The dosimeters used to monitor industrial irradiation processing commonly experience significant temperature rises that must be considered in the dose analysis stage.The irradiation-temperature coefficient for a dosimetry system is derived from the dosimeter's radiation response to the absorbed dose and the irradiation temperature.This temperature coefficient is typically expressed in percent change per degree.The temperature rise in dosimeters irradiated with high-intensity ionizing radiation sources can be appreciable.This is especially true for electron-beam processing in which dosimeter temperatures can approach 80 °C.A recent National Institute of Standards and Technology (NIST) study revealed modest (0.5 % to 1.0 %) deviations from the predicted value at temperatures above 70 °C for absorbed doses of 1 kGy and 20 kGy.However, these data were inconsistent with a concurrent manuscript published by National Physical Laboratory (NPL) researchers that found a significant dose-dependent non-linear alanine response but used dosimeters from a different manufacturer and a different experimental design.The current work was undertaken to reconcile the two studies.Alanine dosimeters from each manufacturer used by NIST and NPL were co-irradiated over a wide range of absorbed dose and irradiation temperature.It was found that though there was a slight variation in the temperature coefficient between the two alanine dosimeter sources both systems were linear with irradiation temperature up to 70 °C and the NPL observations of non-linearity were not reproduced.These data confirmed that there is no fundamental difference in the two commercial alanine dosimeter sources and that temperature corrections could be made on industrial irradiations at the extremes of irradiation temperature and absorbed dose.

Over the course of the last decade, routine monitoring of the alanine dosimetry system revealed a small but significant observation that, after examination, led to the characterization of a previously unknown absorbed-dose-dependent, dose-rate effect for the alanine system. The newly discovered rate effect is of potential concern for electron-beam dosimetry, since electron-beam dosimetry typically derives its traceability to national standards through comparisons to gamma-ray calibrations of the dosimetry system. The largest discrepancy in source dose rates is between gamma-ray sources and electron-beam accelerators. Investigating the influence of temperature on the alanine rate effect is an important first step in preparation for a comparison study between electron-beam and gamma-ray dosimetry. Here, new data is presented on the influence of irradiation temperature (from −40 to +50 °C) on the dose-rate effect measured at 50 kGy.

Quality-control dosimetry is important to the routine operation of a radiation processing facility. For many applications this dosimetry must be traceable to a national primary standard. After irradiation at an industrial facility, National Institute of Standards and Technology (NIST)-supplied transfer dosimeters are certified by measurement and dose interpolation from the NIST calibration curve. However, prior to computing the absorbed dose the dosimeter response must be adjusted for the temperature difference between irradiation temperature for the alanine system calibration and the irradiation temperature for the industrial process. For most industrial applications, the temperature is not controlled and varies during the irradiation process. The alanine dosimeter response has a dependence on irradiation temperature, which is compensated for by applying a correction factor to the dosimeter response to compute the absorbed dose. Moreover, there is no consensus protocol to estimate the irradiation temperature and apply this correction. This work approximates industrial temperature profiles using a 60Co source with a temperature-controlled irradiation chamber, and then compares the relative effectiveness of commonly used industrial methods to correct for irradiation temperature influence on the alanine dosimeter response.

The response of high-dose-range chemical dosimeters is dependent on the dosimeter temperature during irradiation. Typically, irradiation temperatures are estimated by measurements, calculations, or some combination of the two. Then using the temperature coefficient for the dosimetry system, the dosimeter response is adjusted or corrected to be consistent with the irradiation temperature for the calibration curve. Consequently, the estimation of irradiation temperature and the response correction via the temperature coefficient are sources of uncertainty in industrial dosimetry. To date, studies of dosimetry system performance at high temperatures have been limited. The maximum irradiation temperature for temperature coefficient studies of commercial alanine dosimeter formulations has not exceeded 50°C. However, high-energy electron-beam processing can expose dosimeters to temperatures as high as 70°C. This study aims to examine the temperature coefficient above 50°C and assess the accuracy of the dosimeter response corrections. The findings reveal small but significant deviations from linearity above 70°C. The magnitude of this deviation and its implications to dosimetry measurements will be discussed.

