Radiachromic Film Research Articles

Grad-B drift transport and focusing of high-current electron beams

This paper studies, experimentally and theoretically, the grad-B drift transport and focusing of an intense electron beam. The Naval Research Laboratory’s Gamble II generator [J. D. Shipman, Jr., IEEE Trans. Nucl. Sci. NS-18, 243 (1971)] was used to drive a 900 kV, 850 kA beam. This beam drifted in the radial magnetic field gradient produced by an on-axis guide wire carrying a current of 40 kA. An additional axial magnetic field gradient generated by focusing spokes was used to radially compress the beam. Experimental diagnostics included radially resolved calorimetry and radiachromic film to study wall losses. Extensive simulations were performed to better understand the experiments. Energy transport efficiencies were slightly below 70%, and the focusing spokes were observed to compress the beam radius by approximately 10%.

Reduction of edge emission in electron beam diodes

This paper presents measurements of the enhanced current density along the edges of a large area electron beam as well as successful techniques that eliminated this edge effect/beam halo. The beam current is measured with a Faraday cup array at the anode, and the spatial, time-integrated current density is obtained with radiachromic film. Particle-in-cell simulations support the experimental results. Experiments and simulations show that recessing the cathode reduces the electric field at the edge and eliminates the edge effect. However, the cathode recess structure itself emits under long-term repetitive operation. In contrast, using a floating, metallic, electric field shaper that is electrically insulated from the cathode eliminates the beam halo and mitigates electron emission from its surface during repetitive operation.

Radiachromic film as a detector for intense MeV proton beams

A simple technique has been developed to image intense pulsed proton beams with radiachromic film and to measure their spatial distribution. The optical density (OD) of 50 μm thick film, sufficient to stop 1.5 MeV protons, is measured to infer the incident beam fluence. The OD increases nearly linearly with fluence up to 0.25 cal/cm2. This film is used to measure the uniformity of large-area beams as well as the detector in a multiple-pinhole camera to determine the source uniformity and divergence of applied-magnetic field and pinched-beam ion diodes.

Plant and dosimeter stability at a 10MeV electron beam plant

The technique used to measure plant stability (in terms of dose delivered) and the stability of calorimeter, PMMA and radiachromic film dosimetry systems used at AEA Technology's Harwell EB plant is presented. Standard deviations of ≤2.5% for plant stability and 2% for dosimeter stability were recorded over the period of the last 18 months. Preliminary results are also presented from an assessment of a new surface-read dosimetry system useful for dose-mapping at an EB plant.

Measurement of fluence and flux of proton beams using differentially filtered diamond detectors and radiachromic film

Differentially filtered, photoconductive, neutron-irradiated diamond detectors have been employed to investigate the temporal and energy distribution of an intense pulsed proton beam. Results were compared against measurements obtained using differentially filtered radiachromic film, electromagnetic (EM) techniques, time-of-flight techniques, and calorimetric instruments.

Beta-particle dosimetry in radiation synovectomy.

Beta-particle dosimetry of various radionuclides used in the treatment of rheumatoid arthritis was estimated using Monte Carlo radiation transport simulation coupled with experiments using reactor-produced radionuclides and radiachromic film dosimeters inserted into joint phantoms and the knees of cadavers. Results are presented as absorbed dose factors (cGy-cm2/MBq-s) versus depth in a mathematical model of the rheumatoid joint which includes regions of bone, articular cartilage, joint capsule, and tissue (synovium) found in all synovial joints. The factors can be used to estimate absorbed dose and dose rate distributions in treated joints. In particular, guidance is provided for those interested in (a) a given radionuclide's therapeutic range, (b) the amount of radioactivity to administer on a case-by-case basis, (c) the expected therapeutic dose to synovium, and (d) the radiation dose imparted to other, nontarget components in the joint, including bone and articular cartilage.

Performance of the Modified Suss XRS 200/2M X-Ray Stepper at CXrL

An XRS 200 model 2M X-ray stepper has been installed at the Center for X-ray Lithography. This paper describes the capability of the machine and its installation. Of greater interest is the performance the stepper gives with respect to the dose control and the mask/wafer alignment. How robust a process is depends on the latitude of each process parameter and the control tolerance accorded the machines and materials that affect each one. The dose repeatabillty and uniformity is determined by the optical elements in the beamline, the helium delivery system, and the accuracy of the scanning stage. Test results are reported for dose control using three separate methods. The scan speed is measured using Suss supplied equipment and is verified separately by CXrL's own technique. The dose delivered is analysed by the response of radiachromic film. Also important is the behavior and performance of the ALX-100 alignment system. The optical set-up is described as a model that includes the ALX hardware and illumination as well as the mask and wafer. The signal and contrast from the mask and wafer are compared to data for several substrates. A figure of merit is discussed for determining which membranes will give the best overlay.

