忘却からの帰還〜Atomic Age

Harold Knapp continued to concentrate on the St. George area, paying particular attention to the UPSHOT-KNOTHOLE: HARRY shot. The more closely he examined the data—or lack of it—the worse it looked. No monitoring had been done for iodine-I31 or -133. After the detonation, AEC monitor Frank Butrico, assigned to gather milk samples from dairies, had only purchased one quart—from a local store. [24,25] Moreover, Knapp found that because of the concentrating effects on internal emitters—that is, fission products that had been ingested—the AEC had underestimated the radiation dose to various areas in the United States by as much as a thousand times. [26,27]

核実験シリーズOperation Upshot-Knothole(1953)では1発目から住民の居住地域に放射性降下物が流れた。主たる居住地域と離散的な道路沿いの放射線量観測が行われていて、その範囲では問題ないとされた。しかし、実際にはネバダ州Lincoln Mineの住民に屋内退避を助言していた。

FALLOUT IN UPSHOT-KNOTHOLE

The test group's monitoring teams were able to determine fallout patterns very quickly after each shot. The radioactive cloud from the first shot, Annie, did move due east from the test site and dropped fallout on St. George, Utah, but the Commission reported that the maximum radiation level was no more than 0.026 roentgens per hour, far below the guidelines set for offsite exposures. Nancy, the second shot, was somewhat larger than Annie and apparently dumped substantial amounts of fallout in sparsely populated areas northeast of the test site. Because monitoring teams had been stationed only in communities and took only a limited number of readings along roads, it was impossible to know the precise radiation levels in the hinterland. In its public releases the Commission merely reported that there had been no fallout in populated areas, although it was admitted that the small number of residents at Lincoln Mine, Nevada, had been requested to remain indoors for two hours while radiation from fallout exceeded 0.5 roentgens per hour. The third through the sixth shots produced no radioactivity measurable in inhabited areas[16]

実験グループのモニタリングチームは爆発後すぐに放射性降下物パターンを決定できた。最初の爆発であるアニーの放射性雲は実験場から東に流れ、ユタ州St. Georgeに放射性降下物を落としたが、原子力委員会は「最大放射線レベルは0.026レントゲン/時を超えておらず、ガイドラインが実験場外について定めた基準を大きく下回っている」と報告した。2番目の爆発であるNancyはAnnieより少し規模が大きく、実験場の北東方向の人口過疎地域に、相当量の放射性降下物を放出した。モニタリングチームはコミュニティにのみ常駐し、道路沿いには限られた数の計測しか行っておらず、内陸の正確な放射線レベルを知り得なかった。公式発表では、原子力委員会は「住民の居住地域には放射性降下物は降っていない」とのみ報告したが、ネバダ州Lincoln Mineの住民に、放射性降下物レベルが0.5レントゲン/時を超過している2時間は屋内に留まるよう要請したことを認めた。3番目から6番目までの爆発は、住民居住地域には計測可能な放射能は生成されていなかった。


[16] Test Director to Division of Military Application, March 18, 26, April 20, 27, May 9, 1953. These appear in AEC 487/ 45, AEC 487/46, AEC 487/50, AEC 487/52, and AEC 487/54, respectively, all in AEC. Richard G. Hewlett, "Nuclear Weapon Testing and Studies Related to Health Effects: An Historical Summary," in Interagency Radiation Research Committee, Consideration of Three Proposals to Conduct Research on Possible Health Effects of Radiation From Nuclear Weapon Testing in Arizona, Nevada, and Utah (Washington: National Institutes of Health, 1980), pp. 51-54, 78.


[ Richard G. Hewlett, Jack M. Holl, Roger M. Anders:"Atoms for Peace and War, 1953-1961: Eisenhower and the Atomic Energy Commission" (a History of the United States Atomic Energy Commission. Vol. III), Univ of California Press, 1989, pp.153-154 ]

7発目のSimon (43kt)では、放射性降下物が幹線道路を横切って流れたため、検問が行われ、基準値以上に汚染された自動車を、政府負担で洗浄するに至った。

More radiation exposures, however, did occur during the high-yield shots that concluded the series. A wind shift at the time Simon was detonated on April 25 carried the radioactive cloud over two highways in Nevada. When fallout reached 0.46 roentgens per hour, Graves ordered road-blocks set up, and about forty vehicles with interior readings of 0.007 roentgens per hour were washed at government expense.[17]

