Assessment of integrated solar ultraviolet radiation by PM-355 detectors

The increase in environmental solar UV radiation due to depletion of ozone layer is a recent challenge to human health (skin cancer and eye effects) in countries having clear skies. Therefore, applying integrated, passive and inexpensive techniques to assess solar UV radiation is very much essential. Measurements of environmental solar UV radiation in Dhahran, Saudi Arabia area were carried out for a period of two months in the summer period in 1996 using two techniques in parallel namely: passive nuclear track detectors and active solar UV radiometers. Some of the nuclear track detectors were mounted in different conditions such as: under shadow band, on solar tracking mechanism following the solar rays. Others were mounted on perpendicular, tilted and horizontal surfaces in sunlight. All detectors were attached to a wooden background of the same thickness (0.5 cm) to eliminate interference of the heat effect of various support materials and have uniformity of the support materials. The assessment was carried out for different periods extending from two to nine weeks continuously. The investigated period covered the hottest months in Saudi Arabia (July and August) when the sky was clear of clouds. The results indicate linear correlation between alpha track diameters and the integrated exposure to solar UV as measured by the solar UV radiometer for all nuclear track detector positions and orientations. The highest slope has been observed for the detectors placed on solar tracking mechanism following the solar rays and the lowest from detectors oriented under the shadow band on horizontal position (measuring the diffused UV radiation only). The results show that most of the measured UV radiation (60%) were from the diffused UV radiation. The characteristics of the upper layer of the detectors are changed after chemical etching very quickly, with increase in the exposure time to UV solar radiation at certain orientation. The results encourage the use of nuclear track detectors for environmental and personal solar UV dosimetry on a large scale in Saudi Arabia and similar hot and clear-sky countries.     

Environmental gamma and radon dosimetry in Venezuela

Environmental gamma exposure and radon concentration levels measured in Venezuelan regions are presented. A new generation image analyser was used for particle track counting in CR-39 detectors. Mineral water wells from where water is supplied for massive consumption have an alpha activity around 0.450 Bq L⁻¹ and few of them have concentrations above 50 Bq L⁻¹. Coastal potable water activity is on the average around 5.3 ± 12% Bq L⁻¹. Indoor radon national average is 36 ± 5% Bq m⁻³; in two of the 36 monitored sites, the measured average is above 400 ± 5% Bq m⁻³. In air gamma dose values are between 100 and 144 nGy h⁻¹. In soil, ¹³⁷Cs concentration is around 0.5 and 10 Bq kg⁻¹ at the depth of down to 20 cm. Building materials were included in this study. ⁷Be and ¹³⁷Cs were measured in low concentration in tropical plants on Tepuy-s (sacred mountains in the Amazonas State). Geological active faults were identified by radon concentration measurements using LR-115.     

Study of uranium, radium and radon exhalation rate in soil samples from some areas of Kangra district, Himachal Pradesh, India using solid-state nuclear track detectors

LR-115 plastic track detectors have been used for the measurement of radon exhalation rate and radium concentration in soil samples collected from some villages of Kangra district, Himachal Pradesh, India. Uranium concentration has also been determined in these soil samples using fission track technique. Radium concentration in soil samples has been found to vary from 11.54 to 26.71 BqKg⁻¹, whereas uranium concentration varies from 0.75 to 2.06 ppm. The radon exhalation rate in these samples has been found to vary from 15.16 to 35.11 mBqKg⁻¹ h⁻¹ (502.12 to 1162.64 mBqm⁻² h⁻¹).     

Measurements of radon concentration in soil gas by CR-39 detectors

A miniature diffusion chamber with a 25 × 4 × 0.5 mm CR-39 track etch detector (Pershore Moulding Ltd.), mounted on the 1.1 m long pole has been developed for radon gas measurements at 1 meter depth in the soil. For chemically etched CR-39 (7h, 70°C NaOH) and automatic track analysis the lowest detection limit of the chamber was found to be 0.5 MBq h m⁻³ and the useful exposure range from 2 to 20 MBq h m⁻³. The typical exposure time in the soil is between 2 to 14 days. The chamber was tested against the active AlphaGUARD PQ-2000 (Genitron Instruments GmbH) probe. The test yielded consistent results for soils with typical values of permeability and which are not miniature with water. The pilot measurements of radon gas in soil conducted with the miniature diffusion chambers around 48 buildings in Kraków and Silesia regions yielded an average radon concentration of 13 kBq m⁻³. The chambers are to be applied to measure radon concentration in soil before constructing new houses in order to avoid high radon risk areas.     

