Low Background Radiation Research Articles

The Slanic-Prahova (ROMANIA) underground low-background radiation laboratory

A low-background radiation laboratory was constructed and fully commissioned in 2006 in the former Unirea (Slanic-Prahova) salt mine at 208 m below surface (estimated to 560 m water equivalent). Preliminary measurements showed a global reduction of the absorbed dose due to natural factors of about 39 times compared to level on the surface, reaching inside the mine 1.17±0.14 nGy/h. The total gamma background spectrum between 40 KeV and 3 MeV was 100 times smaller at laboratory level with respect to the same spectrum recorder at surface, in open field. All these experimental facts recommend the Slanic-Prahova low-background radiation laboratory, at present time fully operational, as very suitable for various measurements needing a low background.

Radiometric assessment of natural radioactivity levels of bituminous soil in Agbabu, southwest Nigeria

Activity concentrations of primordial radionuclides ( 226Ra, 232Th and 40K) in bituminous soil samples and viscous bitumen sample from Agbabu bitumen deposit, southwest Nigeria, has been measured using a high-resolution (HpGe detector) γ -spectrometry. The average values of 226Ra, 232Th and 40K obtained are lower than the global average values. The Th/U activity ratio is comparable to values reported in literature. The average absorbed dose rate in outdoor air at a height of 1 m above the ground level was found to be 12.65 ± 3.19 nGy h - 1 , which is below the corresponding worldwide population weighted average value of 60 nGy h - 1 . Both radium equivalent and representative level index values measured are lower than the internationally accepted limits for building and road construction materials. The results of the study indicate that the area has low background radiation level; as such no significant radiological hazard is expected in the area.

Effects of Low Doses of Radiation: Joint Statement from the Following Participants at the 15th Pacific Basin Nuclear Conference, Sessions Held in Sydney, Australia, Wednesday 18 October 2006

Effects of Low Doses of Radiation: Joint Statement from the Following Participants at the 15^th Pacific Basin Nuclear Conference, Sessions Held in Sydney, Australia, Wednesday 18 October 2006

The role of the He I and He II metastables in the population of the Sn II, Sn III and Sn IV ion levels

On the basis of the temporal evolutions of the singly, doubly and triply ionized tin (Sn II, Sn III and Sn IV, respectively) spectral line intensities, in the pulsed helium and nitrogen plasmas, the important role of the He I and He II metastables has been observed in the Sn II, Sn III and Sn IV ionization and population processes. According to these processes, one can expect realization of several laser levels in the Sn II (11.07, 11.20, 12.44 and 13.11 eV), Sn III (15.91, 17.82, 19.13 and 20.19 eV) and Sn IV (20.51 eV) spectra. The modified version of the linear, low-pressure, pulsed arc was used as a plasma source operated in helium with tin atoms, as impurities, evaporated from tin cylindrical plates located in the homogenous part of the discharge tube. This plasma source provides good conditions for a generation of the Sn III, Sn IV and Sn V ions at relatively low electron temperatures (below 18,000 K) providing low background radiation around the intense Sn IV and Sn III spectral lines in the helium plasma. The 222.613 ± 0.0005 nm Sn IV line, not observed up to now, has been identified. The marked, but not classified 243.688 nm Sn spectral line is sorted by ionization stages. The shapes of Sn III and Sn IV lines, ranged between 207 nm and 307 nm, have been obtained. At a 17,500 K electron temperature and 1.07 × 10 23 m − 3 electron density the Stark broadening was found as the dominant mechanism in the mentioned lines broadening. The measured Stark widths of the prominent nine Sn IV and seven Sn III lines are the first data in the literature. The Stark widths of the intense 229.913 nm and 288.766 nm Sn IV lines can be used for the plasma electron density and temperature diagnostics purposes.

Radiobiological basis of low-dose irradiation in prevention and therapy of cancer.