In October 2001, first class letters, which were laced with Bacillus anthracis spores, were sent to political and media targets resulting in five deaths and 22 illnesses, significant mail service disruption, and economic loss. The White House Office of Science and Technology Policy established a technical task force on mail decontamination that included three key agencies: the National Institute of Standards and Technology (NIST); the Armed Forces Radiobiology Research Institute; and, the United States Postal Service. A cooperative effort between this task force and industry led to protocols for the processing of letter and parcel mail. Currently, NIST is examining the technical issues and barriers to the use of ionizing radiation to mitigate bioterrorism agents in high-risk passenger luggage. The purpose of this work is to develop irradiation specifications, procedures, and protocols that will ensure that broad classes of bioterrorism agents in passenger luggage will be neutralized without damaging luggage contents and inconveniencing passengers with long delays. This work focuses on three areas: the assembly of critical input data, the development of a coupled computational-experimental verification approach for estimating the radiation dose that can be delivered to passenger luggage and the application of the computations to a larger variety of luggage configurations followed by the development of specifications, procedures, and protocols for the irradiation of passenger luggage. An analysis of the expectations for growth in these and other homeland security areas where irradiation technology can be applied will be discussed.

Early researchers in alanine dosimetry established that, at least in the 0–50°C temperature range, the amplitude of the electron paramagnetic resonance signal of irradiated alanine grows linearly with irradiation temperature. The irradiation temperature coefficient is derived from the slope of this response–irradiation temperature relationship. However, very little data exists on the linearity of the response below 0°C. Thus, the applicability of the irradiation temperature coefficient determined above 0°C to irradiations conducted below 0°C is uncertain. This work investigates the behavior of the alanine response irradiated using a Cobalt-60 gamma source over the temperature range −77°C to +50°C. Since the temperature coefficient is known to be dose dependent [Radiat. Phys. Chem. 57 (2000) 1], a series of dose response studies were conducted over a dose range of 0.5–100 kGy. The study revealed that the temperature response deviates from linearity below −10°C. The implications of these observations to dosimetry will be discussed along with possible chemical mechanisms that would account for these observations.

An Internet-based system for fast, remote certification of high-dose radiation sources against the US national standard is being constructed at the National Institute of Standards and Technology (NIST). The new service will establish traceability (through transfer dosimetry) in real time at a lower cost by using automated routines and the Internet. A prototype of this service was successfully demonstrated in 2000 at the American Society for Testing and Materials (ASTM) Dosimetry Workshop in San Diego. Despite this impressive accomplishment, new developments demanded that several aspects of the service be modified. The new service has been completely redesigned to address these new demands and ensure greater accessibility. A description of the hardware and software configurations of this service as well as the communication and information management aspects will be presented. The Internet-based transfer certification program will provide industry with 24-h, 7-day-per-week, on-demand certifications, immediate turnaround times, and lower cost, ultimately improving the quality of the manufacturing process.

Evaluations on the influence of environmental variabilities on the red fluorescence component of the Sunna Model γ photo-fluorescent dosimeterTM have previously been reported. This present paper describes the environmental effects on the response of the green fluorescence component of the same dosimeter, which is manufactured using the injection molding technique. The results presented include temperature, relative humidity, and light influences both during and after irradiation. The green fluorescence signal shows a significant dependence on irradiation temperature below room temperature at 1%/°C. Above room temperature (approximately 24–60°C), the irradiation temperature effect varies from −0.1%/°C to 1.0%/°C, depending on the absorbed dose level. For facilities with irradiation temperatures between 30°C and 60°C and absorbed dose levels above 10kGy, irradiation temperature effects are minimal. Light-effects results indicate that the dosimeter is influenced by ultraviolet and blue wavelengths during irradiation as well as during the post-irradiation stabilization period (approximately 22h), requiring the use of light-tight packaging. Results also show that the dosimeter exhibits negligible effects from ambient moisture during and after irradiation when in the range of 33–95% relative humidity.

Systematic measurements of the temperature coefficient for alanine electron paramagnetic resonance (EPR) response have been performed for irradiation in the temperature range (10–50)°C and in the absorbed dose range (1–100) kGy at the dose rate 9.5 kGy/h. During the 60Co-ray irradiation, -l-alanine dosimeters were kept in a sealed aluminum holder that provided an effective heat exchange with the temperature-controlled environment. The time between the irradiation and signal measurements was standardized, and a reference sample fixed in the resonant cavity was used to correct the signals for small variations in the spectrometer sensitivity. The temperature coefficient for each dose was determined from approximately 30 experimental points processed by the weighted least-squares technique after the necessary statistical tests were done. The temperature coefficients thus determined were considerably lower than previously reported. The dose dependence of the temperature coefficient features a minimum at (20–30) kGy (about 0.135%/K) with higher values at 1 kGy (0.17%/K) and at 100 kGy ((0.175–0.19) %/K). With the exception of very high doses, no significant distinction was found between the temperature coefficients of Bruker and NIST dosimeters, which differ in shape and binder content.