しかし、さらに多くの放射線被曝が、シリーズを締めくくる高出力爆発の際に起きていた。1953年4月25日にSimonが爆発した時、風向が変わり、ネバダ州の2つの幹線道路上に放射性雲を運んだ。放射性降下物が0.46レントゲン/時に到達すると、[ロスアラモス研究所のAlvin C.]Gravesは道路のバリケードの設置を命じ、0.007レントゲン/時の範囲内にいた40台の自動車は政府負担で除染された。[17]


[17] Operation Upshot-Knothole, Report of Deputy Test Director, Los Alamos Report WT-816, pp. 72, 78, 96-98.


[ Richard G. Hewlett, Jack M. Holl, Roger M. Anders:"Atoms for Peace and War, 1953-1961: Eisenhower and the Atomic Energy Commission" (a History of the United States Atomic Energy Commission. Vol. III), Univ of California Press, 1989, pp.153-154 ]

そして、これらを大きく上回る量の放射性降下物を実験場外に放出したのHarryである。St.Georgeには2時間にわたり、屋内退避が要請された。

By far the most serious was the fallout from the Harry shot on May 19. Postponed three days because of unfavorable weather, Harry was fired under what seemed to be perfect conditions. But a wind shift and a slight increase in wind velocity spread fallout in a pattern about fifty miles square over populated areas east of the proving ground. For the second time in a month roadblocks were set up on major highways to monitor motor vehicles. At 9:10 a.m., about four hours after the shot had been fired, readings as high as 0.32 roentgens per hour were being recorded at the roadblocks. At that time Edward S. Weiss, the Public Health Service officer stationed in St. George, called the sheriff's office and radio station to warn people in the area to take cover. Local schools kept children indoors during the morning recess, and the washing of contaminated cars in St. George was suspended. By 9:40 a.m. most of the population in St. George was under cover, and the community came to a standstill.

はるかに深刻だったのが、1953年5月19日のHarry爆発の放射線降下物だった。気象条件が整わず、3日延期されたあと、完璧と思われる条件下でHarryは爆発させられた。しかし、風向が変わり、少し風速が大きくなり、実験場の東側の住民居住地域に24km四方の領域に放射性降下物が拡散した。その月の2回目の主要幹線道路へのバリケードの設置が行われ、自動車のモニタリングが行われた。爆発4時間後の午前9時10分、道路バリケードで0.32レントゲン/時が記録された。この時点で、St. Georgeに常駐する公衆衛生局のEdward S. Weissは保安官事務所とラジオ局に電話して、その地域の住民に避難するように警報を出した。地域の学校は朝の休み時間、児童生徒を屋内に留めた。St. Georgeでの汚染車両の洗浄は一時中止された。午前9時40分までに、St Georgeの大半の住民は屋内避難し、コミュニティは動きを止めた。

The all-clear came before noon when the first officials from the test site arrived to look over the situation. Because of the understandable tension among the residents, Weiss was ordered to remain in the area for several more days. During that period he considered collecting milk samples from local dairies to check for radioactivity, but because of the uneasiness in the community Weiss concluded that such a survey might create alarm. For that reason he limited his investigation to a few samples of milk purchased in local stores. From measurements at St. George the test group later estimated that the maximum amount of external exposure that could have been received at St. George was 6.0 roentgens and 5.0 roentgens at Cedar City. Scientists later estimated that children living near the test site received thyroid doses from iodine-131 ranging from inconsequential levels to those possibly causing some thyroid abnormalities.[18]

実験場から最初の当局者が現状確認に到着した正午前に警報は解除された。住民の当然の緊張のため、Weissは当該地域にさらに数日留まるよう命じられた。その期間に、彼は地域の乳製品製造所から牛乳サンプルを集めて放射能測定することを検討したが、コミュティの不安から、Weissはそのような調査が恐怖を引き起こす可能性があると判断した。このため、彼は調査を、地域の店舗で購入した牛乳に限定した。St. Georgeでの測定から、実験グループは後に想定される被曝量最大を推定し、St. Georgeで6.0レントゲン/時、Cedar Cityで5.0レントゲン/時と推定した。科学者たちは実験場近くの子供たちの甲状腺のヨウ素131からの線量を取るに足りないレベルから、いくつかの甲状腺異常を引き起こす可能性のあるレベルまでと推定した。[18]


