DOZIMETRIE

1. DOZIMETRIE 1. Tipuri de radiatiinuclearesicaracteristici 2. Interactiaradiatiei cu substanta 3. Actiuneabiologica a radiatiilor 4. Detectori de radiatii

2. TIPURI DE RADIATII NUCLEARE SI CARACTERISTICI • Dozimetriasaudozimetriaradiatiilornucleareeste un capitol al metrologieiradiatiilornucleare care se ocupa cu masurareadozei de radiatiinucleare. • Aplicatiileradionuclizilor se bazeaza in principal pefolosirearadiatiiloremise in procesuldezintegrarii radioactive. • Radiatie-un fascicul de particule in miscare. • Termenul de particula, folositaici in sensulcelmai general, cuprindeatatfotonii (particule cu masa de repausnula) cat sicorpusculele (particule cu masa de repausdiferita de zero). • Fasciculele de fotoniconstituieradiatiileelectromagnetice, iarfasciculele de corpuscule (radiatiilealfa, deuteronii, electronii, protonii etc.) constituieradiatiicorpusculare. • Radiatiilenuclearecuprind o parte din radiatiileelectromagneticesianumecelepenetrante: radiatiile de franare, radiatiile Rontgen (sau X), radiatiile de anihilaresiradiatiile gamma. • Radiatiilecorpuscularesuntformate din particuleelementare (electroni, mezoni, protoni, neutronietc) si din nuclee de atomi (deuteroni, helioni etc.) in miscare. • Caracteristicaprincipala a radiatiilornucleareestefaptulca, prininteractiunea cu substantaeleproduc, direct sau indirect, ionizareaacesteia.

3. Radiatiilealfa Radiatiilealfa, fiindnuclee de heliu, au masa de repaus mare, ceeace le permitesa se deplasezerectiliniusicu parcursmic. In functie de energie, parcursul in aer al radiatiiloralfaestecuprinsintre 2 si 10 cm, iarenergiileemise de acesteasuntcuprinse in intervalul 2÷9 MeV. Intr-un camp magnetic, radiatiilealfaemise de o substantaradioactivasunt deviate sub forma unuifasciculingust, ceeaceinseamnacaelepracticsunt, emise cu aceeasienergie. Acest tip de radiatiiprovoaca o puternicaionizarespecifica. In medie, o particulacu energiade 2 MeV produce in aer 60 000 perechi de ionipe cm. Radiatiile beta Radiatiile beta suntcompuse din particule cu sarcinaelectricanegativasaupozitiva. In literaturasuntcunoscutesub numele de radiatii beta minus (negatroni), respectivradiatii beta plus (pozitroni). Acesteparticule au o masa de repaus de peste 7300 orimai mica decat a particuleloralfa.

4. Intr-un camp magnetic, radiatiile beta emise de o substantaradioactivasunt deviate sub forma unuifascicullarg, distributiaenergiilorfiind continua, de la valorifoartemici (aproape zero) pana la o valoare maxima, bine determinata. Aceastaestenumitalimitasuperioara a spectruluicontinuu beta, iarenergiamedie a unuispectru de radiatii beta emis de o anumitasubstantaradioactiva, reprezintaaproximativ 40% din valoareaacesteia. Spectrul energetic continuu al radiatiilor beta determina un parcurs care variaza in limitefoartelargi. Parcursullor in aerestede la cativa mm pana la cativa m sichiarzeci de metri. Radiatiile gamma si Rontgen Radiatiile gamma si Rontgen suntradiatii de naturaelectromagneticacare se caracterizeazaprintr-un parcursfoarte mare si o ionizarespecifica mica. In functie de energialor, pot strabate in aer un parcurscuprinsintremetrisisute de metri. Celedouatipuri de radiatiielectromagnetice nu se diferentiazaprinnatura.Radiatiilegamma au in general o energiemai mare implicit o lungime de undamai mica fata de radiatiile Rontgen si o puteremai mare de patrundereprintr-un mediu material.