A passive radon dosimeter based on the combination of a track etch detector and activated charcoal

The aim of this work is to test a combination of a Makrofol track detector with a new type of charcoal (Carboxen-564) to design a personal radon dosimeter. The intention is to use this dosimeter as a personal radon dosimeter to measure the monthly radon exposure in workplaces, especially when the occupancy is not ecactly known. The proposed combination was exposed to low and high concentrations of radon in a large range of relative humidity (RH). For the optimal layer thickness, a charcoal bed of 2.2 mm, a specific track density of 5.1 tracks cm⁻²/kBq h m⁻³ was obtained. For a monthly working exposure (170 h) at an average radon concentration of 100 Bq/m³, this means 87 tracks/cm² or 10 times the background of the Makrofol detector, with a statistical uncertainty of 15%.     

Search for the ternary cluster decay of Cm isotopes using SSNTD

Investigation of the ²⁴⁶Cm spontaneous ternary decay into nearly equal clusters using polyethyleneterephthalate track detectors has been carried out. The possibility of ternary cluster decay has been found out to be of less than 10⁻⁶ with respect to all fission modes of ²⁴⁶Cm.     

Detection, dosimetry and microdosimetry using high energy C beams

Samples of polyallyldiglycolcarbonate (PADC) track etch detectors (TED) were exposed to high energy ¹²C nuclei at the particle beam of the Dubna synchrophasotron. The energy of ¹²C nuclei varied between 0.1 and 1.5 GeV per amu.

At the low studied energies the linear energy transfer (LET) of these nuclei is higher than the detector threshold value. Then, the primary particle tracks are directly etched in the detector surface. The detection efficiency approaches to 100% at perpendicular incidence. Their LET has been established by means of standard authomatized procedure recently developed. The LET values found here are in good agreement with theoretical ones.

At 1.5 GeV per amu (LET 8.4 KeV μm⁻¹) the secondary particle tracks were evaluated in all the exposed detectors. The energy deposited by these particles was compared to the energy deposited through primary ionization losses. It was found out that its contribution to the total dose is relatively lower than for protons of comparable energies. In some of these samples even the tracks of the primary nuclei were observed. It follows that the detection threshold of the developed LET spectrometer should be below 10 keV μm⁻¹.     

Search for GUT magnetic monopoles and nuclearites with the MACRO experiment

We present the final results obtained by the MACRO experiment in the search for GUT magnetic monopoles and nuclearites. Several searches were performed with different subdetectors, i.e. scintillation counters, limited streamer tubes and nuclear track detectors. No magnetic monopole or nuclearite candidates were found. The MACRO upper limit to the local flux of GUT magnetic monopoles is at the level of 1.4×10⁻¹⁶ cm⁻² s⁻¹ sr⁻¹.     

Comparative measurements between NTD and GEL detectors for radon gas

Because of the interest in an inexpensive radon monitoring technique and the use of new materials and new methods, this work presents comparative measurements between traditional passive radon detector using nuclear track detector (NTD), and a new method based on the diffusion of radon gas in gels, measuring the quantity of the remainder radioactive solids by the analysis of the gamma radiation from the decay of radon daughters. The methodology of the new detectors is introduced. The preliminary results show a measurable response of the gel material detectors to radon gas. The measurements are compared with those using NTDs CR-39 type for calibration purposes. Both the detection systems, the passive close-end cup system with NTDs and the passive close-end cup gel material detector, were exposed at the same time in the radon calibration chamber to different radon exposition levels from 150 to 3000 Bq/m⁻³.     