A new radiation dosimeter, consisting of an optically-stimulated polymer film containing a photofluorescent sensor, can serve as a routine dosimeter and radiographic imaging medium for high-dose applications in the absorbed dose range 0.1-100 kGy. The flexible, colorless, opalescent film having a uniform thickness of 0.240 (+/- 0.005) mm or certain other films in the thickness range 0.08-0.60 mm, are available in large batches. They can be read rapidly with a simple table-top spectrofluorimeter, excitation wavelength (lambda = 450 nm) and emission wavelength (lambda = 670 nm), giving a type A uncertainty of dose evaluation of < +/- 5% at 95% confidence level. It supplies either,single integrated dose readings or two-dimensional radiographic images with relatively high spatial resolution. The present work focuses on the following gamma-ray response characteristics of the system: inter- and intra-batch reproducibility, pre- and post-irradiation stability, and dependence of dose interpretations on absorbed dose rate and irradiation temperature. (C) 1999 Elsevier Science Ltd, All rights reserved.

The effect of dose rate on radiation-induced current gain degradation was quantified for radiation-hardened poly-Si emitter npn bipolar transistors over the range of 0.005 to 294 rad(Si)/s. Degradation increases sharply with decreasing dose rate and saturates near 0.005 rad(Si)/s. The amount of degradation enhancement at low dose rates decreases monotonically with total dose. In addition, the effect of ambient temperature on radiation-induced gain degradation at 294 rad(Si)/s was investigated over the range of 25 to 240 degrees C. Degradation is enhanced with increasing temperature while simultaneously being moderated by in situ annealing, such that, for a given total dose, an optimum irradiation temperature for maximum degradation results. The optimum irradiation temperature decreases logarithmically with total dose and, for a given dose, is smaller than optimum temperatures reported previously for pnp devices. High dose rate irradiation at elevated temperatures is less effective at simulating low dose rate degradation for the npn transistor than for the pnp transistors. However, additional degradation of the npn device at elevated temperatures is easily obtained using overtest. Differences in the radiation responses of the device types are attributed to the relative effects of oxide trapped charge on gain degradation. High dose rate irradiation near 125 degrees C is found to be suitable for the hardness assurance testing of these devices provided a design margin of at least two is employed.

Dosimetry methods developed at NIST for mapping ionizing radiation fields were applied to canisters used in 137Cs dry-source irradiators designed for insect sterilization. The method of mapping the radiation fields inside of these canisters as they cycled through the gamma-ray irradiators involved the use of radiochromic films, which increase in optical density proportionately to the absorbed dose. A dosimeter film array in a cardboard phantom was designed to simulate the average insect pupae density and to map the dose within the full volume of the canister; the calibrated films were read using a laser scanning densitometer. Previously used dosimetric methods did not allow for the spatial resolution that is possible with these films. Results indicate that this dose-mapping technique is a powerful method of evaluating a variety of radiation fields of commercial radiation sources, with promising applications as a means of dose validation and quality control.

The effect of dose rate on radiation-induced current gain degradation at 20 krad(Si) was quantified for lateral and substrate pnp bipolar transistors over the range of 0.001 to 294 rad(Si)/s. Degradation increases monotonically with decreasing dose rate, such that, at an emitter-to-base voltage of 0.7 V, radiation-induced excess base current differs by a factor of approximately, eight at the extreme dose rates. Degradation shows little dependence on dose rate below 0.005 rad(Si)/s, suggesting that further degradation enhancement at space-like dose rates may be negligible. In addition, the effect of ambient temperature on radiation-induced gain degradation at 294 rad(Si)/s was thoroughly investigated over the range of 25 to 240 degrees C. Degradation is enhanced with increasing temperature while simultaneously being moderated by in situ annealing such that, for a given total dose, an optimum irradiation temperature for maximum degradation results. Optimum irradiation temperature decreases logarithmically with total dose and is larger and more sensitive to dose in the substrate device than in the lateral device. Based on the measurement of midgap interface trap density in the base oxide, enhancement in transistor gain degradation due to elevated temperature is explained as an increase in surface recombination velocity in the base. Maximum high dose rate degradation at elevated temperature closely approaches low dose rate degradation for both devices. Based on high-temperature irradiations, a flexible procedure for the accelerated prediction of low dose rate gain degradation at 20 krad(Si) is developed for each of the devices studied.