Effects of temperature and humidity during irradiation on the response of radiachromic film dosimeters

The effects of temperature and humidity during γ irradiation on the response of two types of film dosimeters (Far Wesr radiachromic and GafChromic films) were studied in the dose range of 0.3–3 kGy. Both films show a significant effect of temperature and humidity and a simple correction function is proposed. This correction is usually between 5 and 10% for the range studied. For the GafChromic film, a colour change at temperatures above 50°C was observed and, consequently, this system cannot be used at these temperatures. At lower temperatures down to - 70°C the sensitivity of both films is reduced and a simple correction is possible. In this study and for the dose ranges used, only a slight dependence on humidity was observed for both films from 0 to 60% r.h. Whereas the GafChromic film at humidities up to 90% r.h. shows only a moderate effect, the Far West films shows a considerable inconsistency for the dose range studied. A simple correction function may be applied for humidity effects, except for the Far West film above 60% r.h. where the effect of humidity is also dose dependent.

Soft X-ray dosimetry using radiachromic nylon films

Abstract This Letter reports on the effectiveness of radiachromic nylon films for soft X-ray dosimetry at high radiation doses. The results indicate that the film is not energy-sensitive but does have a dose range. Application of the results to the calibration of the LBL soft X-ray contact microscopy station are discussed.

Fluence (Dose) Monitoring of Energetic H+, B+, N+, P+, and As+ Ions Using Ionization in a Radiachromic Film

We have measured the increase in optical density vs. ion fluence (dose) of H+, B+, N+, P+, and As+ ions implanted at 80 and 150 keV energies using a radiachromic dye in a nylon matrix. The technique, with some modification to the substrate, would be suitable for automatic, routine monitoring of low ion implant doses in the range of about 1011 to 1013cm−2. The data have been theoretically analyzed, and a model for optical density saturation (or bleaching) at high doses is proposed.

Oxygen effect on the γ-radiation response of FWT-60 radiachromic film dosimeters

The γ-radiation response of FWT-60 dosimeter films was measured varying oxygen concentration and relative humidity of the irradiation atmosphere and using different doses and dose rates. Irradiation under nitrogen resulted in the highest response, oxygen reduces the response between zero (at 86% r.h.) and 24% (at nominal 0% r.h.). From these results it may be concluded that the origin of the dose-rate effect found is derived from a combined action of oxygen diffusion and consumption. It is recommended to use the system at 86% r.h. or under inert gas.

Dose rate and humidity effects on the γ-radiation response of nylon-based radiachromic film dosimeters

At dose rates typical for 60Co γ-radiation sources, the radiation response of hexahydroxyethyl pararosaniline cyanide/50-μm-thick nylon radiachromic films is dependent upon dose rate as well as upon the relative humidity (r.h.) of the surrounding atmosphere. Under equilibrium moisture conditions, the response measured at 606 nm wavelength 24 h after the end of irradiation shows its highest dose rate dependence at about 32% r.h. A decrease in dose rate from 2.8 to 0.039 Gy s −1 results in a decrease in response by 17%. At higher humidities, the sensitivity of the film as well as the rate dependence decreases and at 86% r.h. no discernible dose rate effect could be found. At lower humidities than 32% there is a flat maximum in response. When the films are irradiated at nominal 0% r.h. a second absorption band at 412 nm appears which is converted completely to an additional 606 nm absorption by exposure to a humid atmosphere. After that procedure the resultant response is somewhat lower than when irradiated at 32% r.h. but shows almost the same dose rate dependence as at 32% r.h. For dosimetric purposes, it is recommended to use the films at or near 86% r.h.

Quality assurance for radiation processing

The growth of the Radiation Processing Industry has presented a new set of parameters for QA programs. The large massive doses of radiation required for commercial applications of sterilization, curing, cross linking, etc., needs measurement methods outside the scope of familiar radiation survey instruments. Among the problems that need to be considered by a QA engineer in establishing the validity of a radiation source are; 1) detector response to dose and dose rate, 2) variations due to source spectrum and quality, 3) perturbations due to physical environment, and 4) ease of handling, read-out, and interpretation. In addition, special problems have been encountered in developing proper calibration procedures and selecting transfer instrumentation that supply tracability to primary radiation standards. Thin plastic and dyed plastic films have been used extensively in radiation measurement due to their low cost, ruggedness, ease of handling and read-out, and compatibility to many geometrical configurations. Radiachromic detectors have been developed that minimize problems associated with QA procedures, and may be standardly checked with calibration services available to industry by the National Bureau of Standards. Radiachromic films are now available which provide selected sensitivity over dose ranges of interest to Radiation Processing. Instrumentation is available for single point checks and for one and two dimensional scans which may be used to support QA programs. A variety of instruments may be selected to read-out in 1) transmission, 2) optical density, or 3) directly in absorbed dose.