Response of a tissue equivalent proportional counter to neutrons

The absorbed dose as a function of lineal energy was measured at the CERN-EC Reference-field Facility (CERF) using a 512-channel tissue equivalent proportional counter (TEPC), and neutron dose equivalent response evaluated. Although there are some differences, the measured dose equivalent is in agreement with that measured by the 16-channel HANDI tissue equivalent counter. Comparison of TEPC measurements with those made by a silicon solid-state detector for low linear energy transfer particles produced by the same beam, is presented. The measurements show that about 4% of dose equivalent is delivered by particles heavier than protons generated in the conducting tissue equivalent plastic.     

Amorphization of solids by fast neutrons

The diffraction patterns of amorphous solids prepared in the traditional way and by fast neutron bombardment are systematized. It is found that the diffraction patterns of these two classes of materials are different. In the case of a single crystal of titanium nickelide we have demonstrated here for the first time that these radiation-modified solids belong to the class of amorphous materials of distortion type. Fiz. Tverd. Tela (St. Petersburg) 40, 1584–1588 (September 1998)     

Response of thermoluminescent detectors to charged particles and to neutrons

Thermoluminescent detectors (TLDs) are widely used for the dosimetry of photons and electrons. They are less used for the radiation with higher linear energy transfer (LET). One of the reasons for that is that their TL relative efficiency η decreases for the most of them with increasing LET.

The paper presents first a review of author's experimental results in which η was established for charged particles having LET of the order from 1 to 100 keV/μm in tissue. Among TLDs studied were known materials like LiF:Mn; Ti; Al–P glass; CaSO₄:Dy; Al₂O₃:Na; and Al₂O₃:C. It was found that the dependence of their η on LET is not the same for all TLDs studied.

The response of the same materials to neutrons was also studied. It was found that both η as the relative response (RR) defined in terms of absorbed dose in tissue are different, they depend critically also on the composition. When a TLD contains nuclei like ⁶Li and ¹⁰B, their RR would be rather high. As far as η is concerned, the same tendencies were observed as for charged particles, i.e. when average LET of secondary particles formed in a TLD increases, their η generally decreases.     

Interactions of fast neutrons with45Sc

The surface resistance of lead was measured in a coaxial cavity at frequencies between 375 and 5000 MHz and temperatures between 4.2 and 1.5 °K. The residual resistance was determined from these data.     

Schwinger scattering of fast neutrons in crystals

The coherent effects emerging during fast neutron passage through oriented crystals have been investigated. It has been demonstrated that the cross section of coherent Schwinger neutron scattering in a crystal has maxima at specific entry angles and neutron energies. The effect of energy divergence and angular dispersion in a neutron beam on the coherent peak value has been examined.     

The scattering of fast neutrons from W184

Neutrons with energies of 0.3 to 1.5 MeV are scattered from W¹⁸⁴. Pulsed-beam fast time-of-flight techniques including a magnetic bunching system are utilized to resolve the elastically scattered neutrons from those inelastically scattered. The differential elastic cross section is measured at 50 keV intervals with an ≈20 keV incident neutron energy spread. The differential cross sections for inelastic scattering resulting in the excitation of residual nuclear levels at 111±5, 365±10, 690±40, 900±25, 1000±30, and 1120±30 keV are determined. In all instances the inelastically scattered neutrons are emitted, within experimental error, isotropically. The experimental results are compared with those obtained in previous work and with the predictions of theory.     

Amorphization of oxides under irradiation with fast neutrons

A variant of the solid-state radiation amorphization as a result of accumulation of the critical concentration of defects in the crystal has been considered using the example of oxides with the garnet and perovskite structures irradiated by fast neutrons. It has been shown that such defects can be antisite defects, the formation of which leads to considerable static displacements from the equilibrium sites of nearest ions and, consequently, to the loss of stability of the crystalline structure. The dependences of the root-mean-square displacements of oxygen ions on the concentration of the antisite defects are constructed based on the analysis of the experimental data. It has been established that the so-called critical concentrations of antisite defects, at which the spontaneous amorphization occurs, differ for oxides with the garnet and perovskite structures. As the criterion of the spontaneous radiation amorphization, it is proposed to consider the critical static displacement of the ions, which is identical for studied oxides and equal to ～0.28 Å, or ～0.14 in fractions of interatomic distances, which is close to the well-known Lindemann melting criterion.     

Angular distributions of fast neutrons from the reaction

The angular distributions of neutrons from the reaction Co⁵⁹ (p, n) for 4 values of the proton energyE _p=5.23–4.05 MeV have been measured. The preliminary analysis of the results shows that in the reaction mechanism a certain role is played also by a direct process, most probably of a knock-out type, the relative contribution to the reaction yield of which decreases with decreasing value ofE _p.The authors would like to thank Prof. V. Petrílka for his constant interest in the work, the staff of the Cyclotron Laboratory of the Nuclear Research Institute of the Czechoslovak Academy of Sciences for their cooperation and the group of physicists of the Nuclear Reactions Department of the institute for lending most of the apparatus.     

Effects of fast neutrons on silicon-alloy p-n junctions

Fast-neutron irradiation before alloying reduces the switching lag by increasing the dislocation density.     

Low-temperature photoluminescence in germanium irradiated by fast neutrons

This study was carried out to investigate low-temperature (T=4.2 K) photoluminescence caused by interdopant recombination transitions in n-germanium irradiated by fast (epicadmium) reactor neutrons and subjected to “complete” annealing (+450°C, 24 h). It is shown that lines of interdopant radiative recombination observed in initial and in irradiated and annealed specimens are caused by both initial impurities and (mainly) dopants (As and Ga) implanted by transmutation as well as by defect sets stable at long-time high-temperature annealing that do not contain fine dopants. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 479–482, July–August, 1997.     

