Cosmic-ray neutron spectrometry by solid state detectors

Extensive data have been gathered since the early 1990s on the response of different detectors based on the registration of neutron-induced fission in bismuth, gold, tantalum by the spark replica counter and the thin film breakdown counter. These detectors make it possible to exploit the excellent characteristics of the fission reactions in bismuth, gold and tantalum for the measurements of high-energy neutrons.

Most of the investigations have been carried out at the quasi-monoenergetic neutron beam facility at The Svedberg Laboratory-TSL of the Uppsala University in cooperation with the Khlopin Radium Institute (KRI).

The responses of different fission detectors in the intermediate range of neutron energy (35–180 MeV) have been evaluated: a region where the predictive power of available nuclear reaction models and codes is not reliable yet. For neutron energy greater than 200 MeV, the fission-detector responses have been derived from the data of the proton fission cross-sections.

Finally, by using the ratio of the responses of these detectors, a simple and accurate way to evaluate the spectrum hardness can be obtained, thus providing a tool to obtain spectral information needed for neutron dosimetry without the need to know the entire spectrum.

The experimentally measured spectra obtained to-date have different shapes and they are also different from those calculated.

In this paper, a new approach will be reported to analyse the existing spectra by using response ratios of different detectors. Preliminary data have been already obtained for the high-energy neutron spectrum from the CERN concrete facility.     

Plastics as nuclear track detectors for thermal neutron dosimetry

An attempt is made to determine the response of CR-39 and cellulose nitrate plastic track detectors subjected to thermal neutrons. The α-particles are produced from (n, α) reactions in lithium tetraborate convertor placed in contact with different plastics and are recorded in the detectors. The corrected track density gives a fluence sensitivity and dose sensitivity of the order of 10^?4 tracks per neutron and 10² tracks/cm² mrem respectively. A linear relationship is observed between track density and neutron fluence.     

Gamma and neutron dose measurements with solid state nuclear track detectors

An attempt has been made to explore the possibility of using solid state nuclear track detectors for the estimation of gamma and neutron doses based on the use of changes in activation energy of degradation of these detectors, due to irradiation (gamma-neutron), as a means of dosimetry. Thermogravimetry (TG) has been applied as a tool for these studies carried out on Lexan and CR-39 track detectors. A linear relationship observed between the decrease in activation energy and the dose (gamma-neutron) received by the detectors suggests the possibility of the use of these detectors as gamma and neutron dosimeters.      

Operational and dosimetric characteristics of etched-track neutron detectors in routine neutron radiation protection dosimetry

There are a number of etched-track neutron dosimetry systems in routine use for personal monitoring. In this paper, the operational and dosimetric characteristics of these systems are summarized. Brief details are given of the dosemeter design, the material used, its quality control procedures, background, processing and read methods, neutron energy range, energy and angle dependence of response, decision threshold, linearity, signal storage stability, calibration methods including normalization, effect of influence quantities, and the advantages and disadvantages of the systems in routine application.     

Uranium analysis by neutron induced fissionography method using solid state nuclear track detectors

In this study total twenty samples (eight reference materials and twelve sediment samples) were analysed for their uranium content which is in the range of 1–17 μg/g, by neutron induced fissionography (NIF) method using solid state nuclear track detectors (SSNTDs) in comparison with the results of neutron activation analysis (NAA), delayed neutron counting (DNC) technique or fluorometric method. It is found that NIF method using SSNTDs is very sensitive for analysis of uranium.     

Solid state detectors for neutron radiation monitoring in fusion facilities

The purpose of this communication is to summarize the main solid state based detectors proposed for neutron diagnostic in fusion applications and their applicability under the required harsh conditions in terms of intense radiation, high temperature and available space restrictions. Activation systems, semiconductor based detectors, luminescent materials and Cerenkov fibre optics sensors (C-FOS) are the main devices that are described.     

A global model for annealing in solid state track detectors

A systematic study of annealing phenomenon in solid state track detectors (SSTD) is presented using a quasi-equilibrium approach for the defects migration process. The nonlinear nature of the mechanism is also taken into account, which leads to an interesting formula for rate of annealing. Some of the experimentally tested empirical/semi-empirical formulae can also be deduced from it under certain approximations. The importance of the concept of relaxation time/hopping time is stressed. The temperature dependence of rate of annealing follows automatically from this formulation. Suggestion is made for experimental measurement of half life of fractional thermal fading of tracks so that the nonlinearity parameter can be computed and annealing process can be better understood.     

