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Radiolabeled microorganisms: comparison of different radioisotopic labels.

Radioactively labeled microorganisms are very useful in assessing the in vitro phagocytic capability of human granulocytes and macrophages. Since microorganisms contain amino acids and nucleic acids, they can be radiolabeled by addition of radioactive amino acid and/or nucleic acid components to the culture medium. The isotopes 3H, 14C, 32P, 35S, and 75Se-have been used for bacterial radiolabeling. All of these commonly used isotopes with the exception of 75Se are beta emitters; 75Se is a gamma emitter. The half-lives of these isotopes vary from 14 days for 32P to 5,730 years for 14C. Because of the differences in their physical properties, they pose very different handling problems and require different kinds of safety precautions. In the event of either external or internal contamination, beta emitters deliver a larger localized radiation dose than do gamma emitters. In the case of internal contamination, the radiation dose increases with increases in the half-life of the radioactive isotope. Gamma radiation, on the other hand, is more penetrating than are beta particles and thus a gamma emitter requires appropriate shielding. Both the cost and the special problem of manipulation associated with these radioactive chemicals should be carefully considered before deciding which radioisotope is preferable for the labeling of microorganisms in the laboratory. In spite of the limitations of 75Se as a nonphysiologic element, it offers the simplest methods of handling among the isotopes considered in this review.

Bacteria↗
PubMed2002

Radiations in space: risk estimates.

The complexity of radiation environments in space makes estimation of risks more difficult than for the protection of terrestrial populations. In deep space the duration of the mission, position in the solar cycle, number and size of solar particle events (SPE) and the spacecraft shielding are the major determinants of risk. In low-earth orbit missions there are the added factors of altitude and orbital inclination. Different radiation qualities such as protons and heavy ions and secondary radiations inside the spacecraft such as neutrons of various energies, have to be considered. Radiation dose rates in space are low except for short periods during very large SPEs. Risk estimation for space activities is based on the human experience of exposure to gamma rays and to a lesser extent X rays. The doses of protons, heavy ions and neutrons are adjusted to take into account the relative biological effectiveness (RBE) of the different radiation types and thus derive equivalent doses. RBE values and factors to adjust for the effect of dose rate have to be obtained from experimental data. The influence of age and gender on the cancer risk is estimated from the data from atomic bomb survivors. Because of the large number of variables the uncertainities in the probability of the effects are large. Information needed to improve the risk estimates includes: (1) risk of cancer induction by protons, heavy ions and neutrons: (2) influence of dose rate and protraction, particularly on potential tissue effects such as reduced fertility and cataracts: and (3) possible effects of heavy ions on the central nervous system. Risk cannot be eliminated and thus there must be a consensus on what level of risk is acceptable.

Aerospace Medicine↗
PubMed2002

Dosimetric results from the Mir orbital station.

The Mir Orbital Station provided a unique platform on which to carry out a variety of space radiation dosimetry measurements. A number of experiments were conducted using a combination of passive detectors on the interior of the Mir during 1996-97. Thermoluminescent detectors were used to measure absorbed dose. CR-39 plastic nuclear track detectors were used to measure the LET spectra > or =5 keV.microm(-1). Results from TLDs and CR-39 PNTDs were combined to determine total dose and dose equivalent. Mean dose rate was found to decrease while mean dose equivalent rate and average quality factor increased with increasing shielding. Secondary particles from proton-induced target fragmentation interactions, not primary HZE particles, were found to be the largest contributor to the LET spectrum above 100 keV.microm(-1). During the 1997 measurements, mean quality factor was found to vary from 1.7 to 2.1 as a function of location within the Mir.

Aerospace Medicine↗
PubMed2002

Microdosimetric spectra and LET distributions on board the Mir space station obtained with a particle track detector.

