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Radioactivité médicale
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Radioactivité médicale





Depuis sa découverte à la fin du XIXe siècle, la radioactivité a été mise à profit dans le domaine médical, notamment pour le traitement de différentes formes de cancers. Pour autant, son utilisation n’est pas sans danger.

➜ Quels sont les risques liés à la radioactivité ?


Objectifs

  • Citer des applications dans le domaine médical.
  • Déterminer les isotopes radioactifs d’un élément à partir d’un diagramme ().

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Doc. 1
Histoire de la radioactivité

La découverte de la radioactivité a permis de faire de nombreuses avancées dans le domaine médical avec l’apparition des premières radiographies et des traitements par radiothérapie.

Eras

    Évènements

    1. 1893 - : <span data-content-md-theme="pc-pink" data-content-md-tag="color" data-temp-content-md-index="2089270" class="sc-cIShpX csblnQ lls-viewer-color"><strong data-content-md-tag="b" data-temp-content-md-index="2089269" class="sc-kafWEX fOpWpM lls-viewer-b">Découverte des rayons X</strong> par W. Röntgen (Prix Nobel 1901).</span> |
    2. 1896 - : <span data-content-md-theme="pc-blue2" data-content-md-tag="color" data-temp-content-md-index="2089272" class="sc-cIShpX guqNLN lls-viewer-color"><strong data-content-md-tag="b" data-temp-content-md-index="2089271" class="sc-kafWEX eFSWAk lls-viewer-b">Mise en évidence des rayons uraniques</strong> par H. Becquerel (Prix Nobel 1903).</span> |
    3. 1898 - : <span data-content-md-theme="pc-orange" data-content-md-tag="color" data-temp-content-md-index="2089274" class="sc-cIShpX fIsCvF lls-viewer-color"><strong data-content-md-tag="b" data-temp-content-md-index="2089273" class="sc-kafWEX fyTdaM lls-viewer-b">Découverte du radium et du polonium</strong> par M. Curie (Prix Nobel 1903) et P. Curie (Prix Nobel 1903).</span> |
    4. 1901 - : <span data-content-md-theme="pc-red" data-content-md-tag="color" data-temp-content-md-index="2089280" class="sc-cIShpX gwTDFf lls-viewer-color"><strong data-content-md-tag="b" data-temp-content-md-index="2089276" class="sc-kafWEX edCuNS lls-viewer-b">Curiethérapie et émission <span data-content-md-tag="math" data-temp-content-md-index="2089275" data-content-md-katex="\alpha" class="sc-jqCOkK jSjtEw lls-viewer-math" contenteditable="false"><span><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.43056em;vertical-align:0em;"></span><span class="mord mathnormal" style="margin-right:0.0037em;">α</span></span></span></span></span></span></strong><br data-content-md-tag="br" data-temp-content-md-index="2089277"/> L’atome se scinde en un noyau d’hélium et un atome plus léger.<br data-content-md-tag="br" data-temp-content-md-index="2089278"/> <span data-content-md-tag="math" data-temp-content-md-index="2089279" data-content-md-katex="^A_Z\text{X} \rightarrow \ ^{A-4}_{Z-2}\text{Y} + \ ^4_2\text{He}" class="sc-jqCOkK jSjtEw lls-viewer-math" contenteditable="false"><span><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1.1166619999999998em;vertical-align:-0.275331em;"></span><span class="mord"><span></span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8413309999999999em;"><span style="top:-2.424669em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">A</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.275331em;"><span></span></span></span></span></span></span><span class="mord text"><span class="mord">X</span></span><span class="mspace" style="margin-right:0.2777777777777778em;"></span><span class="mrel">→</span><span class="mspace" style="margin-right:0.2777777777777778em;"></span></span><span class="base"><span class="strut" style="height:1.233324em;vertical-align:-0.351862em;"></span><span class="mord"><span class="mspace"> </span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.881462em;"><span style="top:-2.406469em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span><span class="mbin mtight">−</span><span class="mord mtight">2</span></span></span></span><span style="top:-3.1031310000000003em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">A</span><span class="mbin mtight">−</span><span class="mord mtight">4</span></span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.351862em;"><span></span></span></span></span></span></span><span class="mord text"><span class="mord">Y</span></span><span class="mspace" style="margin-right:0.2222222222222222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222222222222222em;"></span></span><span class="base"><span class="strut" style="height:1.0622159999999998em;vertical-align:-0.24810799999999997em;"></span><span class="mord"><span class="mspace"> </span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8141079999999999em;"><span style="top:-2.4518920000000004em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">4</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.24810799999999997em;"><span></span></span></span></span></span></span><span class="mord text"><span class="mord">He</span></span></span></span></span></span></span></span> |
    5. 1937 - : <span data-content-md-theme="pc-purple1" data-content-md-tag="color" data-temp-content-md-index="2089282" class="sc-cIShpX enDyJR lls-viewer-color"><strong data-content-md-tag="b" data-temp-content-md-index="2089281" class="sc-kafWEX cnvmWT lls-viewer-b">Interdiction du radium non thérapeutique.</strong></span> |