5. Neutronii Neutroniisuntparticulelipsite de sarcinaelectrica, cu masa de repausegala cu a protonilor (nuclee de hidrogen) mai mica de patruoridecat a radiatiiloralfasiaproape de 2 000 orimai mare decat a radiatiilor beta. Parcursullorprintr-un mediu material este in forma de zig-zagdatoritainteractiuniilor cu nucleelesielectroniiatomiloracestuia. Materialeleusoare (parafina, grafit, apa, apagrea, beriliumetalic, oxid de beriliu etc.) sunt material care incetinescneutroniisi se numescmoderatori. Borulsicadmiulabsoarbeneutroniisimaterialelegreleii incetinescmultmaiputin. Functie de energialor, neutroniisuntcalasificatiastfel: - neutronitermici cu energie< 1eV - neutroni de rezonanta cu energie100 eV ÷ 1000 eV - neutroniintermediari (epitermici) cu energie103eV ÷ 106eV - neutronirapizicu energie> 106eV INTERACTIA RADIATIILOR CU SUBSTANTA Procesul de interactiune a radiatiilor cu substantaeste important in cunoastereaefectuluiacestoraasupradetectorilor cat si a organismului. Procesele de interactiune ale radiatiilor gamma Pentruenergiilepe care le au radiatiile gamma emise de surse radioactive uzuale, principaleleprocese de interactiunesunt: a) efectulfotoelectric b) efectul Compton c) formareaperechilor de electroni

6. Efectulfotoelectric - are loc la intalnireafotonului gamma incident cu un electron de peuna din paturileelectronice ale atomuluisubstantei cu care interactioneaza, process prin care fotonulcedeazaelectronuluiintreagasaenergie , acesta din urmafiindsmuls din atom. EfectulCompton - are loc la intalnireafotonului gamma incident de energiehν, cu un electron liber sauusorlegat. Formarea de perechi (efectul de materializare electron-pozitron) – aparecaurmare a interactiuniidintreradiatiagamasau Rontgen cu o energiemai mare de 1.022 MeV sicampulnucleului. Atenuarearadiatiilor Rontgen sigamma La trecerearadiatiilorgamaprintr-o substanta, acesteasuntatenuatetreptat, caurmare a proceselor de interactiune care au loc. Pentrugrosimimaristrabatute, intensitatealorscademult, atenuareafiindexponentialacasi in cazulradiatiilor beta. In acestcazinsa se poatevorbi de o valoaredeterminata a parcursuluilormaxim; atenuareacrestepentrumaterialele cu densitate mare. Procesele de interactiune ale neutronilor Neutroniiinteractioneazanumai cu nucleeleatomilor. Ei nu au sarcinaelectricasinu estenecesarsaaiba o energiecineticaridicatapentru a strabatecampul coulumbian al atomuluipentrua ajunge la nucleu. Cu nucleulinteractionasineutroniicu energiifoartejoase. Probabilitatea de patrundere a neutronilor in nucleuesteridicata, in special cei cu energiecineticascazuta (neutronitermici).

7. La trecereaneutronilorprinmateriesuntposibiletreitipuri de interactiuni: imprastiereelastica, imprastiereneelasticasiabsorbtie (capturaneutronica). Interactiaradiatiiloralfa cu substanta La trecerearadiatiiloralfaprintr-o substanta, elepot suferitreitipuri de interactiuni: ciocnire, franare in camp electric sicaptura de catrenucleu. Ciocnireaestetipul de interactiune care se produce cu probabilitateaceamai mare. In urmaciocniriiuneiparticulealfa in miscare cu un atom, se poate produce o excitare a acestuiacaurmare a ridicariiunui electron pe un nivel de energie superior. Excitarea are loccaurmare a actiuniicampului electric creat de particulaalfarespectivaasupraelectronilororbitali. La revenireaelectronilorpenivelelefundamentale, atomiivoremiteradiatiielectromagnetice, unele in spectrulvizibil. Prininteractiunisuccesive, radiatiaalfaisipierdeenergiasasi se incetinestepanacandenergiaeiscade sub o anumitalimitala care nu maipoate produce ionizari. In aceststadiu, particulelealfacapteazacatedoielectroni de la atomiimediuluistrabatutsi se transforma in atomi de heliu.

8. Atenuareafasciculului de radiatii In urmaproceselor de interactiune, particulelealfaisipierdtreptatenergiasinumai in final suntimprastiate. Numarul de particuledintr-un fascicul incident nu scadepemasuraceacesteastrabat o substantaoarecare. La o anumitagrosime a materialuluielesunt total absorbite, procesulnumindu-se atenuare cu parcurs. Interactiaradiatiilor beta cu substanta Mecanismulinteractiuniloresteasemanatorceluiintalnit in cazulradiatiiloralfa. Existadeosebireaca, pentruradiatiile beta minus, fortele din atomiimaterialelor care actioneazaaupraelectronilorsuntde respingere. Spectrul energetic al radiatiei de franareestecontinuu; energia maxima a limiteisuperioare a spectruluiradiatiei Rontgen de franareestesocotitaegala cu energia maxima a radiatiei beta incidenta. Atenuareafasciculului de radiatii Fascicolul de radiatii beta isipierdeenergia fie interactionand cu electroniiatomilormediuluistrabatut, fie interactionand cu nucleul. La fiecareciocnire, radiatia beta suferamarifluctuatiistatice in ceeaceprivestepierderea de energie.

