neutrons among reactor neutrons

If a pneumatic tube in an experimental hole of a reactor is covered with a cadmium jacket, a sample inserted in the pneumatic tube will be exposed to not only fast and epithermal neutrons but also the few thermal neutrons that will not have been obstructed by the jacket. To obtain a simple method of estimation for the flux of these thermal neutrons, a formula has been made. The ratio of change in thermal-neutron flux due to the setting of the jacket has been expressed as a function of 5 dimensionless numbers. The formula enables one to design a well-proportioned jacket.     

Use of spectroscopy of gamma-radiation from the inelastic scattering of reactor fast neutrons for elemental analysis

Gamma-spectra of stainless-steel and soil samples have been measured to study the potentialities of using spectroscopy of γ-radiation from the inelastic scattering of reactor fast neutrons for element analysis of various materials. Contents of iron, chromium, nickel, manganese, silicon and titanium in stainless steel, and those of silicon, iron, aluminium, magnesium, calcium, sodium, titanium, carbon and oxygen in soil have been determined by comparing the spectra of the samples with those of specially prepared mixtures of elements. The distinguishing features, advantages, and limitations of this method are discussed.     

Activation analysis with fast neutrons using a cyclotron

A systematic study of activation analysis with cyclotron-produced neutrons for (n, 2n), (n, p) and (n, α) reactions is presented. The limits of detection for elements of atomic number from 6 to 80 are given. The possibilities of optimization of irradiation conditions by the choice of the most suitable neutron spectrum are discussed. The potential of this fast neutron activation analysis method is compared with that of 14 MeV neutron activation analysis.     

Measurement of neutron flux and albedo of water for thermal neutrons with foils of indium in a subcritical nuclear reactor

A subcritical nuclear reactor, Model 9000, Nuclear Chicago, is installed and operating at the Aristotle University of Thessaloniki, in the Atomic and Nuclear Physics Laboratory, at Thessaloniki, Northern Greece. The fuel is about 5500 lbs (2495 kgs) natural uranium metal (U₃U₈), the moderator about 3600 lbs (1633 kgs) light water, H₂O and the reflector is also light, water, H₂O. The lattice core is hexagonal, 42 inches (1.07 m) high and of 35 inches (88.90 cm) maximum diameter. The neutron source at the core is Am-Be 5 curies (185 GBq), 1.1·10⁷n·s⁻¹. The reactor is used for the activation of various materials by neutrons such as indium, the determination of the thermal neutrons flux, the horizontal and the vertical distribution of the neutron flux, material buckling, B, and geometric buckling, B, the parameters of the reactor, and the albedo of water for thermal neutrons with foils of indium. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of fertilizer phosphates using reactor neutrons and 14 MeV neutrons

Instrumental neutron activation analysis (INAA) in the absolute version was applied to 32 fertilizer phosphates of natural and industrial origin including three standard reference materials (NBS-SRM 120b, BCR-SRM No 32 and No 33). With reactor neutrons 48 elements were determined and with 14 MeV neutrons 3 additional elements were found. The results were used to assess the environmental toxicity of the fertilizers and to characterize their different origins.     

Determination of reactor neutron spectra with multicomponent activation detectors

A procedure is described for the functional fitting of reactor neutron spectra with C/Eⁿ and fission spectra. The method is applied to multicomponent activation detector measurements in a Triga research reactor. In multicomponent detectors a mixture of several detector materials is irradiated as a single unit and measured simultaneously for all reaction products with a Ge(Li) gamma ray spectrometer.     

Use of cyclotron-produced fast neutrons in activation analysis

The determination of 15 elements: Pb, Sr, Ba, ti, Ca, Sc, Cs, Zr, Rb, Cr, Se, Ni, Y, Co and Zn was investigated by fast neutron activation analysis using 80 MeV deuterons on various environmental samples. Detection limits of these elements from interference-free spectra were calculated.     

Determination of thallium in environmental samples by activation analysis with fast reactors neutrons

A procedure is described for the determination of thallium in coal fly ash by fast neutron activation analysis using the reaction²⁰³Tl/n, 2n/²⁰²Tl. A 31 h reactor irradiatioon under cadmium cover at a fast neutron flux of 3.05×10¹² n.cm^–2.s^–1 is applied. The simple radiochemical separation involves a wet attack in acids followed by an extraction of Tl/III/into diisopropylether from 0.5M HBr. The radiochemical purity is sufficient for immediate -spectrometry. A value of 5.7±0.7 ppm is found in the NBS 1633a coal fly ash.     

