Cellulose Nitrate Track Detectors Research Articles

Performance evaluation of a new reading technique of LR115 cellulose nitrate track detectors

Abstract LR115 cellulose nitrate SSNTD are routinely used for Radon detection. A reading technique with high resolution optical microscope coupled with a scanning system has been recently proposed. In this technique, the efficiency correction that was formerly performed on the residual thickness of the detector is performed on the track area distribution. So all the information that is needed for the measurement is obtained directly during the scanning. This leads to a much simpler and faster reading procedure, when compared to the classical technique that required both spark counting and micrometer residual thickness measure. A complete characterization and performance evaluation of the detector response is discussed, including a measuring range evaluation, a combined uncertainty theoretical calculation and a blind test validation at HPA.

Slow and fast neutron detection using bare CN-85 cellulose nitrate detectors

We report on the application of CN-85 cellulose nitrate track detectors to neutron dosimetry. CN-85 has the ability to register proton tracks and therefore can be used for neutron detection via neutron-induced recoil events within the detector matrix. The CN-85 detectors were used to study the distribution of the weakly moderated spallation neutrons, produced in the irradiation of an extended Pb-target with 1 GeV protons. The results obtained are compared with Monte Carlo simulations using the MCNPX-2.5.c code. The thermal and epithermal neutrons can also be detected by CN-85 detectors without the need for a neutron converter via the 14N(n, p) 14C reaction, which has a positive Q -value of 626 keV.

Detection of charged particle tracks in the volume of CN-85 detectors; attributed to neutrons

We report results of our observations on the detection of tracks in the volume of CN-85 cellulose nitrate track detectors that have not been irradiated intentionally with an external radiation source. It is known that CN-85 can register proton tracks and it was reached to the conclusion that the observed volume tracks are produced by background neutrons in our laboratory environment as well as by exposure to secondary cosmic-ray neutrons in the course of the air transport of the detectors from the country of the origin (France) to Australia. It is concluded that a proton sensitive cellulose nitrate track detector may be a suitable detection medium for secondary cosmic-ray neutrons.

Response of cellulose nitrate track detectors to electron doses

In order to study alternative dose determination methods, the bulk etching velocity and the latent track annealing of LR 115 track detectors was studied during electron irradiation runs from a Pelletron accelerator. For this purpose alpha irradiated and blank detectors were exposed to increasing electron doses from 10.5 to 317.5 kGy. After the irradiation with electrons the detectors were etched under routine conditions, except for the etching time, that was varied for each electron dose in order to reach a fixed residual thickness. The variation of the bulk etching velocity as a function of each one of the electron doses supplied, was interpolated in order to obtain dosimetric response curves. The observed annealing effect on the latent tracks is discussed as a function of the total electron doses supplied and the temperature.

Indoor radon concentrations in the town of Podgorica-Montenegro

Indoor radon survey in the town of Podgorica, capital of Montenegro, was performed in winter season 1994–1995. The town houses were classified on the basis of their construction materials and techniques in 4 distinct types. Radon was measured in 110 dwellings, selected with respect to the types and locations of houses. Measurements were carried out by cellulose nitrate track detectors, exposed for 90 days in living-rooms on ground floors. Equilibrium equivalent concentrations of radon are found to be in (4 – 453) Bq/m 3 range, with a median of 26.4 Bq/m 3. They belong to a log-normal distribution (geometric mean: 21.8 Bq/m 3, geometric standard deviation: 2.20 Bq/m 3). The detached houses built of bricks have the highest average indoor radon level, and the apartment houses made of concrete and bricks, with plaster on the walls, the lowest one.

DC conductivity and dielectric constant of cellulose nitrate detector

The temperature dependence of DC conductivity as well as the temperature and frequency dependence of dielectric constant of cellulose nitrate (CN) track detector was undertaken for better understanding of the track response of the detector. In the temperature range −100° to + 100°C, CN is found to be an insulating semiconductor with activation energies 0.04 eV, 0.78 eV and 1.24 eV. The transition of the activation processes takes place at (−10±1)°C and (60±1)°C. The high activation energy transition temperature coincides with the glass transition temperature of CN. The dielectric constant is found to increase with temperature and decrease with frequency. These results reveal the physical basis of the Ion Explosion Spike model of Fleischer et al. (1975). A possible explanation of the registration temperature effect is also given on the basis of these results.

