Calculation Of Conversion Coefficients Research Articles

Monte Carlo calculation of conversion coefficients for dose estimation in mammography based on a 3D detailed breast model.

At present, the Chinese specification for testing of quality control in x-ray mammography is based on a simple breast model, and does not consider the glandular tissue distribution in the breast. In order to more precisely estimate the mean glandular dose (MGD) in mammography for Chinese women, a three-dimensional (3D) detailed breast model based on realistic structures in the breast and Chinese female breast parameters was built and applied in this study. To characterize the Chinese female breast, Chinese female breast parameters including breast size, compressed breast thickness (CBT), and glandular content were investigated in this study. A mathematical model with the detailed breast structures was constructed based on the Chinese female breast parameters. The mathematical model was then converted to a voxel model with voxels. The voxel model was compressed in craniocaudal (CC) view to obtain a deformation model. The compressed breast model was combined with the Chinese reference adult female whole-body voxel phantom (CRAF) to study the effects of backscatter from the female body. Monte Carlo simulations of the glandular dose in mammography were performed with Geant 4. The glandular tissue dose conversion coefficients for breasts with different glandular contents (5%, 25%, 50%, 75%, and 100% glandularity) and CBTs (3cm, 4cm, 5cm, and 6cm) were calculated, respectively, at various x-ray tube voltages (25 kV, 28 kV, 30 kV, 32 kV, and 35 kV) for various target/filter combinations (Mo/Mo, Mo/Rh, Rh/Rh, and W/Rh). A series of glandular tissue dose conversion coefficients for dose estimation in mammography were calculated. The conversion coefficients calculated in this study were compared with those estimated with the simple breast model. A discrepancy of 5.4-38.0% was observed. This was consistent with the results obtained from the realistic breast models in the literature. A 3D detailed breast model with realistic structures in the breast was constructed based on the Chinese female breast parameters. It was used to calculate glandular tissue dose conversion coefficients for mammography. Although the accuracy of the proposed model could not be directly assessed, the consistency of the obtained results with previously performed analyses increases the confidence in the applicability of the proposed model. The proposed model could be used in dose estimation and dose optimization for mammography of Chinese women.

Calculation of conversion coefficients using Chinese adult reference phantoms for air submersion and ground contamination

The effective and organ equivalent dose coefficients have been widely used to provide assessment of doses received by adult members of the public and by workers exposed to environmental radiation from nuclear facilities under normal or accidental situations. Advancements in phantom types, weighting factors, decay data, etc, have led to the publication of newer results in this regard. This paper presents a new set of conversion coefficients for air submersion and ground contamination (with the use of Geant4) for photons from 15 keV to 10 MeV using the Chinese and International Commission on Radiological Protection (ICRP) adult reference male and female phantoms. The radiation fields, except for energy spectrum at low energies, were validated by the data obtained from the Monte Carlo code YURI. The effective dose coefficients of monoenergetic photons, obtained for the ICRP adult reference phantoms, agree well with recently published data for air submersion and ground contamination with a plane source at a depth of 0.5 g cm−2 in soil, but an average difference of 36.5% is observed for ground surface contamination with the abovementioned radiation field. The average differences in organ equivalent dose coefficients between the Chinese and the ICRP adult reference phantoms are within 6% for most organs, but noticeable differences of up to 70% or even higher are found at photon energies below 30 keV under air submersion. The effective dose coefficients obtained with the Chinese adult reference phantoms are greater than those of the ICRP adult reference phantoms above 30 keV and 0.5 MeV for ground contamination and air submersion, respectively; the average differences from the Chinese adult reference phantoms are about 3.6% and 0.4% in the whole energy range with maximum differences of 31.8% and 27.6% at 15 keV for air submersion and ground contamination respectively. These differences are attributed to anatomical discrepancies in overlying tissue mass of an individual organ and the body mass between the Chinese and the ICRP adult reference phantoms. These monoenergetic photon conversion coefficients are subsequently used to evaluate radionuclides with decay data from ICRP publication 107.

Conversion Coefficients for Proton Beams using Standing and Sitting Male Hybrid Computational Phantom Calculated in Idealized Irradiation Geometries.