A spectrometer measuring energy lost (deltaE) was used to determine linear energy transfer (LET) spectra on board the Mir orbital station during the period from 8 October 1997 to 16 June 2000, i.e. during the 24th, 26th, 27th and 28th basic expeditions. It was found that the LET spectra of secondary particles between 10 and 700 keV.microm(-1) in tissue do not depend on the external radiator, with the average quality factors for the region mentioned being about 6.4 with ICRP 26 quality factors or about 7.4 with ICRP 60 quality factors. Both differential and integral LET spectra are presented for some typical cases. The spectra permitted us to calculate the total doses and dose equivalents due to particles with the LET values in the mentioned region. It was found that these doses are higher when the detector was placed in a less shielded area. It was also found that these doses vary from one expedition to another. The correlation of these variations with the solar activity level was studied.

Aerospace Medicine↗
PubMed2002

Measurement of the neutron and gamma doses accumulated during commercial jet flights from sydney to several major destinations in the northern and southern hemispheres.

As recommended by the ICRP, the European Union (EU) agreed to abide by mandatory monitoring of radiation doses to crew during civil aviation flights operated by the airlines of the EU member states. A large number of measured and theoretically predicted values for the in-flight radiation doses of northern hemisphere flight routes are available. On the other hand very few data have been published for the southern hemisphere. This paper will present the results of Australian domestic and intemational return flight routes originating from Sydney. The paper also presents results of trans-hemisphere air traffic routes. Neutron and gamma doses were measured using superheated bubble dosemeters and semiconductor detectors respectively. Based on our measurements a method is suggested whereby aircrew may share their personal radiation burden by flight crew hemisphere exchange.

Aerospace Medicine↗
PubMed2002

Thermal neutron equivalent dose assessment around the KFUPM neutron source storage area using NTDs. King Fahd University of Petroleum and Minerals.

Area passive neutron dosemeters based on nuclear track detectors (NTDs) have been used for 13 days to assess accumulated low doses of thermal neutrons around neutron source storage area of the King Fahd University of Petroleum and Minerals (KFUPM). Moreover, the aim of this study is to check the effectiveness of shielding of the storage area. NTDs were mounted with the boron converter on their surface as one compressed unit. The converter is a lithium tetraborate (Li2B4O7) layer for thermal neutron detection via 10B(n,alpha)7Li and 6Li(n,alpha)3H nuclear reactions. The area passive dosemeters were installed on 26 different locations around the source storage area and adjacent rooms. The calibration factor for NTD-based area passive neutron dosemeters was found to be 8.3 alpha tracks x cm(-2) x microSv(-1) using active snoopy neutron dosemeters in the KFUPM neutron irradiation facility. The results show the variation of accumulated dose with locations around the storage area. The range of dose rates varied from as low as 40 nSvx h(-1) up to 11 microSv x h(-1). The study indicates that the area passive neutron dosemeter was able to detect accumulated doses as low as 40 nSv x h(-1), which could not be detected with the available active neutron dosemeters. The results of the study also indicate that an additional shielding is required to bring the dose rates down to background level. The present investigation suggests extending this study to find the contribution of doses from fast neutrons around the neutron source storage area using NTDs through proton recoil. The significance of this passive technique is that it is highly sensitive and does not require any electronics or power supplies, as is the case in active systems.

Fast Neutrons↗
PubMed2002

Measurements of X ray absorbed doses to dental patients in two dental X ray units in Nigeria.

Measurements of absorbed doses from radiographic examinations to various anatomical sites in the head and neck of patients with an average age of 45 years using intra-oral dental radiography have been carried out. LiF (TLD-100) dosemeters were used for the measurements of the absorbed dose. The measured absorbed doses to the various anatomical sites in the two units are reported, discussed and compared with results from the literature. Quality control measurements were also performed using a Victoreen quality control test device on the X ray units. The tube voltage accuracies for the two units were found to be within acceptable limits (less than +/- 10%). On the other hand the exposure time accuracies for these units have large deviations (>20%). These results and those that have been reported in the literature may be an indication that high patient doses are common in most dental X ray centres and countries. As a result of this, regular compliance and performance checks of dental diagnostic X ray equipment are essential in order to ensure proper performance and to minimise unnecessary patient and operator doses.

