hiroshima ni measurements with various ground …...893 hiroshima tld measurements with various...

892

Hiroshima 63Ni Measurements with Various Ground Range Evaluations

The following plot shows measurement-to-calculation ratios for 63Ni at originally reportedGR. Plots are all shown as a function of SR.

The next plot shows measurement-to-calculation ratios for 63Ni at the evaluated GR with theDS86 hypocenter.

The next plot shows measurement-to-calculation ratios for 63Ni at the evaluated GR with theDS02 hypocenter.

893

Hiroshima TLD Measurements with Various Ground Range Evaluations

The following plot shows measurement-to-calculation ratios for TLD at the originallyreported GR. Plots are all shown as a function of SR.

The next plot shows measurement-to-calculation ratios for TLD at the evaluated GR with theDS86 hypocenter.


894

Hiroshima Core Comparisons

Measurements in deep cores have been made in Japan for 152Eu and in the United States for36Cl. More discussion about these core measurements is found in a published article by Shizuma(Shizuma 1997) and in Chapter 8, Parts C, D, E, and F.

Motoyasu Bridge Granite Pillar

A comparison of DS86- and DS02-calculated levels of 36Cl from the reaction 35Cl(n,γ)36Clwith all 36Cl and 152Eu measurements in the Motoyasu granite pillar core at 128-m GR is shownin the plot below. The 36Cl measurements have activation from the 39K(n,α)36Cl reactionsubtracted, and 152Eu measurements have been converted to equivalent 36Cl activation. A DS02calculation without thermal neutron poisons Sm, Gd, Eu, and Dy added shows the effect of traceelements in the calculation.

Observation. Except at the surface, there is close agreement between DS02 and 36Cl. There isclose agreement between DS86 and 152Eu. An unexplained difference exists between 36Cl and152Eu. Without trace poison elements in the calculations, the relaxation length of attenuation inthe granite is too long for either set of measurements.

895

Gokoku Shrine Granite and Concrete Cores

A comparison of DS86- and DS02-calculated levels of 36Cl from the reaction 35Cl(n,γ)36Clwith all 36Cl and 152Eu measurements in the Gokoku Shrine concrete base and granite collar at398-m GR is shown in the plot below. The 36Cl measurements have activation from the39K(n,α)36Cl reaction subtracted, and 152Eu measurements have been converted to equivalent 36Clactivation. A DS02 calculation without Sm, Gd, Eu, and Dy added shows the effect of traceelements in the calculation.

Observation. There is close agreement between the DS02 calculation and near-surface 152Eu inconcrete base and 36Cl in the granite collar. DS02 is higher than 36Cl in concrete by 2 to 3 times.There is close agreement between 36Cl and 152Eu in deep concrete, but poor agreement withDS02. Without trace poison elements in the calculations, the relaxation length of attenuation inthe granite is too long for either set of measurements.

Explanation. It is postulated in Chapter 8, Part D that the concrete surface 36Cl has been dilutedwith meteoric Cl in first few cm from the surface. This is more likely with a ground-levelhorizontal concrete sample that is exposed to the weather. Concrete may have ion exchange withthe surface to a greater depth than a granite sample.

It is postulated in Chapter 8, Part D that the deep 152Eu and 36Cl measurements may indicatethat an additional 7 to 9 cm of shielding was present on top of the concrete base at time of exposure,but not covering the granite collar. That would allow DS02 to be consistent with measurements.

896

Shirakami Shrine Rock Core

A comparison of DS86- and DS02-calculated levels of 36Cl from the reaction 35Cl(n,γ)36Clwith all of the 36Cl and 152Eu measurements in the Shirakami Shrine granite rock core at 478-mGR is shown in the plot below. A 5-g/cm2 thick wooden cover representing foliage or a woodenshrine is placed over the rock in the calculation. The 36Cl measurements had activation from the39K(n,α)36Cl reaction subtracted, and the 152Eu measurements have been converted intoequivalent 36Cl activation. A DS02 calculation without Sm, Gd, Eu, and Dy added shows theeffect of trace elements in the calculation.