9. In general se folosesteparcursulmasic maxim Rm max=Rm·ρ (ρ-densitateamaterialului, g/cm3). Calculareaparcursului maxim, pentru o anumitasubstanta se face impartindvaloareaparcursuluimasic maxim la densitateaabsorbantului ρ [g/cm3]. In practica, valorileparcursului maxim al radiatiilor beta in aluminiufunctie de energiaradiatiilorsi se recomanda a fi citit din diagrama. • Actiuneabiologica a radiatiilor • La interactiunileradiatiilorionizante cu substanta vie au locaceleasiprocesecasi la interactiunea cu materiafaraviata, diferentafiindaceeacaefectele finale la care conducacesteinteractiunisuntefectebiologice. • Radiatiileionizante pot actionaasupraorganismului in treimoduri: i)actiunedirecta; • ii) actiuneindirecta; iii) actiune de la distanta. • In urmaactiuniidirecte a radiatiilorasupraorganismuluisuntlezatemacromoleculele de importantavitala (proteine, acizinucleici) care suferatransformaridatoritaionizariisauexcitariidirecte.

10. Mediul principal in care se desfasoaraproceselebiologicefiindapa, efecteleaparcarezultat al ionizariiacesteiaprinaparitiaprodusilor de descompunere (ionisauradicali) care actioneazacaoxidantisireducatoriasupraunorcomponentecelulareesentiale. Astfelesteperturbatabunadesfasurare a proceselorbiologice din acestecelule. • Marimisiunitatifolositepentruevaluareaefectelorbiologice • Diversitateatipurilor de radiatii a impusdefinireaunuisistem de masurare a efectelorbiologice ale radiatiilor cu marimicorespunzatoareintreguluidomeniusiunitati de masurareadecvate. A fostintrodusanotiunea de factor de calitate (FC) pentru a puteaexplicafaptulcauneleradiatiiproducefectemaidaunatoaredecataltele. • Dozaabsorbita D reprezintaraportuldintre ΔW siΔm, in care ΔW esteenergiamediecomunicata de radiatiilenucleareuneicantitati de materie de masaΔm. • Unitatea SI pentrudozaabsorbitaeste gray (Gy), care corespundeuneienergiicedate de un joule pe Kg (1Gy=1J·Kg-1). Se maimentinetemporarsiunitateaspecialadenumita rad (rontgen absorbed dose) • 1rad=10-2Gy=10-2 J·Kg-1sau 1rad=100 er·g-1 • Relatiapentrudozaabsorbitaeste de forma: • D= ΔW/ Δm [Gy] sau [rad]

11. Debituldozeiabsorbite, reprezintavariatiadozeiabsorbite, ΔD, in intervalul de timpΔtsi are caunitate de masuraGysau rad cu multipliisausubmultipliilor, raportata la unitatea de timp: Gy/s; Gy/min; Gy/h sau rad/s; rad/min; rad/h etc. =ΔD/Δt [Gy·h-1] sau [rad·h-1] Echivalentuldozei, H esteprodusul a treitermeni: D, FC si N, intr-un punctconsiderat al tesutuluiundeD estedozaabsorbita, FC estefactorul de calitatesi N esteprodusultuturorcelorlaltifactorimodificatoriintre care sifactorul de distributie; N se considera 1. Pentrufactorul de calitate, orientativ se dauurmatoarelevalori: 1-pentru radiatiirontgen, radiatiilegamasielectroni; 10-pentru neutroni, protonisiparticulele cu sarcinaunica care au o masa de repaussuperioaraunitatii de masaatomica; 20-pentru particulelealfasiparticulele cu sarcini multiple. Unitatea SI a echivalentuluidozei, H, se numeste Sievert (Sv), 1Sv=1J·Kg-1. 1rem=10-2Sv; 1Sv=10-2J·Kg-1sau 1 rem=100 erg/gtesut Relatiapentruechivalentuldozeieste: H=D·(FC) ·N [Sv] sau [rem]

12. Debitulechivalentuluidozei, , reprezintavariatiaechivalentuluidozei, ΔH, in intervalul de timp, Δtsi se masoara in unitatiadecvate, derivate din Svsau rem (multiplisisubmultipli) raportati la unitatea de timp considerate: Sv/s; Sv/min; Sv/h; rem/s; rem/min; rem/h etc. = [Sv·h-1] [rem·h-1] Din punct de vedere al energieicedate,se poateconsideracaexprimareairadierii in unitatilerontgen, rad sau rem suntaproximativechivalente. Efectelebiologicesuntefectesomaticesiefectegenetice. Efectesomatice(asupraorganismului)- se manifestadupa un interval maiscurt: i) efecteimediate cum suntefectelocalizate-eritem, epilare, arsuri ale pielii etc.; ii) efecte care apardupaintervalemai lungi (anisauzeci de ani), efecte tardive.

