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PubMed1990

Beta and electron dose calculations to skin due to contamination by common nuclear medicine radionuclides.

We present dose calculations to the basal cell layer of the epidermis resulting from skin contamination by radionuclides used in nuclear medicine. Dose calculations were made using the computer code VARSKIN, as modified by us to include these radionuclides and to account for their monoenergetic electron emissions. Results indicate that basal skin doses (taken to be at a depth of 0.007 cm) are approximately 1 cGy h-1 per 3.7 X 10(-4) Bq cm-2 (1 rad h-1 per muCi cm-2) from 99mTc, 111In and 201Tl, implying that established limits may be approached under certain circumstances. The implication of these results for small areas of contamination is also discussed.

Accidents, Occupational↗
PubMed1992

A beta spectrometer for monitoring environmental matrices.

In environmental matrices, pure beta emitters are often present with other beta-gamma emitters. This work describes a beta spectrometer that allows measurement of pure beta-emitter activities of about 10(-2) Bq. The detection system consists of a plastic scintillator surrounded in a 4 pi geometry by large anticoincidence NaI(Tl) scintillators. Solid, liquid, and gaseous samples can be analyzed, and no chemical separation is necessary. The system is particularly useful for 90Sr measurement.

Beta Particles↗
PubMed1992

Beta-ray dose distributions from point sources in an infinite water medium.

The ACCEPT Monte Carlo code has been used to calculate radial dose distributions around isotropic point sources of monoenergetic electrons between 0.01 and 10 MeV in an infinite water medium. The results were averaged over beta spectra to derive distributions for 147 beta emitters of which 32 are presented. More extensive tables of distributions will be presented in a report. Distributions for monoenergetic electrons agree with recent ETRAN-code calculations of Berger and Seltzer within 2%, except at very short distances where there are differences up to several percent. Results calculated by the EGS4 code differ by up to a few percent. Distributions for beta emitters are in excellent agreement with both experimental results and ETRAN and EGS4 calculations, except at very short distances.

Beta Particles↗
PubMed1992

A proposed four-element neutron-photon-beta thermoluminescence dosimeter.

It is common practice for a worker exposed to a mixed field with neutrons to wear both a photon-beta dosimeter and a neutron dosimeter. In this study, a thermoluminescence dosimeter has been designed and is proposed for use in mixed fields. The maximum applicable ranges of the mixed field can have photons with unknown energy from 20 keV to 2 MeV, betas with unknown energy from 147Pm to 90Sr-Y, and neutrons of known energy from thermal to 15 MeV. This proposed dosimeter (a combination of Harshaw beta-gamma thermoluminescence dosimeter and albedo neutron thermoluminescence dosimeter) has an advantage of using a minimum number of thermoluminescence dosimeter elements (therefore, making it less costly) to measure the dose equivalents in a mixed field of neutron, photon, and beta radiation. The basic dosimeter design consists of four thermoluminescence elements of TLD-600 and TLD-700 with different filtrations. Using the high-temperature peak methodology for TLD-600 and a filtration algorithm, the neutron, photon, and beta dose equivalents in a mixed field can be determined. The design, detection principle, and three dosimetric algorithms for three versions of the basic design of the four-element dosimeter are presented and discussed. The work that is required for the proposed dosimeter to be usable when it is made is also presented.

Algorithms↗
PubMed1993

Shielding for beta-gamma radiation.

The build-up factor, B, for lead was expressed as a polynominal cubic function of the relaxation length, mu x, and incorporated in a "general beta-gamma shielding equation." A computer program was written to determine shielding thickness for polyenergetic beta-gamma sources without resorting to the conventional "add-one-HVL" method.

Beta Particles↗
PubMed1993

Evaluation of the beta energy spectrum from a distributed uranium mill tailings source.

The beta energy spectra from uranium mill tailings, 90Sr with different absorber thicknesses, and a uranium metal slab were measured and compared to select an appropriate beta source for calibrating a personal dosimeter to measure shallow dose equivalent when exposed to uranium mill tailings. The measured beta energy spectrum from the 90Sr source, with a 111 mg cm-2 cover thickness, was selected as a possible calibration source for a personnel dosimeter. The dose equivalent rate to the skin at 1 cm from a distributed tailings source of infinite thickness, with a 226Ra activity of 56 Bq g-1 (1.5 x 10(3) pCi g-1), was measured to be 0.024 mSv h-1 (2.4 mrem h-1).

