Focus-Science and Technology - - DISCOVERIES -

In the 70-plus years since the US dropped atomic bombs on the Ja­panese cities of Hiroshima and Na­gasaki, sev­eral stud­ies have ex­am­ined the lev­els of ra­di­a­tion to which vic­tims were ex­posed, us­ing tech­niques rang­ing from longterm stud­ies of mu­ta­tion in the DNA of sur­vivors, to mea­sur­ing the lu­mi­nes­cence of quartz grains in brick frag­ments. But now a team at the Univer­sity of São Paulo (USP) in Brazil has suc­cess­fully com­pleted the first such study us­ing ac­tual hu­man tis­sue.

To do this, they em­ployed a tech­nique called ‘elec­tron spin res­o­nance spec­trom­e­try’. The re­search was con­ducted by post­doc­toral re­searcher An­gela Ki­noshita, un­der the su­per­vi­sion of USP’s Prof Oswaldo Baffa, and builds upon 1970s re­search by Prof Sér­gio Mas­caren­has, also of the Univer­sity of São Paulo.

Mas­caren­has dis­cov­ered that ex­po­sure to ra­di­a­tion leaves bones weakly mag­ne­tised. If lev­els of back­ground ra­di­a­tion are known, the ex­tent of this so- called ‘para­mag­net­ism’ can be mea­sured to re­veal a bone’s age. This means that if the age of the bone is known, it can be mea­sured to de­ter­mine how much ra­di­a­tion it has been ex­posed to.

Some four decades on, with the ben­e­fit of more ad­vanced equip­ment, Baffa and Ki­noshita were able to take such read­ings from tiny frag­ments of a vic­tim’s jaw­bone, and de­ter­mine that the in­di­vid­ual had been ex­posed to ap­prox­i­mately 9.46 Grays – al­most twice the fa­tal dose. These find­ings tally with the re­sults of pre­vi­ous stud­ies, demon­strat­ing the new tech­nique’s po­ten­tial as a means of triag­ing pos­si­ble vic­tims of ra­di­a­tion ex­po­sure.

“Imag­ine some­one in New York plant­ing an or­di­nary bomb with a small amount of ra­dioac­tive ma­te­rial stuck to the ex­plo­sive,” said Baffa. “Tech­niques like this can help iden­tify who has been ex­posed to ra­dioac­tive fall­out and needs treat­ment.”

LEFT: Jaw­bone of vic­tim from Hiroshima

BE­LOW: A de­stroyed Hiroshima af­ter the bomb was dropped in 1945

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