Dosimetry Analysis of Project Trinity Participants

Today’s installment concludes The First Atomic Bomb,
our selection from Project Trinity 1945-1946 by Carl Maag and by Steve Rohrer published in 1982.

If you have journeyed through all of the installments of this series, just one more to go and you will have completed a selection from the great works of nine thousand words. Congratulations! For works benefiting from the latest research see the “More information” section at the bottom of these pages.

Previously in The First Atomic Bomb.

Time: July 16, 1945
Place: Old McDonald Ranch House, New Mexico

Monitoring teams resurveyed these towns about one month after the TRINITY detonation. At Bingham, gamma readings of 0.003 R/h and 0.0001 R/h were found at ground level outdoors and at waist level inside a building, respectively. At the town of White, the highest outdoor gamma reading was 0.008 R/h. Inside a building, the highest reading was 0.0005 R/h (11).

Surveys taken in the canyon area one month after the detonation indicated that gamma intensities at ground level had decreased to 0.032 R/h. The occupied ranch house was also surveyed, both inside and outside. The highest reading outdoors was 0.028 R/h, and the highest reading indoors was 0.004 R/h. [11; 19]

Monitoring was also conducted in offsite areas other than those to the north and northeast of ground zero. Monitors found no radiation readings above background levels. [11]

Significant fallout from the TRINITY cloud did not reach the ground within about 20 kilometers northeast of ground zero. From this point, the fallout pattern extended out 160 kilometers and was 48 kilometers wide. Gamma intensities up to 15 R/h were measured in this region several hours after the detonation. One month later, intensities had declined to 0.032 R/h or less. [11]

Chapter 4

Dosimetry Analysis of Participants in Project Trinity

This chapter summarizes the radiation doses received by participants in various activities during Project TRINITY. The sources of this dosimetry information are the safety and monitoring report for personnel at TRINITY, which includes a compilation of film badge readings for all participants up to 1 January 1946, and film badge data from the records of the Reynolds Electrical and Engineering Company, which contain readings through 1946. [1; 16] These sources list individual participants with their cumulative gamma radiation exposures.

4.1 Film Badge Records

During TRINITY, the film badge was the primary device used to measure the radiation dose received by individual participants. The site monitoring plan indicates that film badges were to be issued to participants. The film badge was normally worn at chest level on the outside of clothing and was designed to measure the wearer’s exposure to gamma radiation from external sources. These film badges were insensitive to neutron radiation and did not measure the amount of radioactive material that might have been inhaled or ingested. [1]

Personnel from the Medical Group had responsibility for issuing, receiving, processing, and interpreting film badges for Project TRINITY. The Site Monitoring Group compiled the film badge records for both onsite and offsite personnel. Radiological safety personnel and military police recorded the names and identification numbers of individuals as they entered the test area. This information was recorded in an entry logbook and on a personal exposure data card. Upon leaving the test area, individuals returned their film badges to the check station. When the film badges were processed and interpreted, the reading was entered on the individuals exposure data card. In this manner, the number of times an individual entered the test area and his cumulative exposure history were recorded and maintained. [1]

4.2 Gamma Radiation Exposure

The safety and monitoring report lists film badge readings for about 700 individuals who participated in Project TRINITY from 16 July 1945 to 1 January 1946. [1] This list includes both military and nonmilitary personnel who were involved with the TRINITY operation and postshot activities. However, records are available for only 44 of the 144 to 160 members of the evacuation detachment. [1] In addition, some of these film badge listings may be for personnel who were only peripherally involved with TRINITY activities, such as family members and official guests who visited the site.

According to the safety and monitoring report, by 1 January 1946, 23 individuals had received cumulative gamma exposures greater than 2 but less than 4 roentgens. An additional 22 individuals received gamma exposures between 4 and 15 roentgens. Personnel who received gamma exposures exceeding 2 roentgens represent less than six percent of the Project TRINITY participants with recorded exposures. As described below, these exposures generally resulted when personnel approached ground zero several times. [1]

Information is available regarding the activities of some of these personnel. One of the drivers of the earth-sampling group’s lead-lined tank, an Army sergeant who traveled three times to ground zero, received an exposure of 15 roentgens. A second tank driver, also an Army sergeant, received an exposure of 3.3 roentgens. Three members of the earth-sampling group, all of whom traveled in the tank to ground zero, received exposures of 10, 7.5, and 5 roentgens. An Army photographer who entered the test area six times between 23 July and 20 October received 12.2 roentgens. [1]

Four individuals involved with excavating the buried supports of the TRINITY tower from 8 October to 10 October 1945 received gamma exposures ranging from 3.4 to 4.7 roentgens. Film badge readings for this three-day period indicate that the two individuals who operated mechanical shovels received 3.4 and 4.3 roentgens, while the two who supervised and monitored the excavation received exposures of 4.2 and 4.7 roentgens. The individual receiving 4.7 roentgens during the excavation operation had received 1.3 roentgens from a previous exposure, making his total exposure 6 roentgens. [1]

An Army captain who accompanied all test and observer parties into the ground zero area between 1 September and 11 October 1945 received a total gamma exposure of 2.6 roentgens. [1] The activities and times of exposure are not known for other personnel with exposures over 2 roentgens.

