Thin Lead Foils Research Articles

SU-E-T-151: Enhanced Radiation Attenuation with Multi-Layer Foils

Purpose: To evaluate the effect of increasing the number of thin high Z foils on the dose enhancement and the overall radiation attenuation with a 24MV photon beam. Methods: DOSXYZnrc was used to perform Monte Carlo simulations of multi-layer lead foil configurations. The foil size was 7cm x 7cm. and the foil thickness was adjusted to give a combined thickness of 1mm. The number of foils used was 4, 6, 8, and 10. The separation between foils was also varied from 3 to 9 mm. The Mohan 24MV energy spectrum was used as a photon source. The field size was 5cm x 5cm and SSD was 100 cm. The phantom size was 16cm × 16cm × 28cm. The number of histories ranged from 1 to 2 billion. The percentage difference of the dose between the medium with foils and the homogeneous water was computed along the beam axis. The minimum dose enhancement and the change of integrated dose between the foils were determined. Results: Increasing the number of foils resulted in a decrease in the minimum dose enhancement. The highest dose region occurred in the last section for the 4 and 6 foil cases, whereas the 8 and 10 foil configurations showed the maximum dose region towards the center of the foil group. Increasing the number of foils increased the total integrated dose between foils. For example, the total integrated dose increase between the first and the last foils with a 3mm foil separation were 34.2, 43.4, 57.4, and 64.7% for 4, 6, 8 and 10 foils, respectively. Conclusion: This work showed the degree of dose enhancement around multiple thin lead foils. The results suggest that the total attenuation of photon beam can be increased by increasing the number of foils with a fixed total foil thickness.

SU‐E‐T‐255: Monte Carlo Quantification of Dose Distributions Around Thin Lead Foils

Purpose: Patients are increasingly undergoing radiotherapy procedures, in which small metals are implanted in the body for target localization in IGRT or dose enhancement. Previously we proposed the polymer gel dosimetry technique for measurement of 3D dose distributions around small metallic materials including thin foils. The purpose of this study is to determine the effect of separation between thin metallic objects and 3D dose distributions using a Monte Carlo method and to provide theoretical data which will be compared with the measurement data. Methods: DOSxyz was used to perform Monte Carlo simulations of a two lead foil setup. The Mohan 24MV spectrum was used as a radiation source with 5cm x 5cm collimation at a 100 SSD. The foils had dimensions 1cm × 1cm × 0.5mm and had separations of 2mm, 5mm, 7mm, 10mm and 15mm. The phantom size was 16cm × 16cm × 28cm. Simulations were performed on custom Intel I7 machines with various histories (100 million to 1 billion). Percent depth dose curves were determined, then the minimum dose between the foils was recorded and compared to the dose without the foil. The plots were normalized against the maximum dose point. Results: The minimum dose enhancement ratios between two foils were 1.47, 1.29, 1.18, 1.13 and 1.08 for the separation of 2, 5, 7, 10, and 15 mm, respectively. The dose enhancement ratio exponentially decreased with the separation. The Monte Carlo simulation results were in agreement with experimental data previously obtained with films. Conclusion: The degree of dose enhancement around thin lead foils was determined by the Monte Carlo method. It is expected that other high Z materials such as gold will behave in similar manner. The results would be used to identify optimal placement of materials for measurement by a polymer‐gel dosimeter.

Interaction mean free path of the particles emitted in cosmic ray nuclear explosions

The measurements of the interaction mean free path of the near minimum ionizing particles emitted in cosmic ray nuclear explosions are discussed. A new determination of this mean free path has been made at mountain altitude, using a counter controlled cloud chamber containing thin lead foils. The result is 200±25% g cm−2 Pb.

Excitation functions for the production of 60Fe and 53Mn in the reaction natPb(p,xp/yn)Z

The cross sections for the production of long-lived 60Fe and 53Mn from thin proton-irradiated lead foils in dependence on the proton energy from thresholds up to 2.6 GeV were determined by measuring the radionuclide content with accelerator mass spectrometry (AMS). For the sample preparations subsequent chemical separation procedures were developed. The corresponding excitation functions are shown. The results are compared with theoretical predictions obtained with calculation codes developed within the HINDAS project (5th framework of the EC). The knowledge of the radio nuclide inventory of such spallation targets is essential for the design of accelerator driven systems (ADS).