Beta Particles↗
PubMed1994

The updated BESGE spectrometer for pure beta activities in environmental matrices.

This work describes an updated version of a beta spectrometer that measures pure beta emitter activities. The detection system consists of a plastic scintillator surrounded in a 4 pi geometry by large anticoincidence NaI(Tl) scintillators. A thin silicon detector, inserted between the plastic and the sample, helps to reduce the gamma background. A Monte Carlo code, used to calculate the quite complex spectrometer response function to any isotope, is also described.

Beta Particles↗
PubMed1995

Sensitivity of a mixed field dosimetry algorithm to uncertainties in thermoluminescent element readings.

An error analysis of the effects of the algorithms used to resolve the deep and shallow dose components for mixed fields from multi-element thermoluminescent (TLD) badge systems was undertaken for a commonly used system. Errors were introduced independently into each of the four element readings for a badge, and the effects on the calculated dose equivalents were observed. A normal random number generator was then utilized to introduce simultaneous variations in the element readings for different uncertainties. The Department of Energy Laboratory Accreditation Program radiation fields were investigated. Problems arising from the discontinuous nature of the algorithm were encountered for a number of radiation sources for which the algorithm misidentified the radiation field. Mixed fields of low energy photons and betas were found to present particular difficulties for the algorithm. The study demonstrates the importance of small fluctuations in the TLD element's response in a multi-element approach.

Algorithms↗
PubMed1995

Type testing of the Siemens Plessey electronic personal dosemeter.

This paper presents the results of a laboratory assessment of the performance of a new type of personal dosimeter, the Electronic Personal Dosemeter made by Siemens Plessey Controls Limited. Twenty pre-production dosimeters and a reader were purchased by Ontario Hydro for the assessment. Tests were performed on radiological performance, including reproducibility, accuracy, linearity, detection threshold, energy response, angular response, neutron response, and response time. There were also tests on the effects of a variety of environmental factors, such as temperature, humidity, pulsed magnetic and electric fields, low- and high-frequency electromagnetic fields, light exposure, drop impact, vibration, and splashing. Other characteristics that were tested were alarm volume, clip force, and battery life. The test results were compared with the relevant requirements of three standards: an Ontario Hydro standard for personal alarming dosimeters, an International Electrotechnical Commission draft standard for direct reading personal dose monitors, and an International Electrotechnical Commission standard for thermoluminescence dosimetry systems for personal monitoring. In general, the performance of the Electronic Personal Dosemeter was found to be quite acceptable: it met most of the relevant requirements of the three standards. However, the following deficiencies were found: slow response time; sensitivity to high-frequency electromagnetic fields; poor resistance to dropping; and an alarm that was not loud enough. In addition, the response of the electronic personal dosimeter to low-energy beta rays may be too low for some applications. Problems were experienced with the reliability of operation of the pre-production dosimeters used in these tests.

Beta Particles↗
PubMed1996

32P and beta emitting radionuclides in microbiology and cell biology.

Microbiology and cell biology researchers make extensive use of beta emitting nuclides. Because of the short half-lives or difficulty of direct measurement some researchers do not view radionuclide use with proper care and respect. Radionuclide use in microbiology and cell biology research is unique. Review of the isotopes and processes may be useful to the health physicist and research alike.

Animals↗
PubMed1996

Effects of beta radiation from organically bound tritium on cultured mouse embryonic mid brain cells.