Effect of high gamma dose on the PADC properties

The effect of the properties of PADC nuclear track detectors after exposure to high doses of gamma absorbed doses up to 5×10⁵ Gray (50 Mrad) were studied. The gamma source was a 9.03 PBq (244 KCi), Co-60 source. Results indicate that each of the bulk etch rate (V_b), the tracks etch rate (V_t) and the sensitivity (V) of the detectors increases with the high gamma absorbed dose, but there is a drop in these parameters at the low gamma absorbed dose. Signs of surface roughness were observed by increasing the gamma absorbed doses and changes in color observed for doses larger than 2×10⁵ Gray. The temperature of detectors during irradiation time reached 41°C. The fission fragment tracks (from Cf-252 source) disappeared quickly within the etching time (minutes) for total absorbed doses greater than 3×10⁵ Gray due to their high bulk etch rate.     

Indoor radon measurements in dwellings of four Saudi Arabian cities

An indoor radon survey of a total of 269 dwellings, with one dosimeter per house, distributed in four Saudi Arabian cities was carried out. The objective of this survey was to carry out indoor radon measurements of two cities in the Eastern Province, Khafji and Hafr Al-Batin and to compare this with two cities in the Western Province, Al-Madina and Taif. The survey provides additional information about indoor radon concentrations in Saudi Arabia. The results of the survey in these cities showed that the overall minimum, maximum and average radon concentration were 7,137 and 30 Bqm⁻³, respectively. The lowest average radon concentration (20 Bqm⁻³) was found in Hafr Al-Batin, while the highest average concentration was found in Khafji (40 Bqm⁻³).     

Swelling and structure of radiation induced near-surface damage in CR-39 and its chemical etching

Systematic measurements of swelling of CR-39 nuclear track detector (NTD) due to irradiation with fission fragments and alpha particles over a wide range of fluences from ²⁵²Cf are presented here. Precisely designed and optimized exposure and chemical etching experiments were employed to unfold the structure of radiation induced surface damage. Delays in the startup of the chemical etching of latent tracks in low radiation fluence detectors are measured and are found to contain important information about structure of the surface damage. Simple atomic scale pictures of radiation induced surface damage and its chemical etching are developed using measurements of radiation induced swelling of CR-39 detectors and nuclear track parameters. The computer code SRIM2010 was utilized for the calculations of basic features of latent tracks of fission fragments and alpha particles in CR-39. Another computer code TRACK_VISION was used to compute parameters of etched tracks. Computations and experimental findings in the paper coherently compose a realistic picture of radiation damage.     

Study of cluster decay of Cm using SSNTD

Cluster decay of ²⁴²Cm with emission of ³⁴Si-particles was measured using track-recording phosphate glass detectors. The corresponding partial half-life is (1.4±0.3)×10²³ s. The branching ratio relative to decay is 1.0×10⁻¹⁶ and relative to spontaneous fission 1.6×10⁻⁹.     

Transient thermal lensing measurement in a laser diode pumped NdxY1−xAl3(BO3)4 laser using a holographic shearing interferometer

A new technique for measuring a thermal lens, using a holographic shearing interferometer is presented. This technique was used to measure transient thermal lensing in a laser diode pumped NYAB laser. The measured thermal lensing power was proportional to the pumping laser diode intensity, with a gradient of 1.1 × 10⁻¹ m⁻¹ mm²/W. The transient response time of the thermal lens was 1.5 s, this value being consistent with the temporal decline of the second harmonic power.     

Dosimetry on the Spacelab missions IML1 and IML2, and D2 and on MIR

Detector packages consisting of plastic nuclear track detectors, nuclear emissions, and thermoluminescence detectors were exposed inside BIORACK during the Spacelab missions IML1 and IML2, in different sections of the MIR space station, and inside the Spacelab module at rack front panels or stowage lockers and in the Spacelab tunnel during D2. In addition, during D2, each Payload Specialist (PS) has worn three permanent detector packages; one at the neck; one at the waist; and one at the ankle. Total dose measurements, particle fluence rate and LET spectra, number of nuclear disintegrations and neutron dose from this exposure are given in this report. The results are compared to theoretical calculations and to previous missions results. The dose equivalent (total radiation exposure) received by the PSs were calculated from the measurements and range from 190 to 770 μSv d⁻¹. Finally, a cursory investigation of results from a particle telescope from two silicon detectors, first used in the last BIORACK mission on STS76, is reported.     