According to the dosimetry records for 1946, about 115 people visited the test site that year. No one ventured inside the fence surrounding ground zero, and no one received an exposure greater than 1 roentgen. [1; 16]

COMPLETE LIST OF SOURCES CITED IN THIS SERIES

[1. Aebersold, Paul. July 16th Nuclear Explosion-Safety and Monitoring of Personnel (U). Los Alamos Scientific Laboratory, Atomic Energy Commission. Los Alamos, NM.: LASL. LA-616. January 9, 1947. 170 Pages.]

[2. Bainbridge, K. T. Memorandum to All Concerned, Subject: TR Circular No. 18–Total Personnel at TR. [Base Camp, Trinity Site: NM.] July 3, 1945. 1 Page.]

[3. Bainbridge, K. T. TRINITY. Los Alamos Scientific Laboratory. Los Alamos, NM.: LASL, LA-6300-H and Washington, D. C.: GPO. May 1976. 82 Pages.]

[4. Bramlet, Walt. Memorandum for Thomas J. Hirons, Subject: DOD Participants in Atmospheric Tests, wo/encl. Los Alamos Scientific Laboratory. Los Alamos, NM. ISD-5. February 20, 1979. 4 Pages.]

[5. General Electric Company–TEMPO. Compilation of Local Fallout Data from Test Detonations 1945-1962. Vol. 1: “Continental US Tests.” Washington, D. C.: Defense Nuclear Agency. DNA 1251-1(EX.). 1979. 619 Pages. (A99) AD/AO79 309.]

[6. Groves, Leslie R., LTG, USA. Memorandum for Secretary of War, {Subject: TRINITY}. {Washington, D.C.} 18 July 1945. 13 Pages.]

[7. Groves, Leslie R., LTG, USA (Ret.). Now It Can Be Told: The Story of the Manhattan Project. New York, NY.: Harper and Row. 1962. 444 Pages.]

[8. Headquarters, 9812th Technical Service Unit, Provisional Detachment No. I (Company “B”). {Extract from: Daily Diary, Provisional Detachment No. 1 (Company “B”), 9812th Technical Service Unit.} Army Corps of Engineers, Department of War. {Santa Fe, NM.} 14 July 1945. 2 Pages.]

[9. Headquarters, Special Service Detachment. Supplemental Special Guard Orders, with Appendix. Los Alamos Scientific Laboratory, Manhattan Engineer District. {Alamogordo, NM.} 14 July 1945. 4 Pages.]

[10. Hempelmann, L. H., M.D. {Extracts from: “Preparation and Operational Plan of Medical Group (TR-7) for Nuclear Explosion 16 July 1945.”} Los Alamos Scientific Laboratory, Atomic Energy Commission. Los Alamos, NM.: LASL. LA-631(Deleted). June 13, 1947. 32 Pages.]

[11. Hoffman, J. G. {Extracts from “Health Physics Report on Radioactive Contamination throughout New Mexico Following the Nuclear Explosion, Part A–Physics.”} Los Alamos Scientific Laboratory, Manhattan Engineer District. {Los Alamos, NM.} {1945.} 31 Pages.]

[12. Lamont, Lansing. Day of TRINITY. New York, NY.: Atheneum. 1965. 331 Pages.]

[13. Los Alamos Scientific Laboratory, Public Relations Office. “Los Alamos: Beginning of an Era, 1943-1945.” Atomic Energy Commission. Los Alamos, NM.: LASL. 1967. 65 Pages.]

[14. Oppenheimer, J. R. Memorandum for Group Leaders, Subject: TRINITY Test. Los Alamos Scientific Laboratory. Los Alamos, NM. June 14, 1945. 2 Pages.]

[15. Palmer, T. O., Maj., USA. Evacuation Detachment at TRINITY. {Manhattan Engineer District, Army Corps of Engineers.} {Los Alamos, NM.} {18 July 1945.} 2 Pages.]

[16. Reynolds Electrical & Engineering Company, Inc. {Personnel Radiation Exposures, 1945, 1946} Las Vegas, NV. Microfilm.]

[17. Warren, S. L., COL., USA. Directions for Personnel at Base Camp at Time of Shot. Los Alamos Scientific Laboratory, Manhattan Engineer District. {Alamogordo, NM.} 15 July 1945. 1 Page.]

[18. Warren, S. L., COL, USA; Hempelmann, L. H., M.D. Extracts from: Personal Notes, Subject: Events in Camp Immediately Following Shot–July 16, 1945. 1945. 2 Pages.]

[19. Weisskopf, V.; Hoffman, J.; Aebersold, Paul; Hempelmann, L. H. Memorandum for George Kistiakowsky, Subject: Measurement of Blast, Radiation, Heat and Light and Radioactivity at Trinity. {Los Alamos, NM.} 5 September 1945. 2 Pages.]

This ends our series of passages on The First Atomic Bomb by Carl Maag and Steve Rohrer from their bookProject Trinity 1945-1946 published in 1982. This blog features short and lengthy pieces on all aspects of our shared past. Here are selections from the great historians who may be forgotten (and whose work have fallen into public domain) as well as links to the most up-to-date developments in the field of history and of course, original material from yours truly, Jack Le Moine. – A little bit of everything historical is here.

More information on The First Atomic Bomb here and here and below.