The aim of this study was the calculation of conversion coefficients for absorbed doses per fluence (DT/Φ) using the sitting and standing male hybrid phantom (UFH/NCI) exposure to monoenergetic protons with energy ranging from 2 MeV to 10 GeV. Sex-averaged effective dose per fluence (E/Φ) using the results of DT/Φ for the male and female hybrid phantom in standing and sitting postures were also calculated. Results of E/Φ of UFH/NCI standing phantom were also compared with tabulated effective dose conversion coefficients provided in ICRP publication 116. To develop an exposure scenario implementing the male UFH/NCI phantom in sitting and standing postures was used the radiation transport code MCNPX. Whole-body irradiations were performed using the recommended irradiation geometries by ICRP publication 116 antero-posterior (AP), postero-anterior (PA), right and left lateral, rotational (ROT) and isotropic (ISO). In most organs, the conversion coefficients DT/Φ were similar for both postures. However, relative differences were significant for organs located in the lower abdominal region, such as prostate, testes and urinary bladder, especially in the AP geometry. Results of effective dose conversion coefficients were 18% higher in the standing posture of the UFH/NCI phantom, especially below 100 MeV in AP and PA. In lateral geometry, the conversion coefficients values below 20 MeV were 16% higher in the sitting posture. In ROT geometry, the differences were below 10%, for almost all energies. In ISO geometry, the differences in E/Φ were negligible. The results of E/Φ of UFH/NCI phantom were in general below the results of the conversion coefficients provided in ICRP publication 116.

Organ and effective dose conversion coefficients for a sitting female hybrid computational phantom exposed to monoenergetic protons in idealized irradiation geometries

The conversion coefficients (CCs) relate protection quantities, mean absorbed dose (DT) and effective dose (E), with physical radiation field quantities, such as fluence (Φ). The calculation of CCs through Monte Carlo simulations is useful for estimating the dose in individuals exposed to radiation. The aim of this work was the calculation of conversion coefficients for absorbed and effective doses per fluence (DT/ Φ and E/Φ) using a sitting and standing female hybrid phantom (UFH/NCI) exposure to monoenergetic protons with energy ranging from 2 MeV to 10 GeV. The radiation transport code MCNPX was used to develop exposure scenarios implementing the female UFH/NCI phantom in sitting and standing postures. Whole-body irradiations were performed using the recommended irradiation geometries by ICRP publication 116 (AP, PA, RLAT, LLAT, ROT and ISO). In most organs, the conversion coefficients DT/Φ were similar for both postures. However, relative differences were significant for organs located in the abdominal region, such as ovaries, uterus and urinary bladder, especially in the AP, RLAT and LLAT geometries. Anatomical differences caused by changing the posture of the female UFH/NCI phantom led an attenuation of incident protons with energies below 150 MeV by the thigh of the phantom in the sitting posture, for the front-to-back irradiation, and by the arms and hands of the phantom in the standing posture, for the lateral irradiation.

Comparison of conversion coefficients for equivalent dose in terms of air kerma using a sitting and standing female adult voxel simulators exposure to photons in antero-posterior irradiation geometry

Due to the difficulty in implementing invasive techniques for calculations of dose for some exposure scenarios, computational simulators have been created to represent as realistically as possible the structures of the human body and through radiation transport simulations to obtain conversion coefficients (CCs) to estimate dose. In most published papers simulators are implemented in the standing posture and this may not describe a real scenario of exposure. In this work we developed exposure scenarios in the Visual Monte Carlo (VMC) code using a female simulator in standing and sitting postures. The simulator was irradiated in the antero-posterior (AP) geometry by a plane source of monoenergetic photons with energy from 10keV to 2MeV. The conversion coefficients for equivalent dose in terms of air kerma (HT/Kair) were calculated for both scenarios and compared. The results show that the percentage difference of CCs for the organs of the head and thorax was not significant (less than 5%) since the anatomic position of the organs is the same in both postures. The percentage difference is more significant to the ovaries (71% for photon energy of 20keV), to the bladder (39% at 60keV) and to the uterus (37% at 100keV) due to different processes of radiation interactions in the legs of the simulator when its posture is changed. For organs and tissues that are distributed throughout the entire body, such as bone (21% at 100keV) and muscle (30% at 80keV) the percentage difference of CCs reflects a reduction of interaction of photons with the legs of the simulator. Therefore, the calculation of conversion coefficients using simulators in the sitting posture is relevant for a more accurate dose estimation in real exposures to radiation.