Track-hole formation of alpha-particle and recoil nuclei in an LR-115 nuclear track detector exposed to neutrons

The response function V(REL) of an LR-115 polymeric nuclear track detector has been used to determine the V( R) sensitivity functions for recoil nuclei which are produced by the interactions of fast neutrons with the detector material. For an external radiator placed in close contact with the LR-115 detector, the sensitivity functions have also been determined for the generated nuclei from the (n, α) reaction of thermal neutrons with the radiator material. The REL and the range for the studied nuclei as a function of their energies were calculated by using the BASIC-E version of Henke and Benton's programme. The theory of etch-track kinetics which depends on the V( R) function is used to predict the residual thickness necessary for track-hole formation of a charged particle at different angles by normally incident neutrons. The theoretical treatments were found to be in fair agreement with the previously obtained data for other cellulose nitrate track detectors.

Thermal stability of pores in nuclear track microfilters

CN-85 cellulose nitrate track detectors irradiated with 252Cf in 2π geometry, had undergone post-irradiation thermal annealing and ultraviolet treatments, separately. Diametric measurements of the etched “through holes” have been made. Profiles of the pores affected by the post irradiation treatments have been studied. Thermal annealing of the detectors at 98 °C produces “through holes” of uniform size and relatively of smaller dimensions as compared to the unannealed and U.V. treated filters. Activation energy of annealing has been found to be (0.12 ± 0.01) eV.

Temperature-related effects in radon dosimetry using plastic track detectors

Abstract The effects of temperature-related phenomena in radon dosimetry using CN-85 cellulose nitrate track detectors are reported. In isothermal annealing of α-tracks in CN-85 exposed to radon gas in equilibrium with its daughters, the track density as a function of annealing time follows a curve which is step-like. Such a step-like behaviour has been confirmed by computer simulation of α-tracks from radon both for post-irradiation annealings and for simultaneous irradiation and annealing. Studies on the effect of irradiation temperature on the registration efficiency η of CN-85 detectors show that η is a decreasing function of temperature in the temperature range 26–90°C studied in this work.

An investigation of radon temporal variations in the subsoil atmosphere in Turkmenia using dielectric detectors

The behaviour of subsoil radon depending on meteorogical conditions (atmospheric pressure, air and soil temperature) and on the Ashkabad seismik activity of the region in 1983–1985 has been studied using the LR-115-11 cellulose nitrate track detectors.

Application of Alpha-Track Method to Tritium Production Rate Measurements

The α-track method with a solid state nuclear track detector was used for the measurement of tritium production rates (TPR). Cellulose nitrate track detectors (Kodak LR-115) with Li-containing radiators were placed in a simulated fusion blanket of a Li2O slab assembly with a Be layer and irradiated by D-T neutrons. After chemical etching, the etched-through tracks in the detectors were counted. Lithium metal was the most suitable radiator to distinguish tracks formed by α-particles of the LI(n, α)T reaction from the background. The experimental results agreed well with the calculations. This shows that the indirect α-track method is reliable in estimating TPR distribution.

Application of alpha-track method to tritium production rate measurements.

The α-track method with a solid state nuclear track detector was used for the measurement of tritium production rates (TPR). Cellulose nitrate track detectors (Kodak LR-115) with Li-containing radiators were placed in a simulated fusion blanket of a Li2O slab assembly with a Be layer and irradiated by D-T neutrons. After chemical etching, the etched-through tracks in the detectors were counted. Lithium metal was the most suitable radiator to distinguish tracks formed by α-particles of the LI(n, α)T reaction from the background. The experimental results agreed well with the calculations. This shows that the indirect α-track method is reliable in estimating TPR distribution.

Study of the effects of atmospheric parameters on ground radon concentration by track technique

Radon emanation was continuosly monitored for 24 months, accompanied by measurements of atmospheric parameters. Integrated measurements of radon concentrations have been performed with LR-115 cellulose nitrate track detectors. The monitoring was conducted at 16 observation sites distributed on the Dakar University area. Observed changes in radon concentration are interpreted to be caused by changes in meteorological conditions and ocean tides.

Thermal Neutron Monitoring Using Cellulose Nitrate Track Detector by Means of Spark Counter

Cellulose nitrate films were examined for thermal neutron monitoring in contact with several kinds of (n, α) converter materials such as a plastic sheet doped with 1% boron, a solidified boron oxide plate, a single crystal plate of boron oxide and that of lithium fluoride. After thermal neutron irradiation in a research reactor, the films were etched in alkaline solution. The etch-pits on the films were counted with a spark counter. The single crystal converter of lithium fluoride was found to be the most sensitive for thermal neutron. A method for producing the single crystal converter was described. Linear relation between thermal neutron fluence and spark counts was found to be in the fluence range of 2 × 10−6–3 × 107n/cm2 in case of using a lithium fluoride single crystal converter.

