CORRECTION FACTORS FOR ATTENUATION AND SCATTERING OF THE WALL OF A CYLINDRICAL IONIZATION CHAMBER IN THE 6-7 MeV HIGH-ENERGY PHOTON REFERENCE FIELD.

In high-energy photon reference fields the value of the air kerma rate is determined by using ionization chambers (ICs). From the charge collected inside the IC the dose can be calculated using a set of calibration and correction factors according to ISO 4037-2. A crucial parameter is the correction for the attenuation and scattering of the primary radiation due to the chamber wall. This parameter can be determined using Monte Carlo calculations. The evaluation of the factor was performed for a commercially available IC of the type Victoreen 550-3 under different build-up conditions. The results were verified by measurements in the R-F high-energy photon fields according to ISO 4037-1 at the Physikalisch-Technische Bundesanstalt (PTB) and the Japan Atomic Energy Agency (JAEA).

Comparison of the High-Energy Photon Reference Fields of PTB and JAEA.

A comparison has been conducted between the 6 MeV and 7 MeV (R-F) high-energy photon reference fields of the Physikalisch-Technische Bundesanstalt (PTB) and the Japan Atomic Energy Agency (JAEA). Both fields are set up according to ISO 4037. The results of both participants are in agreement within the combined uncertainties, thus the equivalence of the measurements is demonstrated.

DOSE MEASUREMENTS IN THE STRAY FIELD OF A GE OPTIMA CT660.

Statistics show how important computed tomography (CT) dosimetry has become. In order to estimate the dose distribution in the CT scan room during an examination, measurements of the ambient dose equivalent H*(10) have been performed. The primary aim of this study is the radiation protection of the staff and not the determination of the dose to the patient or in the primary beam. Therefore, the dose outside the primary beam, i.e. in the scattered field of the Physikalisch-Technische Bundesanstalt's GE Optima CT660, is of importance. The results of the dose measurements are analysed in dependence on the settings of the X-ray tube voltage, the collimator width and (with and without) the bow-tie filter of the CT scanner. For the radiation protection measurements, ionisation chambers have been used. Additionally, the influence of the patient on the radiation field and, therefore, on the dose is simulated by using an Alderson body phantom.

Ambient dose and dose rate measurements in the vicinity of Elekta Precise accelerators for radiation therapy.

In radiation therapy, commercially available medical linear accelerators (LINACs) are used. At high primary beam energies in the 10-MeV range, the leakage dose of the accelerator head and the backscatter from the room walls, the air and the patient become more important. Therefore, radiation protection measurements of photon dose rates in the treatment room and in the maze are performed to quantify the radiation field. Since the radiation of the LINACs is usually pulsed with short radiation pulse durations in the microsecond range, there are problems with electronic dose (rate) meters commonly used in radiation protection. In this paper measurements with ionisation chambers are presented and electronic dosemeters are used for testing at selected positions. The measured time-averaged dose rate ranges from a few microsieverts per hour in the maze to some millisieverts per hour in the vicinity of the accelerator head and up to some sieverts per hour in the blanked primary beam and several hundred sieverts per hour in the direct primary beam.

Recent results of irradiations of DIS-1 dosemeters with an XR200 X-ray flash unit.

Earlier measurements have revealed that active electronic dosemeters have deficiencies in pulsed fields of ionising radiation due to the counting technique used. The DIS-1 dosemeter uses a promising technology, which should be basically suitable for measurements in pulsed fields. In this paper, first measurements with the DIS-1 dosemeter at an X-ray flash generator XR200 with pulse durations of ∼115 ns and doses per pulse of a few microsievert are shown.

Determination of relevant parameters for the use of electronic dosemeters in pulsed fields of ionising radiation.

Active electronic dosemeters using counting techniques are used for radioprotection purposes in pulsed radiation fields in X-ray diagnostics or therapy. The disadvantage of the limited maximum measurable dose rate becomes significant in these radiation fields and leads to some negative effects. In this study, a set of relevant parameters for a dosemeter is described, which can be used to decide whether it is applicable in a given radiation field or not. The determination of these relevant parameters-maximum measurable dose rate in the radiation pulse, dead time of the dosemeter, indication per counting event and measurement cycle time-is specified. The results of the first measurements on the determination of these parameters for an electronic personal dosemeter of the type Thermo Fisher Scientific EPD Mk2 are shown.

Adolescents and nuclear arms issues.

Concerned about adolescents' reactions to the ever present nuclear threat, we surveyed 10,720 high school students in New Jersey, U.S.A. Half felt anxious about an accidental war and expected a major nuclear blast. One-quarter expected a nuclear war involving the United States, and one-fifth expected to die in a nuclear blast. Most expected the United States to be destroyed if a major nuclear war occurred, did not believe that long term survival after the initial exchanges is possible, or that civil defense preparations can be effective. Responses were similar across economic background, time period and type of high school.