Calculation of conversion coefficients for air kerma to ambient dose equivalent using transmittedspectra of megavoltage X-rays through concrete

With the fast advancement of technology, (60)Co teletherapy units are largely being replaced with medical linear accelerators. In most cases, the linear accelerator tends to be installed in the same room in which the (60)Co teletherapy unit was previously placed. If in-depth structural remodelling is out of the question, high-density concrete is usually used to improve shielding against primary, scatter and leakage radiation originating in the new equipment. This work presents a study based on Monte Carlo simulations of the transmission of some clinical photon spectra (from 6, 10, 15, 18 and 25 MV accelerators) through concrete, considering two different densities. Concrete walls with thickness ranging from 0.70 to 2.0 m were irradiated with 30 cm×30 cm primary beam spectra. The results show that the thickness of the barrier decreases up to ∼65 % when barite (high-density concrete) is used instead of ordinary concrete. The average energies of primary and transmitted beam spectra were also calculated. In addition, conversion coefficients from air kerma to ambient dose equivalent, H*(d)/K(air), and air kerma to effective dose, E/K(air), for photon spectra from the transmitted spectra were calculated and compared. The results suggest that the 10-mm depth is not the best choice to represent the effective dose.

Neutron dosimetry in organs of an adult human phantom using linacs with multileaf collimator in radiotherapy treatments

To calculate absorbed doses due to neutrons in 87 organs/tissues for anthropomorphic phantoms, irradiated in position supine (head first into the gantry) with orientations anteroposterior (AP) and right-left (RLAT) with a 18 MV accelerator. Conversion factors from monitor units to μGy per neutron in organs, equivalent doses in organs/tissues, and effective doses, which permit to quantify stochastic risks, are estimated. MAX06 and FAX06 phantoms were modeled with MCNPX and irradiated with a 18 MV Varian Clinac 2100C/D accelerator whose geometry included a multileaf collimator. Two actual fields of a pelvic treatment were simulated using electron-photon-neutron coupled transport. Absorbed doses due to neutrons were estimated from kerma. Equivalent doses were estimated using the radiation weighting factor corresponding to an average incident neutron energy 0.47 MeV. Statistical uncertainties associated to absorbed doses, as calculated by MCNPX, were also obtained. Largest doses were absorbed in shallowest (with respect to the neutron pathway) organs. In μGyMU(-1), values of 2.66 (for penis) and 2.33 (for testes) were found in MAX06, and 1.68 (for breasts), 1.05 (for lenses of eyes), and 0.94 (for sublingual salivary glands) in FAX06, in AP orientation. In RLAT, the largest doses were found for bone tissues (leg) just at the entrance of the beam in the body (right side in our case). Values, in μGyMU(-1), of 1.09 in upper leg bone right spongiosa, for MAX06, and 0.63 in mandible spongiosa, for FAX06, were found. Except for gonads, liver, and stomach wall, equivalent doses found for FAX06 were, in both orientations, higher than for MAX06. Equivalent doses in AP are higher than in RLAT for all organs/tissues other than brain and liver. Effective doses of 12.6 and 4.1 μSvMU(-1) were found for AP and RLAT, respectively. The organs/tissues with larger relative contributions to the effective dose were testes and breasts, in AP, and breasts and red marrow, in RLAT. Equivalent and effective doses obtained for MAX06/FAX06 were smaller (between 2 and 20 times) than those quoted for the mathematical phantoms ADAM/EVA in ICRP-74. The new calculations of conversion coefficients for neutron irradiation in AP and RLAT irradiation geometries show a reduction in the values of effective dose by factors 7 (AP) and 6 (RLAT) with respect to the old data obtained with mathematical phantoms. The existence of tissues or anatomical regions with maximum absorbed doses, such as penis, lens of eyes, fascia (part of connective tissue), etc., organs/tissues that classic mathematical phantoms did not include because they were not considered for the study of stochastic effects, has been revealed. Absorbed doses due to photons, obtained following the same simulation methodology, are larger than those due to neutrons, reaching values 100 times larger as the primary beam is approached. However, for organs far from the treated volume, absorbed photon doses can be up to three times smaller than neutron ones. Calculations using voxel phantoms permitted to know the organ dose conversion coefficients per MU due to secondary neutrons in the complete anatomy of a patient.

Zur Strahlenexposition von Kindern in der pädiatrischen Radiologie

Calculation of conversion coefficients for the reconstruction of organ doses from entrance doses for thoracoabdominal babygrams of premature neonates with a gestational age of 23 and 27 weeks and of mature neonates. Using the commercially available personal computer program PCXMC developed by the Finnish Centre for Radiation and Nuclear Safety (Säteilyturvakeskus STUK), conversion coefficients for conventional thoracoabdominal babygrams were calculated with Monte Carlo simulations in mathematical hermaphrodite phantom models describing patients of different ages. Conversion coefficients for the reconstruction of organ doses in approximately 40 organs and tissues of the human body from measured entrance doses during thoracoabdominal babygrams were calculated for the standard sagittal beam projections and the standard focus film distance of 100 cm. The conversion coefficients presented in this paper may be used for organ dose assessments from entrance doses measured during thoracoabdominal babygrams especially in patients in special care baby units.