Antimutagenic DNA damage-control is the central component of the homeostatic control essential for survival. Over eons of time, this complex DNA damage-control system evolved to control the vast number of DNA alterations produced by reactive oxygen species (ROS), generated principally by leakage of free radicals from mitochondrial metabolism of oxygen. Aging, mortality and cancer mortality are generally accepted to be associated with stem cell accumulation of permanent alterations of DNA, i.e., the accumulation of mutations. In a young adult, living in a low LET background of 0.1 cGy/y, the antimutagenic system of prevention, repair and removal of DNA alterations reduces about one million DNA alterations/cell/d to about one mutation/cell/d. DNA alterations from background radiation produce about one additional mutation per 10 million cells/d. As mutations accumulate and gradually degrade the antimutagenic system, aging progresses at an increasing rate, mortality increases correspondingly, and cancer increases at about the fourth power of age. During the past three decades, genomic, cellular, animal and human data have shown that low-dose ionizing radiation, including acute doses up to 30 cGy, stimulates each component of the homeostatic antimutagenic control system of antioxidant prevention, enzymatic repair, and immunologic and apoptotic removal of DNA alterations. On the other hand, high-dose ionizing radiation suppresses each of these antimutagenic protective components. Populations living in high background radiation areas and nuclear workers with increased radiation exposure show lower mortality and decreased cancer mortality than the corresponding populations living in low background radiation areas and nuclear workers without increased radiation exposure. Both studies of cancer in animals and clinical trials of patients with cancer also show, with high statistical confidence, the beneficial effects of low-dose radiation.

The influence of ionizing radiation on spore germination and emergent hyphal growth response reactions of microfungi

The accident at the Chernobyl Atomic Energy Station resulted in radiation contamination of large tracts of land and particularly the reactor building itself. Sustained exposure of microfungi to radiation appears to have resulted in formerly unknown adaptive features, such as directed growth of fungi to sources of ionizing radiation. We evaluate here spore germination and subsequent emergent hyphal growth of microfungi in the presence of pure γ or mixed β and γ radiation of fungi isolated from a range of long term background radiation levels. Conidiospore suspensions were exposed to collimated beams of radiation and percent spore germination and length of emergent hyphae were measured. All fungal species isolated from background radiation showed inhibition or no response in germination when irradiated. Isolates from sites with elevated radiation showed a stimulation in spore germination (69% mixed radiation and 46% for γ irradiation). Most isolates from low background radiation sites showed a significant reduced or no response to exposure to either source of radiation, whereas the stimulatory effect of experimental exposure to radiation appeared to increase in magnitude as prior exposure to radiation increased. We propose that the enhanced spore germination and hyphal growth seen in the exposure trials is induced by prior long term exposure to radiation and these factors could be important in controlling the decomposition of radionuclide-bearing resources in the environment.

The influence of ionizing radiation on spore germination and emergent hyphal growth response reactions of microfungi

The accident at the Chernobyl Atomic Energy Station resulted in radiation contamination of large tracts of land and particularly the reactor building itself. Sustained exposure of microfungi to radiation appears to have resulted in formerly unknown adaptive features, such as directed growth of fungi to sources of ionizing radiation. We evaluate here spore germination and subsequent emergent hyphal growth of microfungi in the presence of pure gamma or mixed beta and gamma radiation of fungi isolated from a range of long term background radiation levels. Conidiospore suspensions were exposed to collimated beams of radiation and percent spore germination and length of emergent hyphae were measured. All fungal species isolated from background radiation showed inhibition or no response in germination when irradiated. Isolates from sites with elevated radiation showed a stimulation in spore germination (69% mixed radiation and 46% for gamma irradiation). Most isolates from low background radiation sites showed a significant reduced or no response to exposure to either source of radiation, whereas the stimulatory effect of experimental exposure to radiation appeared to increase in magnitude as prior exposure to radiation increased. We propose that the enhanced spore germination and hyphal growth seen in the exposure trials is induced by prior long term exposure to radiation and these factors could be important in controlling the decomposition of radionuclide-bearing resources in the environment.