Measuring fluence of fast neutrons with planar silicon detectors

The results of measurements of 1-MeV (Si) equivalent fast neutron fluence with silicon planar detectors are reported. The measurement method is based on the linear dependence of the reverse detector current increment on the neutron fluence: ΔI = α _I × Φ × V. This technique provides an opportunity to measure the equivalent fluence in a wide dynamic range from 108 to 10¹⁶ cm^–2 with an unknown neutron energy spectrum and without detector calibration. The proposed method was used for monitoring in radiation resistance tests of different detector types at channel no. 3 of IBR-2 and for determining the fluence of fission and leakage neutrons at the KVINTA setup.     

Variation of electron concentration in gallium arsenide due to irradiation by fast neutrons

The effects of irradiation by fast neutrons on gallium arsenide crystals with different degrees of initial perfection is investigated. It is shown that for relatively perfect, specially non-doped n-type crystals the degree of damage K is weakly dependent on the integrated radiative flux up to some critical flux determined by the initial current carrier concentration. The decrease in the rate of carrier removal in crystals with an elevated concentration of residual defects is due to the participation of the latter in the kinetics of defect formation. The initial rates of carrier removal are obtained in crystals grown by different methods.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 47–51, January, 1973.     

IR spectra of fused silica irradiated by fast neutrons

IR spectroscopy has been used to study the process of structural damage and changes in some characteristics of fused silica irradiated by fast neutrons over a very broad fluence range (10¹⁷–10²¹ cm⁻²). Features of the change in spectral characteristics of the bending and stretching vibrations of the bridge bonds have been identified, and also a comparative analysis has been carried out with radiation-induced changes in a series of optical spectra in the UV and visible regions, and structural parameters and other characteristics of wafers irradiated by different fluences. A correspondence has been established between the features of the radiation-induced changes in the optical, luminescence, and structural properties, and extremal points have been observed on the dose dependences. Based on the results obtained, a mechanism of radiation-induced rearrangement of the silica structure is suggested. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 494–497, July–August, 2006.     

Scattering of fast neutrons on238U,average energy and angular distributions of fission neutrons

Angular distributions of neutrons elastically and inelastically scattered from²³⁸U have been measured with a time-of-flight spectrometer at seven incident neutron energies between 1.5 and 5.5 MeV. Inelastic angular distributions for groups of unresolved levels are given for incoming neutron energies of 1.5, 1.9 and 2.3 MeV. The corresponding neutron cross-sections were obtained relative to then-p scattering cross-sections. The average energies and angular distributions of the fission neutrons were extracted from the measured fission neutron spectra at 1.5,1.9 and 2.3 MeV. Cross-section calculations based on a spherical optical model have shown to be inadequate to describe the neutron-nucleus interaction in case of strong nuclear deformation. The experimental reality may be better approached, instead, if the calculations are made using a potential which takes into account the deformation of the target nucleus. Some of the present measurements are interpreted in this theoretical perspective.     

N+GaAs subpicosecond photodetector irradiated by fast neutrons

We report experimental results of the characterization of an N⁺GaAs photodetector irradiated by fast neutrons with flux up to doses of 4×10¹⁷ n/cm² using a constructed electro-optic sampling system and illumination with 80-fs-wide laser pulses. The investigated N⁺GaAs sample was compared with the same non-irradiated sample. The device shows a response time of 680 fs full width at half maximum (648 GHz, 3-dB bandwidth) with a voltage amplitude of 3.1 mV. Changes in the shape of the electrical signal for different beam power excitations and bias voltages have been demonstrated. Using X-ray diffraction and diffuse scattering analyses, we have observed a decrease of the lattice constant and an almost three times decreased radius of nanoclusters; the density dislocations increased by over four times after neutron irradiation.     

Triton emission in the interactions of fast neutrons with nuclei

Cross sections have been measured for the formation of tritium in the interactions with Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, Ca, V, Co, As, Y, La, Pr, Tb, Ho and Tl of fast neutrons produced via break-up of 53 MeV deuterons on a Be target (E_n = 11.5–43.5 MeV; I_max at 22.5 MeV; FWHM = 15.8 MeV). The activation technique in combination with vacuum extraction and low-level gas phase β^? counting of tritium was employed. Furthermore, cross sections were measured for isotopes of the elements Ne, Mg, Ar, Ca, Ti, Cr, Fe, Ni, Zn, Ge, Se, Zr, Mo, Pd, Te, Ba, Pr, Dy, W, Tl and Pb by γ-ray spectroscopic analysis of the radioactive reaction products. A comparison of the two sets of cross sections shows that for nuclei with A > 40 the emission of three single particles (lp2n) is much more probable than the emission of a bound tri-nucleon (³H). The cross-section data obtained via tritium counting show that the (n, t) cross sections for the lightest nuclei are exceptionally large, probably due to direct interactions, and the process competes with other modes of de-excitation; for elements with Z > 20, on the other hand, the cross section is low (< 0.25 % ofσ_n.e.) and practically constant, showing thereby that in the medium and heavy mass regions the probability of emission of a triton is relatively independent of the target nucleus. A comparison of the cross-section systematics at E_n = 14.6 MeV and for the neutron spectrum described above is presented; the trends are somewhat similar.