Natural radioactivity of building materials

Experiments were designed to measure trace uranium concentration and the rate of radon exhalation from masonry structural materials, both bare and surface finished and coated. LR115 cellulose nitrate track detectors were used to record the alpha emission from structural material surface. Fission track, neutron activation and fluorometric analysis methods were used to determine the uranium content. Most types of paints studied will reduce alpha contribution and radon emanation from building materials.

On the determination of alpha activity in airborne particulate from zircon sand using cellulose nitrate track detectors

An application of cellulose nitrate as a nuclear track detector for determining the alpha activity from natural radionuclides 238 U, 232 Th and their daughters in zircon sand was studied. The air suspended particulate having been deposited onto Millipore filters was examined. Using a new experimental procedure we were able to obtain accurate track detection. Depending on the working site, measured alpha activity ranged from 0.4 to 4.5. 10 -2 Bq. m -3 .

Thermal neutron monitoring using cellulose nitrate track detector by means of spark counter.

Cellulose nitrate films were examined for thermal neutron monitoring in contact with several kinds of (n, α) converter materials such as a plastic sheet doped with 1% boron, a solidified boron oxide plate, a single crystal plate of boron oxide and that of lithium fluoride. After thermal neutron irradiation in a research reactor, the films were etched in alkaline solution. The etch-pits on the films were counted with a spark counter. The single crystal converter of lithium fluoride was found to be the most sensitive for thermal neutron. A method for producing the single crystal converter was described. Linear relation between thermal neutron fluence and spark counts was found to be in the fluence range of 2 × 10−6–3 × 107n/cm2 in case of using a lithium fluoride single crystal converter.

Radon emanometry in soil gases and activity in ashes from El Chichon Volcano

Radon (222Em) emanation measurements in soil gases are reported in connection with the 1982 eruptions of El Chichon Volcano.222Em detection is performed with LR-115 cellulose nitrate track detectors. Results show a general decreasing pattern of222Em concentration in soil with time after the eruptions. Activity measurements of radon daughters in ashes show that a large amount of222Em and220Em was released from magma degassing during the eruptions, and that only a fraction of the degassed magma was erupted. An important fluid interaction between the magma chamber and the surrounding sedimentary rock is also suggested.

Effect of electric field on cellulose nitrate track detector

The influence of d.c. electric fields (0−3.5 × 10 7 V· m −1) applied for different durations (0−2 h) on the track recording characteristics of CA80-15 Kodak Pathe's cellulose nitrate, is reported. It is observed that at a lower etch time of 30 min (2.5. N NaOH, 55°C, without stirring), etched track diameters of normally incident 4 MeV α-particles remain unchanged almost up to the applied electric fields 0−3 X 10 V·m −1 irrespective of the time duration of application of field. Track diameter increases on increasing the field further. At higher etching times (interrupted etching with 30 min step) track diameter and bulk etch velocity V g go on decreasing in general at first, attain a minimum and then show an upward trend at fields ≈3 X 10 V· m −1. However, for field values >3 X 10 7 V· m −1 and longer field times (1.5−2 h), downward trend is indicated. Average bulk etch velocity calculated for a total etch time of 180 min for the samples treated with different electric fields for a maximum time of 2 h, increases first, acquires a maximum and then exhibits a failing trend with increasing fields. Average track etch velocity, V t , however, decreases initially and then increases with the field followed by an abrupt rise at higher field values. The etch velocity ratio, V ( = V t / V g ) shows peaking at 3.5 X 10 7 V· m −1 in the upward direction. The etching efficiency, η, changes from 82% to 97% for the field values changing from 1 X 10 7V·m −1 to 3.5 X 10 7 V·m −1 for a field duration of 2 h and total etch time of 180 min. An attempt has been made to correlate the observed results with the possible increased crystallinity with the application of electric field leading to the electret phenomenon involving molecular orientations and the ozone effects.

Energy-Dependent Neutron Detection Sensitivity of Cellulose Nitrate Track Detector

A cellulose nitrate track detector, LR-115 (Type II), was studied experimentally to observe its neutron energy response when a radiator, such as fissionable material, is absent. The detector was exposed to monochromatic neutrons from the D (d, n) He reaction produced by a Van de Graaf accelerator. Through-etched and almost through-etched tracks in the detector were counted by two different methods: 1) optical microscope counting with an automatic image analyzing system and 2) spark counting. The detection sensitivity was obtained in the neutron energy region lower than 5 MeV and it was found that only α-particles from (n, α) reactions could be detected in both counting methods. We derived the counting probability of α-tracks induced in the detector and the threshold energies for neutron detection.