Short-lived Radioactive Isotopes Research Articles

Optimization of the charge state distribution of the ion beam extracted from an EBIT by dielectronic recombination

The dielectronic recombination resonance (DRR) processes for highly charged krypton ions have been investigated through simultaneously observing the x-ray emission and the ions extracted at the Heidelberg EBIT while slowly scanning the electron beam energy. It was found that at their DR resonance electron energies, the yield of the He-like krypton ions was substantially reduced, whereas that of the Li-like krypton ions was correspondingly increased. At slightly higher electron energies similar features were observed for the Li- and Be-like krypton ions. From the observed ratios of the Li-like/He-like krypton ion currents, we have deduced the dielectronic recombination (DR) strength for the He-like ions, which was found to be in reasonable agreement with theoretical calculations. We have also concluded from the present experiments that the DRR processes can be used to modify the ion charge state distributions and to concentrate the extracted ion currents into particular charge states. This is particularly important for future charge breading experiments with short-lived radioactive isotopes.

Progress at the Heidelberg EBIT

Two years after the relocation of the Heidelberg EBIT, several experiments are alreadyin operation. Spectroscopic measurements in the optical region have delivered the most precisereported wavelengths for highly charged ions, in the case of the forbidden transitions of Ar XIV andAr XV. The lifetimes of the metastable levels involved in those transitions has been determined withan error of less than 0.2%. A new, fully automatized x-ray crystal spectrometer allows systematicmeasurements with very high precision and reproducibility. Absolute measurements of the Lymanseries of H-like ions are currently underway. Dielectronic recombination studies have yieldedinformation on rare processes, as two-electron-one photon transitions in Ar16+, or the interferenceeffects between dielectronic and radiative recombination in Hg77+. The apparatus can now operateat electron beam currents of more than 500 mA, and energies up to 100 keV. A further beam energyincrease is planned in the near future. Ions can be extracted from the trap and transported to externalexperiments. Up to 4 × 107 Ar16+ ions per second can be delivered to a 1 cm diameter target at 10 m distance. Charge-exchange experiments with U64+ colliding with a cold He atomic beam havebeen carried out, as well as experiments aiming at the optimization of the charge state distributionof the extracted via dielectronic recombination. Two new EBITs, currently in advanced state ofconstruction in Heidelberg, will be used for experiments at the VUV free electron laser at TESLA(Hamburg) and for the charge breeding of short-lived radioactive isotopes at the TRIUMF ISACfacility.

Investigation of Heavy Metal Release during Thermal Waste Treatment on a Forward‐Acting Grate by Means of Radiotracers

AbstractThis paper deals with the determination of location, time and quantity of the release of heavy metals in a pilot‐scale grate system by means of short‐lived radioactive isotopes during the incineration of municipal waste. The isotopes 69mZn (half life: 13.8 hours) and 64Cu (half life: 12.7 hours) were used to represent heavy metals which can be released relatively well and more difficultly, respectively. Due to the implementation of isotopes which emit gamma rays, all measured values could be acquired without direct contact and without the need to take samples. The location of release was determined by means of NaI(Tl)‐scintillation detectors positioned alongside the outer walls of the grate. The time and the quantity of the release were measured with a detector located in a special absorption vessel for the purification of a partial flow of the exhaust gases.

Magnetic Flaring in the Pre–Main‐Sequence Sun and Implications for the Early Solar System

To address the role of energetic processes in the solar nebula, we provide a detailed characterization of magnetic flaring in stellar analogs of the pre-main sequence Sun based on 23 hours observations of 43 analogs of the young Sun in the Orion Nebula Cluster obtained with the Chandra X-ray Observatory. We find the X-ray luminosities are strongly elevated over main sequence levels with average = 30.3 erg/s and = -3.9 (0.5-8 keV), and dozens of flares are present. Analogs of the <= 1 My old pre-main sequence Sun exhibit X-ray flares 10^{1.5} times more powerful and 10^{2.5} times more frequent than the most powerful flares seen on the contemporary Sun. Extrapolating the solar relationship between X-ray luminosity and proton fluence, we infer that the young Sun exhibited a 10^5-fold enhancement in energetic protons compared to contemporary levels. Unless the flare geometries are unfavorable, this inferred proton flux on the disk is sufficient to produce the observed meteoritic abundances of several important short-lived radioactive isotopes. Our study thus strengthens the astronomical foundation for local proton spallation models of isotopic anomalies in carbonaceous chondritic meteorites. The radiation, particles and shocks produced by the magnetic reconnection flares seen with Chandra may also have flash melted meteoritic chondrules and produced excess 21-Ne seen in meteoritic grains.