13. Efectegenetice(asupraurmasilor)- cele care reclama o diminuare a calitatilorurmasilorsiaparpana la 3 sau 4 generatii. Numarulmutatiilorgeneticedepindenumai de dozatotalaabsorbita la nivelulgonadelorsi nu de debituldozei. In functie de modul de expunere, respective de repartizare a iradierilor, distingem: iradiereprofesionala; iradiereapopulatiei. Iradierileprofesionalesuntatuncicandrezulta din activitati legate direct de lucrul cu surse de radiatiinucleare (ex.-personalulunitatilornucleareesteexpusprofesionalactiuniiradiatiilorionizante). Limitaanuala a echivalentuluidozeiefectivpentrulucratorieste de 20mSv (2 rem). Iradierilepopulatieisuntatuncicand nu rezulta direct din efectuareaunorlucrari cu substante radioactive sausurse de radiatiiionizante. Limitaanuala a echivalentuluidozeiefectivpentrupersoanele din public este de 1mSv (0.1 rem).

14. Limitadozeiadmisapentru organism, organ sautesutoarecaretrebuieinteleasacadozaprimitaatatpriniradierileexternepedurataorelor de lucru cat sipriniradierile interne. • In NormeleRepublicane de SecuritateRadiologica (NSR) sunt date atatactivitatile maxim admise in organul critic cat siconcentratiile maxim admise (CMA) in aersiapapentrufiecareradionuclidin parte. • Detectareasimasurarearadiatiilor • Detectorii de radiatii se bazeaza in special peefecteleproduse de radiatii la interactiunealor cu substanta. • Detectori de radiatii • Detectoriiutilizati in mod curent in activitatilenucleare: • -detectoribazatipeionizareagazelorsiconectareaionilor (camerele de ionizare, contoriiproportionali, contorii Geiger-Muler); • -detectoribazatipeionizareacristalelor (contori cu cristal); • -detectori la bazacarorastafenomenul de impresionare a emulsiilorfotografice (emulsiilenucleare, filmeledozimetrice etc.); • -detectoribazatipefenomenul de luminiscenta (contorii cu scintilatie); • -detectoribazatipefenomenele de termoluminiscentasifotoluminiscenta (detectoritermoluminiscenti).

15. DozimetrulRontgen-gama VA-J-15Aeste un aparatportabildestinatmasuratorilor de doze sidebite de doze date de radiatiile Rontgen sigama cu un spectrularg de energie 20 KeV…1,2 MeV casi a detectariicalitative a radiatiilor beta emise de diferitiradionuclizi. Aparatul are ca detector o camera de ionizare cu aer (mediul in care se face masuratoarea). Detectorulestecuplat la parteaprincipala a aparatului. Domeniulde masurareestelarg, impartit in douadomenii. Fiecaredomeniu are cate 6 scale atatpentrudebituldozei cat sipentrudozaintegrata. Eroareade masurareeste±15%.

16. Dozimetrul Rontgen-gama VA-J-15Acuplareasondeiprincablu de legatura

17. 1-stecherul de legatura cu aparatul principal 2-instrumentul de masurat 3-surubul pentrupozitionareapunctului zero mecanic 4-fixatorul punctului zero electric 5-salterul, domeniul de masurare fin 6-cureaua de purtare 7-cuplajul pentruinscriptor 8- lacasulbateriilor 9- calul de legatura 10-stecherul capului de masurare 11- salterul “domeniul de masuraregrosier” 12-butonul pentrusursa de radiatii de control 13- camera 14-capacul de protectie al camerei

18. Gamarad DL-7-estedestinatmasuratorilor de debite ale expuneriiexterne in campuri de radiatiirontgensigama in scopulradioprotectieipersonalului cu expunereprofesionala la radiatii din unitatileradiologicefig 4.7, pg 71 El esteutilizat in situatii specific ca: i) supraveghere a zonelor de radiatii (monitor); ii) masuratori de rutina ale debitelorexpunerii; iii)localizareasurselor de radiatii; iv)sesizareacazurilor de contaminare.