Nuclear Data Sheets for A = 103

The 2001 evaluation on mass A = 103 (2001De37) has been revised, taking into account all data available before March 2009. Experimental information is presented from the neutron rich nucleus 103Sr to the neutron deficient 103Sn nucleus. The experimental information on excited states for 103Sr and 103y is very scarce New (HI, xnγ) data sets for several nuclides have been evaluated and new and more accurate data for γ intensities and multipolarities obtained. The BRICC code has been used for the calculation of conversion coefficients.

Zur Strahlenexposition von Kindern in der pädiatrischen Radiologie - Teil 6: Konversionsfaktoren zur Rekonstruktion von Organdosen bei Abdomenaufnahmen

PURPOSE Calculation of conversion coefficients for the reconstruction of organ doses from entrance doses for abdomen radiographs of 0, 1, 5, 10, 15, and 30-year-old patients in conventional pediatric radiology for the radiographic settings recommended by the German and European guidelines for quality management in diagnostic radiology. MATERIALS UND METHOD: Using the commercially available personal computer program PCXMC developed by the Finnish Center for Radiation and Nuclear Safety (Sateilyturvakeskus STUK), conversion coefficients for conventional abdomen radiographs were calculated performing Monte Carlo simulations in mathematical hermaphrodite phantom models describing patients of different ages. The possible clinical variation of beam collimation was taken into consideration by defining optimal and suboptimal radiation fields on the phantoms' surfaces. RESULTS Conversion coefficients for the reconstruction of organ doses in about 40 organs and tissues of the human body from measured entrance doses during abdomen radiographs for 0, 1, 5, 10, 15, and 30-year-old pediatric patients were calculated for the standard sagittal and lateral beam projections and the standard focus film distances of 100 cm and 115 cm. CONCLUSION The conversion coefficients presented in this paper may be used for organ dose assessments from entrance doses measured during abdomen radiographs of patients of all age groups and all beam collimations within the optimal and suboptimal standard beam collimations.

Zur Strahlenexposition von Kindern in der pädiatrischen Radiologie

Calculation of conversion coefficients for the reconstruction of organ doses from entrance doses for abdomen radiographs of 0, 1, 5, 10, 15, and 30-year-old patients in conventional pediatric radiology for the radiographic settings recommended by the German and European guidelines for quality management in diagnostic radiology. MATERIALS UND METHOD: Using the commercially available personal computer program PCXMC developed by the Finnish Center for Radiation and Nuclear Safety (Säteilyturvakeskus STUK), conversion coefficients for conventional abdomen radiographs were calculated performing Monte Carlo simulations in mathematical hermaphrodite phantom models describing patients of different ages. The possible clinical variation of beam collimation was taken into consideration by defining optimal and suboptimal radiation fields on the phantoms' surfaces.Conversion coefficients for the reconstruction of organ doses in about 40 organs and tissues of the human body from measured entrance doses during abdomen radiographs for 0, 1, 5, 10, 15, and 30-year-old pediatric patients were calculated for the standard sagittal and lateral beam projections and the standard focus film distances of 100 cm and 115 cm.The conversion coefficients presented in this paper may be used for organ dose assessments from entrance doses measured during abdomen radiographs of patients of all age groups and all beam collimations within the optimal and suboptimal standard beam collimations.