[18] AEC-DOD Test Information Office, Las Vegas, Press Releases 70, 71, 72, all on May 19, 1953, all in AEC. Weiss described his experiences in St. George in Transcript of Meeting on Statistical Considerations on Field Studies on Thyroid Diseases in School Children in Utah Arizona, Dec. 3, 1965, pp. 3-5, Document 9735, PHS Archives. For another eyewitness account of incidents at St. George, see Frank A. Butrico to William Johnson, n.d., in House Committee on Interstate and Foreign Commerce, Subcommittee on Oversight and Investigations, Hearings on Low-Level Radiation Effects on Health, April 23-Aug. 1, 1979, Serial 96-129 (Washington: Government Printing Office, 1979), pp. 78184 (hereafter cited Radiation Effects Hearings).


[ Richard G. Hewlett, Jack M. Holl, Roger M. Anders:"Atoms for Peace and War, 1953-1961: Eisenhower and the Atomic Energy Commission" (a History of the United States Atomic Energy Commission. Vol. III), Univ of California Press, 1989, pp.153-154 ]

なお、Harryを含む1950年代の大気圏内核実験による、ネバダ州・ユタ州・アリゾナ州・カリフォルニア州の住民の被曝線量は以下のように推定されている。。総線量の大半をリンカーン郡、ワシントン郡、アイアン郡の住民が占めていた。また数多くの核実験の中でもHarry爆発の放射性降下物が約7割を占めていた。

Cumulative population exposures estimated for test series conducted between 1951 and 1959 are listed in Table IV-2. They include population centers within 300 miles of the Nevada Test Site. About 50% of the total population exposure resulted from the Upshot-Knothole series conducted in 1953, and of this, 75% resulted from fallout released from Shot Harry conducted on May 19. Fallout from Shot Harry traveled eastward and passed almost directly over St. George, Utah (Figure IV-17). Radiation exposures estimated at different locations in Utah, Nevada, Arizona, and California are shown in Table IV-3. These represent cities and towns that experienced the highest population exposures in each state. Calculated exposures to individuals who would have lived at each of these locations for the duration of the test series were as large as 4.3 R. However, single sites in Nevada that had very low populations during the 1950s were estimated to have cumulative exposures up to 15 R. (p.64)

1951〜1952年に実施された核実験シリーズでの累積集団被曝線量は表IV-2の通りである。これらにはネバダ実験場から480km圏内の住民を含む。1953年のUoshot-Knotholeシリーズでは、全住民の約50%被曝し、このうち75%が5月19日に実施されたHarry爆発で放出された放射性降下物によるものだった。Harry爆発からの放射性降下物は東へ流れて、直接ユタ州St. George上空を通過した。ユタ州、ネバダ州、アリゾナ州、カリフォルニア州での推定被曝線量を表IV-3に示す。これらは、各州で最大の集団被曝を経験した都市や町を表している。実験シリーズ期間中、これらの場所に居住していた人への推定被曝線量は最大4.3 Rだった。ただし、1950年代に人口が非常に少ないネバダ州の一地点トでは、累積被曝が最大15 Rと推定された。（p.64）


Table IV-2: Cumulative Radiation Exposures to Populations Living Within 300 Miles of the Nevada Test Site from Nuclear Weapons Tests Conducted Prior to 1959 (Anspaugh and Church 1983)

Test Series Year Cumulative Population Exposure in R
Buster-Jangle 1951 610
Tumbler-Snapper 1952 4,700
Upshot-Knothole 1953 40,000
Teapot 1955 19,000
Plumbob 1957 11,000
Hardtack II 1958 1.500
Total 76,810


Table IV-3 Cumulative Radiation Exposures to Individuals and Populations Living in Cities and Towns Near the Nevada Test Site Between 1951 and 1959 (Anspaugh and Church 1983)

