{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T20:08:23Z","timestamp":1792786103056,"version":"4.5.0"},"reference-count":44,"publisher":"Oxford University Press (OUP)","issue":"9","license":[{"start":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T00:00:00Z","timestamp":1790640000000},"content-version":"vor","delay-in-days":31,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Department of Energy National Nuclear Security Administration","id":[{"id":"https:\/\/ror.org\/03sk1we31","id-type":"ROR","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026,8,29]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>The B8 pile, built in April 1945, was a natural uranium, heavy water reactor experiment and the culmination of Nazi Germany\u2019s nuclear program. Its designer, Werner Heisenberg, claimed in a 1947 Nature article that the B8 was \u201cjust insufficient\u201d in achieving self-sustaining fission, lacking only a \u201crelatively small amount of uranium.\u201d In the following decades, historians have then suggested that the Germans should have pursued graphite reactors like the Americans. Here, we present forensics and document-based archaeology of the B8\u2019s uranium, heavy water, and graphites. We create a neutronics model that is validated by in situ 1945 measurements. Our calculations show that the B8, as built, had keff=0.94. To achieve self-sustaining fission at keff=1.0, the Germans would have needed about 2.0 times the uranium and about 2.2 times the heavy water than they used, far exceeding Heisenberg\u2019s predictions; these inventories were about 1.2 and 1.8 times, respectively, Germany\u2019s estimated available wartime inventories. Furthermore, we determine that their graphite, with 3.4 wppm boron impurities and re-used from the prior B7 experiment, would not allow criticality in a hypothetical graphite-natural uranium pile. German graphites were made of metallurgical coke, which naturally carry more boron than petroleum coke-based graphites, which were available in America and uniquely enabled Chicago Pile 1\u2019s criticality. Our findings indicate that Germany could not have built either a heavy water nor a graphite reactor in World War II.<\/jats:p>","DOI":"10.1093\/pnasnexus\/pgag282","type":"journal-article","created":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T12:29:52Z","timestamp":1790684992000},"source":"Crossref","is-referenced-by-count":0,"title":["Nuclear archaeology reassesses Heisenberg\u2019s last reactor experiment"],"prefix":"10.1093","volume":"5","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7223-1834","authenticated-orcid":false,"given":"Patrick J","family":"Park","sequence":"first","affiliation":[{"name":"Department of Applied Physics, Columbia University , New York, NY ,","place":["USA"]},{"name":"Department of Physics, Reed College , Portland, OR ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Brittany","family":"Robertson","sequence":"additional","affiliation":[{"name":"Pacific Northwest National Laboratory , Richland, WA ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5773-3713","authenticated-orcid":false,"given":"Miriam E","family":"Hiebert","sequence":"additional","affiliation":[{"name":"Department of Materials Science and Engineering, University of Maryland , College Park, MD ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jason","family":"Zhao","sequence":"additional","affiliation":[{"name":"Department of Computer Science, Texas A&M University , College Station, TX ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2250-8898","authenticated-orcid":false,"given":"Ciara B","family":"Sivels","sequence":"additional","affiliation":[{"name":"Applied Physics Laboratory Johns Hopkins University , Laurel, MD ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0082-0514","authenticated-orcid":false,"given":"Timothy W","family":"Koeth","sequence":"additional","affiliation":[{"name":"Department of Materials Science and Engineering, University of Maryland , College Park, MD ,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"286","published-online":{"date-parts":[[2026,9,29]]},"reference":[{"key":"2026092908294625200_pgag282-B1","author":"Gordin","year":"2025"},{"key":"2026092908294625200_pgag282-B2","first-page":"237","volume-title":"The Uranium Club: unearthing the lost relics of the Nazi nuclear program","author":"Hiebert","year":"2023"},{"key":"2026092908294625200_pgag282-B3","doi-asserted-by":"crossref","first-page":"211","DOI":"10.1038\/160211a0","article-title":"Research in Germany on the technical application of atomic energy","volume":"160","author":"Heisenberg","year":"1947","journal-title":"Nature"},{"key":"2026092908294625200_pgag282-B4","author":"Atomic Heritage Foundation: Richard Rhodes\u2019 Interview","year":"2016"},{"key":"2026092908294625200_pgag282-B5","volume-title":"The wages of destruction: the making and breaking of the Nazi economy","author":"Tooze","year":"2006"},{"key":"2026092908294625200_pgag282-B6","doi-asserted-by":"crossref","DOI":"10.7208\/chicago\/9780226388625.001.0001","volume-title":"Making jet engines in World War II: Britain, Germany, and the United States","author":"Giffard","year":"2016"},{"key":"2026092908294625200_pgag282-B7","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1017\/9781009479264","volume-title":"Hitler\u2019s