Zur Strahlenexposition von Kindern in der pädiatrischen Radiologie

Calculation of conversion coefficients for the reconstruction of organ doses from entrance doses for chest radiographs of 0, 1, 5, 10, 15, and 30-year-old patients in conventional pediatric radiology for the radiographic settings recommended by the German and European guidelines for quality management in diagnostic radiology. The conversion coefficients for pediatric chest radiographs were calculated using the commercially available personal computer program PCXMC developed by the Finnish Centre for Radiation and Nuclear Safety (Säteilyturvakeskus STUK). PCXMC is a Monte Carlo program for computing organ and effective doses in about 40 organs of mathematical hermaphrodite phantom models describing patients of different ages. The possible clinical variation of beam collimation was taken into consideration by defining optimal and suboptimal radiation fields on the phantoms' surfaces. Conversion coefficients for the reconstruction of organ doses from measured entrance doses during chest radiographs for 0, 1, 5, 10, 15, and 30-year-old pediatric patients were presented. Conversion coefficients were calculated for the standard sagittal and lateral beam projections and the standard focus film distances of 100 cm, 115 cm, and 150 cm using the standard radiation qualities according to the recommendations of the German and European guidelines for quality management in diagnostic radiology. These conversion coefficients allow the reconstruction of the absorbed dose in about 40 organs and tissues of the human body for optimal and suboptimal radiation field collimations. The conversion coefficients presented in this paper may be used for organ dose assessments from entrance doses measured during chest radiographs of patients of all age groups with all beam collimations within optimal and suboptimal standard beam collimations. While the influence of the beam collimation on organ doses of organs localized near the center of the beam is expectedly low, the radiation exposure of organs and tissues near the boundaries of the radiation field can be considerably reduced by an optimal beam collimation. The conversion coefficients calculated for the STUK phantoms are in good conformity with values published for the GSF phantoms "Adam", "Golem" and "Visible Human".

Evaluation of the fluence to dose conversion coefficients for high energy neutrons using a voxel phantom coupled with the GEANT4 code

Crews working on present-day jet aircraft are a large occupationally exposed group with a relatively high average effective dose from galactic cosmic radiation. Crews of future high-speed commercial flying at higher altitudes would be even more exposed. To help reduce the significant uncertainties in calculations of such exposures, the male adult voxels phantom MAX, developed in the Nuclear Energy Department of Pernambuco Federal University in Brazil, has been coupled with the Monte Carlo simulation code GEANT4. This toolkit, distributed and upgraded from the international scientific community of CERN/Switzerland, simulates thermal to ultrahigh energy neutrons transport and interactions in the matter. The high energy neutrons are pointed as the component that contribute about 70% of the neutron effective dose that represent the 35% to 60% total dose at aircraft altitude. In this research calculations of conversion coefficients from fluence to effective dose are performed for neutrons of energies from 100 MeV up to 1 GeV, irradiating MAX with mono-energetic beams in the mode Anterior-Posterior. An alternative methodology is developed too, using the atmospheric neutrons spectrum simulated with GEANT4 code at aircraft altitude instead of the traditional method that uses mono-energetic beams. To obtain the neutrons spectrum 1.5×105 extensive atmospheric showers are simulated by cosmic rays interactions with atmospherics atoms. The main characteristics of the spectrum are in agreement with literature confirming the validity of GEANT4. For 100 MeV energy the conversion coefficient calculated with spectrum shows a decrease of 8%, pointing out the importance of the environment influence.

Effective doses in angiography and interventional radiology: calculation of conversion coefficients for angiography of the lower limbs

The present study reports on investigations that we have performed to allow the calculation of effective doses (E) in interventional radiology. The use of published conversion tables might not allow sufficient guidance for the establishment of optimization strategies for procedures in interventional radiology. With the Monte Carlo N-Particle transport code (MCNP4B), conversion coefficients, linking dose-area product (DAP) measurements with E, are calculated for angiography of the lower limbs in six hospitals. The influence of various parameters on the calculation of these conversion coefficients is studied in a systematic way using the 2(n) factorial design. In this design the effect of different parameters and their pair-wise interactions on a certain variable is explored. In our study, the relevant parameters are tube potential, total filtration and field size and position. We concluded that the influence of radiation spectrum (kVp + filtration) is large and that the effect of field position and size is moderate, except when differences are observed in respect of the gonads. In that case, the variation in conversion coefficients is large. The results of this statistical analysis are then applied to the differences observed between the conversion coefficients, calculated for angiography of the lower limbs in the six hospitals. Recommendations for optimization of patient doses are given.

Calculation of conversion coefficients for clinical photon spectra using the MCNP code.

In this work, the MCNP4B code has been employed to calculate conversion coefficients from air kerma to the ambient dose equivalent, H*(10)/Ka, for monoenergetic photon energies from 10 keV to 50 MeV, assuming the kerma approximation. Also estimated are the H*(10)/Ka for photon beams produced by linear accelerators, such as Clinac-4 and Clinac-2500, after transmission through primary barriers of radiotherapy treatment rooms. The results for the conversion coefficients for monoenergetic photon energies, with statistical uncertainty <2%, are compared with those in ICRP publication 74 and good agreements were obtained. The conversion coefficients calculated for real clinic spectra transmitted through walls of concrete of 1, 1.5 and 2 m thick, are in the range of 1.06-1.12 Sv Gy(-1).