Non-classical neutron beams for fundamental and solid state research

The curious dual nature of the neutron, sometimes a particle, sometimes a wave, is wonderfully manifested in the various non-local interference and quantum contextuality effects observed in neutron interferometry. Non-classical states may become useful for novel fundamental and solid state research. Here we discuss unavoidable quantum losses as they appear in neutron phase-echo and spin rotation experiments and we show how entanglement effects in a single particle system demonstrate quantum contextuality. In all cases of interactions, parasitic beams are produced which cannot be recombined completely with the original beam. This means that a complete reconstruction of the original state would, in principle, be impossible which causes a kind of intrinsic irreversibility. Even small interaction potentials can have huge effects when they are applied in quantum Zeno-like experiments. Recently, it has been shown that an entanglement between external and internal degrees of freedom exists even in single particle systems. This contextuality phenomenon also shows that a quantum system carries much more information than usually extracted. The path towards advanced neutron quantum optics will be discussed.      

Equation of state for neutron matter in the presence of a pion condensate

The energy density for neutron matter including a pion condensed phase is studied, with particular emphasis on the role of Δ-isobars. Relativistic corrections to vertex functions involving isobars are considered and turn out to be important in the high density region. We arrive at a simple schematic model in which the inclusion of isobars leads to an effective enhancement of the axial vector coupling constant, which competes with an effective reduction due to the Lorentz-Lorenz correction. In the equation of state, inclusion of a pion condensed phase can lead to an appreciable reduction of total pressure.     

The microdosimetric one-hit detector model for calculating the response of solid state detectors

The microdosimetric one-hit detector model has been developed and applied to calculate the dose response, energy response and relative efficiency of thermoluminescent LiF:Mg,Cu,P and CaF₂:Tm detectors, and of the free-radical alanine dosimeter, after their exposure to radiation of different quality. The one-hit detector is described by two model parameters: the target diameter, d and the saturation parameter, α. Combining these parameters with microdosimetric distributions in nanometer-size targets calculated using Monte Carlo track structure codes TRION and MOCA-14, it was possible to describe and predict a great variety of experimental data for photon, X-ray, beta-electron, proton, alpha-particles and heavy ion irradiation. Within the framework of this biophysical model of radiation action, some mechanistic insight into the physics of radiation action in solid state detectors can be obtained.     

Study of semiconductors using solid state nuclear track detectors

Uranium trace characterization of crystalline GeS, sputtered thin films of GeS and amorphous SiH on quartz substrates, and crystalline p-type Si using the technique of solid state nuclear track detectors is reported. Concentration and distribution of uranium in these materials studied are presented. Using uranium as microprobe, it is observed that uranium prefers to be in the cleavage planes of GeS crystals. There seems to be a link between uranium concentration and the thermally induced defects in Si.     

Studying the response of CR-39 and BD-100R detectors for neutron dosimetry in the light of ICRP-60 recommendations

The latest radiobiological findings show that the damage caused by the neutrons to human body is far greater than was previously thought. The International Commission on Radiological Protection, therefore, revised Q for neutrons and made recommendations in their Report No. ICRP-60 which have serious consequences for many operational neutron dosimetry services. The new recommendations include the reduction in dose limits from 50 mSv to 20 mSv per year, change in the quality factors and the dose estimation in some circumstances down to a few mSv per year. The overall effect of the ICRP-60 recommendations is to reduce the detection threshold in order to account for the reduction in the effective equivalent dose. We have studied the impact of ICRP-60 recommendations on the response of CR-39 based cubical neutron dosimeter and BD-100R bubble detector and the results obtained are presented in this article.     

