{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"bc2f921d03200ef90626973db15955fb64343a77cc5adb91b71ee9fec71ad2ca","created":"2026-10-03T07:18:06Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"b5f40ddf76908a5ade02a78019c70ba6238503d879f8950158521689c4798561","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"med.dosimetry.water-ivalue","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"How quickly a charged particle slows down in water depends on one material constant, the average energy needed to excite a water molecule. Its uncertainty alone produces millimetre-scale uncertainty in where a proton beam stops in water.","posed_since":"","precise":"Determine the mean excitation energy $I$ of liquid water, which enters the Bethe stopping-power formula, to an uncertainty below 1 eV; the ICRU 90 recommendation is $I = 78 \\pm 2\\,\\mathrm{eV}$, and published experimental and dielectric-response values spread over several eV around it. An answer is a value with uncertainty consistent between direct range or stopping-power measurements and optical-data calculations.","problem_ref":null,"references":"","settled_by":"Precision range measurements of monoenergetic protons and ions in liquid water at 1 to 250 MeV combined with an evaluation of the optical oscillator strength of liquid water.","status_note":"","title":"Mean excitation energy of liquid water","topic_ref":"be2989252171f9f987d92f4b562e96075370f97879f879218827602913f7731c"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"a468378cea7aba60203fbfa7717dd1791d5ef22ee8ff197632c670c9b2d42334","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"7bd524e4d936e642d173a985eaa10eb1c06347aa34743a0909c7e15515a8040f","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"vDEysQh9Is7AIvpcOHE2UxXb88pihZG2ROrzBb_RT4fx8P-gg3sdQbaLWYVV_XDrI0gBBC8_XBiBPPytZHIxAw"},"schema":"pubphys.envelope/1"},"record_hash":"a468378cea7aba60203fbfa7717dd1791d5ef22ee8ff197632c670c9b2d42334","leaf_index":1678}