The First Atomic Explosion, 16 July 1945

To prepare for the Trinity Test, especially to help scientists and technicians calibrate and prepare measuring instruments and communications systems, Kenneth Bainbridge supervised a test on 7 May 1945 that exploded 108 tons of high explosives stacked in a tower at the Alamogordo site. Because there had been no previous tests with massive blast effects, Bainbridge saw it as a necessary “dress rehearsal.”[10]

With Los Alamos health and safety experts already concerned about fallout that the Trinity test would produce, a major purpose of the 100-ton test was to estimate the dispersal of fission products. To make that possible, the scientists obtained from the Hanford reprocessing plant a “slug” of plutonium that they dissolved in chemicals and then placed in flexible tubing that technicians strung through the stack of high explosives [See Film 1].

In his report to General Groves on the test, Richard T. Tolman observed that it produced a “highly luminous sphere, which then spread out into an oval form,” that was followed by the “ascent of the expected hot column which mushroomed out at a height of some 15000 ft.”[11] Herbert Anderson, one of the scientists who worked on the 100-ton test, later reported that of the 9,500 cubic feet of earth displaced and loosened by the blast, 40 percent was dispersed outside the crater. Pulverized earth carried most of the radioactivity with the finest particles being three times more radioactive than the larger ones. As Brodie has observed, “This should have raised alarms given the serious windstorms that swept through the New Mexico plains, but apparently did not.”[12]

Anderson reported on the latest survey of radiation above the crater 41 days after the test. The purpose was to determine the “permanence of the [radio]active deposit exclusive of the effect of the radioactive decay.” There was substantially less radioactive material “due to the effect of the wind in dispersing the ... material outside the region in which there was measurable activity.”

Dr. Louis Hempelmann, the director of medical and health affairs at Los Alamos, found that there were “slight” risks from the test’s dispersal of radioactive products. The explosion produced a cloud that lofted 98 percent of the material rising to a height of 13,000 to 15,000 feet. Project meteorologists concluded that thermal air currents contributed to the cloud’s “rapid dispersion.”

With the first atomic test approaching, doctors and scientists at Los Alamos began looking closely at precautions and radiation safety measures. Louis Hempelmann prepared the first part of a memorandum that described the effects that could pose dangers, such as blast, radiation, and radioactive materials. Discussing what later became known as fallout, Hempelmann wrote that the “worst possible hazard from radioactive dust would seem to be the one in which the explosion is of sufficient energy to only get the material in the form of a cloud of fine dust.” If the particles fell on a nearby shelter, it would be “dangerous … to breathe for more than 6 minutes.”

To make it possible for real-time measurements of beta and gamma radiation and airborne fission products and to protect staff from radiation, the second part of the memorandum, prepared by electronics specialist Richard Watts, recommended deploying measuring instruments at shelters and mobile units and the organizational structure needed for this work.

Kenneth Bainbridge, the chief planner for the Trinity test, likely saw the Hempelman-Watts memorandum and spoke with General Groves about the “medical legal” problem. Point by point, Bainbridge reviewed the nearby human settlements and installations that radiation could affect, including ranches, towns, and military personnel. In the event that evacuation was necessary, Groves believed that officers would have to accompany military police along with some physicists who would take measurements. Groves also wanted to involve experts on earth shock, blast effects, and the spread of radioactivity, all of whom could be consulted. Owing to the risk of contamination by various fission products, “certain legal problems will arise because some of this land is homestead entry land, some is vacant land, and some is state grazing land.”

Two Los Alamos scientists, John Magee, a physical chemist, and Joseph Hirschfelder, a physicist working in the Ordnance and Engineering Division, reinforced Hempelmann’s message about likely hazards. Perhaps influenced by Anderson’s finding about fine particles, Hirschfelder and Magee cited the “definite danger of dust containing active material and fission products falling on towns near Trinity and necessitating their evacuation.”[13] Looking at what could happen to people in the area, they suggested that an individual could receive “approximately 22 R” in the hours after the explosion. That was over 100 times higher than the then-current official safety standard of 0.1 R.[14] To mitigate the risk and curtail the spread of radioactive dust, they proposed deploying crushed rock, concrete slurry and a film of oil at the test site.