Constant and pulse power capabilities of lead-acid batteries made with thin metal film (TMF®) for different applications

Abstract Conventional power sources are able to deliver high energy, but high-power demands can be met only with advanced electrochemical or heavy battery devices. BOLDER Technologies has developed a high-power cell (86 g, 1.0 A h, 2 V) based on patented Thin Metal Film (TMF®) Technology which is capable of delivering very high constant or pulse power for several applications. Six cells in a 0.5–1 kg pack are capable of delivering 1 to 1000 A with a stiff voltage plateau of 12 V for periods ranging from 1 h to a few milliseconds, respectively, and constant power not provided by any other battery chemistry. The BOLDER TMF® cells are made of thin lead foil and PbO active material, which gives enormous cost advantages compared with existing lead-acid batteries or with competing battery systems. This paper presents the high constant-power and pulse-power delivery characteristics of batteries made with TMF technology. The new concept of developing hybrid power sources with proton exchange membrane fuel cells (PEMFCs) or other battery types for electronic communication and turbine-starting applications is also discussed.

Observer variation in the radiographic assessment of the bone level on the buccal and lingual surfaces of mandibular molars.

To assess accuracy and precision of observers' diagnostic performance in locating the buccal/lingual bone level using conventional periapical radiographs. Standardized radiographs of molar regions of 10 dried mandibles were obtained. The bone crest on buccal and lingual surfaces of first and second molars was then marked with thin lead foil strips and fresh radiographs taken. A series of increasingly extensive furcation defects was created by sequential bone removal and radiographs with and without markers obtained after each step. The radiographs without indicators were presented to 10 observers on two separate occasions and the most apically located bone level marked on a transparent film. The distance between observers' markings and 'true' bone level on the radiographs was determined. There was wide interobserver variation which increased as the bone loss increased. Lack of consistency was largely attributable to intra-observer variation except when a furcation defect was present. The underestimation of bone loss became more marked as the amount of bone loss increased. Radiographic determination of bone loss on buccal and lingual surfaces is associated with a considerable lack of accuracy and precision, both of which get worse as bone loss increases.

A new high rate lead acid battery

A new approach to the design of lead acid batteries has been developed based on the use of very thin lead foil current collectors. The basic cell construction and the performance characteristics for the new cell are described. Spiral wrap cells based on this electrode concept exhibit extremely high power output with excellent capacity maintenance. Additionally, these cells exhibit very flat voltage at all currents, and are capable of very rapid recharge. Applications for this high power technology cover a broad spectrum such as portable power tools, UPS systems, electrically heated catalytic converters, military pulse power applications and electric and hybrid vehicles.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dosimetric characteristics, air-kerma strength calibration and verification of Monte Carlo simulation for a new ytterbium-169 brachytherapy source

Purpose : Ytterbium-169 ( 169Yb) is a promising new isotope for brachytherapy with a half life of 32 days and an average photon energy of 93 KeV. It has an Ir-192-equivalent dose distribution in water but a much smaller half-value layer in lead (0.2 mm), affording improved radiation protection and customized shielding of dose-limiting anatomic structures. The goals of this study are to: (a) experimentally validate Monte Carlo photon transport dose-rate calculations for this energy range, (b) to develop a secondary air-kerma strength standard for 169Yb, and (c) to present essential treatment planning data including the transverse-axis dose-rate distribution and dose correction factors for a number of local shielding materials. Methods and Materials : Several interstitial 169Yb, sources (type 6) and an experimental high dose-rate source were made available for this study. Monte-Carlo photon-transport (MCPT) simulations, based upon validated geometric models of source structure, were used to calculate dose rates in water. To verify MCPT predictions, the transverse-axis dose distribution in homogeneous water medium was measured using a silicon-diode detector. For use in designing shielded applicators, heterogeneity correction factors (HCF) arising from small cylindrical heterogeneities of lead, aluminum, titanium, steel and air were measured in a water medium. Finally, to provide a sound experimental basis for comparing experimental and theoretical dose-rate distributions, the air-kerma strength of the sources was measured using a calibrated ion chamber. To eliminate the influence of measurement artifacts on the comparison of theory and measurement, simulated detector readings were compared directly to measured diode readings. The final data are presented in the format endorsed by the Interstitial Collaborative Working Group. Results : The in-air calibration revealed that the air-kerma strength per unit activity (mCi), as quoted by the vendor, varied from 1.30 to 1.57 cGy · cm 2/mCi · h depending on seed design. The maximum difference between measured and MCPT-simulated absolute diode readings on the transverse axis was less than 2% indicating that MCPT accurately predicts dose rate in medium for brachytherapy sources in this energy range. Comparison of measured and simulated HCFs for each of the 16 different cylindrical heterogeneities demonstrated 1–3% agreement. The HCFs vary by as much as 200% with respect to distance and by as much as 48% as a function of disk diameter, showing that HCF is strongly dependent on heterogeneity location and lateral dimensions as well as thickness. The dose-rate constant for water medium was found to be 1.225 cGy/h per kerma unit air-strength and 1.962 cGy/h per unit mCi as measured by the vendor. Conclusion : Monte Carlo simulation is an accurate and powerful tool for dosimetric characterization of brachytherapy sources in this energy range. Thin lead foils produce shielding factors comparable to standard shielded applicators for 137Cs. Meaningful theoretical absolute dose calculations in brachytherapy require accurately implemented airkerma strength standards.