Effects of beta radiation from four kinds of organically bound tritium compounds were investigated on cultured mouse embryonic mid brain cells, isolated from 11-d-old mouse embryos. The MBC showed a critical time when they were more radiosensitive. Although dose-dependent inhibition was found for both cellular proliferation and differentiation, the differentiation was more sensitive to radiation than proliferation when compared at ID50, the inhibitory dose that reduced assessment value by 50% of the control. Dose-dependent decrease of DNA and protein contents were also observed. The relative biological effectiveness values, ranging from 4.6 to 8.7, of beta ray from organically bound tritium compounds were obtained when compared with x irradiation at their ID50s on the inhibition of cell proliferation and differentiation, and on the decrease of DNA and protein contents of the cultures. The mixed exposure to x ray and one kind of organically bound tritium compound or to any two kinds of organically bound tritium compound resulted in a more efficiently inhibitory effect on differentiation than the exposure to x ray or to any one kind of organically bound tritium compound alone, especially when methyl-3H-thymidine was used. Doses as low as 0.05 Gy (5 cGy) from a mixed exposure resulted in detectable inhibitory effects.

Animals↗
PubMed1997

Monte Carlo simulation of depth-dose distributions in TLD-100 under 90Sr-90Y irradiation.

In this work the depth-dose distribution in TLD-100 dosimeters under beta irradiation from a 90Sr-90Y source was investigated using the Monte Carlo method. Comparisons between the simulated data and experimental results showed that the depth-dose distribution is strongly affected by the different components of both the source and dosimeter holders due to the large number of electron scattering events.

Beta Particles↗
PubMed1998

Monte Carlo simulation of in vivo measurements of 90Sr + 90Y bremsstrahlung.

The purpose of this study was to calculate the 90Sr + 90Y bremsstrahlung yield generated in bone quantitatively, and to determine the optimum conditions required for in vivo measurements of the yield, assuming that a given amount of contamination, due to the ordinary activities of 137Cs and 40K, is present within the human body. Several approximations in the distribution of activities in various body phantoms, simulating the human leg, waist and head, were made for simplicity. All the calculations were carried out using an in-house Monte Carlo code. The photon spectra incident on a detector window, of diameter 200 mm, positioned 1 mm from the surface of each phantom were obtained. A pseudo-peak of 90Sr + 90Y bremsstrahlung was observed at approximately 50 keV with a full width at half maximum of 60 keV (FWHM). The signal-to-background ratio, eta, where eta represents the ratio of the number of photons in the energy interval between 30 to 160 keV in the bremsstrahlung spectrum produced by 1 Bq kg(-1) of 90Sr and the background spectrum, which is assumed to comprise of 1 Bq kg(-1) of 137Cs and 60 Bq kg(-1) of 40K, was evaluated in order to determine the optimum measuring conditions. An optimum eta value of 0.0353 was obtained for the leg phantom, of bone diameter 30 mm, covered by a 1 mm layer of soft tissue. Combining the present calculations with the conventional measurements, a new and simpler method for evaluating the body burden activity of a beta emitter, such as 90Sr, is proposed.

Beta Particles↗
PubMed1998

Accuracy in external dosimetry of ionizing radiation.

A new approach to defining and calculating accuracy and uncertainty in external dosimetry is described. It is more comprehensive and mathematically rigorous than other approaches currently in use, while at the same time being practical to implement. The type testing required to demonstrate the performance of a dosimeter is described, and an example of the calculation of accuracy and uncertainty is given. The paper concludes with some recommendations concerning performance testing and independent testing.

Analysis of Variance↗
PubMed1998

Diagnosis of acute localized irradiation lesions: review of the French experimental experience.

In the last 50 years several radiation accidents occurred in which industrial radiographers and others suffered severe radiation injuries from inadvertent contact with radiation sources. Such accidents involving acute localized injuries are characterized by a severe initial reaction progressing through erythema to skin necrosis with a spontaneous resolution of the lesion over a 2-mo period for the lower doses. However, the early symptoms observed on the skin give no indication as to the in-depth pathology, and cutaneous and muscular radionecrosis started generally from early epithelial, microvascular, and vascular lesions and from delayed muscular and connective tissue lesions. In a case of acute localized irradiation, different biophysical techniques are able to give real responses in biological dosimetry. More numerous are the methods, especially imaging methods, that make it possible for the clinician to evaluate the extent of the early injuries and to manage the medical intervention. We have developed animal experimental models of acute localized irradiation: overexposure to the gamma rays of a 192Ir industrial radiographic collimated source (in the pig and the rabbit) and overexposure to the beta rays of a 90Sr-90Y collimated source (in the pig). In these experimental models, most of the imaging techniques used in clinical practice, as infra-red thermography, microwave thermography, cutaneous and tissular vascular scintigraphy (beta or gamma emitters), cutaneous blood flow measurements by cutaneous laser Doppler, x ray computed tomography, nuclear magnetic resonance imaging, and skin topography, were correlated with clinical evaluation and histopathological observations, after high doses of gamma or beta irradiations ranging from 4 to 340 Gy at the skin surface. All these techniques are not for isolated use and the present review indicates that their combination is necessary to give an improved diagnostic and prognostic picture of early and late delayed radiation damage to the skin and subcutaneous tissues.