Detection probabilities for photon-counting avalanche photodiodes applied to a laser radar system

Arrays of photon-counting avalanche photodiodes with time-resolved readout can improve the performance of three-dimensional laser radars. A comparison of the detection and false-alarm probabilities for detectors in linear mode and in Geiger mode is shown. With low background radiation their performance is comparable. It is shown that in both cases it will be necessary to process several laser shots of the same scene to improve detection and reduce the false-alarm rate. Additional calculations show that the linear mode detector is much better at detecting targets behind semitransparent obscurations such as vegetation and camouflage nets.

Improvements in food analysis by thermal neutron capture prompt gamma-ray spectrometry

The thermal neutron prompt gamma-ray activation analysis (PGAA) facility, operated by the US Food and Drug Administration and National Institute of Standards and Technology Center for Neutron Research, has been redesigned to lower background radiation levels and improved analytical capabilities. Analysis of 22 element standards and food and botanical certified reference materials revealed significant sensitivity increases and lower limits of detection for H, B, C, N, Na, Al, P, S, Cl, K, Ca, Fe, and Cd. Mass fractions for these elements, as well as Mg, Al, Si, Ti, Mn, Fe, Cu, I, Zn, Sm, and Gd, were determined for 6 dietary supplements.

MEGA: a low-background radiation detector

The multiple-element gamma assay (MEGA) is a low-background detector designed to support environmental monitoring and national security applications. MEGA also demonstrates technology needed for Majorana, a next generation neutrino mass experiment. It will employ active and passive shielding to reduce backgrounds. It will also exploit multicoincidence signatures to identify specific radioactive isotopes. MEGA is expected to begin testing in late 2003 for eventual installation at the Waste Isolation Pilot Plant, Carlsbad, NM.

Performance of CdTe, HPGe and NaI(Tl) detectors for radioactivity measurements

The characteristics and performances of the NIST High-Purity Germanium (HPGe), Sodium Iodide (NaI(Tl)) and Cadmium Telluride (CdTe) gamma-ray detectors were studied. The efficiencies, the minimum detectable activities and the energy resolutions of each were measured and compared. The data were analyzed using different software packages. The measurements were performed in a low background radiation environment using calibrated point sources. The CdTe detector showed a higher energy resolution than the NaI(Tl) detector but a lower efficiency than both the HPGe and NaI(Tl) detectors. This makes it a suitable detector only for relatively high activity measurements restricted to the 35 keV to 200 keV energy range.

Development of x-ray topographic microscopy for the study of electromigration in interconnects

We have performed x-ray topography experiments in a new configuration using a Fresnel zone plate to form a magnified image of the sample intensity distribution on the detector plane. The main difference from the x-ray topography techniques where no optics is used between the sample and the detector, is the absence of free space propagation effects in the image and the possibility to form a magnified image. Other advantages include large working distance around the sample and low background radiation on the detector. As a first application, we recorded x-ray topographs of an Al interconnect structure as a function of time in an in situ electromigration experiment. The contrast in the images is explained in terms of lattice deformations caused by the stress in the metal films. The results show the evolution of stress due to the electromigration process. The technique should make it possible to obtain best possible spatial resolution allowed by the sample in x-ray topography.

Developmental Instability and Sexual Selection in Stag Beetles from Chernobyl and a Control Area

Radioactivity may have both phenotypic and genetic effects through its disruption of physiological processes and mutations. I studied the size and asymmetry of secondary sexual and ordinary morphological characters of stag beetles (Lucanus cervus) in two areas in the Ukraine: near Chernobyl, where levels of radiation are high, and in a control area with low background radiation. Developmental instability of morphological characters was estimated from the degree of fluctuating asymmetry using the restricted maximum likelihood parameter estimation (REML) method to partition measurement error from asymmetry. The degree of asymmetry estimated from unsigned differences in size of right and left secondary sexual character was similar to estimates based on the REML method. Beetles from the contaminated area had a significantly elevated level of fluctuating asymmetry in the secondary sexual character compared with animals from the control area. Male stag beetles found with a female had significantly lower asymmetry than males found alone. While mated males did not differ in asymmetry between areas, unmated males from Chernobyl were much more asymmetric than unmated males from the control area. These findings provide evidence for radiation disrupting developmental homeostasis, and thereby affecting the mating status of free‐living beetles.