Hirschfelder and Magee experienced pushback very quickly—no one wanted to credit their forecast, but they were prescient. Hirschfelder later recalled that “very few people believed us when we predicted radiation fallout from the atom bomb,” observing that the government “acted very cavalierly toward the danger.”[15]

Captain James F. Nolan, Hempelmann’s deputy, prepared a report on plans for monitoring radiation and the evacuation of nearby towns in the event of an emergency. The premise was that no individual should “receive more than five (5) r[oentgen] at one exposure.” Five was an arbitrary figure and possibly dangerous in itself, as it was fifty times higher than the prevailing safety standard.[16]

Requiring high-level approval for the safety plan, Los Alamos Medical Group Deputy Director Nolan flew to “Site X” to meet with General Groves on 19 July. “Site X” was the gaseous diffusion plant in Clinton, TN (later known as Oak Ridge Laboratory), that produced the highly-enriched uranium used in the “Little Boy” weapon. Years later, Nolan recounted the difficult encounter to Lansing Lamont (author of Day of Trinity). After waiting outside Groves’ office, Nolan was ushered in. According to his account, after Groves read the report, he “sniffed,” saying, “What's the matter with you, are you a Hearst propagandist?” Nolan recounted that Groves “seemed genuinely sore at [him] for bringing up the prospects of radioactive contamination.” It later took the intervention of the higher-level official Stafford Warren to convince Groves to approve the plan.[17] What upset Groves was the prospect that evacuations could put MED security at risk by attracting the attention of the media, although he may also have been unsettled by the subject of bomb-connected radiation.

A few days after meeting with Groves, Nolan and Hempelmann jointly responded to the Hirschfelder/Magee memorandum (Document 6). Their response has been controversial, with some historians believing that it downplayed the radiation danger while others took the opposite view. Compared to Hirschfelder and Magee, Nolan and Hempelmann saw “less likelihood of serious damage to individuals in neighboring towns,” but they allowed for the possibility of “serious” hazards and the necessity for evacuation. Certainly, the efforts to get Groves to approve a monitoring system suggested recognition of the need for safeguards, but it is possible that the higher-level downplaying of radiation dangers encouraged Nolan and Hempelmann to find a middle position. Informing the decisions to monitor Trinity-produced radiation was the need to gather evidence in the event of future legal claims against the government.[18]

A week before the test, Los Alamos lab director Robert Oppenheimer met with radiation experts, including Stafford Warren, James F. Nolan, Louis Hempelmann, and Victor Weisskopf. After reviewing the mechanisms that produced fallout and its dispersal, they heard a briefing on optimum weather conditions: the wind velocity should not be too “too high” and a wind to the south would be best because there were no nearby towns and the mountains that would block the spread. A tolerance dose (maximum level) of up to a 100 roentgen was acceptable unless there was further exposure. If the total “integral dose” (total amount absorbed by the body) was in the 60-100 roentgen range, however, evacuations would then be necessary.

The Trinity test planners prepared for the evacuation of any endangered civilians by positioning a small force of 140 enlistees, four officers, and 140 vehicles, equipped with tents, drinking water, rations, coffee, sugar, and milk, among other supplies. The shelter and supplies were estimated to be enough for 450 people for two days. The detachment’s headquarters were set up near Bingham, “the center of the area in the most immediate danger.” Two press releases had been prepared: one concerning the explosion of an ammunition dump, the other explaining the presence of “gas shells” at the ammunition dump that necessitated evacuation for 24 hours to protect people “from the gas and degree of contamination.”

Radiation monitors worked from the base near Bingham and reported to Joseph Hoffman and Joseph Hirschfelder. On 16 July at about 1 p.m., when any possibility of “serious contamination” had passed, Hoffman released the special detachment from further duty.