19. Gamarad DL-7

20. Aparaturapentrusupraveghereadozimetricaindividuala Printresistemele de dozimetrieindividuala se practicasupravegherea cu: 1. camere de ionizare (stilodozimetre); 2. fotodozimetre; 3. dozimetre TL Camera de ionizare (stilodozimetru)- estedestinatcontroluluidozimetric individual la iradierea cu radiatii Rontgen, gamasi beta dure (beta moifiindoprite de peretiistiloului). Existasistilodozimetre cu electroscop (cu fir), acesteafiindprevazute cu sistem optic cepermitecitirea direct, in milirontgen, expunerea in intervalul de timp cat a fostexpusradiatiei. Pentrustilodozimetreestenecesarasiinstalatia de incarcare, utilizatainainte de a fi purtat. Periodic estenecesaraetalonareasi cu aceastaocazie se verificasiautodescarcareastilodozimetrelor. La terminarealucrului, stilodozimetrelesuntdepozitate in locferit de actiunearadiatiilor.

21. Dozimetrul individual cu film (fotodozimetru) Acesta se compune din film dozimetricsicaseta cu filtremetalice in care se inchidefilmul. Este destinatmasurariidozelor de radiatiigama, Rontgen, beta sineutronitermiciincasatepetimpullucrului de persoanapurtatoare. Filmuldozimetric are douapelicule de sensibilitatidiferitepentruacoperireaunui interval de masurare. Parametriidozimetricicecaracterizeazafilmul: - este un dozimetru integrator; - are interval larg de masurare (0.17 mSv-1Sv); - raspunsuldozimetricfunctie de energiaradiatiilorionizanteeste mare, ceeaceimpuneutilizarea de filtreatenuatoaresidiscriminatoare de energie; -precizia de masurareeste ≤ 30%; -imagineafotografica se pastreazatimpindelungat

22. Dozimetrul individual cu detectoaretermoluminiscente (dozimetru TL) Acesta se compune din caseta cu filtremetaliceasezate in lacasuriamenajate in care se pun detectoaretermoluminiscente. Este destinatmasurariidozelor de radiatiigama, Rontgen, beta sineutronitermiciincasatepetimpullucrului de persoanapurtatoare. Detectoareletermoluminiscentesunt de diferiteforme (pudra, cips, tablete etc.) cu sensibilitate mare pentruacoperireaunui interval larg de masurare. Parametriidozimetricicecaracterizeazadozimetrul TL: - este un dozimetru integrator; - are interval larg de masurare (0.10 mSv-1Sv); - raspunsuldozimetricfunctie de energiaradiatiilorionizanteesteneglijabila. - eroarea de masurareeste ≤ 10%; - citireadetectoarelortermoluminiscenteesterapida; - se pot refolosiduparegenerarepana la 80 ori.

23. DOSIMETRY 1. Types of nuclear radiation and characteristics2. Interaction between radiation and substance3. Biological effect of radiaton4. Radiation Detectors

24. Types of nuclear radiation and characteristics Nuclear radiation dosimetry and dosimetry metrology is a chapter dealing with nuclear radiation nuclear radiation dose measurement. Dosimetry or radiation dosimetry is a part of nuclear radiation wich treats the measurement of radiation doses. Radionuclide applications are mainly based on the use of radiation emitted in radioactive decay process. The term of “particle” is used here in the most general sense, including both photons (particles with zero rest mass) and corpuscles (particles with nonzero rest mass). Photon beams is electromagnetic radiation and beams corpuscles (alpha, deuterons, electrons, protons etc..) are corpuscular radiations. Electromagnetic radiation is made up of photon beams and beams corpuscles (alpha, deuteronis, electrons, protons, etc..) constitutes corpuscular radiations. Nuclear radiation includes some of the electromagnetic radiations, namely the penetrating electromagnetic radiations are: braking radiation, Rontgen rays (or X) annihilation and gamma radiations. Corpuscular radiations are made up of elementary particles (electrons, mesons, protons, neutrons, etc.) and the moving nuclei of atoms (deuteron, helion etc.). The main feature of nuclear radiation is that, by interacting with a substance they produce, directly or indirectly, its ionization.