Location Population Indevisuals Popukaion
R Person R
Utah St. George 5000 3.7 18000
Hurricane 1375 3.5 4800
Cedar City 6106 0.64 3900
Kanab 1900 1.6 3100
Washington 435 3.3 1400
La Verkin 387 3.7 1400
Santa Clara 319 4.3 1400
Panguitch 1500 0.7 1000
Nevaa Las Vegas 47000 0.21 9900
Ely 3558 1.2 4300
Lincoln Mine 100~500 6 3000
N. Las Vegas 13000 0.2 2600
McGill 2300 0.77 1800
Tonopah 1375 1.1 1500
Mesquite 590 2.1 1200
East Ely 1000 1.2 1200
Arizona Kingman 5500 0.04 220
Short Creek 90 1.6 140
Littlefield 45 1.9 84
Mt. Trumbull 100 0.16 16
California Bishop 2830 0.06 170
Barstow 3330 0.03 100
Lone Pine 1375 0.08 110
Ridgecrest 4000 0.02 80



Because some parameters of the models used to calculate radiation doses from nuclear weapons test fallout vary with a person's age, the location of their residence and many lifestyle factors, doses must be calculated for single individuals or well -characterized populations based upon detailed personal information. This has been obtained from questionnaires distributed to people who lived in Nevada, Utah, and Arizona during the atmospheric test series. The results were used to calculate doses to individuals involved with law suits against the Federal Government and to other populations. Sample calculations are shown in Table IV-5 for residents of Lincoln County, Nevada as well as Washington and Iron counties in Utah. These counties are directly east of the Nevada Test Site and within 250 miles. The exposures resulted from three atmosphere tests, Annie (3-17-53), Harry (5-19-53) and Smoky (8-32-57), which caused more than 90% of the total estimated radiation doses to residents of Lincoln, Washington, and Iron counties. Shot Harry alone contributed about 70% of the total dose. Lifetime residents of Washington County received 2 to 4 times more radiation than the average doses shown in Table IV-5, whereas residents of Lincoln and Iron counties received about one-half of the listed doses. Doses to the total body, bone marrow, liver, lung, and kidney were estimated to be more than 90% due to external penetrating radiations. Seventy-six percent of the doses to the lower large intestine and 97% of the doses to the thyroid were estimated to be caused by ingested and inhaled fallout radionuclides. (p.69)

核実験の放射性降下物からの放射線量を計算するのに使用するモデルのパラメーターには、当人の年齢・居住地・多くのライフスタイル要因などにより異なるものがあるため、詳細な個人情報に基づいて個人、あるいは十分に特徴もわかっている集団の線量を計算する必要がある。この譲歩は、大気圏内実験シリーズの際に、ネバダ州・ユタ州・アリゾナ州の住民に配布したアンケートで取得された。その結果は、連邦政府に対する訴訟に関与した個人および集団への線量計算のために使用された。表IV-5に、ネバダ州リンカーン郡の住民およびユタ州ワシントン郡とアイアン郡の計算例を示す。これらの郡はネバダ実験場のすぐ東の440km圏内にある。被曝線量は、Annie (1953/3/17)とHarry (1953/5/19)と、Smoky (1957/8/31)の3つの大気圏内核実験の結果であり、推定された総線量の90%以上をリンカーン、ワシントン、アイアン郡で占めた。Harry爆発だけで総線量の約70%を占めた。ワシントン郡の生涯居住者は、表IV-5に示されている平均線量より2〜4倍多くの放射線被曝したが、リンカーン郡とアイアン郡の居住者は、記載された線量の約半分を被曝した。全身、骨髄、肝臓、肺、および腎臓への線量は、外部透過放射線によるものの90％以上と推定された。大腸下部への線量の76%、および甲状腺への線量の97%は、摂取および吸入したた放射性降下物の放射性核種が原因であると推定された。 （p.69）


Table IV-5: Average Radiation Doses to Residents of Lincoln, Washington, and Iron Counties From Nuclear Weapons Tests Annie, Harry, and Smoky (U. S. Department of Energy, 1982 through 1983)

Organ External Internal Total (rad)
Radiation (rad) Radionuclides (rad)
Skin 26 (100) -- 26
Total Body 1 (92) 0.08 (8) 1.08
Red Marrow 0.9 (91) 0.09 (9) 0.99
Liver 0.86 )93) 0.06 (7) 0.92
Lungs 0.90 (97) 0.03 (3) 0.93
Kidneys 0.90 (94) 0.06 (6) 0.96
Lower Large 0.81 (24) 2.6 (76) 3.41
Intestine Wall
Thyroid 1.1 (3) 36.5 (97) 37.6

[ Richard G. Cuddihy and George J. Newton: "Human radiation exposures related to nuclear weapons industries" (1985) ]

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