Measurement of alpha particle energy using windowless electret ion chambers.

Electret ion chambers are inexpensive, lightweight, robust, commercially available, passive, charge-integrating devices for accurate measurement of different ionizing radiations. In an earlier work a chamber of dimensions larger than the range of alpha particles having aluminized Mylar windows of different thickness was used for measurement of alpha radiation. Correlation between electret mid-point voltage, alpha particle energy, and response was developed and it was shown that this chamber could be used for estimating the effective energy of an unknown alpha source. In the present study, the electret ion chamber is used in the windowless mode so that the alpha particles dissipate their entire energy inside the volume, and the alpha particle energy is determined from the first principles. This requires that alpha disintegration rate be accurately known or measured by an alternate method. The measured energies were within 1 to 4% of the true values for different sources (230Th, 237Np, 239Pu, 241Am, and 224Cm). This method finds application in quantitative determination of alpha energy absorbed in thin membrane and, hence, the absorbed dose.

Electret ion chambers for estimating alpha particle energy.

Electret ion chambers (EICs) are inexpensive, lightweight, robust, commercially available, passive, charge-integrating devices for measuring different radiations. At Florida International University's Hemispheric Center for Environmental Technology (FIU-HCET), EIC performance was evaluated with the goal of providing the U.S. Department of Energy (DOE) with a low-cost, low-risk means of alpha contamination monitoring using an existing commercial technology. During this evaluation, sensitivity of electrets in 960-mL hemispherical ion chamber (radius: 7.6 cm) was observed to increase with alpha particle energy because alpha particles expended their entire energy in the chamber volume. This observation prompted us to explore another EIC application: estimation of alpha particle energy. Correlation between electret mid-point voltage, alpha particle energy, and response was developed for the 960-mL EIC and was used to determine energy of an unknown source. The response (change in voltage per disintegration) is the ratio of the change of voltage per unit time and alpha particle activity. Since an EIC measures only the change in voltage per minute, to determine the alpha particle energy, the source activity should be accurately determined by another method.

Measurement of surface alpha contamination using electret ion chambers.

Electret ion chambers are inexpensive, light-weight, commercially available, passive charge-integrating devices for accurate measurement of different radiations. Performance of electret ion chambers for surface alpha contamination measurement was evaluated. Ion chambers of two types and electrets of three thicknesses were used for the study. Calibration of the electret ion chambers was performed using reference alpha standards of different energies and radioactivities. Effects of various parameters such as chamber dimensions, electret thickness, alpha particle energy, position of alpha source from the chamber centerline, source localized or uniformly distributed, level of alpha contamination, Mylar window covering the chamber, and ambient radon and gamma radiation on the response of the electret ion chambers were determined. Suitable combinations of chambers and electrets to measure surface alpha contamination were determined.