Los Alamos staffer Arthur Breslow was in the group monitoring radioactivity after the test. After taking readings from “falling particles from the cloud which had passed overhead,” a radio failure prevented him from communicating the readings. Leaving his crew behind, he drove quickly to find another radio and saw that the valley in front of him was covered “with a strata of sand-like dust” forming clouds.  Discovering that he had not taken his respirator, he closed the windows and used a slice of bread as a filter! Once he had reached a radio close to Bingham, Breslow learned that “there was danger of an immediate evacuation and the count was rising rapidly.” He drove back to warn his crew but by then the readings were lower and no evacuation decision was made.[19]

Stafford Warren’s report dovetailed with Breslow’s account because of his serious concern about the radioactive debris: “the dust outfall from the various portions of the cloud was potentially a very serious hazard over a band almost 30 miles wide extending almost 90 miles northeast of the site.” Warren was close to using the term “fallout,” but “outfall” conveyed the idea. He also observed that there was still “a tremendous amount of radioactive dust floating in the air.” These problems informed his recommendation that any future tests should take place not in Alamogordo but in a region “with a radius of at least 150 miles without population.”

The cloud column mass and top reached a phenomenal height, variously estimated as 50,000 to 70,000 feet,” which towered over the northeast corner of the site for several hours.” Referring to a “deserted canyon” 20 miles northeast of Zer, Warren reported that “intensities ... were high enough to cause serious physiological effects.” He further reported to Groves that it was his opinion “that lethal or severe casualties would occur to exposed personnel up to two miles from a variety or combination of causes, i.e., blast, heat, ultraviolet and missiles.” Those were some of the effects that would be demonstrated at Hiroshima and Nagasaki, although Warren did not mention radioactivity as a lethal factor and perhaps confused it with ultraviolet.

Attached to Warren’s memorandum were diagrams showing the “path of the cloud,” information about the “hot canyon” and the nearby “house with family” [See Document 16], and the cover note to a map showing “isodose curves” indicating the spread of radioactivity.

On 22 July 1945, Warren wrote privately to Nolan, giving him far more alarming impressions: radiation monitors “found radiation at levels as high as thirty to forty roentgens ‘near a lot of houses’ and, in ‘one hot canyon’ northeast of Bingham, radiation ‘totaling 230r.’” Warren further wrote: “Boy what a narrow escape. If we had laid it down in a steady wind as planned when you left we would have had a high mortality!! It was terrific.”[20]

The information in Warren’s report may have prompted Groves to call Warren and ask him about a “certain family there.” Groves received a follow-up call informing him that Hymer Friedell’s “boys had made some further observations and are “concerned about one family [no doubt the Ratliffs] to the extent that they want to get in touch with [them] to see how they feel” [See Documents 15 and 16]. While Friedell’s group wanted advice on the “legal end,” Groves said that “there was nothing I could do about it” and that they should confer with Warren. All that was done was to keep an eye on the Ratliff family.

After providing measurements for the test itself, Victor Weisskopf and his colleagues described the “extremely high” radioactivity in and around the crater but which “decreased rapidly during the first few days.” The final section discussed the fallout on northeastern New Mexico, for which there was a “swath of fairly high radioactivity on the ground covering an area of about 100 miles long by 30 miles wide.” In what was likely a reference to the Ratliff family [See Document 16], “One ranch house east of Bingham received an initial radiation intensity calculated to be 7 r/hr [roentgen per hour].” Moreover, “gamma radiation was found in measurable but very low intensities in Santa Fe, Los Vegas, Raton and even in Trinidad, Colorado (260 miles from zero point).”

Joseph Hoffman, who directed the radiation monitoring activities for the area beyond the Trinity site, produced a detailed account of the monitoring immediately at the time of the July 1945 test. According to Hoffman, “one half of all the [radio]activity available was precipitated in the two weeks after the explosion” and 90 percent of it was in New Mexico. As Brodie noted, Hoffman acknowledged “that a localized ‘hot spot’ might have occurred, none was found, and the actual contamination indicated a uniform distribution at a concentration which is considered not to constitute a health hazard.” No monitoring occurred near the Mescalero Apache Reservation or at Ruidoso, the location of a girls camp that “received significant fallout.” With respect to the Apache reservation, Brodie suggests that the test planners chose a day when the “most likely wind direction blew to the north,” thus avoiding the area around that territory.

Almost all of the names of the radiation monitors and other officials mentioned in this report were excised for “privacy reasons.” For example, Arthur Breslow’s name was excised (and Hoffman did not mention his vivid account). Given that the excisions were probably made decades after Hoffman produced this report, they were likely a misuse of the Privacy Act; the individuals mentioned were probably long retired from government service. The National Security Archive has requested an unredacted copy of the report.