Observation. There is close agreement between DS02 calculation and 152Eu and 36Clmeasurements at depth. Trace poison elements are needed to match the slope. The surface 36Clmeasurement is low by 3 times. The following plot illustrates the poor agreement without a woodcover.

897

Kirin Brewery Concrete Core

A comparison of DS86- and DS02-calculated levels of 36Cl from the reaction 35Cl(n,γ)36Clwith all of the 36Cl measurements in the Kirin Brewery concrete wall core at 671-m GR is shownin the plot below. The 36Cl measurements have activation from the 39K(n,α)36Cl reactionsubtracted. A DS02 calculation without Sm, Gd, Eu, and Dy added shows the effect of the traceelements in the calculation. The pebble measurements are less likely to exchange withenvironmental Cl, than does concrete.

Observation. The calculations are about a factor of 2 high at all depths greater than 5 cm.Without trace poison elements in the calculations, the DS02 attenuation slope in the granite islonger than was measured. There is poor agreement between measurement and calculation at thesurface, where the 36Cl measurement is almost zero.

Explanation. It is postulated in Chapter 8, Part D that these results can be explained if 4 to 5 cmof new grout and tile was added to the wall after the A-bomb exposure, and if this replaced anexisting 10 to 12 cm facade of brick or concrete. The bomb-activated 36Cl leached from theoriginal wall out into the new cement, explaining the downward trend toward the surface. Theadditional 6 to 7 cm of shielding at the time-of-bombing would help the DS02 calculations to beconsistent with the pebble and deep cement measurements all the way from 12-cm to 30-cmdepth.

898

City Hall Building Concrete Core

A comparison of DS86- and DS02-calculated levels of 36Cl from the reaction 35Cl(n,γ)36Clwith all 36Cl measurements in the City Hall concrete wall core at 1,054-m GR is shown in theplot below. The 36Cl measurements have activation from the 39K(n,α)36Cl reaction subtracted. ADS02 calculation without Sm, Gd, Eu, and Dy added shows the effect of trace elements in thecalculation.

Observation. The agreement is close with DS02 for all depths greater than 5 cm. The agreementwith DS86 and the “no-poison” DS02 is not as close as with DS02. There is poor agreementbetween measurement and calculation at the surface, where the 36Cl measurement is 30% lower.

899

Distant Concrete Cores

A comparison of DS86- and DS02-calculated levels of 36Cl from the reaction 35Cl(n,γ)36Clwith all 36Cl measurements in four distant concrete wall cores at 1,368-m, 1,470-m, 1,501-m,1,607-m GR is shown in the plot below. The 36Cl measurements have activation from the39K(n,α)36Cl reaction subtracted. A DS02 calculation without Sm, Gd, Eu, and Dy added showsthe effect of trace elements in the calculation.

Teishin Building Core

Red Cross Building 9-m Height Core

900

Red Cross Building 20-m Height Core

Postal Savings Bureau Building Cores

Observation. The calculations and measurements are very small, yet generally agree withinuncertainty. There is poor agreement between measurements and calculation at the wall surface,where 36Cl measurements are 3 to 10 times higher than DS02. The fractional uncertainty is toolarge to know if there is agreement or disagreement at depths greater than 10 cm. One exceptionis the 9-m high Red Cross Hospital core with a large measurement at 7 cm, but this core has asinusoidal attenuation curve that cannot be from atomic-bomb activation.

Explanation. It is postulated in Chapter 8, Part D that the surface discrepancy for these distant,lightly exposed concrete cores is explained, if the surface cement is exposed to a high amount of36Cl from the Hiroshima environment. The 36Cl could come from the bomb-activated soil or fromworldwide fallout from nuclear testing. The 36Cl then diffused into the first 1 to 2 cm by surfacecontamination on the original wall, or was applied with patching material, causing elevatedvalues at the surface. The measurement at 5 cm of the 9-m high Red Cross Hospital core haslarge sulfur contamination, and it has been recommended by the measurer that it be dropped fromconsideration.

