Radiation exposure and disease questionnaires of early entrants after the Hiroshima bombing

It is popularly known that people who entered into the ground-zero area shortly after the atomic bombings in Hiroshima and Nagasaki suffered from various syndromes similar to acute radiation effects. External exposures from neutron-induced radionuclides in soil have recently been reassessed based on DS02 calculations as functions of both distance from the hypocentres and elapsed time after the explosions. Significant exposure due to induced radiation can be determined for those who entered the area within 1000 m from the hypocentres shortly after the bombing. Although it was impossible to track the action of each of the survivors over the days or weeks following the bombings in order to make reliable dose estimates for their exposures to soil activation or fallout, four individuals among those early entrants were investigated here to describe useful information of what happened shortly after the bombing.     

Options for the modified radiation weighting factor of neutrons

The recent ICRP Report 92 has noted that the current radiation weighting factor, wR, depends on the energy of the incident neutrons in a manner that differs substantially from the dependence, which results from the current convention, QL. At all neutron energies, but most conspicuously below 1 MeV, the values of wR exceed those of the effective quality factor, qE. The discrepancy is largely due to the fact that--in the absence of computed values of the effective quality factor for neutrons--wR has been patterned after the values of the ambient quality factor, which accounts insufficiently for the low-linear energy transfer (LET) gamma ray component from neutron capture in the human body. There are different options to remove the discrepancy. Option 1 is to reduce wR substantially at all neutron energies to make it equal to qE for a standard condition, such as isotropic incidence of the neutrons. Since such a reduction may cause problems in those countries where the current wR values are already legally implemented, ICRP 92 has proposed what is here termed Option 2. It recommended to replace QL by the increased value 1.6 QL - 0.6 and, accordingly, to make the radiation weighting factor equal to 1.6 qE - 0.6. With Option 2 the radiation weighting factor needs to be decreased appreciably at low neutron energies, but for fission neutron spectra the overall changes are minor. To guide--regardless which option is chosen--the selection of the numerical values, the effective quality factor, qE, is computed here for different directional distributions of neutrons incident on the anthropomorphic phantoms ADAM and EVA. None of the sex averaged numerical values is found to deviate much from those for isotropic incidence. Isotropic incidence can, thus, be used as an adequate standard condition. A numerical approximation is proposed for the standard qE that is nearly equivalent to a formula invoked by ICRP 92, but is somewhat simpler and provides realistic values of qE even for the extremely high neutron energies in space. In line with ICRP 92, it is emphasised that wR needs to be seen as a derived quantity related to the LET-dependent weighting factor.     

DS86 and DS02 organ dose calculations

A brief review of the techniques used to calculate organ doses for the atomic-bomb survivors at Hiroshima and Nagasaki is provided using the original dosimetry system 1986 (DS86) and revised dosimetry system 2002 (DS02). The DS02 study was undertaken to address a serious discrepancy between calculated and measured values for neutron activation at Hiroshima that had caused a lack of confidence in the previous dosimetry, designated as DS86. Some potential improvements to the organ dose calculations that were not considered during the DS02 study due to time and funding limitations are recommended in this paper.     

Spectra of scattered photons in large absorbers and their importance for the values of radiation weighting factor wR

In its review of the present values of radiation weighting factor w(R) and of possible revisions of this factor, the German Radiation Protection Commission has recommended to maintain the approach of ICRP 60 to base the selection of the w(R) value for a given radiation (e.g. fission neutrons) on observed values of the relative biological effectiveness (RBE) of this radiation 'regardless of whether the reference radiation is X rays or gamma rays'. The physical background of the German recommendation is the buildup of a strong field of energy-degraded Compton scattered photons in the human body if exposed to an external field of high-energy photons, so that the total radiation field inside the body is a mixture comprising low and high photon energies. Therefore, it is appropriate that the selection of the w(R) value of the given radiation is guided by RBE values averaged over X rays and gamma rays as the reference radiations. In support of this rationale, the present paper provides a sample of Monte Carlo calculated scattered photon spectra in large absorbers exposed to high-energy photons. Depth-dependent fractional dose contributions of the scattered photons are tabulated for incident energies from 1 to 10 MeV, and estimates of the influence of their degraded energies on the biological effectiveness of the incoming radiation are presented. Accordingly, we point out that it is appropriate to use, for the purposes of 'risk projection', RBE values averaged over X and gamma reference radiations.     

