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Rp001 introduction to ionizing radiation
- 1. 11 An Introduction to IonizingAn Introduction to Ionizing RadiationRadiation H.L.Anil RanjithH.L.Anil Ranjith Head-Div of Radiation ProtectionHead-Div of Radiation Protection Atomic Energy AuthorityAtomic Energy Authority
- 2. 22 Composed of :Composed of : Solid - Eg : gold, copper, common saltSolid - Eg : gold, copper, common salt Liquid - Eg : water, milk, mercuryLiquid - Eg : water, milk, mercury Gas - Eg : air, oxygenGas - Eg : air, oxygen The Structure of MatterThe Structure of Matter
- 3. 33 ELEMENTELEMENT AN ELEMENT IS A PURE SUBSTANCEAN ELEMENT IS A PURE SUBSTANCE WHICH CAN NOT BE BROKEN IN TOWHICH CAN NOT BE BROKEN IN TO OTHER SUBSTANCES BY ANY OTHEROTHER SUBSTANCES BY ANY OTHER METHOD.METHOD. ATOMATOM SMALLEST PARTICLE OF AN ELEMENT THATSMALLEST PARTICLE OF AN ELEMENT THAT HAS ALL THE CHEMICAL PROPERTIES OF THEHAS ALL THE CHEMICAL PROPERTIES OF THE GIVEN ELEMENT.GIVEN ELEMENT.
- 4. 44 COMPOUNDCOMPOUND A COMPOUND IS FORMED WHEN TWO OR MOREA COMPOUND IS FORMED WHEN TWO OR MORE ELEMENTS COMBINE TOGETHER CHEMICALLYELEMENTS COMBINE TOGETHER CHEMICALLY TO PROVIDE A MORE COMPLEX KIND OFTO PROVIDE A MORE COMPLEX KIND OF MATTER.MATTER. MOLECULEMOLECULE SMALLEST PARTICLE OF ACOMPOUND THATSMALLEST PARTICLE OF ACOMPOUND THAT CAN EXIST WITHOUT LOOSING CHEMICALCAN EXIST WITHOUT LOOSING CHEMICAL PROPERTIES OF THE COMPOUND.PROPERTIES OF THE COMPOUND.
- 5. 55 THE STRUCTURE OF THE ATOMTHE STRUCTURE OF THE ATOM BASICALLY CONSISTS OF TWO PARTSBASICALLY CONSISTS OF TWO PARTS:: NUCLEUS :NUCLEUS : CENTRAL CORE WHERE ALMOST ALL THE MASS OF THECENTRAL CORE WHERE ALMOST ALL THE MASS OF THE ATOM RESIDES.ATOM RESIDES. CONSISTS OF: POSITIVELY CHARGED PROTONS ANDCONSISTS OF: POSITIVELY CHARGED PROTONS AND ELECTRICALLY NEUTRAL NEUTRONS.ELECTRICALLY NEUTRAL NEUTRONS. (THESE TWO(THESE TWO PARTICLES ARE COMMONLY CALLED “NUCLEONS”)PARTICLES ARE COMMONLY CALLED “NUCLEONS”) ELECTRON :ELECTRON : LIGHT WEIGHT NEGATIVELY CHARGED PARTICLESLIGHT WEIGHT NEGATIVELY CHARGED PARTICLES ORBITING THE NUCLEUS, A GREAT DISTANCE AWAY.ORBITING THE NUCLEUS, A GREAT DISTANCE AWAY.
- 6. 66 Structure of the AtomStructure of the Atom Protons 1 1p (1.007276 amu) Neutrons 1 0n (1.008665 amu)Electrons (0.0005486 amu)
- 7. 77 ATOMIC NUMBER(Z)ATOMIC NUMBER(Z) NO OF PROTONS IN THENO OF PROTONS IN THE NUCLEUSNUCLEUS THE ATOMIC NUMBER DETERMINES THETHE ATOMIC NUMBER DETERMINES THE CHEMICAL PROPERTIES OF THECHEMICAL PROPERTIES OF THE ELEMENTELEMENT
- 8. 88 MASS NUMBER(A)MASS NUMBER(A) TOTAL NUMBER OF PROTONS ANDTOTAL NUMBER OF PROTONS AND NEUTRONS IN THE NUCLEUS.NEUTRONS IN THE NUCLEUS.