901

Nagasaki Near-Surface Europium

A comparison of DS02-calculated levels of 152Eu from the reaction 151Eu(n,γ)152Eu with all152Eu measurements in Nagasaki is shown in the plot below. Measurements have been convertedto FIA equivalent 152Eu activation. The plot is specific activity versus slant range. A singletransmission factor for all europium is used, because detailed models of sample shielding are notavailable.

The next plot shows the measurement-to-calculation (M/C) ratios.

Observation. The 152Eu measurements generally range from one to ten times DS02 calculations,and the measurements are widely scattered. At far distances, DS02 only matches the 1998Nakanishi measurements. The Shizuma measurement set, while in disagreement with DS02beyond 800-m SR, appears to come into agreement with DS02 results at the closer SRs.

902

The plot below shows a comparison of FIA equivalent measurements to DS86 and DS02. Thedata are plotted versus ground range.

The next plot is expanded to show a comparison of FIA equivalent measurements to DS86and DS02 within 500-m GR.

Observation. The validity of DS02 or DS86 cannot be determined because of the large scatter inthe 152Eu measurements. At the hypocenter the measurements envelop DS02 and DS86. DS02seems to be in best agreement with the 1991 measurements of Miyajima. There were no newmeasurements or reanalysis of older measurements made at Nagasaki for DS02. See Chapter 4 tofind references to these older measurements.

903

Nagasaki Near-Surface Europium by Investigator

A comparison of DS02-calculated levels of 152Eu from the reaction 151Eu(n,γ)152Eu with 152Eumeasurements in Nagasaki for six investigators is shown in the plot below. Measurements havebeen converted to FIA equivalent 152Eu activation. The plot is specific activity versus slant range.A single transmission factor for all europium is used, because detailed models of sampleshielding are not available.

Iimoto

Nakanishi

Komura

904

Shizuma

Miyajima

Okumura

Observation. The validity of DS02 or DS86 cannot be determined because of the large scatter inthe 152Eu measurements. At the hypocenter the measurements envelop DS02 and DS86. DS02seems to be in best agreement with the 1991 measurements of Miyajima.

905

Nagasaki Near-Surface Cobalt

A comparison of DS02-calculated levels of 60Co from the reaction 59Co(n,γ)60Co with all 60Comeasurements in Nagasaki is shown in the plot below. Measurements have been converted intoFIA equivalent 60Co activation. The plot is specific activity versus slant range. Error bars are onlyfrom the measurements. A single transmission factor for all 60Co is used, because detailed modelsof all of the sample shielding are not available.


Observation. The 60Co data have too much scatter for the DS02 to obtain agreement withmeasurements.

906



Observation. The 60Co measurements have too much scatter to draw many conclusions. Near thehypocenter DS86 appears to be a little closer to the measurements than does DS02. There wereno new measurements or reanalysis of older measurements made at Nagasaki for DS02. SeeChapter 4 to find references about these older measurements.

907

Nagasaki Near-Surface Chlorine

A comparison of DS02-calculated levels of 36Cl from the reaction 35Cl(n,γ)36Cl with all 36Clmeasurements in Nagasaki is shown in the plot below. Measurements have been converted intoFIA equivalent 36Cl activation, after the calculated amount of activation from the 39K(n,α)36Clreaction has been subtracted. The plot is of atoms of 36Cl per atom of Cl versus slant range. Acustomized calculated transmission factor was used for most samples.


Observation. DS02 is in close agreement with the 36Cl measurement, with a small uncertainty, at800-m SR. The farther measurements, though having much larger uncertainties, do not supportthe idea of a slope discrepancy as large as was suggested by previous thermal neutron activationmeasurements.

