Data from the survivors of the atomic bombs serve as the major basis for risk calculations of radiation-induced cancer in humans. A controversy has existed for almost two decades, however, concerning ...the possibility that neutron doses in Hiroshima may have been much larger than estimated. This controversy was based on measurements of radioisotopes activated by thermal neutrons that suggested much higher fluences at larger distances than expected. For fast neutrons, which contributed almost all the neutron dose, clear measurement validation has so far proved impossible at the large distances (900 to 1,500 m) most relevant to survivor locations. Here, the first results are reported for the detection of 63Ni produced predominantly by fast neutrons (above about 1 MeV) in copper samples from Hiroshima. This breakthrough was made possible by the development of chemical extraction methods and major improvements in the sensitivity of accelerator mass spectrometry for detection of 63Ni atoms (refs 8-11). When results are compared with 63Ni activation predicted by neutron doses for Hiroshima survivors, good agreement is observed at the distances most relevant to survivor data. These findings provide, for the first time, clear measurement validation of the neutron doses to survivors in Hiroshima.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The detection of ⁴¹Ca atoms in tooth enamel using accelerator mass spectrometry is suggested as a method capable of reconstructing thermal neutron exposures from atomic bomb survivors in Hiroshima ...and Nagasaki. In general, ⁴¹Ca atoms are produced via thermal neutron capture by stable ⁴⁰Ca. Thus any ⁴¹Ca atoms present in the tooth enamel of the survivors would be due to neutron exposure from both natural sources and radiation from the bomb. Tooth samples from five survivors in a control group with negligible neutron exposure were used to investigate the natural ⁴¹Ca content in tooth enamel, and 16 tooth samples from 13 survivors were used to estimate bombrelated neutron exposure. The results showed that the mean ⁴¹Ca/Ca isotope ratio was (0.17 ± 0.05) × 10⁻¹⁴ in the control samples and increased to 2 × 10⁻¹⁴ for survivors who were proximally exposed to the bomb. The ⁴¹Ca/Ca ratios showed an inverse correlation with distance from the hypocenter at the time of the bombing, similar to values that have been derived from theoretical free-in-air thermal-neutron transport calculations. Given that γ-ray doses were determined earlier for the same tooth samples by means of electron spin resonance (ESR, or electron paramagnetic resonance, EPR), these results can serve to validate neutron exposures that were calculated individually for the survivors but that had to incorporate a number of assumptions (e.g. shielding conditions for the survivors).
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The detection of 41Ca atoms in tooth enamel using accelerator mass spectrometry is suggested as a method capable of reconstructing thermal neutron exposures from atomic bomb survivors in Hiroshima ...and Nagasaki. In general, 41Ca atoms are produced via thermal neutron capture by stable 40Ca. Thus any 41Ca atoms present in the tooth enamel of the survivors would be due to neutron exposure from both natural sources and radiation from the bomb. Tooth samples from five survivors in a control group with negligible neutron exposure were used to investigate the natural 41Ca content in tooth enamel, and 16 tooth samples from 13 survivors were used to estimate bomb-related neutron exposure. The results showed that the mean 41Ca/Ca isotope ratio was (0.17 ± 0.05) × 10−14 in the control samples and increased to 2 × 10−14 for survivors who were proximally exposed to the bomb. The 41Ca/Ca ratios showed an inverse correlation with distance from the hypocenter at the time of the bombing, similar to values that have been derived from theoretical free-in-air thermal-neutron transport calculations. Given that γ-ray doses were determined earlier for the same tooth samples by means of electron spin resonance (ESR, or electron paramagnetic resonance, EPR), these results can serve to validate neutron exposures that were calculated individually for the survivors but that had to incorporate a number of assumptions (e.g. shielding conditions for the survivors).
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41Ca is produced mainly by absorption of low-energy neutrons on stable 40Ca. We used accelerator mass spectrometry (AMS) to measure 41Ca in enamel of 16 teeth from 13 atomic bomb survivors who were ...exposed to the bomb within 1.2 km from the hypocenter in Hiroshima. In our accompanying paper (Wallner et al., Radiat. Res.174, 000–000, 2010), we reported that the background-corrected 41Ca/Ca ratio decreased from 19.5 × 10−15 to 2.8 × 10−15 with increasing distance from the hypocenter. Here we show that the measured ratios are in good correlation with γ-ray doses assessed by electron paramagnetic resonance (EPR) in the same enamel samples, and agree well with calculated ratios based on either the current Dosimetry System 2002 (DS02) or more customized dose estimates where the regression slope as obtained from an errors-in-variables linear model was about 0.85. The calculated DS02 neutron dose to the survivors was about 10 to 80 mGy. The low-energy neutrons responsible for 41Ca activation contributed variably to the total neutron dose depending on the shielding conditions. Namely, the contribution was smaller (10%) when shielding conditions were lighter (e.g., outside far away from a single house) and was larger (26%) when they were heavier (e.g., in or close to several houses) because of local moderation of neutrons by shielding materials. We conclude that AMS is useful for verifying calculated neutron doses under mixed exposure conditions with γ rays.