New transparent radiochromic films, GafChromic MD-55 and NMD-55, which turn from colourless to deep blue upon irradiation, have been designed particularly for measuring radiation therapy absorbed doses (1 Gy to 100 Gy). They are also useful for high resolution mapping of dose distributions, radiographic imaging, treatment planning dosimetry, beam penumbra measurements, and interface dosimetry with ionising photons, electrons and protons. The gamma ray responses are linear with dose in terms of increase of optical absorbance at 670, 633, and 600 nm and are independent of absorbed dose rate and relative humidity. The radiochromic images show a slight gradual post-irradiation increase in absorbance especially during the first 24 h. In addition, there is a small but predictable variation of sensitivity with temperature, both during irradiation and during spectrophotometry. The films also have a slight sensitivity to ultraviolet radiation (250 to 350 nm) in direct sunlight. Experiments with X ray beams show no appreciable energy dependence relative to dose in water at photon energies greater than 100 keV, but they have a sensitivity that gives readings of about 60% of the dose in water for photons at 20 to 40 keV.

Nylon-base radiochromic films (FWT-60TM and FWT-460TM) are commercially-available, thin dosimeters that are widely used in radiation processing. These films cover the following ranges of absorbed dose: 2 × 103 to 5 × 104 Gy for FWT-60TM and 5 × 103 Gy to 105 Gy for FWT-460TM. Based on some earlier studies, their response functions have been reported to be dependent on the temperature and relative humidity during irradiation. The present study investigates differences in response over practical ranges of temperature, relative humidity, dose, and for different recent batches of films of both types. It is observed that for each new batch of film to be used for radiation processing, the effects of such parameters on response to both gamma rays and electrons should be investigated. It is also suggested that the films should be packaged under controlled atmospheric conditions (relative humidity) and should be calibrated under environmental conditions (temperature) at which they will be used routinely.

Cancer therapy studies using proton accelerators are underway in several major medical centers in the U.S., Russia, Japan and elsewhere. To facilitate dosimetry intercomparisons between these laboratories, alanine-based detectors produced at the National Institute of Standards and Technology and commercially available radiochromic films were studied for their possible use as passive transfer dosimeters for clinical proton beams. Evaluation of characteristics of these instruments, including the LET dependence of their response of proton energy, was carried out at the Institute of Theoretical and Experimental Physics. Results of absolute dose measurements were regarded as a preliminary step of dose intercomparison between ITEP and NIST. Measurements made in a number of experiments showed average agreement between the ITEP and NIST dosimetry standards to 2.5%.

On 11 December 1991, a radiation overexposure occurred at an industrial radiation facility in Maryland. The radiation source was a 3-MV potential drop accelerator designed to produce high electron beam currents for materials-processing applications. This accelerator is capable of producing a 25 milliampere swept electron beam that is scanned over a width of 112.5 cm and which emerges from the accelerator vacuum system through a titanium double window assembly. During maintenance on the lower window pressure plate, an operator placed his hands, head, and feet in the beam. This was done with the filament voltage of the electron source turned "off," but with the full accelerating potential on the high voltage terminal. The operator's body, especially his extremities and head, were exposed to electron dark current. In an attempt to reconstruct the accident, radiochromic film and alanine measurements were made with the accelerator operated at two beam currents. Measured dose rates ranged from approximately 40 cGy s-1 inside the victim's shoe to 1,300 cGy s-1 at the hand position. Approximately 3 mo after the accident, it was necessary to amputate the four digits of the victim's right hand and most of the four digits of his left hand. Electron paramagnetic resonance spectrometry, which measures the concentration of radiation-induced paramagnetic centers in calcified tissues, was used to estimate the dose to the victim's extremities. A mean dose estimate of 55.0 +/- 3.5 Gy (95% confidence level) averaged over the mass of the bone was obtained for the victim's left middle finger (middle phalanx).

A new dosimetry system based on the EPR response of polyvinyl alcohol is presented. The dose response was measured from 10–105 Gy and the persistence of the signal was monitored over a period of 14 days.