The development of fetal dosimetry and its application to A-bomb survivors exposed in utero

The cohort of the atomic bomb survivors of Hiroshima and Nagasaki comprises the major basis for investigations of health effects induced by ionising radiation in humans. To study the health effects associated with radiation exposure before birth, fetal dosimetry is needed if significant differences exist between the fetal absorbed dose and the mother's uterine dose. Combining total neutron and gamma ray free-in-air fluences at 1 m above ground with fluence-to-absorbed dose conversion coefficients, fetal doses were calculated for various exposure orientations at the ground distance of 1500 m from the hypocentres in Hiroshima and Nagasaki. The results showed that the mother's uterine dose can serve as a good surrogate for the dose of the embryo and fetus in the first trimester. However, significant differences exist between doses of the fetus of different ages. If the mother's uterine dose were used as a surrogate, doses to the fetus in the last two trimesters could be overestimated by more than 20 % for exposure orientations facing towards and away from the hypocentre while significantly underestimated for lateral positions relative to the hypocentre. In newer fetal models, the brain is modelled for all fetal ages. Brain doses to the 3-month fetus are generally higher than those to an embryo and fetus of other ages. In most cases, brain absorbed doses differ significantly from the doses to the entire fetal body. In order to accurately assess radiation effects to the fetal brain, it is necessary to determine brain doses separately.     

Point defects and the blue emission in fired quartz at high doses: a comparative luminescence and EPR study

The fundamental assumption implicit in the use of the atomic bomb survivor data to derive risk estimates for occupational and medical exposures is that the gamma rays of Hiroshima and Nagasaki are considered as equal efficiencies to other low LET radiations up to an LET of 10 keV.micron-1. For breast cancer induction, neoplastic cell transformation, mutation, reciprocal translocations and dicentrics in human lymphocytes, a strong and very similar dependence of the RBE values on photon energy or on LET is observed. Experimental data on mutation induction and neoplastic cell transformation in human cells show that 29 kVp X rays are by a factor of 4 and 3.4, respectively, more effective compared with 200 kVp X rays. These data are in excellent agreement with the data in the literature.     

The impact of ICRP publication 92 on the conversion coefficients in use for cosmic ray dosimetry

ICRP Publication 92 presents a proposal to achieve coherence between radiation weighting factors and quality factors. In particular, the radiation weighting factors for incident protons and neutrons have been revised and new values have been proposed. On the basis of the proposed values, sets of conversion coefficients fluence-to-effective dose for protons and neutrons have been derived for the irradiation geometries of interest for cosmic ray dosimetry.     

Impact of the introduction of ICRP Publication 103 on neutron dosimetry

The impact of the introduction of ICRP Publication 103 on neutron dosimetry was analysed by calculating effective doses in various operational neutron fields, using dose conversion coefficients derived from the recommendations given in ICRP 103 and ICRP 60. It was found from the analysis that effective doses based on ICRP 103 are generally smaller than those based on ICRP 60, mainly owing to the revision of w(R) assigned to neutrons. The results also indicate that H*(10) can provide a conservative estimate for ICRP 103-based effective doses in most neutron fields. These tendencies suggest that the radiological protection system currently adopted in accelerators and nuclear facilities can be maintained after the introduction of ICRP 103, with respect to neutron dosimetry.     

Weighting factors for radiation quality: how to unite the two current concepts

The quality factor, Q(L), used to be the universal weighting factor to account for radiation quality, until--in its 1991 Recommendations--the ICRP established a dichotomy between 'computable' and 'measurable' quantities. The new concept of the radiation weighting factor, w(R), was introduced for use with the 'computable' quantities, such as the effective dose, E. At the same time, the application of Q(L) was restricted to 'measurable' quantities, such as the operational quantities ambient dose equivalent or personal dose equivalent. The result has been a dual system of incoherent dosimetric quantities. The most conspicuous inconsistency resulted for neutrons, for which the new concept of wR had been primarily designed. While its definition requires an accounting for the gamma rays produced by neutron capture in the human body, this effect is not adequately reflected in the numerical values of wR, which are now suitable for mice, but are--at energies of the incident neutrons below 1 MeV--conspicuously too large for man. A recent Report 92 to ICRP has developed a proposal to correct the current imbalance and to define a linkage between the concepts Q(L) and wR. The proposal is here considered within a broader assessment of the rationale that led to the current dual system of dosimetric quantities.     