Diagnostic Imaging↗
PubMed2003

Relationship between protection and operational quantities in dosimetry of photon external exposure-deficiencies of Hp(10).

It is commonly assumed that, for a variety of conditions, the E/Hp(10) conversion coefficient is below unity, i.e., Hp(10) can be used as a conservative surrogate of effective dose. The validity of this assumption was checked by Monte Carlo simulation of E and Hp(10) as determined by a practical dosemeter. The calculations concerned irradiation by parallel photon beams with directions varying within a 4pi solid angle and energy ranging from 50 keV to 1 MeV. Observed dependences of conversion coefficients on irradiation geometry, photon energy and dosemeter position demonstrate that in strongly anisotropic radiation fields straightforward application of Hp(10) for assessment of effective dose may lead to significant underestimation of the latter. For photon energy of 80 keV this underestimation may be up to 16-fold. For simulation of real life situations, irradiation by photons coming within broad cones (with solid angle pi) was considered. It was found that even for this irradiation geometry, E/Hp(10) may be as high as 4.3. At the same time, for radiation coming from the frontal hemisphere, the values of the conversion coefficient for a typically positioned (i.e., the left chest pocket) personal dosemeter do not exceed unity. The conclusion was reached that prior to application of Hp(10) as a surrogate of effective dose, the information regarding angular distribution of radiation fields must be taken into account.

Body Burden↗
PubMed2003

Electron spectra measurements and Monte Carlo calculations for a 60Co standardised hot particle source.

A benchmark set of measured beta particle spectra for a standardised 60Co hot particle source is presented. The spectra were obtained for conditions similar to those encountered in practical dosimetric applications. The measured spectra were compared with Monte Carlo calculations using the MCNP code. These comparisons provided information to guide the selection of the optimal set-up parameters of the code. Important differences were observed in the MCNP calculated spectra when ITS and the default indexing style algorithm were used. Overall the calculations using the default mode of MCNP version 4B provide the best agreement with the measured electron spectra.

Body Burden↗
PubMed2003

Radiological protection philosophy for the 21st century.

The International Commission on Radiological Protection (ICRP) has stated that its recommendations will be reviewed at least every 10-15 years. It is now some 13 years since the main commission released, for comment, a draft of what was to become the 1990 Recommendations of the ICRP. These have become the basis for international basic safety standards and have been adopted in almost all countries that have radiological protection legislation. Therefore, the ICRP has been stimulating discussion, during the last three years, on the best way of expressing protection philosophy for the next publication of its recommendations, which it hopes will be by 2005. It is now beginning to prepare a draft of these recommendations, with a view to distributing an early version for comment, even though the background work is incomplete.

Humans↗
PubMed2001

In radiological protection, the protection quantities should be expressed in terms of measurable physical quantities.

It is somewhat of a truism that is expressed in the often quoted statement that you can't go home again. In the days when life was simpler, we could assume that a measurement performed with a portable survey instrument yielding a value for exposure rate in terms of roentgens/hour was a sufficient approximation to the value for the dose equivalent rate or absorbed dose rate at a point in a radiation field. As our understanding of radiological protection grew more sophisticated, we found it necessary to introduce additional rigor into the definitions of the radiation protection quantities. As mentioned earlier, we demand a lot from the definitions of these quantities. They need to satisfy many conditions, perhaps too many. When they are examined from the point of view of a metrologist, they may be considered to be deficient in many respects. When they are viewed by a radiobiologist, they may appear to be naïve or overly simplistic. A radiation protection technologist at a nuclear power plant may have difficulty understanding their sometimes-subtle implications. The ICRU and ICRP have worked for quite some time to incorporate all the necessary requirements into the definitions of the operational and protection quantities. From the arguments of our debaters, one might conclude that after careful consideration of past developments, additional refinements will be devised in the future.

Dose-Response Relationship, Radiation↗