atomic bomb: history, legend, and the twin legacies of Auschwitz and 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Jahren 1940\u20131945","volume":"3","author":"Wirtz","year":"1947","journal-title":"Phys Bl\u00e4tter"},{"key":"2026092908294625200_pgag282-B12","first-page":"365","volume-title":"An annotation to papers on the Uranium Project (1939\u20131945)","author":"Wirtz","year":"1989","edition":"1st ed"},{"key":"2026092908294625200_pgag282-B13","first-page":"595","volume-title":"Bericht \u00fcber einen versuch mit 1,5 to D2O und U und 40 cm Kohler\u00fcckstreumantel (B7)","author":"Bopp","year":"1989","edition":"1st ed"},{"key":"2026092908294625200_pgag282-B14","doi-asserted-by":"crossref","first-page":"237","DOI":"10.1080\/08929889308426386","article-title":"Nuclear archaeology: verifying declarations of fissile-material production","volume":"3","author":"Fetter","year":"1993","journal-title":"Sci Glob Sec"},{"key":"2026092908294625200_pgag282-B15","first-page":"95","article-title":"Document-based nuclear archaeology","volume":"30","author":"Reistad","year":"2022","journal-title":"Sci Glob 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Knut Haukelid dated February 21, 1966","author":"Larsen","year":"2023"},{"key":"2026092908294625200_pgag282-B24","volume-title":"Letter to David Irving dated July 24, 1966","author":"Larsen","year":"2023"},{"key":"2026092908294625200_pgag282-B25","first-page":"271","volume-title":"Atomic: the first war on physics and the secret history of the atomic bomb, 1939\u20131949","author":"Baggot","year":"2015"},{"key":"2026092908294625200_pgag282-B26","doi-asserted-by":"publisher","first-page":"1","DOI":"10.1140\/epjh\/s13129-025-00098-7","article-title":"Myths of nuclear graphite in World War II, with original translations","volume":"50","author":"Park","year":"2025","journal-title":"Eur Phys J H"},{"key":"2026092908294625200_pgag282-B27","author":"Wikle","year":"1945"},{"key":"2026092908294625200_pgag282-B28","first-page":"7","volume-title":"January 1940","author":"Joseph Meehan","year":"1940"},{"key":"2026092908294625200_pgag282-B29","first-page":"12","article-title":"Initiation of the chain reaction: the search for pure materials","volume":"4","author":"Allison","year":"1962","journal-title":"Int At Energy Agency Bull"},{"key":"2026092908294625200_pgag282-B30","author":"Groueff","year":"1965"},{"key":"2026092908294625200_pgag282-B31","author":"Bothe","year":"1941"},{"key":"2026092908294625200_pgag282-B32","author":"Nuclear Engineering Division","year":"."},{"key":"2026092908294625200_pgag282-B33","volume-title":"Atomic energy for military purposes","author":"DeWolf Smyth","year":"1945"},{"key":"2026092908294625200_pgag282-B34","volume-title":"Heisenberg and the Nazi atomic bomb project, 1939-1945: a study in German culture","author":"Lawrence Rose","year":"2001"},{"key":"2026092908294625200_pgag282-B35","first-page":"252","volume-title":"The wages of destruction: the making and breaking of the Nazi economy","author":"Tooze","year":"2006"},{"key":"2026092908294625200_pgag282-B36","author":"Perrycoste","year":"1946"},{"key":"2026092908294625200_pgag282-B37","first-page":"248","volume-title":"The Uranium Club: unearthing the lost relics of the Nazi nuclear program","author":"Hiebert","year":"2023"},{"key":"2026092908294625200_pgag282-B38","author":"Conlin","year":"2005"},{"key":"2026092908294625200_pgag282-B39","author":"Brown","year":"2005"},{"key":"2026092908294625200_pgag282-B40","author":"Anderson","year":"1942"},{"key":"2026092908294625200_pgag282-B41","author":"Popp","year":"2025"},{"key":"2026092908294625200_pgag282-B42","doi-asserted-by":"crossref","first-page":"769","DOI":"10.1007\/BF01330637","article-title":"Die wechselwirkung von neutronen und \u03b3-Strahlen mit beryllium","volume":"122","author":"F\u00fcnfer","year":"1944","journal-title":"Z Phys"},{"key":"2026092908294625200_pgag282-B43","author":"Rolphton Nuclear Training Centre","year":"1980"},{"key":"2026092908294625200_pgag282-B44","volume-title":"Book III: the P-9 Project","author":"Manhattan Engineer District","year":"1947"}],"container-title":["PNAS Nexus"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/academic.oup.com\/pnasnexus\/article-pdf\/5\/9\/pgag282\/71405328\/pgag282.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/academic.oup.com\/pnasnexus\/article-pdf\/5\/9\/pgag282\/71405328\/pgag282.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T12:29:58Z","timestamp":1790684998000},"score":1,"resource":{"primary":{"URL":"https:\/\/academic.oup.com\/pnasnexus\/article\/doi\/10.1093\/pnasnexus\/pgag282\/8836799"}},"subtitle":[],"editor":[{"given":"Derek","family":"Abbott","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"editor"}]}],"short-title":[],"issued":{"date-parts":[[2026,8,29]]},"references-count":44,"journal-issue":{"issue":"9","published-print":{"date-parts":[[2026,8,29]]}},"URL":"https:\/\/doi.org\/10.1093\/pnasnexus\/pgag282","relation":{},"ISSN":["2752-6542"],"issn-type":[{"value":"2752-6542","type":"electronic"}],"subject":[],"published-other":{"date-parts":[[2026,9]]},"published":{"date-parts":[[2026,8,29]]},"article-number":"pgag282"}}