Impact and perspectives of radioactive beam experiments for the rp-process

Nuclear Astrophysics is concerned with the study of nuclear processes at stellar temperature and density conditions and its influence on nucleosynthesis and energy generation in stars and stellar explosions. Of particular interest is the understanding and interpretation of hot and explosive stellar scenarios and the concomitant nucleosynthesis involving nuclear processes far off β-stability. Neutron induced explosive processes occur in the neutrino-wind driven shock front of supernova explosions or can be triggered by the merging of two neutron stars. Hydrogen induced explosive processes occur in the thermonuclear runaway on the surface of an accreting white dwarf (novae) and in the hydrogen rich electron degenerate accreted material in the atmosphere of neutron stars (X-ray bursts, X-ray pulsars). The associated nuclear reaction and decay processes are far away from β-stability and need to be measured by using radioactive ion beams or radioactive targets. Limitations for these experiments are low beam intensities and high background radiation. Several radioactive beam facilities are already in operation and more are expected based on improved technological developments allowing reliable studies of reaction processes far off stability. We will discuss recent results of radioactive beam experiments and their implications for explosive stellar hydrogen burning in novae, X-ray bursts, and X-ray pulsars. We will also identify specific needs for nuclear reaction and decay data of specific importance for explosive hydrogen burning for future radioactive ion beam experiments.

Tryptophan phosphorescence as a monitor of protein conformation in molecular films

This report enquires on the potentiality of Trp phosphorescence for probing the conformational state of proteins deposited on solid dry films. Thin, amorphous protein films were fabricated with Apoazurin, alcohol dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase and glutamate dehydrogenase the protein being incorporated into a DEAE-dextran matrix and deposited on quartz slides. The results, obtained with appositely constructed instrumentation, demonstrate that thanks to the low background radiation associated with long-lived, delayed emission phosphorescence can be readily detected down to single protein layer matrices and that both spectrum and lifetime are important indicators of the integrity of the protein globular fold. In fact, denaturation of the proteins by guanidinium hydrochloride or heat treatment points out that disruption of the native fold leads to a red shift and broadening of the spectrum with loss of vibronic structure, accompanied to considerably shorter-lived and more heterogeneous decay kinetics. It is also shown that the sensitivity of the phosphorescence lifetime towards the detection of altered, looser conformations of the polypeptide are remarkably enhanced on partial hydration of the sample.

The “Discovery” of alpha activity in lead and solder

More than 15 years ago the presence of 210Pb activity in lead was found to create significant background in a low-background radiation detection spectrometer. Shortly thereafter, 210Po alpha particles emitted from the surface of a solder joint were directly observed with this spectrometer. Antiquity lead was used to eliminate these sources of radioactivity. The experiments leading up to these “discoveries” are described. The magnitude of the effect of 210Pb in lead on the experiment is discussed. The sensitivities of various techniques for measuring 210Pb in lead are compared, and a practical limit for alpha activity in lead is proposed.

Radiation biophysics at the Gran Sasso laboratory: influence of a low background radiation environment on the adpative response of living cells

Mammalian cells were cultured in parallel at the Istituto Superiore di Sanita', in the presence of standard radiation background, and at the INFN-Gran Sasso underground Laboratory, exposed to low radiation background. Both cultures were grown for up to six months and periodically tested to check for the onset of metabolic changes and different sensitivity to genotoxic damage caused by ionizing and UV radiation, as well as by chemical agents. These tests include measurements of enzyme activities protecting from oxidative cell damage, induction of apoptosis and mutation.

On the Use of a Recombination Chamber for Radiation Measurements in CERN-EU High Energy Reference Fields

Ambient dose equivalent was determined in high energy reference radiation fields at CERN (CERF facility) using a recombination chamber and recombination methods developed in IAE. The chamber was also used for measuring the low LET background radiation which locally accompanies the fields at CERF. The measurements included determination of the absorbed dose and recombination index of radiation quality at different beam intensities. It was shown that the background might considerably influence the measurements of the absorbed dose, however, its influence on the ambient dose equivalent remains important only at low beam intensities.