During the weeks and months after Trinity, Dr. Louis Hempelmann and Los Alamos colleagues visited people who lived near the test site and collected data on beta burns on dogs and ranch cattle. In July 1947, Los Alamos published a compilation of the reports and memoranda that Hempelmann had prepared after the test.

One downwinder family that Hempelmann and others visited several times were the Ratliffs, a pair of grandparents and their grandson, who had been completely unnoticed during the pre-test surveys. They lived near the “Hot Canyon” where fallout levels had been high. The grandson was at school on 16 July so he had less exposure during those hours. The grandparents did not report anything unusual about that day, although during his initial visit, Hempelmann wrote that there was “rain in this area on the night after the shot: this means that some of the [radio]activity was carried into their drinking water and may have been drunk on the following day and thereafter.” [Page 7] During a subsequent visit, on 11 November, Mr. Ratliff told Hempelmann something that he had not mentioned before: “an interesting story of the appearance of the ground immediately after the shot.” The “ground and fence posts had the appearance of being covered with light snow, or of being ‘frosted’ for several days after the shot” [Page 69].

The Los Alamos staffers took samples of the drinking water but apparently none of them mentioned possible health risks to the Ratliffs or others. According to Hempelmann’s calculations during the two weeks after Trinity, the Ratliffs received an estimated 47.0 roentgens of gamma radiation when the “allowable limit” was 1.4 roentgens (Page 9). In any event, during the weeks after the test, Hempelmann reported that the Ratliffs appeared to be in “excellent health.” Other nearby families who experienced the fallout were completely overlooked.[21] Years later, Hempelmann observed, “a few people were probably overexposed, but they couldn’t prove it and we couldn’t prove it. So we just assumed we got away with it.”[22]

Much of this compilation consists of reports, some highly clinical, focusing on the fallout exposure of farm animals, mostly cattle, but also cats and dogs on the Ratliff ranch and elsewhere. With respect to cattle, Hempelmann and others reported lesions on the skin and hair loss, although the cattle appeared normal in other respects. Data collected by the Army indicated that up to 600 cattle in the Trinity area “showed signs of beta rays damage” [Page III-8, after page 69]. The Army purchased 75 of the most affected cattle, with 17 going to Los Alamos and 61 shipped to “Site X.” At Oak Ridge, they experienced various health problems, including skin cancer, with the last surviving member, “Granny,” living until she was euthanized in 1964.[23]

Medical doctor and radiation expert Joseph Hamilton was participating in human radiation experiments by the time he presented Stafford Warren (who had become a dean at UCLA) with a proposal for long-term studies of the impact on New Mexico of the Trinity explosion. After providing some “sketchy information” concerning the presence of “fission product activity” in a 100 square mile area adjacent to the test site, he suggested a research program divided into two areas.

One area was the “immediately practical questions which relate to the possibilities of biological injury to flora and fauna of the area and to man so as to provide whatever data may be necessary to meet any medical legal considerations which may arise.” The other and “more important” area of research had military implications. It involved the “accumulation and analysis of sufficient data which make possible the prediction of the various chains of events which may take place following the contamination of large land areas with the release of fission products” whether by accident or military action.

From Hamilton’s perspective, the long-range need was to “secure as wide a fund as possible of general information about the contaminated region and any adjacent area which may possess a comparable degree of radioactivity.” Thus, major items for detailed study would be the distribution of fission products in plant life and livestock as well as studies of soil samples. In the meantime, the U.S. “should not open any new areas for grazing until two points are settled, first, the degree of uptake of radioactivity by the livestock, and second, adequate monitoring of all areas which may be contaminated by fission product and plutonium activity.”

Among Hamilton’s conclusions was that the “basic knowledge gained from such studies is indispensable to an evaluation of what the future may bring and the steps which may be taken to meet these problems.” Warren accepted Hamilton’s proposal, and within months the AEC was funding studies at UCLA of the long-term impact of the Trinity test.[24]

Albert W. Bellamy, a professor of zoology and biophysics at UCLA, became the director of the Atomic Energy Project’s research on the effects of the Trinity Test.  Having attended a conference on the radiation effects at Socorro, NM, he sent a senior AEC official some of the “more significant impressions and conclusions” concerning the area contaminated by the test. He did not see a “total body radiation” hazard in the area “unless someone should chose to spend about two days or more lying in the ground in the most active area.” There were, however, possible hazards from “wind-blown dust that is in the air, which is of frequent occurrence ... especially as regards alpha emitters,” which in the aggregate could “in time induce lung tumors in mice.” But more data was needed. He also mentioned “evidence that certain plants will take certain elements from very low concentrations in the soil and concentrate them in high degree.”

