Alpha Contamination Research Articles

Characteristics of a Foil-Type Electret Dosimeter for a Surface Alpha Contamination Monitor

To develop a convenient and simple low-level alpha contamination monitoring method for large quantities of radioactive wastes, a foil-type electret dosimeter was examined. For the electret material, fluoride polymer was used, and the polymer foils weer charged and polarized by applying a high voltage in air while heating at approx. =150/sup 0/C. The surface charge density of the electret foil before and after irradiation was measured by converting to a piezoelectret signal through use of a polyvinylidene fluoride. In the experiments, using a 2.5 kV/mm electric field in electret foils, an electron avalanche effect was produced, and surface charge decay was multiplied. The maximum multiplication factor obtained was approx. =200. The detection limit of alpha surface contamination was confirmed as 10/sup -6/ ..mu..Ci/cm/sup 2/ (3.7x10/sup 2/ Bq/m/sup 2/) for a 5-h irradiation time.

A Contribution to Optimizing Radiological Protection in a U Mine

This article presents an optimization study for radiological protection in a U mine. The mathematical model of the alpha contamination associated with short-lived Rn daughters allows the comparison of various protection strategies through a cost-effectiveness analysis. Determining the optimal protection strategy is carried out by choosing a value for the mansievert. This procedure may be of use as a decision-aiding tool within the framework of radiological protection.

Radiocarbon Dating of Millimole-Sized Gaseous Samples

As an alternative to the accelerator technique, a simple, compact, small counter system has been developed and tested for routine 14C dating. Our small counter is an all-metal design made of the OFHC copper with quartz supports for the anode (25μm stainless steel). Careful selection of materials for the counter construction was made based on the measurements of the alpha contamination. Methane as the counter filling gave better resolution and gas gain stability, whereas CO2 gave lower background counting rate and it was easier to prepare and to handle. The long term run using CH4 showed that the gas gain remained stable within 1–2% for months after the initial drop which followed the counter filling. A 7-day counting period was sufficient to achieve a 3% relative standard deviation which was considered acceptable for routine dating of younger samples.

Remote micro-encapsulation of curium-gold cermets

A technique has been developed to produce miniature, high-density capsules of curium-244 oxide contained in three concentric jackets of metallic gold or silver. The final capsules are right circular cylinders, 6.350 mm diameter by (3.18±0.05) mm long, with a minimum density of 11.0 g/cm 3. Each level of containment was soldered or brazed closed, with the outer surface free of detectable alpha contamination. Fabrication was performed in three separate small cells operated by standard master-slave manipulators. Production capsules have been stored for up to five years without indication of dimensional growth or leakage of radioactive contents. The dimensional stability of the capsules is attributed to the microporous structure of the plated-gold structure which permits helium gas resulting from alpha decay to diffuse through the capsule wall while retaining all radioactive materials.

The use of 237Np in personal dosimeters for fast neutrons.

As the radiator for a damage-track, fast neutron dosimeter, 237Np has advantages over 232Th, the most important being its lower energy threshold. It has not been used in personal dosimeters because of possible hazards from alpha contamination and gamma dose to the wearer. This paper describes the manufacture and properties of two types of Np radiators (as an alloy with Al and a sintered mixture with Au) for which the removable surface activity is less than about 2 dis/min/cm2 foil. Expressions are given for the neutron detection efficiency of detectors having radiators of pure or diluted fissionable material, with or without a protective coating. These show that adequate containment of the activity need not reduce the efficiency of a given amount of Np by more than 50%. A Np-alloy radiator (0.6 mg of Np) producing 270 tracks per rad of fission-spectrum neutrons gives a dose equivalent of 34 mrem in 2000 hr at 5 cm. Circumstances in which thermal neutrons or high energy gamma radiation may interfere with fast neutron measurements are discussed.

Alpha Contamination of the Skin

Recently it has been reported that the thickness of the epidermal layer of skin can be as low as 2–4 mg/cm2 in certain parts of the body (HARVEY, 1971; WHITTON, 1971; WHITTON, 1973). In these areas, alpha contamination could result in the irradiation of basal layer cells. In order to evaluate the associated hazard, the energy distribution and dose of alpha particles from 210Po and 242Cm have been measured at various depths. By computing the LET distribution, the Quality Factor (QF) for alpha irradiation of basal cells has been calculated to be 20. If an average epidermal thickness of 4 mg/cm2 is accepted for radiation protection purposes (WHITTON, 1973), contamination by alpha particles of energy 5.7 MeV and above can result in the irradiation of basal layer cells. For the current permissible skin contamination value of 10−5microCi/cm2, the dose rate at this depth from 242Cm (6.11 MeV) is about 45 mrem/hr. Thus the dose to the skin becomes the limiting factor for arriving at the permissible skin contamination. Hence, it is desirable to lower the contamination level for energetic alpha particles.

