Determination Of Fluence Research Articles

Verifikation des VEF-Strahlerkopfmodells für Photonen zur Dosisberechnung mit dem Voxel-Monte-Carlo-Algorithmus

The VEF linac head model (VEF, virtual energy fluence) was developed at the University of Tübingen to determine the primary fluence for calculations of dose distributions in patients by the Voxel-Monte-Carlo-Algorithm (XVMC). This analytical model can be fitted to any therapy accelerator head by measuring only a few basic dose data; therefore, time-consuming Monte-Carlo simulations of the linac head become unnecessary. The aim of the present study was the verification of the VEF model by means of water-phantom measurements, as well as the comparison of this system with a common analytical linac head model of a commercial planning system (TMS, formerly HELAX or MDS Nordion, respectively). The results show that both the VEF and the TMS models can very well simulate the primary fluence. However, the VEF model proved superior in the simulations of scattered radiation and in the calculations of strongly irregular MLC fields. Thus, an accurate and clinically practicable tool for the determination of the primary fluence for Monte-Carlo-Simulations with photons was established, especially for the use in IMRT planning.

41Ca – a possible neutron specific biomarker in tooth enamel

The measurement of long-lived radionuclides, produced by neutrons originating from the atomic-bomb explosions, offers the possibility to reconstruct neutron fluences to which survivors in Hiroshima and Nagasaki were exposed. The long-lived radionuclide, 41Ca (T1/2=103000 years), is suggested here as a means for a retrospective determination of thermal neutron fluences, directly within the human body of a survivor. As proper material tooth enamel is proposed. The 41Ca signal in tooth enamel may be correlated with the exposure to A-bomb induced thermal neutron fluences, provided the natural background level of 41Ca/Ca is significantly lower. Therefore, tooth samples of unexposed survivors of the A-bomb explosions have been examined by means of accelerator mass spectrometry, in order to quantify the natural background level of 41Ca/Ca. Measured 41Ca/Ca ratios were confirmed to be as low as about 2×10−15. Thus, the A-bomb induced additional signal should be detectable for survivors at epidemiological relevant distances. Since tooth enamel had already been used as a dosemeter for gamma radiation from the A-bomb explosion, the detection of 41Ca in tooth enamel would allow, for the first time, an assessment of both, γ-ray and neutron exposures in the same biological material.

41Ca ? a possible neutron specific biomarker in tooth enamel

The measurement of long-lived radionuclides, produced by neutrons originating from the atomic-bomb explosions, offers the possibility to reconstruct neutron fluences to which survivors in Hiroshima and Nagasaki were exposed. The long-lived radionuclide, 41 Ca ( T 1/2 =103 000 years), is suggested here as a means for a retrospective determination of thermal neutron fluences, directly within the human body of a survivor. As proper material tooth enamel is proposed. The 41 Ca signal in tooth enamel may be correlated with the exposure to A-bomb induced thermal neutron fluences, provided the natural background level of 41 Ca/Ca is significantly lower. Therefore, tooth samples of unexposed survivors of the A-bomb explosions have been examined by means of accelerator mass spectrometry, in order to quantify the natural background level of 41 Ca/Ca. Measured 41 Ca/Ca ratios were confirmed to be as low as about 2 × 10 −15 . Thus, the A-bomb induced additional signal should be detectable for survivors at epidemiological relevant distances. Since tooth enamel had already been used as a dosemeter for gamma radiation from the A-bomb explosion, the detection of 41 Ca in tooth enamel would allow, for the first time, an assessment of both, γ-ray and neutron exposures in the same biological material.

Thermoluminescent response of TLD-100 irradiated with 20 keV electrons and the use of radiochromic dye films for the fluence determination

We have measured the LiF:Mg,Ti (TLD-100) fluence response and supralinearity function to 20 keV electrons in the fluence interval between 5 × 10 9 and 4 × 10 12 cm −2. TLD-100 shows linear response up to 2 × 10 10 cm −2, followed by supralinearity and saturation after 10 12 cm −2. Peak 5 is slightly supralinear, f( n) max=1.1±0.1, while high temperature peaks reach up to f( n) max≈8. Peak 5 saturates at n≈1×10 11 cm −2, fluence smaller than any of the saturating fluences of the high temperature peaks. We have also measured the glow curve shape of TLD-100 irradiated with 40 keV electrons, beta particles from a 90Sr/ 90Y source and 1.3 and 6.0 MeV electrons from accelerators. Results are interesting and unexpected in that, for a given macroscopic dose, electrons show a smaller relative contribution of high-temperature peaks with respect to peak 5 than heavy ions or X- and γ-rays. The 20 and 40 keV electron irradiations were performed with a scanning electron microscope using radiochromic dye film to measure fluence. Since film calibrations were performed using 60Co γ-rays which expose the totality of the film volume, the use of this method with low energy electrons required to develop a formalism that takes into account the sensitive thickness of the film in relation to the range of the incident particles.