One of the conference’s conclusions was the need to “determine, with a minimum of time and expense, whether or not biological hazards still exist in the area.” That would involve a “bioassay” of livestock that had grazed in the “active area” for over two years. He suggested “bringing in about 20 head of young stuff from outside the Socorro region” with one group to be “maintained in the most active area on the Chupadera” and the other “in a nearby uncontaminated area.” Also recommended was “greenhouse-laboratory work on plants … to estimate the probability of long range hazards.”

With respect to the trinitite—the soil that the explosion turned into a glass-like substance—at the test site, the conference discussed the “feasibility of preparing a release for the Socorro paper to give the local population some idea of the dangers of getting too familiar with the greenglass and beads.”

Radioactive contamination at the test site continued to invite discussion. During a meeting of the AEC’s Advisory Committee on Biology and Medicine, James Herbert Jensen, chief of the AEC’s biology staff, discussed a recent visit to the Trinity site. “The question whether the area should be fenced off as a hazardous area was thoroughly discussed.” With the grasses showing “a fairly high level of activity,” he proposed purchasing 10 head of cattle to determine whether “anything of a detrimental nature accumulated in these animals.” With respect to the trinitite found on the test site, the Committee decided that “active measures should be taken to remove this as a potential hazard.”

This is the first report on Trinity radiation prepared by Albert Bellamy’s Alamogordo Project at UCLA in keeping with the AEC’s authorization to “conduct a systematic survey of the area ... to estimate the probability that hazards now exist or may arise in the future as a result of widespread low grade radioactivity.” The territory in New Mexico surveyed was the area around Trinity, the Red and Grey Hills Region, the Oscuro Mountains, the Chupadera Mesa, and the Rolling Plains Region, an area comprising 1130 square miles.

According to the report, “all [radio]activities outside the Crater are found in the upper two inches of soil,” and “spread by wind and water, particularly in the Trinity Region.” A radiological survey of 402 small animals “found that activity when present was associated with the digestive tract,” with “no substantial indication of tissue accumulation.” At the detonation point area “radioactivity is still present to create a strong presumption of hazard to living things that remain continuously in this area.” That made it necessary to enclose 145 acres with a fence. Otherwise, “the amount of radioactive fission product to be found in any one place throughout this area are relatively small.”

On the Chupadera Mesa, a grazing area controlled mainly by four ranch owners, “there is a larger amount of radioactivity than in any other place except near the Crater”: “enough radioactive material … settled out over this area to produce superficial skin ‘burns’ on cattle grazing there.” Nevertheless, the report found that “the greatest concentration of radioactive fission products are not great enough anywhere in the contaminated region and especially outside the Crater Area to present a significant immediate hazard to man or his domestic animals from total body exposure to beta gamma contamination.” That conclusion was “gratifying … but it would be rash to conclude, in the absence of specific information, that no hazards associated with products of the bomb detonation exist in this area, the harmful effects of which may not appear for a number of years.”

This study is listed on OpenNet as being in the NTA collection and the editor has requested a PDF from the Department of Energy. Only the excerpts collected by Ferenc Szasz and his notes are available at present.

In this research update, the UCLA scientists reported that they had found plutonium in soil and plants collected from various locations “along the line of Fall-out for at least a distance of eighty-five miles from the Fenced Area.” They also found “alpha emitters, presumably plutonium, … in airborne material from the Crater Region and the Chupadera Mesa.” While concentrations in the soil were variable, the “maximum concentrations ... outside the Fenced Area are found approximately twenty-eight miles from Zero in the downwind trail of the Fall-out.” The scientists suggested that the “air-borne material ... because of its particle size and level of alpha activity appear[ed] at this time, to be of greatest concern.”