    6. 1950 - : <span data-content-md-theme="pc-green3" data-content-md-tag="color" data-temp-content-md-index="2089288" class="sc-cIShpX eCSNtu lls-viewer-color"><strong data-content-md-tag="b" data-temp-content-md-index="2089284" class="sc-kafWEX hxbzjA lls-viewer-b">Tomographie et émission <span data-content-md-tag="math" data-temp-content-md-index="2089283" data-content-md-katex="\beta ^+" class="sc-jqCOkK jSjtEw lls-viewer-math" contenteditable="false"><span><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.9657709999999999em;vertical-align:-0.19444em;"></span><span class="mord"><span class="mord mathnormal" style="margin-right:0.05278em;">β</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.771331em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mbin mtight">+</span></span></span></span></span></span></span></span></span></span></span></span></span></strong><br data-content-md-tag="br" data-temp-content-md-index="2089285"/> L’atome se scinde en un atome fils et une particule chargée positivement : un positon.<br data-content-md-tag="br" data-temp-content-md-index="2089286"/> <span data-content-md-tag="math" data-temp-content-md-index="2089287" data-content-md-katex="^A_Z\text{X} \rightarrow \ ^{\quad A}_{Z-1}\text{Y} + \ ^0_1\text{e}^+" class="sc-jqCOkK jSjtEw lls-viewer-math" contenteditable="false"><span><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1.1166619999999998em;vertical-align:-0.275331em;"></span><span class="mord"><span></span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8413309999999999em;"><span style="top:-2.424669em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">A</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.275331em;"><span></span></span></span></span></span></span><span class="mord text"><span class="mord">X</span></span><span class="mspace" style="margin-right:0.2777777777777778em;"></span><span class="mrel">→</span><span class="mspace" style="margin-right:0.2777777777777778em;"></span></span><span class="base"><span class="strut" style="height:1.174993em;vertical-align:-0.333662em;"></span><span class="mord"><span class="mspace"> </span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8413309999999999em;"><span style="top:-2.424669em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span><span class="mbin mtight">−</span><span class="mord mtight">1</span></span></span></span><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mspace mtight" style="margin-right:1.4285714285714286em;"></span><span class="mord mathnormal mtight">A</span></span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.333662em;"><span></span></span></span></span></span></span><span class="mord text"><span class="mord">Y</span></span><span class="mspace" style="margin-right:0.2222222222222222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222222222222222em;"></span></span><span class="base"><span class="strut" style="height:1.0622159999999998em;vertical-align:-0.24810799999999997em;"></span><span class="mord"><span class="mspace"> </span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8141079999999999em;"><span style="top:-2.4518920000000004em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">1</span></span></span><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">0</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.24810799999999997em;"><span></span></span></span></span></span></span><span class="mord"><span class="mord text"><span class="mord">e</span></span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.771331em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mbin mtight">+</span></span></span></span></span></span></span></span></span></span></span></span></span></span> |
    7. 1951 - : <span data-content-md-theme="svt-pink1" data-content-md-tag="color" data-temp-content-md-index="2089294" class="sc-cIShpX eidyqG lls-viewer-color"><strong data-content-md-tag="b" data-temp-content-md-index="2089290" class="sc-kafWEX fPeCMP lls-viewer-b">Scintigraphie et émission <span data-content-md-tag="math" data-temp-content-md-index="2089289" data-content-md-katex="\beta ^-" class="sc-jqCOkK jSjtEw lls-viewer-math" contenteditable="false"><span><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.9657709999999999em;vertical-align:-0.19444em;"></span><span class="mord"><span class="mord mathnormal" style="margin-right:0.05278em;">β</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.771331em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mbin mtight">−</span></span></span></span></span></span></span></span></span></span></span></span></span></strong><br data-content-md-tag="br" data-temp-content-md-index="2089291"/> L’atome se scinde en un atome fils et une particule chargée négativement : un électron. <br data-content-md-tag="br" data-temp-content-md-index="2089292"/> <span data-content-md-tag="math" data-temp-content-md-index="2089293" data-content-md-katex="^A_Z\text{X} \rightarrow \ ^{\quad A}_{Z+1}\text{Y} + ^{\enspace 0}_{-1}\text{e}^-" class="sc-jqCOkK jSjtEw lls-viewer-math" contenteditable="false"><span><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1.1166619999999998em;vertical-align:-0.275331em;"></span><span