Experimental simulation of A-bomb gamma ray spectra for radiobiology studies

Improved radiation protection of humans requires a better understanding of the mechanisms of radiation action and accurate estimates of radiation risk for both internal and external radiations. The Japanese atomic bomb survivors represent one of the most important sources of human data on the late carcinogenic effects of ionising radiations. The present study was undertaken to investigate whether it would be possible to use hospital radiotherapy/radiobiology equipment to mimic the spectra encountered in Hiroshima and Nagasaki. The estimated total gamma ray fluence spectra (including both prompt and delayed photons) at both Hiroshima and Nagasaki, for distances of 500, 1000, 1500 and 2000 m have been evaluated using DS86 data and previously unpublished information for delayed gamma radiations which constitute the major contribution to survivor doses. Monte Carlo (EGS4) simulations were performed to transport these photons through the body in order to investigate the variation in electron spectra for various body organs. The electron spectra obtained for these fluences at, for example, the colon, have been matched with combinations of electron spectra produced by linear accelerators to within 5% SD. These will, for the first time, enable a direct link to be made between radiobiological studies (for example, on mammography spectra) and the epidemiological data from Japan, which currently underpin radiation risk estimates.     

Measurement of lineal-energy distributions for neutrons of 8 keV to 65 MeV by using a tissue-equivalent proportional counter

The lineal-energy spectra for monoenergetic and quasi-monoenergetic neutrons of 8 keV to 65 MeV were obtained using a tissue-equivalent proportional counter (TEPC). The frequency-mean lineal energy, the dose-average lineal energy and mean quality factor were estimated from the measured data. The neutron absorbed doses obtained with this TEPC were compared with the kerma coefticient for A-150 plastic defined by ICRP 26 and the mean quality factors were compared with the data of ICRP 74. respectively. These comparisons indicated good agreement between them.     

Determinations of H(10) and its dose components onboard aircraft

Aircrew is in general receiving a higher average annual dose than other occupationally exposed personnel, and about half of the effective dose is deposited by high-LET neutron secondaries. A recent investigation of the cancer incidence following the atomic bombs at Hiroshima and Nagasaki has put forward the possibility that the relative biological efficiency for neutrons could be underestimated. If so, the effective dose to aircrew from this component would increase and the estimation of this component will become even more important. Different ambient dose equivalent measurement techniques and calculation methods have recently been compared on a dedicated flight. The experimental results are compared with calculations made with the codes EPCARD 3.2 and an updated version of FLUKA and different galactic proton spectra. The aircraft circulated within the target areas at two constant altitudes with a flight route variation of only about 1 degrees in longitude and latitude to reduce the influence from variations in atmospheric and geomagnetic shielding. The instrumentation consisted of tissue-equivalent proportional counters (TEPC) and a silicon diode spectrometer. Measurements were performed for 2 h to reduce the statistical uncertainties in the results. The TEPCs were evaluated either according to single-event analysis techniques or the variance-covariance method. Besides the total ambient dose equivalent, the instruments can be evaluated to reveal the low- and high-LET components. The EPCARD and FLUKA simulations can determine the contribution from each type of particle directly. The ratio between the calculated and the measured average value of the ambient dose equivalent rate was 1.00 +/- 0.08 with all instruments included for EPCARD and 0.97 +/- 0.07 when FLUKA was used. The measured high-LET component and the calculated neutron component are not quite identical, but should be similar. The agreement was always within 20%. The high-LET component contributed with about 57% at N57 E8 and 48% at N42 E12.     

Uncertainties in dose coefficients for intakes of tritiated water and organically bound forms of tritium by members of the public