25. Alpha radiation Alpha radiation, being helium nuclei, have a big rest mass,( the helium nuclei have large rest mass,) allowing them to move straight and on a short distance (go small). Depending on the energy of alpha radiation, the distance traveled in duringair is between 2 and 10 cm, and the energy emitted is between 2 and 9 MeV.In a magnetic field, alpha radiation emitted by a radioactive substance are diverted as a narrow beam, which means that they basically are emitted with the same energy.This type of radiation causes a strong specific ionization. On average, a particle with the energy of 2 MeV produces, in air, 60.000 pairs of ions per cm. Beta radiation Beta rays are composed of particles with negative or positive electrical charge.In literature they are known as beta minus radiation (negatrons) and beta plus radiation (positrons). These particles have a rest mass over 7300 times smaller than alpha particles.

26. In a magnetic field, beta radiation emitted by a radioactive substance are deflected in the form of a broad beam and energy distribution is continuous from very small values ​​(close to zero) to a maximum value well determined. This is called the upper limit of the continuous beta spectrum and average energy of a beta radiation spectrum emitted by a radioactive substance, represents approximately 40% of its value. Continuous energy spectrum of beta radiation causes a period which in large limits. The distance traveled in air is between a few millimeters to several meters and even tens of meters. Gamma and Rontgen radiation Rontgen rays and gamma rays are electromagnetic in nature and are characterized by a great distance traveled and a small specific ionization. Depending on their energy can cross, in air, a distance of meters and hundreds of meters.The two types of electromagnetic radiation are not different in nature. Gamma rays generally have a higher energy implying a lower wavelength than the Rontgen rays and more power to penetrate through a material medium.

27. Neutrons Neutrons are particles without an electrical charge, with a rest mass equal to that of protons (hydrogen nuclei), four times smaller than that of alpha radiation and almost 2000 times larger than beta radiation. Their course through a material medium is shaped in a zigzag because of their interaction with nuclei and electrons of atoms. Lightweight materials (wax, graphite, water, heavy water, beryllium metal, beryllium oxide etc.) are materials which slow down the neutrons and are called moderators.Boron and cadmium absorbs neutrons and heavy materials slow them down less. Depending on their energy neutrons are classified as: - Thermal neutrons with energy <1eV- Resonance neutrons with energy 100 eV to 1000 eV- Intermediate neutrons (epithermal) with energy 103eV ÷ 106eV- Fast neutrons with energy> 106eV

28. RADIATION INTERACTION WITH SUBSTANCE The interaction of radiation with substance is important in knowing their effect on detectors and on the body .Processes of interaction of gamma radiation For the energies of gamma rays emitted by common radioactive sources, the main interaction processes are:a) the photoelectric effectb) Compton effectc) formation of electron pairs Photoelectric effect – when a gamma photon meets and electron of an atom with which it interacts, the photon gives up all its energy and the electron is plucked away from the atom.Compton effect - happens when a gamma photon with hν energy meets a free electron or a slightly connected one.Formation of pairs (electron-positron materialization effect) – apearsfrom the interaction of gamma rays or Rontgen with an energy greater than 1.022 MeV and core field??? .Rontgen rays and gamma attenuationWhen passing through a substance, the gamma rays are gradually weakened as a result of the interaction processes. The attenuation is exponential as for beta radiation and, for thick layers the intensity drops a lot. But in this case we can speak of a determined travel distance ; attenuation increases proportional to the density of materials.

29. Interaction processes of neutronsNeutrons interact only with nuclei. They have no electrical charge and do not require a high kinetic energy to cross the coulombian field and to reach the nucleus . Low energy neutrons can also interact with the nuclei . The probability of neutrons penetrating in the nucleus is high, particularly those with low kinetic energy (thermal neutrons). When passing through matter, neutrons have three possible interactions: elastic scattering, inelastic scattering and absorption (neutron capture).Alpha radiation interaction with substanceWhen passing through a substance, alpha radiation can suffer three types of interaction: collision, slowing down in an electric field and capture by the nucleus. The clash is the interaction with the highest probability . Alpha particles in a collision with a moving atom can produce its excitation due by lifting an electron to a higher energy level. Excitation occurs as an effect of the electric field produced by the alpha particle on the orbital electrons . When the electrons return to fundamental levels, the atoms emit electromagnetic radiation, some in the visible spectrum. Through successive interactions, alpha radiation loses its energy and slows down until its energy falls below a certain limit after which it can not longer produce ionization. At this stage, alpha particles capture two electrons from atoms and turn into helium atoms.