class="mord"><span></span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8413309999999999em;"><span style="top:-2.424669em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">A</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.275331em;"><span></span></span></span></span></span></span><span class="mord text"><span class="mord">X</span></span><span class="mspace" style="margin-right:0.2777777777777778em;"></span><span class="mrel">→</span><span class="mspace" style="margin-right:0.2777777777777778em;"></span></span><span class="base"><span class="strut" style="height:1.174993em;vertical-align:-0.333662em;"></span><span class="mord"><span class="mspace"> </span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8413309999999999em;"><span style="top:-2.424669em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span><span class="mbin mtight">+</span><span class="mord mtight">1</span></span></span></span><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mspace mtight" style="margin-right:1.4285714285714286em;"></span><span class="mord mathnormal mtight">A</span></span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.333662em;"><span></span></span></span></span></span></span><span class="mord text"><span class="mord">Y</span></span><span class="mspace" style="margin-right:0.2222222222222222em;"></span><span class="mbin"><span class="mbin">+</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8141079999999998em;"><span style="top:-2.451892em;margin-left:0em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">−</span><span class="mord mtight">1</span></span></span></span><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mspace mtight" style="margin-right:0.7142857142857143em;"></span><span class="mord mtight">0</span></span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.30643899999999996em;"><span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2222222222222222em;"></span></span><span class="base"><span class="strut" style="height:0.771331em;vertical-align:0em;"></span><span class="mord"><span class="mord text"><span class="mord">e</span></span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.771331em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mbin mtight">−</span></span></span></span></span></span></span></span></span></span></span></span></span></span> |
    8. 1951 - : <span data-content-md-theme="svt-pink1" data-content-md-tag="color" data-temp-content-md-index="2089300" class="sc-cIShpX eidyqG lls-viewer-color"><strong data-content-md-tag="b" data-temp-content-md-index="2089296" class="sc-kafWEX fPeCMP lls-viewer-b">Émission <span data-content-md-tag="math" data-temp-content-md-index="2089295" data-content-md-katex="\gamma" class="sc-jqCOkK jSjtEw lls-viewer-math" contenteditable="false"><span><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.625em;vertical-align:-0.19444em;"></span><span class="mord mathnormal" style="margin-right:0.05556em;">γ</span></span></span></span></span></span></strong><br data-content-md-tag="br" data-temp-content-md-index="2089297"/> Un noyau excité redescend vers un niveau d’énergie plus stable en émettant un photon.<br data-content-md-tag="br" data-temp-content-md-index="2089298"/> <span data-content-md-tag="math" data-temp-content-md-index="2089299" data-content-md-katex="^A_Z\text{Y}* \rightarrow \ ^A_Z\text{Y} + \gamma" class="sc-jqCOkK jSjtEw lls-viewer-math" contenteditable="false"><span><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1.1166619999999998em;vertical-align:-0.275331em;"></span><span class="mord"><span></span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8413309999999999em;"><span style="top:-2.424669em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">A</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.275331em;"><span></span></span></span></span></span></span><span class="mord text"><span class="mord">Y</span></span><span class="mord">∗</span><span class="mspace" style="margin-right:0.2777777777777778em;"></span><span class="mrel">→</span><span class="mspace" style="margin-right:0.2777777777777778em;"></span></span><span class="base"><span class="strut" style="height:1.1166619999999998em;vertical-align:-0.275331em;"></span><span class="mord"><span class="mspace"> </span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8413309999999999em;"><span style="top:-2.424669em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">A</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.275331em;"><span></span></span></span></span></span></span><span class="mord text"><span class="mord">Y</span></span><span class="mspace" style="margin-right:0.2222222222222222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222222222222222em;"></span></span><span class="base"><span class="strut" style="height:0.625em;vertical-align:-0.19444em;"></span><span class="mord mathnormal" style="margin-right:0.05556em;">γ</span></span></span></span></span></span></span> |
    9. 1976 - : <span data-content-md-theme="pc-dark-blue" data-content-md-tag="color" data-temp-content-md-index="2089302" class="sc-cIShpX lnvhwv lls-viewer-color"><strong data-content-md-tag="b" data-temp-content-md-index="2089301" class="sc-kafWEX lcBhoy lls-viewer-b">Interdiction du radium thérapeutique,</strong> remplacé par l’iridium et le césium. </span> |