908


The next plot is expanded to show DS86 and DS02 within 500-m GR.

Observation. DS02 is more consistent with the 36Cl data than is DS86. However there are nomeasurements near the hypocenter. For more discussion about these measurements see Chapter 8,Part D.

909

Nagasaki Sulfur Calculations (no measurements available)

The following plot shows DS02-calculated 32P from the reaction 32S(n,p)32P in units dpm 32Pper milligram versus slant range. Unlike for Hiroshima, at Nagasaki the tilt of the weapon wouldnot affect sulfur measurements.

The next plot shows a comparison of DS86 and DS02. The data are plotted versus ground range.

The next plot is expanded to show a comparison of DS86 and DS02 within 500-m GR.

910

Nagasaki Copper Calculations (no measurements available)

The following plot shows DS02-calculated 63Ni from the reaction 63Cu(n,p)63Ni in unitsatoms of 63Ni per gram of Cu versus slant range. Unlike for Hiroshima, at Nagasaki the tilt of theweapon would not affect copper measurements.

The next plot shows a comparison of DS86 and DS02. The data are plotted versus ground range.

The next plot is expanded to show a comparison of DS86 and DS02 within 500-m GR.

911

Nagasaki TLD Measurements

A comparison of DS02 calculations with all TLD measurements in Nagasaki is shown in theplot below. Measurements have been converted to FIA equivalent TLD response. The plot is intissue absorbed dose (gray) versus slant range.

The next plot is the measurement-to-calculation (M/C) ratios.

Observation. DS02 is in agreement with TLD measurements from 1,200-m out to 2,100-m SR.Near the hypocenter the TLD measurements are about 80% of the DS02 calculation.

912



Observation. DS02 is almost unchanged from DS86 near the hypocenter. TLD measurements atthe hypocenter are lower than either DS02 or DS86 calculations near the hypocenter. At distance,both DS02 and DS86 agree with the TLD measurements. For more explanation see Chapter 7.

913

Plot of measurement-to-calculation ratios for JNIRS.

Plot of measurement-to-calculation ratios for NUE.

Plot of measurement-to-calculation ratios for Durham University.

Plot of measurement-to-calculation ratios for University of Utah.

Plot of measurement-to-calculation ratios for Oxford University.

914

Nagasaki 152Eu Measurements with Various Ground Range Evaluations

The following plot shows measurement-to-calculation ratios for 152Eu at the originallyreported GR. Plots are all shown as a function of SR.

The next plot shows measurement-to-calculation ratios for 152Eu at the evaluated GR with theDS86 hypocenter.

The next plot shows measurement-to-calculation ratios for 152Eu at the evaluated GR with theDS02 hypocenter.

915

Nagasaki 60Co Measurements with Various Ground Range Evaluations

The following plot shows measurement-to-calculation ratios for 60Co at the originallyreported GR. Plots are all shown as a function of SR.

The next plot shows measurement-to-calculation ratios for 60Co at the evaluated GR with theDS86 hypocenter.

The next plot shows measurement-to-calculation ratios for 60Co at the evaluated GR with theDS02 hypocenter.

916

Nagasaki 36Cl Measurements with Various Ground Range Evaluations

The following plot shows measurement-to-calculation ratios for 36Cl at the originally reportedGR. Plots are all shown as a function of SR.

The next plot shows measurement-to-calculation ratios for 36Cl at the evaluated GR with theDS86 hypocenter.

The next plot shows measurement-to-calculation ratios for 36Cl at the evaluated GR with theDS02 hypocenter.

917

Nagasaki TLD Measurements with Various Ground Range Evaluations

The following plot shows measurement-to-calculation ratios for TLD at the originallyreported GR. Plots are all shown as a function of SR.