30. Radiation beam mitigation After the interaction process, alpha particles gradually lose energy and only at the end, they are scattered. The number of particles in an incident beam does not decrease as they travel through a certain substance. After a certain travel distance through the material they are totally absorbed, the process being called the mitigation of course. The interaction of Beta radiation with substanceThe interaction mechanism is similar to that of alpha radiation. The difference is that, for beta minus radiation, the forces of atoms acting on electrons are of repulsion. The energy spectrum of the braking radiation is continuous; Rontgen radiation’s braking specter has a maximum energy, considered the upper limit, equal to the maximum energy of the incident beta radiation.Radiation beam attenuationBeta radiation beam loses energy by interacting with electrons and also nuclei of the atoms from the environment it corsses. After each collision, beta radiation has a great static fluctuation regarding energy loss.

31. Generally, the maximum mass travel, Rmax = Rm · ρ (ρ- material density, [g/cm3]), is used. To calculate the maximum travel distance, for a given substance, the maximum mass travel is divided to the absorbant’sdenisity ρ [g/cm3]. In reality, the maximum travel distance of beta radiation ​​in aluminum depends on the radiation energy and is recommended to be read from the diagram. Biological action of radiationJust as with matter, radiation interacts with living substance in the same way, only that the effects are biological.Ionizing radiation can affect the body in three ways: i) direct action;   ii) indirect action; iii) action from a distance.Following the direct action of radiation on the body macromolecules of vital importance are damaged (proteins, nucleic acids) which are processed due to direct ionization or excitation. The main environment in which biological process occur is water. The effects appear as a result of ionization and that leads to the formation of ions and radicals, which act as ?redox? On essential cellullar components.

32. Quantities and units used to evaluate the biological effectsThe diversity of radiation led to the creation of a system used to measure the biological effects of radiation corresponding to all scales and units. The notion of quality factor (QF) was introduced in order to explain that some radiation are more harmful than others. Absorbed dose D is the ratio between ΔW and Δm, where ΔW is the mean energy of nuclear radiation transmitted to a mass, Δm.The SI unit for the absorbed dose is the gray (Gy), which corresponds to an energy of one joule per kilogram transferred (1Gy = 1J · kg-1). Another unit sometimes used is the rad (Rontgen absorbed dose). 1rad = 10-2GY = 2.10 J · kg-1 or 1rad = 100 erg ·g-1The relative absorbed dose is:D = ΔW / Δm [Gy] or [rad]

33. The rate of dose absorbtion, 𝐷 ̇, is defined as the variation of the absorbed dose, ΔD, in the time interval Δtand it’s measured in Gy, multiples or submultiples divided by unit of time: Gy/s, Gy/min, Gy /h or rad /s, rad /min, rad / h etc.𝐷 ̇ = Dd / Dt [Gy · h-1] or [rad · h-1] The dose equivalent, H, is the product of three terms: D, QF and N, in a point considered of tissue volume, where D is the absorbed dose, QF is the quality factor and N is the product of all other modifying factors among which if distribution factor;N is considered 1. Concerning the quality factor, the following guidance values are given:1-for Rontgen rays, gamma rays and electrons;10-for neutrons, protons and particles with a single charge rest mass atomic mass unit higher;20-for alpha particles and particles with multiple tasks.The SI unit of dose equivalent, H, is called the Sievert (Sv), 1Sv = 1J · kg-1.1rem = 2 ·10-1Sv; 1Sv = 10-2J · kg-1 or 1 rem = 100 erg / g tissueThe formula of dose equivalent is: H = D · (CF) · N [Sv] or [rem]

34. The equivalent dose rate , 𝑯, ̇ represents the equivalent dose variation, ΔH, in time, Δt and is measured in appropriate units derived from Sv or rem (multiples and submultiples) per unit of time: Sv / s; Sv / min; Sv / h; rem /s; rem / min; rem / h etc.𝑯 ̇ = Δ 𝐻 / Δ 𝑡 [Sv · h-1] [rem · h-1]In terms of energy transferred, the irradiation expressed in Rontgen, rad or rem are approximately equivalent. Biological effects are somatic and genetic.Somatic effects (on the body) - occur after a shorter interval: i) immediate effects such as localized effects-erythema, epilation, skin burns and so on, ii) effects that occur after longer intervals (years or decades) , late effects. Genetic effects (on the descendants) – are those that reduce reduction in offspring qualities and remain up to 3 or 4 generations. The number of gene mutations depends only on the total dose absorbed by the gonads and not the dose rate.Depending on the exposure, respectively on the distribution of irradiation, we can distinguish:i)Professional irradiation;ii) Population irradiation.