Molecular biology, epidemiology, and the demise of the linear no-threshold (LNT) hypothesis

The prime concern of radiation protection policy since 1959 has been protecting DNA from damage. The 1995 NCRP Report 121 on collective dose states that since no human data provides direct support for the linear no threshold hypothesis (LNT), and some studies provide quantitative data that, with statistical significance, contradict LNT, ultimately, confidence in LNT is based on the biophysical concept that the passage of a single charged particle could cause damage to DNA that would result in cancer. Current understanding of the basic molecular biologic mechanisms involved and recent data are examined before presenting several statistically significant epidemiologic studies that contradict the LNT hypothesis. Over eons of time a complex biosystem evolved to control the DNA alterations (oxidative adducts) produced by about 10 10 free radicals/cell/d derived from 2–3 % of all metabolized oxygen. Antioxidant prevention, enzymatic repair of DNA damage, and removal of persistent DNA alterations by apoptosis, differentiation, necrosis, and the immune system, sequentially reduce DNA damage from about 10 6 DNA alterations/cell/d to about 1 mutation/cell/d. These mutations accumulate in stem cells during a lifetime with progressive DNA damage-control impairment associated with aging and malignant growth. A comparatively negligible numbers of mutations, an average of about 10 −7 mutations/cell/d, is produced by low LET radiation background of 0.1 cGy/y. The remarkable efficiency of this biosystem is increased by the adaptive responses to low-dose ionizing radiation. Each of the sequential functions that prevent, repair, and remove DNA damage are adaptively stimulated by low-dose ionizing radiation in contrast to their impairment by high-dose radiation. The biologic effect of radiation is not determined by the number of mutations it creates, but by its effect on the biosystem that controls the relentless enormous burden of oxidative DNA damage. At low doses, radiation stimulates this biosystem with consequent significant decrease of metabolic mutations. Low-dose stimulation of the immune system may not only prevent cancer by increasing removal of premalignant or malignant cells with persistent DNA damage, but used in human radioimmunotherapy may also completely remove malignant tumors with metastases. The reduction of gene mutations in response to low-dose radiation provides a biological explanation of the statistically significant observations of mortality and cancer mortality risk decrements, and contradicts the biophysical concept of the basic mechanisms upon which, ultimately, the NCRPs confidence in the LNT hypothesis is based.

Tritium concentration measurements in the Joint European Torus divertor by optical spectroscopy of a Penning discharge

Obtaining precision measurements of the relative concentrations of hydrogen, deuterium, tritium, and helium in the divertor of a tokamak is an important task for nuclear fusion research. Control of the deuterium–tritium isotopic ratio while limiting the helium ash content in a fusion plasma are key factors for optimizing the fuel burn in a fusion reactor, like the International Tokamak Experimental Reactor. A diagnostic technique has been developed to measure the deuterium–tritium isotopic ratio in the divertor of the Joint European Torus with a species-selective Penning vacuum gauge. The Penning discharge provides a source of electrons to excite the neutral hydrogen isotopes in the pumping duct. Subsequently, the visible light from the hydrogen isotopes is collected in an optical fiber bundle, transferred away from the tokamak into a low radiation background area, and analyzed in a high resolution Czerny–Turner spectrometer, which is equipped with a fast charge coupled device camera for optical detection. The intensity of the observed line emission (Dα−6561.03 Å and Tα−6560.44 Å) is directly proportional to the partial pressure of each gas found in the divertor. The line intensity of each isotope is calibrated as a function of pressure. The ratio of the line intensities thus provides a direct measurement of the deuterium–tritium isotopic ratio. The lower limit for the determination of the deuterium–tritium isotopic ratio is about 0.5%. The applicable pressure range for this system is from 10−5 to a few times 10−3 mbar.