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In a fusion reactor and also in future advanced reactor types, long-lived activation products may lead to significant long-term waste disposals and radiation damage. Many of these production cross ...sections are not well-known, making it difficult to calculate concentration limits. Some prominent long-lived activation products comprise ^(10)Be, ^(14)C, and ^(26)Al; in the medium-mass range the radionuclides ^(53)Mn, ^(55;60)Fe, ^(59;63)Ni; and for heavier isotopes ^(202m)Pb, ^(210m)Bi. Since a few years the technique of accelerator mass spectrometry (AMS) has been applied at the Vienna Environmental Research Accelerator (VERA) facility for the detection of long-lived radionuclides for such studies. In this respect, samples were irradiated with quasi-monoenergetic neutrons at TU Dresden's 14-MeV neutron generator and the van de Graaff accelerator at IRMM. After the activations the samples were prepared for isotope ratio measurements via AMS. Production of long-lived ^(53)Mn and ^(59)Ni was measured via AMS utilizing the 14-MV tandem of the Maier-Leibnitz- laboratory, TU Munich. Radionuclides ^(10)Be, ^(14)C, ^(26)Al, ^(55)Fe, ^(210m)Bi, and ^(202g)Pb are measured at the VERA facility. KCI Citation Count: 0
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
⁴¹Ca is produced mainly by absorption of low-energy neutrons on stable ⁴¹Ca. We used accelerator mass spectrometry (AMS) to measure ⁴¹Ca in enamel of 16 teeth from 13 atomic bomb survivors who were ...exposed to the bomb within 1.2 km from the hypocenter in Hiroshima. In our accompanying paper (Wallner et al., Radiat. Res. 174, 000-000, 2010), we reported that the background-corrected ⁴¹Ca/Ca ratio decreased from 19.5 × 10⁻¹⁵ to 2.8 × 10⁻¹⁵ with increasing distance from the hypocenter. Here we show that the measured ratios are in good correlation with γ-ray doses assessed by electron paramagnetic resonance (EPR) in the same enamel samples, and agree well with calculated ratios based on either the current Dosimetry System 2002 (DS02) or more customized dose estimates where the regression slope as obtained from an errors-in-variables linear model was about 0.85. The calculated DS02 neutron dose to the survivors was about 10 to 80 mGy. The low-energy neutrons responsible for ⁴¹Ca activation contributed variably to the total neutron dose depending on the shielding conditions. Namely, the contribution was smaller (10%) when shielding conditions were lighter (e.g., outside far away from a single house) and was larger (26%) when they were heavier (e.g., in or close to several houses) because of local moderation of neutrons by shielding materials. We conclude that AMS is useful for verifying calculated neutron doses under mixed exposure Conditions With γ rays.
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For the time period from 1.5 to 4 Myr before the present we found in deep ocean ferromanganese crusts a 53Mn excess concentration in terms of 53 Mn / Mn of about 4 × 10−14 over that expected for ...cosmogenic production. We conclude that this 53Mn is of supernova origin because it is detected in the same time window, about 2.5 Myr ago, where 60Fe has been found earlier. This overabundance confirms the supernova origin of that 60Fe. For the first time, supernova-formed 53Mn has been detected and it is the second positively identified radioisotope from the same supernova. The ratio 53Mn / 60 Fe of about 14 is consistent with that expected for a SN with a 11–25 M ⊙ progenitor mass and solar metallicity.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
High energy beams of high ion currents from a Tandem accelerator are a common requirement in nuclear physics, materials science and Accelerator Mass Spectrometry (AMS) research. In many cases, ...molecular beams are chosen from the ion source to achieve a high ion source yield for the negative ions, or, as for AMS, to suppress isobaric interference. For this reason we have studied the use of consecutive stripper foils, double stripping, to increase the ion yield in conjunction with increased energy of injected molecular beams through a Tandem accelerator. By this method we could achieve a shift in the yield towards higher charge states.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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