35. Professional irradiation is when it results from activities directly related to manipulation of nuclear radiation sources (eg: the personnel of nuclear units is occupationally exposed to the action of ionizing radiation.The annual limit of effective dose equivalent for workers is 20mSv (2 rem). Population irradiation is when people are not directly irradiated as a result from carrying out work with radioactive substances or ionizing radiation sources.  The annual limit of effective dose equivalent for members of the public is 1mSv (0.1 rem). The allowable dose limit for the body, any organ or tissue is to be understood as both the external radiation dose received during office hours and as internal irradiation.In the Republican Radiological Safety Norms (NSR) are given both the maximum permissible activities in the critical organ and maximum permissible concentrations (MPC) in air and water for each radionuclide separately.

36. Radiation detection and measurement Radiation detectors are based mainly on the effects of radiation in their interaction with substance. Radiation DetectorsDetectors currently used in nuclear activities:- detectors based on the ionization gas the connection of ions (ionization chambers, proportional counters, Geiger counters, Muler);- detectors based on the ionization of crystals (crystal counters);- detectors based on the phenomenon of photographic emulsions (nuclear emulsions, dosimeticfilms etc.).- detectors based on the phenomenon of luminescence (scintillation counters);- detectors based on the phenomenon of thermoluminescence and photoluminescence (thermoluminescent detectors)

37. Rontgen-gamma dosimeter , VA-J-15A, is a portable device used to measure doses and dose flow data given by Rontgen and gamma rays with a wide spectrum of energy: 20 keV ... 1.2 MeV and also the qualitative detection of beta radiation emitted by different radionuclides ???? Cevreisazici????.The device uses as a detector an air ionization chamber (the environment in which the measurements are made). The detector is connected to the main unit. Measuring spectrum is wide, divided into two areas. Each domain has 6 scales for both dose rate and the integrated dose. The measurement error is ± 15%.

39. 1-stecherul de legatura cu aparatul principal 2-instrumentul de masurat 3-surubul pentrupozitionareapunctului zero mecanic 4-fixatorul punctului zero electric 5-salterul, domeniul de masurare fin 6-cureaua de purtare 7-cuplajul pentruinscriptor 8- lacasulbateriilor 9- calul de legatura 10-stecherul capului de masurare 11- salterul “domeniul de masuraregrosier” 12-butonul pentrusursa de radiatii de control 13- camera 14-capacul de protectie al camerei

40. DL-7-Gamarad, is used to measure the flow of external exposure in fields of gamma and Rontgenn radiation of the staff with occupational exposure for radiation protection purposes Figure 4.7, pg 71It is used in specific situations such as:i) monitoring radiation areas (monitor);ii) Routine measurements of flow exposure;iii) location of radiation sources;iv) finding cases of contamination.

42. Equipment for monitoring individual dosimetry Among individual dosimetry systems practiced with supervision:1. ionisation chambers (pen dosimeters); 2. fotodosimeters; 3. TL dosimetersIonization chamber (pen dosimeter) - is designed to control individual dosimetric Rontgen ray irradiation, gamma and hard beta (beta soft walls being stopped by pen). There pen dosimeters the electroscope (wired), which is equipped with an optical system that allows direct reading in milirontgens, exposure time was exposed as radiation.For pen dosimeters is required and loading gear, used before being worn. Periodic calibration is necessary, on this occasion to check and tipping of the pen dosimeters. After work, the pen dosimeters are stored in a place inaccessible to the action of radiation.

43. Individual dosimetricalfilm (fotodosimeter) It consists of dosimetrical film and metal filter box that closes the film. Is intended to measure radiation dose range, Rontgen, beta and thermal neutrons collected in person whilst carrying.Dosimetrical film has two different sensitivities to cover a measuring range. Dosimetrical parameters characterizing the film: - Is an integrator dosimeter;- Has a wide measurement range (0.17 mSv-1Sv);- Dosimetrical response by ionizing radiation energy is high, requiring the use of filters and attenuators discriminatory power;-measurement precision is ≤ 30%;-photographic image is preserved for a long time

44. Individual dosimeter wichthermoluminescent detectors (TL dosimeter) It consists of metal filter box placed in places arranged to be placed thermoluminescent detectors. Is intended to measure radiation dose range, Rontgen, beta and thermal neutrons collected in person whilst carrying.Thermoluminescent detectors come in different forms (powder, potato chips, tablets etc.) High-sensitivity covering a wide range of measurement. TL dosimeter dosimetry parameters characterizing:- Is an integrator dosimeter;- Has a wide measurement range (0.10 mSv-1Sv);- Dosimetric response by ionizing radiation energy is negligible.- Measurement error is ≤ 10%;- Reading thermoluminescent detectors is fast;- Can be reused after regeneration up to 80 times.