Study of stabilizing CaF2:Dy ultraviolet sensitivity by double annealing treatment.

The intrinsic thermoluminescent response to ultraviolet radiation of CaF2:Dy phosphor is enhanced by pre-irradiation high-temperature annealing treatment. The thermoluminescent response is stabilized by adding a medium temperature annealing treatment after the previous annealing. The experimental results show that the annealing treatment of 1 h 850 degrees C high-temperature annealing followed by 1 h 350 degrees C medium-temperature annealing is the optimum treatment to have high thermoluminescent response and good stability. The results also show that (1) the thermoluminescent response to 253.7 nm ultraviolet radiation is increased and stabilized, (2) the thermoluminescent sensitivity and glow curve distribution to 235.7 nm ultraviolet radiation are retained, and (3) the thermoluminescent response to 253.7 nm ultraviolet is linear from 3 to 1 x 10(3) Jm(-2), but there is no linear response with respect to 365 nm ultraviolet.

Radon concentrations in spa water taken from hot and cold springs in Taiwan.

Spa water samples taken from hot and cold springs throughout Taiwan were analyzed for waterborne radon concentrations using electret ion chambers. The highest radon concentration was detected at Yangmingshan National Park, where it is closed to the action level of 11.0 kBq m-3. Next comes a sea-water hot spring at Green Isle on the east coast of Taiwan. The spa water used by the nearby inhabitants may increase the indoor radon concentration by a factor of two in extreme cases.

Monitoring of 222Rn in Taiwanese hot spring spa waters using a modified electret ion chamber method.

222Rn concentrations in some Taiwanese hot spring spa waters have been monitored using commercially available electret ion chambers (EIC). The use of two EIC units for measuring radon concentrations in the air phase and voltage dependent correction factors for subtracting gamma contributions resulted in improved accuracy.

Discrimination of airborne radioactivity from radon progeny.

Naturally occurring radon and thoron progeny are the most interfering nuclides in the aerosol monitoring system. The high background and fluctuation of natural radioactivity on the filter can cause an error message to the aerosol monitor. A theoretical model was applied in the simulation of radon and thoron progeny behavior in the environment and on the filter. Results show that even a small amount of airborne nuclides on the filter could be discriminated by using the beta:alpha activity ratio instead of gross beta or alpha counting. This method can increase the sensitivity and reliability of real-time aerosol monitoring.

Radon exhalation rate from various building materials.

Solid-state alpha-track detectors using cellulose nitrate films were used to measure the radon exhalation rates from building materials. The radon flux emitted from the surface of the building material was measured by placing an inverted cup on the top of the building material. Cellulose nitrate film was placed within the cup. Tracks due to alpha particles from radon that migrate from the building material into the air space in the cup were registered on the cellulose nitrate film. The films were etched in a solution consisting of 10(-3) m3 2.5 N NaOH solution. A spark counter or microscope was used to record the tracks appearing on the cellulose nitrate film. The average exhalation rate of radon was obtained by means of a simple mathematical approach that can be used to estimate the maximum possible radon concentration in a closed room due to building materials alone. Infiltration and ventilation effects were excluded in this work. This new technique and simple approach can be used to establish the data base for average radon exhalation rates from all available building materials and walls or floors. The maximum indoor radon concentration can be estimated from the measured average radon exhalation rate by using this simplified model.

Evaluation of natural radiation in houses built with black schist.

Natural radiation in houses built with black schist slabs located at an altitude of 1,000 m in the mountainous southern part of Taiwan were investigated by studying the naturally occurring radionuclides present in the black schist. Both indoor and outdoor radon concentrations were monitored. The cosmic-ray contribution to the dose received by the inhabitants was also estimated. Gamma-ray spectroscopy was performed for radionuclide analyses. In situ measurements were carried out using a survey meter coupled to a sodium iodide detector. Cellulose nitrate films, ZnS (Ag) scintillation cells, and alpha spectroscopy were used to study radon and radon daughters. Radiation doses due to all natural sources were calculated and compared with that incurred in common concrete dwellings at lower altitudes.

Radon concentration in two largest cities in semitropical Taiwan.

Grab sampling either using the active charcoal method in combination with an ionization chamber or using a working level monitor was performed for the measurement of radon concentration in Taiwan's two largest cities Taipei and Kaohsiung. Long-term monitoring of radon concentration in dwellings and business buildings was also carried out with cellulose nitrate films as the alpha detectors. The average indoor radon concentration in these two cities is 17 +/- 6 Bq m-3. The outdoor radon concentration is about one-half of that on average. As assessed according to the model of UNSCEAR 1988, the induced effective dose equivalent is 0.67 mSv y-1. Radon concentration in coal mines showed an average of 88.5 +/- 9.5 Bq m-3.