Accommodation coefficient of HOBr on deliquescent sodium bromide aerosol particles

Abstract. Uptake of HOBr on sea salt aerosol, sea salt brine or ice is believed to be a key process providing a source of photolabile bromine (Br2) and sustaining ozone depletion cycles in the Arctic troposphere. In the present study, uptake of HOBr on sodium bromide (NaBr) aerosol particles was investigated at an extremely low HOBr concentration of 300 cm-3 using the short-lived radioactive isotopes 83-86Br. Under these conditions, at maximum one HOBr molecule was taken up per particle. The rate of uptake was clearly limited by the mass accommodation coefficient, which was calculated to be 0.6 ± 0.2. This value is a factor of 10 larger than estimates used in earlier models. The atmospheric implications are discussed using the box model "MOCCA'', showing that the increase of the accommodation coefficient of HOBr by a factor of 10 only slightly affects net ozone loss, but significantly increases chlorine release.

Short-Lived Radioactivities and the Birth of the Sun

Now extinct short-lived radioactive isotopes were apparently extant in the early solar system. Their abundances can be inferred from isotopic effects in their daughter nuclei in primitive meteorites, and the deviation of these abundances from expectations from continuous galactic nucleosynthesis yields important information on the last nucleosynthetic events that contributed new nuclei to the solar system and on the general circumstances of the Sun’s birth. In this paper we present a rudimentary model that attempts to reconcile the abundances of ten short-lived radioactivities in the early solar system. In broad outlines, the picture requires 1) that Type Ia Supernovae maintained a steady ISM supply of 53Mn and 146Sm, 2) that the r-process events that slowly admixed new 107Pd, 129I, 182Hf, and 244Pu nuclei to the solar system occurred over an interval of several hundred million years prior to solar system formation, and 3) that a massive star, by injecting only material outside its helium-exhausted core into the proto-solar nebula, contributed 26Al, 36Cl, 41Ca, 60Fe, and 182Hf no more than one million years prior to the Sun’s birth. In this picture, the live 182Hf present in the early solar system was not due to r-process production but rather to a fast s-process in helium or carbon burning shell in the massive star. We conclude with a possible chemical-memory explanation for the putative 53Cr/52Cr gradient in the solar system.

How the Hectic Young Sun Cooked Up Stony Meteorites

WINSTON-SALEM, NORTH CAROLINA-- Inspired by glimpses of the turmoil around young stars, a team of astrophysicists has presented a radically new theory of chondrites, stony meteorites that date back to the early days of the solar system. Some researchers have argued that several different processes must have contributed to the making of these objects--a stew of dust, rocks that were flash melted and resolidified, and the remains of short-lived radioactive isotopes. But the new theory, presented here at a meeting of the American Astronomical Society last week, holds that all of these ingredients were cooked up by explosive flares and powerful winds near the young sun.

Laser ion sources for on-line isotope separators

The application of resonant photoionisation using tuneable pulsed laser systems for the production of short-lived radioactive isotopes is discussed. The different ways the laser ionisation is implemented at existing on-line isotope separators is reviewed and the properties, limitations and expectations of the laser ion sources are highlighted.

Radioactive ion beams and penning traps

Penning traps are well known as high precision mass spectrometers mainly employed for the investigation of stable particles. For accurate mass measurements of short-lived radioactive isotopes one Penning trap system is operational today. It is the ISOLTRAP spectrometer installed at the ISOLDE facility at CERN/Geneva. Another Penning trap system is presently under construction at the TASCC facility in Chalk River. Beside the very accurate determination of nuclear masses Penning traps can play an important role in the preparation of ISOL-beams for their further post-acceleration, as it is planned in the REX-ISOLDE experiment at CERN.

Collinear laser spectroscopy of high-energy Li-like 11B beam

As part of the RIKEN RIBF (RI beam factory) program, high-resolution x-ray spectroscopy for highly-charged radioactive isotope beams, is proposed in order to make a systematic study of the mean-square nuclear charge radii and moments of short lived radioactive isotopes far from the line of stability. To examine the feasibility of the experiment, we are now performing a test experiment using a laser beam and Li-like ion beams from RIKEN ring cyclotron. The D1 resonance line of a 11B2+ beam was clearly observed for the first time.