Uranium and thorium thin film calibrations by particle track techniques

Particle track techniques, which enable estimation of the uranium and thorium contents in films where energy self-absorption is negligible, are presented. These techniques allow calibration of uranium and thorium thin films with adequate precision to be used in neutron fluence determinations for fission-track dating. Calibration via a particles is relatively simple for the case of uranium films, whereas for thorium films it is necessary to use the spectrometric characteristics of the employed track detector. Besides those based on a particles, calibration procedures via fission fragments are presented both for uranium as well as for thorium films.

Measurements of 60Co in spoons activated by neutrons during the JCO criticality accident at Tokai-mura in 1999

Neutron activated items from the vicinity of the place where the JCO criticality accident occurred have been used to determine the fluence of neutrons around the facility and in nearby residential areas. By using underground laboratories for measuring the activation products, it is possible to extend the study to also cover radionuclides with very low activities from long-lived radionuclides. The present study describes γ-ray spectrometry measurements undertaken in a range of underground laboratories for the purpose of measuring 60Co more than 2 years after the criticality event. The measurements show that neutron fluence determined from 60Co activity is in agreement with previous measurements using the short-lived radionuclides 51Cr and 59Fe. Limits on contamination of the samples with 60Co are evaluated and shown to not greatly affect the utility of neutron fluence determinations using 60Co activation.

Standardization of Methods for Fluence (UV Dose) Determination in Bench-Scale UV Experiments

Ultraviolet (UV) disinfection is now an accepted technology for inactivation of a variety of waterborne pathogens in wastewater and drinking water. However, the techniques used in much of the previous research aimed at providing information on UV effectiveness have not yet been standardized. Thus in many peer reviewed published literature, it is not clear how the UV irradiations were carried out, nor how the average \Ifluence\N (or UV dose) given to the microorganisms has been determined. A detailed protocol for the determination of the fluence (UV dose) in a bench scale UV apparatus containing UV lamps emitting either monochromatic or broadband UV light was developed. This protocol includes specifications for the construction of a bench scale UV testing apparatus, methods for determination of the average irradiance in the water, details on UV radiometry, and considerations for microbiological testing. Use of this protocol will aid in standardization of bench scale UV testing and provide increased confidence in data generated during such testing.

Hydraulic Calibration and Fluence Determination of Model Ultraviolet Disinfection System

The objective of this project was to determine the impact hydraulic dispersion has on the calibration of a flow-through model ultraviolet (UV)-disinfection system with chemical actinometry (potassium ferrioxalate) and MS 2 bacteriophage. Fluence was supplied by a medium-pressure ultraviolet lamp to a quartz tube (19 mm diameter) situated in a ventilated galvanized casing. The UV lamp was attached to a vertical position guide, for UV fluence to be varied by positioning the UV lamp at various vertical heights above the quartz tube. Water was pumped through the quartz tube at rates of 100-300 mL/min. An in-line pipe mixer was installed prior to the UV system to ensure adequate mixing with the bulk liquid and chemical actinometer and to mitigate jet formation within the quartz tube. Tracer studies were conducted with and without the in-line mixer using potassium chloride (3 mM). Dispersion coefficients were obtained from the tracer study and incorporated into an axial-dispersion model to determine the rate coefficient of potassium ferrioxalate in the model UV system. A numerical model was used to determine the fluence supplied by the lamp with a reduction in exposure time. After dispersion and kinetics are accounted for within the UV system, the model predicted UV fluence that was in general agreement with UV design curves for inactivation MS 2 bacteriophage. The differences in the design curves and the fluence-response model in the present investigation were found to be related to the experiment errors introduced from using a flowing system and because a medium pressure lamp was used in the present investigation.

Measurement of 235U, 238U, 209Bi and natPb Fission Cross Sections using Quasi-monoenergetic Neutrons with Energies from 30 MeV to 150 MeV

The cross sections for neutron induced fission of 235U, 238U, 209Bi and natPb were measured in the energy range from 30 MeV to 150 MeV using parallel-plate ionization chambers. Proton recoil telescopes and a 238U ionization chamber were employed for the determination of the incident neutron fluence. With the exception of a few deviating data points, the experimental results for 235U(n, f), 238U(n, f) and 209Bi(n, f) are close to the recommended cross sections. For natPb(n, f) the measured cross sections are about 30% lower than the results of a recent evaluation.