A search for narrow lines in the gamma spectra from [formula omitted]D annihilation at rest

The γ ray spectrum from pd annhilations at rest was studied by stopping antiprotons in liquid deuterium and analyzing the gamma rays using a magnetic pair spectrometer. No clear evidence is found for monochromatic γ rays and the upper limit for the branching ratio pp → γX with 1100 MeV/c2 < mx < 1770 MeV/c2 is less than 5 × 103 at the 95% confidence level.The search for narrow lines in the gamma ray spectrum produced in antiproton-proton annihilations at rest has been intense. Despite the predictions of various models1 and earlier experimental evidence for their existence,2 exotic four quark states (qqqq), known as baryonium, have not been confirmed by recent experiments.3 Evidence for bound pN states has also been claimed in the pionic and gamma ray spectra resulting from the annihilation of antiprotons in deuterium.4 Prompted by such claims, we conducted an experiment to measure the inclusive gamma ray spectrum from the annihilation of antiprotons at rest in liquid deuterium. In this report we present the results of a high-resolution, high-statistics measurement of the gamma spectrum from the annihilation of antiprotons at rest in liquid deuterium, using the well-understood PS183 magnetic pair spectrometer.The 350 MeV/c antiproton beam entered a 7 cm diameter, 70 cm long liquid deuterium target and the antiprotons annihilated at rest after ranging through approximately 17 cm of deuterium. A cylindrical multiwire proportional chamber surrounding the target was used to measure the charged multiplicity of each event and planar drift chambers were used to determine the stopping vertex. The gamma rays from the annihilation were converted into electron-positron pairs in a thin lead foil (10% of a radiation length) which was situated at the front of the magnet aperture and subtended 1.5% of 4π solid angle. Depending upon the momentum of the particle, the magnetic field of 7.5 kG either reflected the particle back out of the magnet (R track), trapped it within the magnet aperture (T track), or allowed it to penetrate (P track). The gamma ray events analysed in this report fall into one of three different types; RR, RT, TT. The acceptance for penetrating tracks was too low at this magnetic field setting to accumulate sufficient statistics. Details of the detector can be found elsewhere.6The momentum of a particle was reconstructed using the radius of a circle fit to the multiwire proportional chamber hits times a correction factor to correct for the inhomogeneities in the field. Hit patterns in the chambers and time-of-flight between various scintillators ensured a high-quality sample of events from annihilations at rest. Of 2.8 million gamma-triggered events written to tape, 750000 survived all the cuts and made their way into the spectra presented in Figure 1. The acceptance and resolution functions of the spectrometer were obtained from a Monte Carlo simulation of the detector using the GEANT3 code developed at CERN.The spectra were fit with low-order polynomials and the search for narrow states was carried out by stepping through the spectra bin-by-bin and fitting with the global polynomial plus a gaussian constrained to have a width consistent with the spectrometer resolution at the energy of the bin. No clear evidence for narrow structures is seen in the spectra. Figure 2 shows the 95% confidence level upper limits on the yield of narrow structure.

The effect of mechanical pressure on the critical transport properties of superconducting lead

We study the effect of mechanical pressures up to 16 kbar on the critical-current density J tc and on the pinning-force density F p in thin lead foils. The pressure is applied at 4.2 K by means of a temperature-regulated clamp-type device based on Bridgman's opposed anvil technique. We ascertain that on the average 70% of the increase of of J tc and F p under pressure already occurs in the low-pressure region ( p < 5 kbar). The resistance ratio β on the other hand, gradually increases even at higher pressures, proving that the lattice defects which are introduced at high pressures are not as effective in pinning the flux structure. A J tc( B z.sfnz) relationship which fits the experimental data over the entire pressure and temperatures ranges is proposed.

I-125, A New Radioisotope for the Labeled Hippuran Renogram

making radioisotope renograms. Its long half-life of 60 days is convenient, and it emits low-energy 27.2-35.4kev photons that are inherently directional because about half of them are absorbed by the all-or-none photoelectric process. They are readily absorbed by brass, steel, or thin lead foils. This makes it simple to shield against them and to achieve effective collimation of them by much lighter and less bulky apparatus than is required with I/sup 131/ The soft I/sup 125/ photons are absorbed efficiently in thincrystal scintillation detectors that have much lower background counting rates than those used previously for making renograms with hippuran-I/sup 131/. I/sup 125/ does not emit useless and undesirable BETA -particles; consequently, the photon merit ratio (usable photons/absorbed energy) is high. Radiation exposures to the patient are lowered when I/sup 125/ replaces I/sup 131/. Risk of decomposition due to selfirradiation of photon carrier compounds is decreased when I/sup 125/ is used to label them. (H.H.D.)

