[H-CG22] Monitoring the Comprehensive Nuclear-Test-Ban Treaty: Status, operations, and scientific application

[HCG22-12] Plaster wall was altered by the “Black rain” generated by the Hiroshima bombing.

*Tadashi Mukai^1,2, Tomonori Adachi^1,3, Naoki Toe¹, Yuji Shibahara¹, Maiko Ikegami¹, Hiroshi Yashima¹, Satoshi Fukutani¹, Koichi Takamiya¹, Jun Inoue², Yuichi Kurihara⁴, Yasuhito Igarashi¹ (1. Institute for Integrated Radiation and Nuclear Science, Kyoto University, 2. Osaka Metropolitan University, 3.ATOX CO.,LTD. , 4. The University of Tokyo)

Keywords:black rain , acid rain, plaster walls, calcium sulfate dihydrate

(Introduction)The black rain itself has been studied along with surveys and research reports on the estimation of the black rain rainfall area after the atomic bombings of Hiroshima and Nagasaki in 1945, but mainly from the viewpoint of radioactive substance, and there have been few studies on the main components of rain except for soot[1]. Last year, we reported that analysis of a gold folding screen (western gold leaf) preserved at Hiroshima Peace Memorial Museum that contained traces of “black rain” suggested a mixture of nitric acid (N) and sulfuric acid (S) (hypothesis). This year, to test this hypothesis, we also analyzed a plaster wall (provided by Hiroshima Peace Memorial Museum) found in the vicinity of the folding screen, which still retains traces of “black rain,” and attempted to simulate acid rain by using a model plaster.
(Sample)The plaster wall samples were No.1 and No.2 as control areas, and No.3 and No.4 as black areas (Fig.1).
(Methods and Results)Observation of No.3 and No.4 in the black area under an optical microscope revealed scattered fine black granulate.SEM/EDX analysis showed that elemental nitrogen (N) was not detected in any of the samples, but elemental sulfur (S) was detected in the surface layer. The difference between the control and black areas is the distribution of S. The dendritic nature of the former indicates that SOx (gas phase) in the air reacted with calcium carbonate (solid phase) in the plaster, while the polygonal nature of the latter indicates that liquid sulfuric acid (liquid phase) may have reacted with calcium carbonate (solid phase) in the plaster. S compounds in all samples were determined to be calcium sulfate dihydrate by XRD analysis. The results of a simulated experiment in which a drop of sulfuric acid solution with black ink was dropped onto a model plaster showed S in the surface layer, although it could not be identified as calcium sulfate hydrate. In addition, calcium sulfate dihydrate was not detected in the black areas as reported in last year's report on the gold folding screen.
From the above, we speculated that the calcium sulfate dihydrate observed in the surface layers of No.3 and No.4 may have been formed by the reaction of liquid sulfuric acid with the plaster. The non-detection of N is presumably due to the high degradability of nitric acid compounds.
References: [1] Fields DE, Cole LL, Summers S, Yalcintas MG, Vaughan GL. Generation of aerosols by urban fire storm.
Acknowledgments: This research was supported by Grant-in-Aid for Scientific Research JP24H00367 and the Ministry of Health, Labour and Welfare of Japan. We would like to thank the staff of Hiroshima Peace Memorial Museum, especially the curatorial staff, the bereaved family members, Professor Satoru Endo of Hiroshima University, Dr. Tatsuya Katsuno of the Electron Microscope Laboratory, Center for Integrated Anatomy, Graduate School of Medicine, Hiroshima University, Professor Takuo Okuji of our Institute, Mr. Keita Takahashi, Mr. Tatsuo Fukui and Dr. Kazuaki Sawada of NIKON SOLUTIONS CO.,LTD.