The International Commission on Radiological Protection (ICRP) provides models for the calculation of doses from intakes of radionuclides, including intakes of tritium as tritiated water (HTO) or organically bound tritium (OBT). The ICRP models for HTO and OBT are explained and the assumptions made are examined. The reliability of dose estimates is assessed in terms of uncertainties in central estimates for population groups. The models consider intakes of HTO and OBT by ingestion and inhalation by adults and children and doses to the fetus following intakes by the mother. The analysis includes uncertainties in the absorption of OBT to blood, incorporation of tritium into OBT in body tissues, retention times in tissues, transfer to the fetus and the relative biological effectiveness (RBE) of tritium beta emissions compared with gamma rays. Heterogeneity of dose within tissues and cells is also considered. For intakes as HTO, dose is predominantly due to distribution and retention of HTO in body water and it was concluded that adult doses are reliable to within a factor of 2. For intakes of OBT, the extent of incorporation into OBT in body tissues results in greater uncertainties with estimates relying on animal data for selected compounds. The analysis indicated that adult doses from OBT can be considered to be known to within a factor of 3. Greater uncertainties in estimated doses for children and for in utero exposures were considered. Central values from the uncertainty analyses of doses for HTO and OBT were greater than the corresponding ICRP dose coefficients by about a factor of 2, mainly due to the inclusion of uncertainties in RBE for tritium. A detailed assessment of doses using appropriate parameters and considering uncertainties would be of particular importance in situations where the dose may approach dose limits or constraints. For exposures to known forms of OBT, specific dose assessments may be required.     

Effective quality factors for neutrons based on the revised ICRP/ICRU recommendations

The quality factor (Q) is intended to relate the biological effectiveness of a radiation to the absorbed dose delivered in tissue. Quality factors are defined as a function of the unrestricted linear energy transfer (L) relationship in water and are used with operational quantities. Radiation weighting factors (wR) are used in protection quantities to take into account total radiation detriment. While the International Commission on Radiological Protection (ICRP) defines the Q(L) relationship, the International Commission on Radiation Units and Measurements (ICRU) recommends the charged particle stopping power and range data. If either of these data recommendations change, the quality factors must be recomputed. The latest guidance from both organisations applicable to neutron quality factors are the ICRP Publication 60 (Q(L) relationship) and the ICRU Report 49 (stopping power and range data). In the present study, absorbed dose conversion coefficients (pGy cm2) were calculated for two operational quantities defined by the ICRU--the ambient absorbed dose and the personal absorbed dose. Dose-equivalent (pSv cm2) conversion coefficients were also computed using mean quality factors based on ICRP 60 and ICRU 49 recommendations. Effective quality factors were then calculated from the ratio of the dose-equivalent to the absorbed dose conversion coefficients for both the personal dose-equivalent and ambient dose-equivalent and compared to values reported in the literature.     

Heavy ion RBE and microdosimetric spectra

Reliable values for the relative biological effectiveness (RBE) of the complex field of heavy ions is essential for radiation therapy with carbon beams. Clinical experience with this novel form of therapy is still quite narrow and it is, therefore, desirable to compare and combine relevant clinical findings and theoretical approaches. One major source of available information comes from neutron therapy. The approach towards the determination of RBE for neutron therapy is, therefore, tentatively applied to the heavy ion therapy. This includes the determination of microdosimetric spectra and their numerical evaluation towards the determination of RBE. A microdosimetric detector on the basis of a tissue-equivalent proportional counter (TEPC) was developed for measurements in the heavy ion fields of the GSI, Darmstadt. Measurements were performed first near the perspex phantom surface with carbon ion energies between 89 MeV.amu-1 and 430 MeV.amu-1. Subsequently, measurements were taken at various depths in the neighbourhood of the Bragg region. The numerical techniques that were developed for neutron therapy lead to tentative values of the RBE that are compared to the RBE values from the biophysical model developed at the GSI. The comparison is still preliminary but can be helpful in modifying the microdosimetric approach for its application in heavy ion therapy.     

The impact of ICRP/ICRU quantities on high energy neutron dosimetry: a review

Unlike other fields of toxicology, radiation protection has a dual system of quantities, one set for assessment and the derivation of authorised limits and another set for monitoring radiation performance and compliance. Neutrons are an important or dominant constituent of the radiation field around high energy accelerators and the evolution of the radiation protection quantities used to measure neutrons is described. In 1990 ICRP introduced a new quantity, the effective dose. E. with which to express its protection limits. E represented a radical departure from previous advice of the Commission, particularly in the manner by which it weighted the absorbed dose deposited by high LET radiations. This advice had profound consequences for neutron dosimetry. Over the past decade analyses have revealed logical flaws and inconsistencies in the definition of effective dose. These are briefly discussed with most emphasis being placed on inconsistencies in radiation weighting. Suggestions are made with a view to resolving these inconsistencies.     