Ultraviolet response of CaF2:Tm with high-temperature treatment.

The thermoluminescent (TL) response to ultraviolet irradiation of CaF2:Tm phosphor is affected by pre-irradiation high-temperature treatment. The experimental results indicate that the maximum intrinsic TL output is about 2000 times higher for 1000 degrees C treatment than when not treated. TL stability for this phosphor occurs when the optimum temperature range and time are 800 degrees to 900 degrees C and 1 h. However, the intrinsic sensitivity is only about 50 times higher than with no treatment, which limits the application of this phosphor as a personal UV dosimeter.

[An investigation of radiation exposure on pediatric patients and doctors during cardiac catheterization and cineangiography].

Cardiac catheterization and cineangiography are invasive diagnostic radiological examinations which exposure the patient to a relatively high radiation dose, the largest radiation dose of any diagnostic examination. Sixty-one infants and children, aged 28 days to 15 years, were randomly selected into this study to assess such questions regarding cardiac catheterization in children as; (1) How much the pediatric patient's and doctor's radiation exposure is during a routine cardiac catheterization and cineangiography? (2) What difference are there in exposure to various areas of the body? (3) How much radiation exposure is related to cineangiography compared with fluoroscopy? (4) How much radiation exposure may be reduced by lead apron worn by doctors? Thermoluminescent dosimeters containing 80 mg of CaSO4: Dy were applied to the body for the measurement of radiation exposure during cardiac catheterization. In hemodynamic assessment of catheterization (mean time 6 +/- 5 min), dosimeters were placed on various areas of the patient's skin and unexposed dosimeters were attached to mid sternum and right lateral chest during cineangiography (mean time 11 +/- 5 sec). Average skin doses over the patients' organs during catheterization and cineangiography were: eye 51 mu Gy, thyroid 746 mu Gy, sternum 5,102 mu Gy, right lateral chest 10,098 mu Gy, umbilicus 123 mu Gy and gonad 24 mu Gy. The radiation exposure during cineangiography at sternum and right lateral chest contributed to 61% and 70% of total exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Monitoring underground radiation fields using powdered calcium sulfate thermoluminescent dosimeters.

Powered thermoluminescent dosimeters, CaSO4:Dy, were used to monitor underground radiation fields. Methods of monitoring at selected sites in Taiwan are described; exposure rates above ground at the monitoring sites are also included for comparison. Differences in exposure rates between above ground at 1 m and underground at -2 m may reach 0.516 nC kg-1 h-1. The key factor affecting exposure rates underground is the water content in soil or precipitation that may reduce the diffusion of Rn. The difference in exposure rates between rainy days and sunny days may reach 0.774 nC kg-1 h-1. An example of applying this monitoring technique at a radwaste repository is given.

Radiation exposure of pediatric patients and physicians during cardiac catheterization and balloon pulmonary valvuloplasty.

Thermoluminescent dosimeters were applied to various areas of 61 pediatric patients and physicians to measure radiation doses during routine cardiac catheterization and during 4 cases of balloon pulmonary valvuloplasty. Radiation doses were measured during chest roentgenography, fluoroscopy and cineangiography. Average skin dose to the chest was 121 microGy during chest x-ray, 5,182 microGy during catheterization and 641 mGy during valvuloplasty. For the eyes, thyroid and gonads of the patients, the exposure during routine catheterization was equal to 0.4, 6 and 0.2 chest x-rays, respectively. Radiation dose of the operator was 3 microGy for the eyes and 6 miCroGy in the thyroid. About 56% of the operator's dose could be reduced by thyroid shields, and 80% by lead aprons. The assistant received only 1 microGy outside the thyroid shield. Therefore, we have concluded that the patients' dose during routine catheterization is largely based on our experimental results, but the dose is acceptable based on the risk factor analysis. The skin dose to the right lateral chest of the patient during valvuloplasty is extremely high, perhaps as high as the equivalent of 1,000 chest x-rays. Besides the clinical benefits of valvuloplasty, the long-term radiation-related hazards to the patient should be carefully monitored.

Natural radiation background in metropolitan Taipei.