A rapid transportation facility for irradiation with thermal and fast neutrons

A rapid vertical transportation system for irradiation with thermal and fast neutrons is devised and partly constructed for inserting samples into the central thimble of our TRIGA MARK II reactor. Fast neutrons will be produced by a⁶LiD-converter, so that the energy distribution of neutrons is hardened by absorption of thermal and by the production of 14 MeV neutrons. In pulse irradiation, the 14 MeV-neutron flux is expected to be in the order of 10¹²/s. The transportation time is to be below 30ms to enable determination of short-lived nuclides down to 15ms. Helium will be used as propelling gas.     

Observations relative to epithermal and fast neutrons in INAA

Various theoretical and practical aspects of epithermal neutron activation analysis (ENAA) and fast-neutron-induced reaction interferences in conventional instrumental thermal neutron activation analysis (TNAA) have been considered. A new generalized advantage factor which reflects a practical improvement of detection limits in ENAA is proposed. In the determination of practical advantage factors, consideration is also given to the different irradiation channels available for the experiment in a given reactor, or even in several accessible reactors. Fast neutron reaction interference factors are tabulated for both ENAA and TNAA and examples are given of specific interferences in TNAA for some biological and geological matrices.     

Yields of 28Mg in the irradiation of magnesium and aluminium with reactor neutrons

The yield of ²⁸Mg was determined for neutron irradiation of magnesium and aluminium. The cross-section of the ²⁸Mg(n,γ)²⁸Mg reaction with thermal neutrons was deduced to be 0.07±0.02 barn, while that of the ²⁸Al(n,p)²⁸Mg reaction with fast neutrons was concluded to be less than 2 mbarn. The observed cross-section for the ²⁷Mg(n,γ)²⁸Mg reaction was compared with that prediction by the hard sphere capture model.     

Yields of 66Ni and 57Ni in the irradiation of nickel with reactor neutrons

Nickel metal was irradiated with reactor neutrons and yields of ⁶⁶Ni and ⁵⁷Ni were determined. The thermal neutron cross section of the ⁶⁵Ni(n,γ)⁶⁶Ni reaction was found to be 20.4 ± 2.4 barn, while the resonance integral was less than 60 barn. The cross section of the ⁵⁸Ni(n,2n)⁵⁷Ni reaction with fission neutrons was determined to be 3.8 ± 0.5 μ barn. A simple formula is proposed for the systematics of the (n,2n) reactions, which permits prediction of the cross sections more accurately than previously proposed formulae.     

Determination of aluminium in a "nimonic" alloy by activation with fast neutrons

Aluminium at the 6% level was determined in a 15-component "nimonic" alloy with a coefficient of variation of +/-8.7% by using fast-neutron activation followed by pulse-height analysis of gamma-ray spectra. The possibility of determining chromium, iron, cobalt and manganese is discussed.     

Review of semiconductor detectors for nuclear radiation

The basic requirements on semiconductor materials for nuclear radiation detectors are reviewed. Comparison between the different properties with respect to energy resolution, γ-detection efficiency, low energy X-ray detection, room temperature performance etc. for detection of Si, Ge or less common materials such as HgI₂, CdTe, GaAs, diamond etc. is based on materials parameters such as bandgap, atomic number of the constituents, carrier mobility and lifetime and degree of crystal purity and perfection obtainable.The influence of noise sources in the detector and preamplifier on spectrometer resolution is treated with a simple model, which also clarifies the influence of material properties. This gives a background for understanding present development work in which the common Si and Ge detectors are replaced by other materials in specific detection situations.The advantages then gained are illustrated by a brief discussion of the obtained performance for some newer designs described in the literature, including semiconductor scintillation counters.     

Radon exhalation rate in building materials using plastic track detectors

The radon flux emitted from building material samples and from the surface of building materials could be determined using a simple and reliable method. This method was based on the use of cellulose nitrate films (LR-115 II). The samples and the detectors were placed in a closed can of known dimensions. Tracks due to alpha-particles of radon that migrate from the building material into the air space in the chamber were registered on the LR-115 film. The detectors were chemically etched in 2.5N NaOH solution at 60±1 °C for 115 minutes. Exhalation rates of various building material samples and of building surfaces of various building components were determined. The results obtained by this technique could be used to establish a database for average radon exhalation rates for all available building materials and walls or floors.