Radiation Exposure and other Factors that Predispose to Human Thyroid Neoplasia

Radiation exposure is the only known etiologic factor clearly associated with an increased risk of thyroid cancer. External beam radiation treatment for medical therapy, acute gamma ray exposure from environmental sources (nuclear weapons, nuclear power plant accidents), and ingestion of short-lived radioactive iodine isotopes are the primary sources of radiation exposure, which increases the risk of benign and malignant thyroid neoplasia. Relative risk is directly proportional to the exposure dose and is inversely proportional to the age at exposure.

High collection efficiency in a laser trap.

We present the results of the first study of the fundamental processes governing collection efficiency of neutral atoms in a vapor cell laser trap. The experimental test of our model of the collection process closely agrees with our predictions based on the measured properties of the laser beams and cell. This study has led to the development of special vapor cell wall coatings. We have demonstrated a collection efficiency of 6% for cesium and predict more than 50% could be achieved under optimum conditions. This work develops the concepts for and demonstrates the feasibility of new experiments using short-lived radioactive isotopes.

Laser trapping of short-lived radioactive isotopes.

We describe an experiment which demonstrates the feasibility of trapping significant quantities of short-lived radioactive atoms with laser light. A thermal beam of 22.5 sec half-life $^{21}\mathrm{Na}$ atoms was produced on-line at the LBL 88'' Cyclotron. After decelerating the beam using a Zeeman-tuned slowing technique we stored about 4\ifmmode\times\else\texttimes\fi{}${10}^{3}$ $^{21}\mathrm{Na}$ atoms in a magneto-optical trap. The number of trapped atoms is large enough to be used in experimental studies of the beta decay of $^{21}\mathrm{Na}$. The basic method can be adapted for other rare isotopes.

Pathogenesis and recent therapeutic approaches to graft-versus-host disease

Effective prophylaxis of acute GVHD should bring about improved patient survival by decreasing severe infections during the first 3 months after transplantation and reducing the incidence of chronic GVHD while not compromising the quality of hematopoietic engraftment or increasing the incidence of leukemic relapse by impairing the graft-versus-leukemia effect. None of the current approaches to prevention of GVHD succeed at meeting these expectations, although postgrafting immunosuppressive therapy comes closest to the ideal. The technique of T cell depletion has been very effective in reducing the incidence of GVHD, but conditioning programs must be developed that will be more successful at eliminating host immune and malignant cells. It is doubtful that this will be achieved with systemic chemotherapy and total body irradiation. Innovative approaches such as the use of monoclonal antibodies, either alone or linked to short-lived radioactive isotopes with short linear energy transfer, promise to result in less toxic but more efficient programs, not only providing better eradication of malignant disease but also ameliorating the problem of graft failure. It is conceivable, however, that it will never be possible to kill all leukemic cells with chemoradiotherapy of any form, and the graft-versus-leukemia effect may be essential. Perhaps in the future it will be possible to distinguish lymphocytes causing the graft-versus-leukemia effect from those causing GVHD, isolate them, and use them in attempts at therapy. In the meantime, postgrafting immunosuppressive drugs are used most frequently to prevent and treat GVHD, and steadily improving survival statistics can be expected.

The Inchworm ® as a precision translator in a high magnetic field and uhv environment

A new set-up has been designed and tested for on-line, high-precision mass measurements of short-lived radioactive isotopes via a determination of the ion cyclotron resonance. Ions delivered by the on-line isotope separator ISOLDE at CERN/Geneva are stored in a Penning trap installed in a superconducting solenoid. Due to severe space limitations in the bore of the solenoid, it is impossible to use conventional mechanical feedthroughs for the necessary manipulations inside the uhv chamber. Instead, a number of Inchworms, a high-precision positioning device based on the piezo-electric effect are employed. This publication reports on the first application of this device in a uhv environment at a magnetic field of nearly 6 T.