Nuclear track radiography of “Hot” aerosol particles

Nuclear track radiography was applied to identify aerosol “hot” particles which contain elements of nuclear fuel and fallout after Chernobyl NPP accident. For the determination of the content of transuranium elements in radioactive aerosols the measurement of the -activity of “hot” particles by SSNTD was used in this work, as well as radiography of fission fragments formed as a result of the reactions (n,f) and (γ,f) in the irradiation of aerosol filters by thermal neutrons and high energy gamma quanta. The technique allowed the sizes and alpha-activity of “hot” particles to be determined without extracting them from the filter, as well as the determination of the uranium content and its enrichment by ²³⁵U, ²³⁹Pu and ²⁴¹Pu isotopes. Sensitivity of determination of alpha activity by fission method is 5×10⁻⁶ Bq per particle. The software for the system of image analysis was created. It ensured the identification of track clusters on an optical image of the SSNTD surface obtained through a video camera and the determination of size and activity of “hot” particles.     

Modifications in track registration response of PADC detector by energetic protons

It has been well established that different ionising radiations modify the track registration properties of dielectric solids. In an effort to study the response of Polyallyl diglycol carbonate (PADC Homalite) detector towards fission fragment, PADC detectors were exposed to 10⁴ Gy dose of 62 MeV protons and then one set of samples were exposed to fission fragments from a ²⁵²Cf source. Two of these detectors were containing a thin layer of Buckminsterfullerene (C₆₀). The study of the etched tracks by Leitz Optical Microscope reveals that the track diameters are enhanced by more than 70% in the proton irradiated zone as compared to that in the unirradiated zone. Scanning Electron Microscopy was performed after etching the sample in 6 N NaOH at 55°C for different etching times, to study the details of the surface modifications due to proton irradiation of PADC detectors with and without C₆₀ layer. Our observations revealed that the diameters and density of proton tracks have increased with etching time on the surface facing the fullerene layer as well as the other surface. However, a relatively more open structure of the etched surface containing C₆₀ as compared to the bare one may be an indication of the extra damage caused by the energy released upon the destruction of C₆₀ molecules by energetic protons.     

Increased surface roughness by oxygen plasma treatment of graphite/polymer composite

The technology of selective plasma etching was applied to increase the surface roughness of graphite/polymer composite. Etching was performed with a low pressure weakly ionised oxygen plasma created with a RF generator of the output power of 200 W and frequency of 27.12 MHz. The density of charged particles, density of neutral oxygen atoms and the electron temperature was about 1×10¹⁶ m⁻³, 4×10²¹ m⁻³, and 5 eV, respectively. The effects of plasma treatment were observed by scanning electron microscope (SEM), electron microprobe (EMPA) and Talysurf. It was found that the surface roughness was increased by approximately 15 times, from a virgin sample at the roughness of R_a=0.27 μm to a very rough surface with R_a=4 μm. The roughness increased with increasing plasma exposure time. The EMPA results showed that the amount of sulphur in the surface layer decreased with increasing etching time indicating that PPS polymer was the material etched preferentially.     

Lattice location of light implanted ions in Si and Ge after laser annealing

Abstract

Radiation damage produced by short ranged (ranges 20–30 μm) charged particles (alpha particles and fission fragments) in thick plastic track detectors (thickness ≈ 150 μm) has been enlarged to produce “through” holes by using a combination of electrochemical and chemical etching processes. A series of experiments were conducted with a view to optimize the operating conditions required to produce through holes with most suitable profiles for a particular application at hand. This novel technique has been employed in producing thick nuclear track filters using fission fragments from U-235 fission and alpha particles from radon and its daughters.