The effects of neutron irradiation damage on the superconducting properties of Nb3Sn

Specimens of Nb₃Sn have been irradiated by fast neutrons at 70°C to doses in the range 3 × 10²¹ neutrons m^?2 to 9 × 10²³ neutrons m^?2. Their critical temperatures were depressed linearly with dose, to less than 4.2 K after about 3 × 10²³ neutrons m^?2. The critical temperature recovered to their initial values in anneals of 2 hours at 900°C, and in 64 hours at 750°C.The critical current can be enhanced by low neutron doses, particularly at high fields, but is always depressed by higher doses.The observations are shown to be consistent with a qualitative model, and in the light of this the likely consequences of irradiation at operating temperature are considered.     

Measurement of neutron dose with an organic liquid scintillator coupled with a spectrum weight function

A dose evaluation method for neutrons in the energy range of a few MeV to 100 MeV has been developed using a spectrum weight function (G-function), which is applied to an organic liquid scintillator of 12.7 cm in diameter and 12.7 cm in length. The G-function that converts the pulse height spectrum of the scintillator into the ambient dose equivalent, H*(10), was calculated by an unfolding method using successive approximation of the response function of the scintillator and the ambient dose equivalent per unit neutron fluence (H*(10) conversion coefficients) of ICRP 74. To verify the response function of the scintillator and the value of H*(10) evaluated by the G-function. pulse height spectra of the scintillator were measured in some different neutron fields, which have continuous energy, monoenergetic and quasi-monoenergetic spectra. Values of H*(10) estimated using the G-function and pulse height spectra of the scintillator were compared with those calculated using neutron energy spectra. These doses agreed with each other. From the results, it was concluded that H*(10) can be evaluated directly from the pulse height spectrum of the scintillator by applying the G-function proposed in this study.     

Response of Harshaw neutron thermoluminescence dosemeters in terms of the revised ICRP/ICRU recommendations

To monitor workers for external neutron radiation dose, the Y-12 National Security Complex utilises the thermoluminescence dosemeters (TLDs) manufactured by Harshaw. At Y-12, the majority of external dose to workers is due to low-energy photon and/or beta particles emitted from uranium and its progeny. However, some neutron dose is expected since neutrons are produced from (alpha,n) reactions in various compounds found at the plant, including UF4 and UF6. Neutron sources, such as 252Cf, are also used throughout the complex. The Harshaw neutron dosemeter consists of two gamma-sensitive elements (7Li) and two neutron-sensitive elements enriched in 6Li with various shielding/filter materials placed around each of them. In this work, the energy response of the dosemeter to neutrons has been calculated using the Monte Carlo transport code MCNP Version 4-C and, these results are compared with the measured response of the dosemeter to unmoderated and D2O-moderated 252Cf neutrons. The response of the dosemeter has also been determined in terms of the personal absorbed dose and personal dose equivalent as a function of neutron energy based on the recommendations of the ICRP Publication 60 and ICRU Report 49. The energy response of the dosemeter characteristics can be used to generate spectral conversion coefficients for routine neutron absorbed dose and dose equivalent calculations.     

'Lifestyle' and cancer rates in former East and West Germany: the possible contribution of diagnostic radiation exposures

Breast and prostatic cancer as well as leukaemia in childhood have remarkably increased over some decades in the Federal Republic of Germany as well as in several other highly developed industrial nations. Such increase was much less or not observable in East Germany between 1960 and 1989 where diagnostic exposures were applied to a lesser extent. Low-level radiation can cause these diseases and the difference of cancer rates gives rise to renewed evaluation of current risk estimates. Risk factors for radiation-induced childhood leukaemia and breast cancer are derived from the literature, considering a higher relative biological effectiveness of diagnostic X rays in comparison to the A-bomb gamma rays in Hiroshima and Nagasaki. The prostate is not considered as radiation sensitive by the ICRP. But following a variety of low-level findings in the last two decades it was shown by Myles et al. in the UK that prostatic cancer is inducible by diagnostic X-ray procedures. From their study in men below the age of 60, a doubling dose of about 20 mSv can be estimated. Medical exposures of the considered tissues are taken from published data for East and West Germany. The difference in breast cancer mortality can be explained by diagnostic exposures. The contribution of these to prostatic cancer and childhood leukaemia must be regarded as relevant in current incidences. Reduction of diagnostic exposures would be an important measure for preventing several prominent cancer diseases.