Computation of conversion coefficients relating air Kerma to Hp(0.07,α), Hp(10,α), and H*(10) for x-ray narrow spectrum from 40 to 140 kV

A computation method was implemented to predict the conversion coefficients and the angular dependence factors relating air Kerma to Hp(0.07,alpha), Hp(10,alpha), and H*(10) in an ICRU slab phantom for tungsten anode x-ray spectra for tube potentials from 40 to 140 kV. The simulation of the unfiltered x-ray spectra is based on the Boone and Seibert model. The calculation of conversion coefficients were performed for an x-ray narrow spectrum at any filtration material and tube potentials in the diagnostic radiology range. This computation method has been checked for five narrow x-ray spectra using a comparison of the results with published data given by the International Organization for Standardization (ISO), and American National Standards Institute (ANSI). In all cases, the mean deviation of the calculated mean conversion coefficients values do not exceed 1% for Hp (0.07,alpha) and 1.5% for Hp (10,alpha), except at 60 degrees where a mean deviation from the ISO values of 1.72% and of 2.27% was, respectively, found. But it is still lower than the mean deviation of 2.31% for Hp(0.07,alpha), and of 3.08% for Hp(10,alpha) observed at this angle between ISO and ANSI values. Otherwise, the computed values of conversion coefficients of H*(10) differ by only 0.41% from the ISO values. The results of this computation method can be considered satisfactory considering the accuracy required in radioprotection fields, and can allow an appreciable estimation of conversion coefficients for the narrow x-ray spectra indispensable to calibrate the personnel dosimeters in terms of the personal dose equivalent.

Fluence to Dose Equivalent Conversion Data and Radiation Weighting Factors for High Energy Radiation

Calculations of conversion coefficients from fluence to ambient dose equivalent and from fluence to maximum dose equivalent, along the principal axis of the ICRU sphere, have been performed for protons, muons and pions of energies up to 10 TeV. All of the results were obtained using the Monte Carlo transport code FLUKA. The values of the effective quality factors at 10 mm depth and at the depth at which the maximum occurs have been derived. The calculated results have been compared with the data sets of ICRP Publication 51. The application of the ICRP's recommended approximation to radiation weighting factors when they are not explicitly given (ICRP Publication 60, Section A.8., Paragraph (A14)), and of the recommended depth for measuring the ambient dose equivalent (ICRU Report 51, Paragraph I.4.3.1.1), have been analysed in the high energy region. The values of the radiation weighting factors for positive and negative pions have been determined as a function of incident pion energy. Three main conclusions can be achieved: (1) compared with the value of effective quality factor at 10 mm depth in the ICRU sphere, the value of 5, recommended for the radiation weighting factor of protons, appears overestimated by a factor of between 2.5 and 4.5 depending on proton energy; (2) for all kinds of radiation investigated, the ambient dose equivalent, H*(10), gives a conservative estimate of the effective dose only in a limited low energy range; (3) as far as ambient dose equivalent is concerned, there is no depth d of the ICRU sphere that is appropriate for area monitoring at very high energies.

Fluence to Dose Equivalent Conversion Data and Effective Quality Factors for High Energy Neutrons

Calculations of conversion coefficients from fluence to ambient dose equivalent and from fluence to maximum dose equivalent, along the principal axis of the ICRU sphere, have been performed for neutron energies up to 10 TeV, using the Monte Carlo transport code FLUKA. The results obtained are compared with those of other authors. An attempt is made to analyse the values of the radiation weighting factors recommended in ICRP Publication 60 in relation to several effective quality factors. Three main conclusions can be reached: the ambient dose equivalent, H * (10), gives a conservative estimate of the effective dose in a limited neutron energy range; a single value of depth, d, which would make H * (d) an appropriate operational quantity irrespective of incident neutron energy cannot be specified; the value of 5, recommended for the radiation weighting factor of high energy neutrons, is expected to lead to an overestimate up to a factor 3 of the risks of exposure to the higher neutron energies.

The decay of 73As

The relative intensities of the gamma and X rays of 73As have been measured with a Si(Li) spectrometer and the information used for the calculation of conversion coefficients. These are compared with theoretical values.Sufficiently precise gamma energy measurements have been made to remove an ambiguity in the ordering of two close energy levels.

A test of M subshell conversion coefficients at threshold energies

The M subshell rations of the 2.23 keV E3 transition in 99 Tc m have been measured to test new calculations of conversion coefficients at threshold. The experimental and theoretical values agree.