Low-level detector for alpha contamination monitor in continuosly flowing process waste water

A low-level alpha detector was designed and developed for monitoring waste water continuously flowing from radiochemical processing plants and other facilities to determine whether these discharges contain alpha contamination. This detector enables constant and automatic monitoring, with actuation of an alarm signal immediately on detection of alpha contamination. The alpha particles are detected by a 6″ diam. zinc sulfide scintillator, and the light flashes from the scintillator are detected by a 2 diam. photomultiplier tube. The alpha sensitivity of the detector is ≈ 1 × 10 −9 Ci/ml of 238U. Ten units have been fabricated and placed in service at Oak Ridge National Laboratory.

Manufacture of clad fissionable foils for ZPR measurements

Clad fissionable foils are required to make reaction rate measurements for heterogeneous fast reactors. The foils are described, and the production procedures for fuel alloying, casting, rolling, assembling, and pressure welding are detailed. Fuel weight and weight uncertainty results are shown for the various foil types produced. Both weighing and analytical errors are discussed, and calculated results show their influence on fuel weight uncertainty. Foil rolling and alpha contamination problems in production are discussed and corrective steps described.

Health physics aspects of fast breeder reactors.

General health physics aspects of breeder reactors will for the most part be similar to those associated with other power reactors. The specific aspects which may differ can be conveniently grouped according to segments of reactor operations. During handling of unirradiated lutonium bearing fuel, additional health physics requirements will be involved due to neutron and gamma radiation levels and due to potential problems from surface contamination. uring reactor operation, occasional cladding failures may result in plutonium contamination in the primary coolant, although the hazard associated with this type of contamination ill probably never outweigh that of fission products. In handling of irradiated elements in the fuel replacement cycle, there is the possibility, after extended periods, for the buildup of low-level alpha contamination in the facility. Under certain hypothetical accident conditions where fuel vaporization could occur, plutonium could be the dominant hazard. Since at least the first commercial breeder reactors will almost certainly be liquid metal (Na) cooled, certain safety aspects of this material must be considered.

Alpha Monitor for Rapid Contamination Screening of Hands and Shoes

Alpha contamination on the hands and shoes of personnel can be quickly detected with large-area air proportional counters modified to overcome sensitivity to microphonics and humidity. The monitor requires practically no servicing and is easily decontaminated.

Isothermal Drop Calorimeter for Alpha Active, Pyrophoric Materials

A copper block drop calorimeter to measure the heat content of intensely alpha active materials has been constructed. The furnace, calorimeter, and aluminum isothermal jacket are contained within an inert atmosphere glovebox. This permits the use of unencapsulated materials without exposing personnel to an alpha contamination hazard. The inert atmosphere also permits measurements to be made on materials which are pyrophoric in air. The apparatus is equipped with a suppressed range recorder to monitor continuously the resistance thermometer signal with a resolution of ±0.4 cal/μV. Electrical calibration of the calorimeter yielded a precision of ±0.08% in the thermometer and recording system. The heat content of a sample of Calorimetry Conference sapphire obtained from the National Bureau of Standards was measured, and the results deviated from the Bureau's reported data a maximum of 1.0% at 1008°K. The useful range of the apparatus extends from 306 to about 1450°K.

Very Large Boron Trifluoride Proportional Counters

More than 50 very large BF3 counters, each approximately 6 ft (180 cm) long and 6 in. (15 cm) in diameter have been made for cosmic-ray monitors. During the fabrication of these counters, the characteristics at varying gas pressures have been studied and the alpha backgrounds of the various metals used for cathodes have been determined. The counters have excellent characteristics at pressures up to 30 cm Hg and perfectly acceptable characteristics to 60 cm Hg pressure. With anode diameter 0.008 in. (0.2 mm) and gas amplification 35, the operating voltage for a filling of 20 cm Hg pressure of pure BF3 is 2800 V; at 30 cm Hg it is 3400 V. Counters with copper cathodes have backgrounds due to residual alpha contamination of about 2 counts/min, and with stainless steel cathodes, about 5 counts/min. Using a BF3–Ar filling a value of 6.30±0.05% has been obtained for the branching ratio of the B10(n,α)Li7 reaction.

Industrial hygiene techniques in the decontamination of a building contaminated with radium.

Abstract Radium contamination had built up in a large office building over a period of forty years. The radiation levels were as high as 500 mrem/hr with alpha contamination >40,000 d/m/100 cm2. From an industrial hygiene point of view, the major problems associated with the decontamination of the facility were: (1) keeping from tracking contamination into clean areas, (2) keeping the workers from becoming contaminated, (3) keeping the workers' exposure to external ionizing radiation as low as possible, (4) keeping inhalation and/or ingestion of radium from occurring, and (5) keeping future inhabitants of the building from receiving any radiation exposure as a result of their working in the building. The building was decontaminated to a maximum of 0.2 mr/hr at a distance of one foot from any surface and the radon plus its daughter's activity was reduced to levels of less than 10−9 μc/ce.