The researchers studied rodents that had been collected 28 to 30 miles from the Crater and found alpha activity in their bones, liver, muscle and connective tissue. By contrast, they did not find alpha activity in rodents that were collected in and near the Crater. With respect to the data’s “biological significance,” they could not evaluate it because it was not “possible under the present circumstances ... to assess the potential hazard of plutonium found to the people and cattle living on the Chupadera Mesa.” According to the report, “this area is not suitable for the collection of field data on food ordinarily consumed by humans and no good study has been possible with cattle in the area.”

Open-Net provides details on this report, but like the previous UCLA study, DOE has yet to provide a PDF. Based on 1949 and 1950 radiological surveys of soil and plant life and their interrelations, this detailed report included disquieting findings concerning the residual radioactivity of the Trinity Fall-out. For example, “measurable amounts of radioactive fission products ... still are present” in the Ratliff area (near the “Hot Canyon”), the Chupadera Mesa, and “Area 21” (28 miles northeast of Zero). On the Mesa, radioactive contamination was “still concentrated in the upper one or two inches of soil,” while “downward migration of the radioactive fission products may be taking place.” Further, “the relatively greater uptake observed in 1950, compared to 1949, points out that as a potential biological hazard the remaining … fission product contamination of the Chupadera Mesa is relatively greater now than in the past.”

The researchers found “no hazard from external total body exposure to penetrating ionizing radiation (gamma rays) exists any place outside of the Fenced Area,” but they would not “assume at this point that that no hazard exists outside of the Fenced area from the widespread fission product contamination.” In addition, outside the Fenced Area there are “many potential long term insidious hazards from the present low level contamination which is the focal point of these studies.” Evidence from the annual biological surveys was “beginning to accumulate … that such hazards exist.”

The degree of danger, specifically the “absence, presence, or magnitude of the biological hazard” was nevertheless indeterminate because the area was in “flux.” Before conclusions could be drawn, annual surveys and related laboratory research were necessary to “determine the mechanisms by which the long and medium half-life fission products and the important alpha emitters are absorbed and metabolized by important crops and animals.”

If any at the AEC had hoped that radiation would dissipate, this UCLA report, Janet Farrell Brodie later explained, “gave even less reassurance as the investigators resurveyed areas studied earlier and corrected earlier findings.” Using new data, the report found that that “the area originally contaminated by fall-out from the Trinity detonation was greater than the 1,100 square miles estimated by the 1948 survey,” although a square mile estimate was not provided. The researchers found plutonium “in amounts up to 0.007 micrograms per square foot of soil, one-half inch deep, at a distance of 88 miles northeast of the site of detonation,” with even more, l07 micrograms per square foot, on the Chupadera Mesa 28 miles northeast of the detonation site. Thus, there had been “no appreciable decrease in plutonium content of the soils … due to erosional factors.”

This 1972 report by Los Alamos scientists several decades after the test found the same overall pattern of plutonium distribution in soil, vegetation and rodents (“as a function of distance from GZ [Ground Zero]”) that Olafson, et al. had observed in 1957. Further, they noted an “increased migration of PU [plutonium] into the soil since the last measurements were made about 20 years ago.”

Beginning in 1999, the Center for Disease Control began supporting a detailed study to “identify all available information concerning past releases of radionuclides and chemicals from the Los Alamos National Laboratory.” Based on wide access to a number of archives, the final report, published in 2010, covered a variety of public exposure issues associated with activities at Los Alamos, from plutonium reprocessing and beryllium use to hot cell activities and reactor operations. A major chapter looked closely at the Trinity Test and its “potential doses to members of the public.” As Brodie observed, “For the first time, a publicly available government report provided explanations, tables, and maps of the post-test radiation.” One particularly shocking finding was that radioactive exposure rates in public areas” near the test site “measured at levels 10,000 times higher than currently allowed.”[25]

Despite the data provided on post-test radiation, the report did not draw conclusions about adverse health impacts. According to the report, “Studies of public exposure had been incomplete because they had not “reflected the internal doses received by residents [near the Trinity test] from intakes of airborne radioactivity and contaminated water and food.” Thus, “too much remains undetermined about exposures from the Trinity test to put the event in perspective as a source of public radiation exposure or to defensibly address the extent to which people were harmed” (10-50). A recent study by NCI and DOE researchers attempts to fill the gap by estimating numbers of excess cancers [See endnote 6].