A New Investigation of Iron Cross Sections via Spherical-Shell Transmission Measurements and Particle Transport Calculations

We are engaged in a multi-year project to study neutron scattering interactions in iron, the principal objective of which is to investigate the well-known deficiency that exists in reactor pressure vessel neutron fluence determinations. Specifically, we are using the spherical-shell transmission method, employing iron shells with different thicknesses, and neutron time-of-flight measurements of the scattered neutrons, in an effort to precisely determine specific energy regions over which deficiencies in the non-elastic scattering cross section for neutron scattering in iron appear to exist. The analysis of the experimental data involves correlating the data with theoretical calculations of neutron transport through the iron spheres in order to evaluate the degree to which the calculated neutron spectra predict the measured spectra relative to different types of particle interactions. In doing so, we have developed new methodologies for performing neutron transport calculations that will be useful to a range of transport problems. Preliminary results show good agreement between the experimental data and the calculated distribution of neutron flight times over much of the data range, except for the contribution due to breakup neutrons.

Proton beam dosimetry for radiosurgery: implementation of the ICRU Report 59 at the Harvard Cyclotron Laboratory

Recent proton dosimetry intercomparisons have demonstrated that the adoption of a common protocol, e.g. ICRU Report 59, can lead to improved consistency in absorbed dose determinations. We compared absorbed dose values, measured in the 160 MeV proton radiosurgery beamline at the Harvard Cyclotron Laboratory, based on ionization chamber methods with those from a Faraday cup technique. The Faraday cup method is based on a proton fluence determination that allows the estimation of absorbed dose with the CEMA approximation, under which the dose is equal to the fluence times the mean mass stopping power. The ionization chamber technique employs an air-kerma calibration coefficient for 60Co radiation and a calculated correction in order to take into account the differences in response to 60Co and proton beam radiations. The absorbed dose to water, based on a diode measurement calibrated with a Faraday cup technique, is approximately 2% higher than was obtained from an ionization chamber measurement. At the Bragg peak depth, the techniques agree to within their respective uncertainties, which are both approximately 4% (1 standard deviation). The ionization chamber technique exhibited superior reproducibility and was adopted in our standard clinical practice for radiosurgery.

Proton recoil telescopes for fluence measurement in neutron beams of 20–200 MeV energy

Two proton recoil telescopes (PRTs) for the precise determination of neutron fluences are described. The first covers the neutron energy range from 20 to 65 MeV and the second is applicable up to 200 MeV neutron energy. We report in detail on the experimental set-up and describe the response simulation using two different Monte Carlo codes. The two telescopes are compared in a 62 MeV quasi-monoenergetic neutron beam. The measurement uncertainties are discussed.

Some contributions from SSNTD towards nuclear science: from multifragmentation towards accelerator driven systems (ADS)

Three examples are chosen to show the importance of SSNTD as one of the essential tools in nuclear science: (1) Multifragmentation into more than two heavy reaction products: Starting with the observation of three heavy reaction products in the interaction of relativistic protons or 414 MeV 40Ar with actinides in the early 1960s, up to the observation of five heavy reaction products in the interaction of 2400 MeV 238U with uranium, SSNTD had a leading role in this research. (2) In the search for superheavy elements (SHE: Z around 114): Many different techniques are used. However, SSNTD are exclusively decisive in the possible observation of SHE within the heavy element component of galactic cosmic rays. (3) Accelerator driven systems: They are increasingly important in the discussion of energy producing nuclear power stations and in the corresponding ability to transmute long-lived poisonous radioactive materials (above all plutonium) into shorter lived fission fragments or stable nuclides. SSNTDs play an important role in the determination of the energy dependent neutron fluence in small volumes (≈cm 3) or in the exact beam profile determinations of the primary proton beams. This contribution ends with an outlook into possible future fields of physics research: With the advent of a new generation of relativistic heavy ion accelerators, such as the NUCLOTRON at the JINR in Dubna, Russia, and RHIC in Brookhaven in the United States, one can continue to study (and finally confirm or disprove) all phenomena mentioned already, as well as additional controversial phenomena, such as “enhanced nuclear cross-sections over short distances”, called colloquially “anomalons”. Again SSNDT can be used in at least a twofold manner as an important tool: (a) the enhanced neutron production with 12C ions or heavier ions in thick targets at energies above approximately 50 GeV and (b) the reduced “mean-free-path” of secondary fragments produced by the same heavy and energetic ions.