918

Nagasaki TLD Measurements Using Additional Reduction Factors

Many Nagasaki samples were shielded by neighboring buildings or woods, as discussed inChapter 4. Detailed shielding calculations have not been done, but likely additional shieldingfactors can be estimated from observing shielding effects in Chapter 11, Part B. Also, Nagasakisample conditions near the hypocenter were more extreme than any at Hiroshima. Dose levelsand temperatures were higher. To determine the maximum plausible effect it is assumed that theTLDs under-respond by 20% in these conditions. Maximum additional reduction factors thataffect each TLD measurement are estimated and given in Table 2. The comparison using theseassumptions is shown in the plot below. The Nagasaki TLD average M/C value given in Table 1changes from 0.80 to 0.91 with the likely additional shielding, and then to 0.93 with themaximum limit of plausible annealing or saturation effects included. The weighted average for allneutron and gamma Nagasaki measurements changes from 0.90 to 0.97 with the likely additionalshielding, and then to 0.98 with annealing or saturation effects included. Because the estimate ofthe likely additional shielding has a significant effect on the agreement, in the future detailedshielding studies of these Nagasaki TLD samples should be performed.

Nagasaki TLD measurement to calculation comparison when additionalreduction factors are postulated to affect TF calculation

Summary

The DS02 free-field fluence calculations, extending from the hypocenter to 2,500-m GR, aresupported by measurements of gamma-rays, thermal-neutron and fast-neutron activations, withinthe limits of the measurement and TF uncertainties. The measurement-to-calculation ratios varysubstantially, even for the “best” measurements. The weighted measurement-to-calculation ratiosfor each isotope are within the reported calculation uncertainty at Hiroshima and at Nagasaki.The average of the isotope ratios is almost unity at Hiroshima and near unity at Nagasaki. This isdiscussed in Chapter 13.

920

In Hiroshima, the improvement of DS02, compared to DS86, is especially noticed near thehypocenter, due to raising the height of burst from 580 to 600 m. The addition of theintercomparison europium and chlorine measurements helps to confirm the long-distance, DS02-calculated thermal neutron activation. The new copper activation measurements have confirmedthe reliability of the sulfur data as an indicator that is sensitive to the main bomb parameters andthe tilt of the Hiroshima weapon.

The scarcity of good neutron measurements in Nagasaki limits the direct confirmation of theneutron fluence at that city. The limited chlorine measurements are the best direct support for theneutron fluence. The absence of fast neutron activation measurements at Nagasaki means thatconfirmation relies on measurements made from similar bombs detonated at the atomic-bomb testsites.

In both cities the gamma-ray TLD measurements confirm the doses at survivor distanceswithin uncertainties. There appears to be a slight over-estimation from calculation or under-estimation from measurements near the hypocenter in Nagasaki, indicating possible problemswith either TLD measurements at those extremely high doses and temperatures or in thehydrodynamic rise of the debris fission source in the fireball. At survivor ranges of interest theseissues are not important, as exhibited by the good agreement further away from the hypocenter.

Conclusions about Survivor Doses

The survivor doses, which are calculated from the free-field radiation fluence, are crediblebecause of the generally good agreement between the calculations and measurements ofactivation in samples. The method of calculating shielded doses and organ doses for survivors isthe same as is done for calculating shielded activation in samples. Thus the bomb parameters andoutput, the radiation transport, and shielding method for survivor dosimetry is tested and shownto be adequate.

References

Roesch, W. C.; ed. US-Japan Joint Reassessment of Atomic Bomb Radiation Dosimetry in Hiroshima

and Nagasaki, Final Report, Vol. 1. Hiroshima, Japan: Radiation Effects Research Foundation; 1987.

Shizuma, K.; Iwatani, K.; Hasai, H.; Hoshi, M.; Oka, T. “152Eu Depth Profiles in Granite and Concrete

Cores Exposed to the Hiroshima Atomic Bomb. Health Phys. 72: 848-855; 1997.

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