Neutron-Electron Interaction proposed by Kikuchi

IT is known that a Geiger-Muller counter operated near a source of fast neutrons gives a rather large number of counts. Kikuchi, Aoki and Husimi1,2, working with a D-D source of neutrons, have postulated that these counts arise in part from a direct interaction of fast neutrons with electrons in the thin lead foil surrounding their counter. However, the recent discovery by Kallmann and Kuhn3 that gamma-rays are emitted in the D-D reaction seems to offer a simple and more satisfactory explanation for the phenomena observed by Kikuchi and co-workers. Confirmatory evidence is the discovery by Bonner4 of two groups of neutrons from the D-D reaction.

Gamma-Radiation from Fluorine Bombarded with Protons

In our recent work (1) on the gamma-radiation from Li7+H1 we have shown that the pairs ejected from thin lead foils in a Wilson cloud chamber gave a more accurate determination of the energy of very high energy gamma-radiation than do the recoil electrons.

Scattering of Hard γ-Rays and Annihilation Radiation

To determine the relative importance of the annihilation of positive electrons in the phenomenon of the scattering of hard γ-rays, observations were made on the secondary γ-radiation from thin lead foils irradiated with thorium C γ-rays (25 mgm.). With a scattering angle of about 140°, 0.8 cm. effective lead filter was sufficient to absorb practically all the Compton scattering, and still leave predominant the softer of the two components in the anomalous scattering, namely, the component which has been attributed to the annihilation of positive electrons.

Scattering of Hard Gamma Rays by Lead, and the Annihilation of Positive Electron

THE following experiment was carried out to make a further test of the hypothesis, proposed by Blackett and Occhialini, that the nuclear scattering of hard rays by heavy elements is due to the annihilation of positive electrons produced by the rays1. rays from an emanation tube were used, the source being. placed at S (Fig. 1). Observations were made on the ionisation produced in the chamber I due to the introduction of a thin lead foil (0·1 mm.) into the position BB first, with an aluminium sheet (3 mm. thick) at AA, secondly without the aluminium sheet. According to the above hypothesis, the ionisation should be greater in the first case, because the positive electrons which are produced in the lead foil and escape from it in the forward direction, are stopped in the aluminium sheet. In the second case they are practically lost from the neighbourhood of the ionisation chamber, and therefore also their annihilation radiation. Apart from this, the only difference between the two cases is that, in the first, the lead foil absorbs some of the radiation scattered by the aluminium. This tends to make its effect smaller than in the second case, and is therefore in the opposite direction to the above positive electron effect. Quantitatively, the absorption effect is, however, quite small, being only 2 per cent of the total effect of the lead foil.

The magnetic susceptibility of some binary alloys

The object of this research has been to find a connection between the mass susceptibility and chemical composition of a number of binary alloys of several metals. The susceptibility measurements were made with the aid of a Curie and Cheneveau magnetic balance, the permanent magnet of which produced a field with an intensity of about 640 gauss. It was found early in the work that the method of attachment of the torsion wire to the balance beam and to the torsion head was not satisfactory; consequently the hook and loop arrangement was replaced by a small clamp and screw, which was attached to the beam of the balance and the torsion head. Since the torsion wire was very thin it became necessary, in order to fasten it rigidly at both ends, to face the jaws of the clamps with thin lead foil. This arrangement ensured a perfectly satisfactory attachment of the torsion wire. The torsion wires used were of platinum 0.10 mm. diameter. To obtain concordant readings it was found necessary to anneal the wires before use. This was achieved by suspending the wire under a slight stress and passing a slowly increasing current of electricity through it, over a period of 30 minutes, until the temperature reached 150°C. When this temperature was reached, the current was maintained steady for 30 minutes and then slowly reduced to zero, a further 30 minutes being taken for the reduction. During the heating the wire was seen to untwist, so that the effect of annealing appears to be the removal of a twist imparted to the wire during drawing. Annealed torsion wires gave reproducible deflections which, on the whole, were greater than those obtained with unannealed wires. The experiments to be described were made with materials of low susceptibility, and consequently the difference between the deflections for the two positions of the permanent magnet was rather small. To increase the accuracy of the readings, a method of oscillation was adopted. The magnet was placed in one of the positions of maximum deflection and the balance arm with its load allowed to oscillate freely. After a few minutes the oscillation had died down sufficiently for the turning points of a spot of light, reflected from a mirror on the balance arm, to be read easily on a millimetre scale situated 200 cms. from the mirror. Five successive turning points were taken, three on one side of the zero and two on the other side, from which the position of rest was calculated. This position was obtained five times for each position of the magnet, and the mean values for each position accepted as the deflection due to the specimen. Adoption of this practice enabled the deflections to be read to 0.05 mm. The readings obtained in this way were identical with those obtained by allowing the beam to come to rest, and they were obtained much more rapidly.