System for calibration of track detectors used in gaseous and solid alpha radionuclides monitoring

A laboratory system for the calibration of track detectors and charcoal detectors used in monitoring of radon and its decay products/their aerosols in air, is proposed. The system consists of three main components: (i) the alpha exposure chambers, including alpha monitoring devices and the connection with the ²²⁶Ra radioactive source. The CR-39 track detectors are mounted in the monitoring devices pre-equipped or not with paper filter; (ii) the calibrated  ²²⁶Ra source. Among the three tested sources: ²²²Rn, ²²⁶Ra+²²²Rn and ²²⁶Ra, the ²²⁶Ra source is considered the most appropriate radon source for our calibration system. It is kept into an airtight flat bottom flask, the radionuclide ²²⁶Ra being always in the radioactive equilibrium with their descendants. In the alpha exposure chambers, the source assures the radon at a constant rate; (iii) the ALFAUURASE program for the computation of radioactive accumulation of the alpha ²²⁶Ra descendants. For any initial mass of the parent, the amount and the activity of each alpha decay product and of all the decay products can be calculated by this computation program. Each component of the calibration system is described in the paper. The use of the system for the calibration of CR-39 track detectors in radon measurements is tested.     

Electrochemical etching technique for neutron dosimetry

In the present work we have employed allyl diglycol carbonate (CR-39) and cellulose triacetate (CTA) plastic for detection of neutron recoil tracks without radiator. For CR-39, the results reveal that registration efficiency is a function of duration of chemical pre-etching and the best results are obtained with chemical pre-etching of 3 hours. It was also investigated that the ac field strength of 28 kV/cm having 2.5 kHz frequency was optimum for revelation of tracks. Interestingly the sensitivity is fluence dependent and it was constant up to a fluence of about 10⁸ n/cm². The sensitivity abruptly decreased with increased fluence. At optimum experimental conditions the minimum detection limit for CR-39 was found to be 0.47 mSv. For CTA, the tracks have been revealed by electrochemical etching (ECE) only and the minimum detection limit was found to be 0.85 mSv at optimum experimental parameters.      

Impact of BaF2 detectors on nuclear solid state investigations

High resolution time differential angular correlation, now achievable at low cost by the fast and efficient BaF₂ detectors, will be introduced from some examples recently worked out. The results obtained manifest a new impetus for this technique in its extended application to particular problems in nuclear solid state research.     

Stand for testing scintillation neutron detectors

A stand for studying the characteristics of time-of-flight neutron detectors is described. Plastic scintillation detectors in the form of rectangular prisms with cross sections of 100 × 100 and 100 × 200 mm² and lengths of 300, 400, and 500 mm are viewed through by photomultipliers from the two ends. The detectors are irradiated with a collimated 14-MeV neutron beam produced in the d + t → n+ ⁴He reaction. The collimated beam makes it possible to investigate the spatial resolution of long detectors. The interaction point is determined either from the arrival time of light pulses to the opposite ends of the scintillators or from the ratio of the amplitudes of the signals at the ends of the scintillators. The stand proposed also makes it possible to measure the absolute efficiency of detectors of different length at a neutron energy of 14 MeV.     

Ferrofluidic masking of solid state nuclear track detectors during etching

This work presents a novel method for determining bulk etch rate of CR-39 during prolonged etching by masking the surface with a ferrofluidic film held in position by magnetostatic forces. The CR-39 etching conditions were 6.25 M NaOH solution for 24 h at temperatures ranging from 50 to 80 °C. After etching, the heights of the resulting un-etched plateaus were measured using a Talyscan 150 profilometer. The removed layer thicknesses ranged from 12 to 85 μm, giving corresponding bulk etch rates in the range 0.5–3.54 μm/h.     

Environmental neutron measurements with solid state track recorders

Abstract

The suitability of using ¹⁰B and ⁵LiF in contact with cellulose acetate butyrate (CAB) for the measurement of slow neutron densities has been investigated. The upper energy threshold of clear Diacel cellulose nitrate (CN) and of the CAB have also been measured. The CAB in good contact with thick ¹⁰B or ⁵LiF sources offers good promise for the detection of slow neutrons. For the actual CAB samples used, the CAB-¹⁰B combination had an efficiency of ～1.3 × 10^?2 tracks per thermal neutron incident in a 2π solid angle. The corresponding number for the CAB⁶-Li combination is ～5.6 × 10^?3 tracks per thermal neutron.     

Theory of neutron scattering from magnetised solid state plasmas

The spin and orbital components of the inelastic neutron cross-section for scattering from a magnetised, degenerate plasma are calculated treating the Coulomb interaction in the RPA. Particular attention is focussed on results for small wavevectors where effects of the magnetic field are most pronounced. It is shown that a collective mode is excited at small wavevectors with a frequency that is the square root of the sum of the squares of the plasmon and cyclotron frequencies.