Thick target photon yields and angular distributions for the 19F(p,αγ) 16O source reaction at incident proton energies between 1.5 and 4.0 MeV

The absolute thick target yield of 6.129, 6.917 and 7.116 MeV γ-rays produced from the 19F(p,αγ) 16O source reaction has been measured for incident proton energies between 1.5 and 4.0 MeV. The angular distributions of the respective γ-lines have been determined for incident proton energies of 2.0 and 3.0 MeV. The experiments were performed at the 4.5 MV Tandem Van der Graaff accelerator at the Ohio University Edwards Accelerator Laboratory in Athens, Ohio, using a thick CaF 2 target and a 7.62 cm×7.62 cm Na(I) scintillation detector. The Monte Carlo code MCNP was used to calculate detector response functions for the three individual γ-rays. A least-squares fit of these functions to a selected region in the pulse height spectrum was carried out to determine the relative intensities of these γ-rays. The uncertainty in the fluence determination is based on the χ 2 of the fit, the uncertainty in the response functions, the statistics of the data, and the uncertainty in the recording of the proton charge. A maximum photon yield of 1.316×10 7 γ/μC/sr (at 90°) was determined for the sum of these three γ-rays at the highest incident proton energy of 4.0 MeV. The contribution of the individual lines to the total photon yield depends strongly on the incident proton energy. The angular distributions are isotropic to within 15%.

00/01018 A model of an evaporative cycle for heat and power production

We developed, characterized, and tested a new dual-collimation aqueous UV reactor to improve the accuracy and consistency of aqueous k-value determinations. This new system is unique because it collimates UV energy from a single lamp in two opposite directions. The design provides two distinct advantages over traditional single-collimation systems: 1) real-time UV dose (fluence) determination; and 2) simple actinometric determination of a reactor factor that relates measured irradiance levels to actual irradiance levels experienced by the microbial suspension. This reactor factor replaces three of the four typical correction factors required for single-collimation reactors. Using this dual-collimation reactor, Bacillus subtilis spores demonstrated inactivation following the classic multi-hit model with k = 0.1471 cm2/mJ (with 95% confidence bounds of 0.1426 to 0.1516).

Fluence determination by scattering measurements

An alternative method to determine particle fluence is proposed, which is particularly suitable for irradiations with low-energy charged-particle beams. The fluence is obtained by measuring the elastic scattering produced by a composite thin target placed upstream of the sample. The absolute calibration is performed by comparison with the measured radioactivation of vanadium and copper samples. The composite thin target, made of aluminium, carbon and gold, allows not only the fluence to be measured, but also a continuous monitoring of the beam space distribution. Experimental results with a 27 MeV proton beam are reported and compared with Monte Carlo simulations.

Measurement of trace element concentration in a metal matrix using total reflection X-ray fluorescence spectrometry

Total reflection X-ray fluorescence spectroscopy (TXRF) has been used in combination with synchrotron radiation in order to determine detection limits and lowest limits of concentration of trace elements in metal matrices. Two applications on irradiated material are described, where the TXRF method has some advantages, as compared to other detection methods, because only few micrograms of material is needed for the measurements. The first application is devoted to radiation damage studies on first wall material of future fusion reactors. Therefore, metal foils were irradiated with 590 MeV protons at PSI and the transmutational elements produced in the foils were measured. The second application is the assessment of radiation damage of core components in a nuclear power plant, e.g. the reactor pressure vessel. This is performed by the determination of the fast neutron fluence on the components using an activation reaction of 93Nb which is a trace element in most reactor steels. Detection limits of a few picograms have been found in the experiments.

Effect of the composition of radiation on the radiation damage to graphite

A statistical analysis is performed of the results on the determination of the critical neutron fluence in MR, SM-2, and BOR-60 with different irradiation temperature. It is shown that the critical neutron fluence depends not only on the irradiation temperature but also, and to an even greater extent, on the radiation composition factor (ratio of the neutron and γ-ray flux densities). Thus the critical neutron fluence for irradiation at 600°C in MR (radiation composition factor 0.13) is 17·1021 cm−2 and in SM-2 (radiation composition factor 0.1) 11·1021 cm−2 at the same temperature. When the same graphite is irradiated in the region of the outer corner of a working block of RBMK, where the radiation composition factor is 0.55, it is expected that the critical neutron fluence will be 31.7·1021 cm−2.

Effect of the nonuniformity of graphite samples on their shape change under irradiation

It is shown that the use of the initial characteristics of samples makes it possible to decrease substantially the variance and the bias in the determination of the critical neutron fluence for GR-280 RBMK graphite. It is recommended that a graphite model that includes neutron fluence and the initial value of the elastic modulus be used as an approximation for dimensional changes of graphite samples. 2 figures, 2 tables, 3 references.

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.