    Supplément numérique

    CEA / Com Ci Com Com Ca.

    Doc. 2
    Diagramme (, ) de Segrè

    On répertorie actuellement 118 éléments chimiques et 287 noyaux stables pour près de 2 800 noyaux radioactifs que l’on peut représenter sur le diagramme de Segrè avec en abscisse le numéro atomique et en ordonnée le nombre de neutrons .

    Diagramme de Segrè
         
    Diagramme de Segrè

    Supplément numérique

    Cliquez ici pour découvir un diagramme (, ) de Segrè animé, afin d’observer la structure atomique de chaque isotope et de découvrir leur stabilité ou types d’émissions.

    Doc. 3
    Radioprotection

    Radioprotection

    Doc. 4
    Exposition à la radioactivité

    L’exposition à la radioactivité naturellement présente dans l’air et dans l’alimentation est quasi-permanente. Elle peut varier en fonction de la zone géographique.
    Une exposition ponctuelle est également possible lors d’examens médicaux ou de voyages en transports aériens, par exemple, avec des doses radioactives parfois importantes.
    Ces différentes expositions peuvent entraîner des problèmes de santé à plus ou moins long terme.

    Exposition à la radioactivité

    Compétences

    RAI/MOD : Modéliser une transformation

    RAI/ANA : Utiliser et interpréter des documents

    Questions

    1. Proposer une explication au fait que le radium non thérapeutique ait finalement été interdit.


    2. Identifier la zone du diagramme (, ) correspondant à chaque type d’émission et citer la ou les particules en excès dans chaque cas.


    3. Dans le milieu médical, le carbone 11 est utilisé pour la tomographie, l’iode 131 pour la scintigraphie et le radium 226 pour la radiothérapie. À l’aide d’une classification périodique, écrire les équations des désintégrations associées.


    4. Préciser à quoi servent les protections dans les salles de radiothérapie.
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    Synthèse de l'activité

    Lister les risques encourus en cas d’exposition lors d’une radiographie.
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