Animals↗
PubMed1999

The relative effectiveness of exposure to 131I at low doses.

There is much interest in estimating the thyroid cancer risks to children exposed to low doses of (131)I from nuclear fallout. Direct epidemiological studies of individuals exposed as children to low doses of (131)I have insufficient power to yield useful risk estimates. Consequently, extrapolation from risk estimates for acute exposure to kilovoltage x rays are used to generate (131)I risk estimates. There are two distinct effects that might need to be considered in modifying the x-ray generated risk estimates: first, the differing quality of the radiations and, second, the lower overall dose rates for (131)I exposure. We suggest that it is helpful to split the overall correction factor into its component parts-radiation quality and radiation dose rate-and consider them separately, in that a good deal is known separately about each. There is good radiobiological evidence that electrons emitted in (131)I decays are less biologically effective than kilovoltage x rays, and the microdosimetric/radiobiological analyses described here suggest that the low-dose relative effectiveness is around 0.6 compared to kilovoltage x rays. Use of different endpoints suggests that this estimate is quite robust, and it agrees well with available animal data. Any correction factor for dose-rate effects is likely to be close to unity.

Beta Particles↗
PubMed1999

A method to detect low-level 63Ni activity for estimating fast neutron fluence from the Hiroshima atomic bomb.

The Hiroshima and Nagasaki atomic bombs resulted in the worst reported exposure of radiation to the human body. The data of survivors have provided the basis for the risk estimation for ionizing radiation, and thus are widely used as the basis of radiation safety. In this report we have studied a new method to detect the low-level 63Ni activity in copper samples in order to estimate the fast neutron fluence from the Hiroshima atomic bomb. Only 0.8 x 10(-3) Bq g(-1) of 63Ni is expected to be produced by the atomic bomb in a copper sample with the 63Cu(n, p)63Ni reaction at a distance of 500 m from the hypocenter. Our method has the required level of sensitivity for determination of the fast neutron fluence out to distances of at least 500 m, and perhaps as far as 1,000 m. We have already investigated and collected some bomb-irradiated copper samples for further study.

Beta Particles↗
PubMed1999

Induction of apoptosis by beta radiation from tritium compounds in mouse embryonic brain cells.

Induction of apoptosis by tritium exposure was investigated in both cultured embryonic mid brain cells and brain sections of embryos and of newborns in mice. In the cultures of mid brain cells, addition of methyl-3H-thymidine (3H-TdR) (21 kBq mL(-1)) and tritiated water (5.616 MBq mL(-1)) induced late appearances and low percentages of apoptosis when compared to x-irradiation at the ID50 dose, the inhibitory dose that reduced cellular differentiation by 50% of the control. A significant increase in p53 protein was detected about 2 h before the marked appearance of apoptosis. The pregnant mice were given an intraperitoneal injection of tritiated water at the concentration of 481.8 kBq g(-1) of body weight on gestation day 12.5, by which treatment behavioral changes in the offspring occurred. Increased apoptotic cells were observed in the neural tube of embryos from 1 d after the injection to 1 wk postnatal age. Apoptosis induced by x-rays appeared 2 h after irradiation, with a peak at 4 h. Increase of apoptotic cells was also found in the brain cortexes of newborns. The percentage of apoptosis in the brain was higher in the prenatal tritiated water exposed mice than in the prenatal x-irradiated mice. Possible mechanisms on apoptosis and its relation to the higher relative biological effectiveness value of tritium beta-rays are discussed.

Animals↗