A high-pressure ionization chamber was used to measure the natural background radiation in metropolitan Taipei, Taiwan, R.O.C. during a period in 1987-1988. The average exposure rate was 27.55 x 10(-10) C kg-1 h-1 including cosmic radiation, but the radon contribution was excluded. Scintillation survey meter, gamma-ray spectroscopy for soil samples, in-situ measurement with a NaI(Tl) detector coupled to a portable multichannel analyzer, instrumental neutron activation analysis of rock samples, and even thermoluminescent dosimeters were used as complementary measuring devices. Areas of higher radiation background were detected. They are the radium-bearing Peitou stones, an unusual occurrence of uraniferous zone at Sanhsia, and uranium precipitation in the glassy olivine basalt in a tea field at Tachi. All these areas are located in suburban sites of Taipei. Three types of building in Taipei City were selected for radon detection. No significantly elevated level of radon was detected, since Taipei is located in a semitropical area where ventilation of buildings is not a problem.

Body K and 40K in Chinese subjects measured with a whole-body counter.

More than 380 Chinese adults of both sexes were studied for their total body K and 40K using the National Tsing Hua University whole-body counter. The K values were found to have an average of 1.75 +/- 0.4 g K kg-1 body weight for males and 1.41 +/- 0.1 g K kg-1 body weight for females. The average K value for both sexes was 1.69 +/- 0.4 g K kg-1 body weight. The annual absorbed dose for the average male was calculated to be 0.21 +/- 0.04 mGy and for the average female was 0.17 +/- 0.01 mGy. The average for both sexes was 0.20 +/- 0.04 mGy. The 40K activity per unit body weight varied inversely with slenderness, and total body K varied directly with body-build index.

Changes in per capita and collective dose equivalent due to natural radiation in Taiwan (1950-1983).

This paper deals with the changes in per capita and collective dose equivalent in Taiwan in the past three decades based on the measured terrestrial and cosmic radiation levels and the population distribution as well. Over 70% of the population is concentrated in three population centers which have been naturally formed in the north, middle and south of Taiwan along the west coast as a result of industrialization and population growth. The population has increased 2.5 times in the past 33 y and reached to 1.9 X 10(7) persons, yet the migration of population was from the rural areas where the natural radiation is usually high to the urban areas where the natural radiation is usually low. The resulting collective dose equivalent has been increasing, yet the per capita dose equivalent, on the contrary, has been decreasing.

Comparison of risk estimates using life-table methods.

Risk estimates promulgated by various radiation protection authorities in recent years have become increasingly more complex. Early "integral" estimates in the form of health effects per 0.01 person-Gy (per person-rad) or per 10(4) person-Gy (per 10(6) person-rad) have tended to be replaced by "differential" estimates which are age- and sex-dependent and specify both minimum induction (latency) and duration of risk expression (plateau) periods. These latter types of risk estimate must be used in conjunction with a life table in order to reduce them to integral form. In this paper, the life table has been used to effect a comparison of the organ and tissue risk estimates derived in several recent reports. In addition, a brief review of life-table methodology is presented and some features of the models used in deriving differential coefficients are discussed. While the great number of permutations possible with dose-response models, detailed risk estimates and proposed projection models precludes any unique result, the reduced integral coefficients are required to conform to the linear, absolute-risk model recommended for use with the integral risk estimates reviewed.

Cosmic-ray ionization in the lower atmosphere.

A high-pressure ion chamber filled with 2.5825 X 10(5) kg m-2 argon as used to measure the dose rates of several sites of interest in an attempt to evaluate the dose rates contributed by cosmic rays. Observation sites included two water reservoirs deeper than 110 m, Mount Ali which is higher than 2500 m, airliners flying at altitudes higher than 6700 m, and some sites at sea level. The results of this investigation were compared with those reported by the United Nations Scientific Committee on the Effects of Atomic Radiation and used for the determination of background radiation monitored with thermoluminescent dosimeters and sodium iodide detectors.

Sorption of low-level radwaste by Spirulina.

The feasibility of using spirulina as adsorbent for the treatment of low-level liquid radwaste is studied. The experimental results indicate that the sorption capacity of spirulina is good for the di- and trivalent metallic ions at pH 3-7, but rather poor for the mono-valent metallic ions and non-metallic ions. Some factors affecting metal ion uptake by spirulina such as the content of detergent, sodium ion in liquid radwaste and the stability of spirulina under gamma irradiation were also investigated.

Occupational radiation exposures in Taiwan, 1962-1983.

This paper presents an updated compilation of occupational radiation exposures in Taiwan, Republic of China, for the years 1962-1983. The highest collective dose equivalent occurred in 1981 and was estimated to be 535.318 man-rem, and the average measurable dose equivalent per worker is about 0.25 rem in the same year. All data analyzed were plotted on log-probability paper. A brief prospectus on the health implications of the annual occupational dose equivalents is also provided, using the year 1981 as an example.