Stable isotopes in physiological ecology and food web research

Mention the word ‘isotopes’ and most people will think of short-lived radioactive isotopes. Yet far more abundant than the radioactive forms and perhaps much more useful for ecological studies are the stable isotopes. Early interest in stable isotope analyses developed in the geological sciences, and their application in environmental biology has developed slowly until recently. Over the past few years, innovative applications of stable isotope analyses to studies of biological processes have been expanding rapidly, and there is every indication that stable isotope approaches will lead to major advances over the next decade in our understanding of physiological processes and fluxes through ecological systems. Studies of plant and animal physiological ecology and food webs will benefit greatly.

Submillisecond on-line mass separation of nonvolatile radioactive elements: An application of charge exchange and thermalization processes of primary recoil ions in helium.

Transportation of thermalized primary recoil ions from nuclear reactions by helium flow has been investigated as a means of injecting short-lived radioactive nuclides into an on-line isotope separator. Several short-lived radioactive isotopes of highly nonvolatile elements such as B, Sc, Nb, and W have been separated. The efficiency for heavy nuclides with half-lives above 1 ms is between 1 and 10%. The shortest-lived activity identified in an on-line separation is the 182-\ensuremath{\mu}s isomeric state in $^{207}\mathrm{Bi}$.

An In Vitro System for Measuring Intrinsic Dietary Mineral Exchangeability: Alternative to Intrinsic Isotopic Labeling

The primary purpose for the in vitro system described here was to provide an alternative method to intrinsic isotopic labeling for determining exchangeability of intrinsic food mineral with extrinsic inorganic mineral or one of its isotopes. In this system, foods or food mixtures extrinsically tagged with an isotope of the mineral of interest are incubated successively in media simulating peptic or pancreatic digestion. Radioactivity and mineral measurements are made on a) the mixture before digestion and after b) peptic and c) successive peptic pancreatic (P-Pa) digestion. Exchangeability is determined by comparing the specific activity in the peptic and P-Pa digest supernatants to that in the mixture before digestion. In addition, determination of the total soluble mineral after P-Pa digestion provides a measurement of potential bioavailability. The procedure was tested for calcium (Ca) exchangeability and bioavailability from a number of foods and food combinations with 45Ca as the tracer. It could be used for any mineral, however, including non-nutrient or toxic elements. It is likely to be most useful in association with human studies carried out with extrinsic stable (non-radioactive) or short-lived radioactive isotopes that are unsuitable for intrinsic labeling.bioavailability calcium in vitro digestion isotope dilution

Gr��e und Form der Atomkerne Die Ladungsverteilung

The principles of elastic electron scattering and of the nuclear-volume effect in muonic atoms are explained in a simple way. Recent measurements for the proton, the α particle, and heavy spherical and deformed nuclei are given as examples. Precise relative measurements reveal the different charge distributions of neighboring stable nuclei. Charge radii of short-lived radioactive isotopes can be determined by the old method of optical isotope shifts.

Apparatus for the crossed-beam measurement of reactive scattering using short-lived radioactivity

A new method is described for crossed molecular beam measurements of differential cross sections. One of the reagent beams is labeled with a short-lived radioactive isotope, and detection utilizes counting of radioactive disintegrations. It is shown theoretically that for optimal sensitivity in crossed-beam scattering measurements, nuclides with half lives in the range 10−5–10−1 sec should be chosen for labeling. The usefulness of the new method was demonstrated by making measurements of differential cross sections for reactive scattering. The labeling nuclide chosen for development and testing was 0.032-sec 217At, and the chemical reactions used were Cl+HAt→HCl+At and Br+HAt→HBr+At. For the latter reaction, the total reaction cross section is only 1.5 Å2 under the conditions of the experiment. Background levels are sufficiently small that differential cross sections as small as 10−2 Å2 sr−1 could be measured at a resolution of 0.05 sr, if the primary beam intensity could be made large enough. One of the most useful features of this technique is that the measurement of absolute differential cross sections is readily carried out. Methods are described for making the requisite calibrations for the beam monitor and detector. In the prototype apparatus described here, the labeling nuclide was continuously generated by the radioactive decay of only 1–2 mCi of a long-lived precursor, 10-day 225Ac. However, it is calculated that on-line use of a nuclear accelerator to generate the short-lived nuclide will permit labeled beams 105 times more intense than those used in this demonstration experiment. Consequently, it should be possible to measure differential cross sections for reactions having total reaction cross sections significantly smaller than 1 Å2, and further development of this technique is therefore justified.