- 9. 99 An atom of elementAn atom of element having samehaving same number of protonsnumber of protons (z) and different(z) and different number ofnumber of neutrons (n) isneutrons (n) is called an isotope ofcalled an isotope of the element.the element. Eg:Eg: 191191 Ir,Ir, 192192 Ir,Ir, 193193 IrIr (Z=77)(Z=77) 5858 CoCo 5959 CoCo 6060 CoCo (Z=27)(Z=27) An IsotopeAn Isotope
- 10. 1010 An IsotopeAn Isotope Hydrogen Deuterium Tritium Hydrogen, deuterium, and tritium all have the same atomic number Z: Their chemical properties are the same, but their mass numbers are different.
- 11. 1111 Nuclear StabilityNuclear Stability Impairs by presence of too many or tooImpairs by presence of too many or too few neutrons in the nucleusfew neutrons in the nucleus
- 12. 1212 Too many or too few neutronsToo many or too few neutrons in the nucleusin the nucleus causecause UNSTABILITYUNSTABILITY of the atomof the atom Unstable atom seeks to become stable by breakingUnstable atom seeks to become stable by breaking and emits energy asand emits energy as RADIATION.RADIATION. The process isThe process is calledcalled RADIOACTIVITYRADIOACTIVITY and the Atom is said to beand the Atom is said to be RadioactiveRadioactive Isotopes of elements which are radioactive are called RADIONUCLIDERADIONUCLIDE SS
- 14. 1414 RadioactivityRadioactivity The process of rearrangements of nuclei byThe process of rearrangements of nuclei by changing the relative no. of neutrons andchanging the relative no. of neutrons and protons in the nuclei of unstable atomsprotons in the nuclei of unstable atoms The rearrangements will cause release ofThe rearrangements will cause release of energy in the form of particles orenergy in the form of particles or electromagnetic radiation (commonly calledelectromagnetic radiation (commonly called radiation)radiation)
- 15. 1515 Discovery of RadioactivityDiscovery of Radioactivity Maria Curie 1867-1934 Henri Becquerel 1852-1908
- 16. 1616 Radiation DecayRadiation Decay Half-life is the time itHalf-life is the time it takes for half of the nucleitakes for half of the nuclei in a substance to undergoin a substance to undergo radio-active decayradio-active decay Isotopes found in natureIsotopes found in nature typically have long half-typically have long half- lives; medical isotopeslives; medical isotopes typically have short half-typically have short half- liveslives Typically the shorter theTypically the shorter the half-live the morehalf-live the more radioactive the materialradioactive the material
- 17. 1717 Radioactive Decay (RadioactiveRadioactive Decay (Radioactive DisintegrationDisintegration Time taken to decay half of the atoms in a sample at certain time. Half-life (THalf-life (T1/21/2))
- 18. 1818 RADIATIONRADIATION Ionising radiationIonising radiation Alpha radiationAlpha radiation Beta radiationBeta radiation Gamma radiationGamma radiation X- radiation etcX- radiation etc Neutron radiationNeutron radiation Non ionising radiationNon ionising radiation Micro wavesMicro waves Radio wavesRadio waves Lasers etc.Lasers etc.
- 19. 1919 Non Ionizing RadiationNon Ionizing Radiation SourcesSources Ultraviolet lightUltraviolet light Visible lightVisible light Infrared radiationInfrared radiation MicrowavesMicrowaves Radio & TVRadio & TV Power transmissionPower transmission
- 20. 2020 Non Ionizing RadiationNon Ionizing Radiation
- 21. 2121 Ionizing RadiationIonizing Radiation When radiation has enough energy to alter the matter that it collides with or passes through it is referred to as ionizing radiation Since humans are made up of matter, ionizing radiation can affect us adversely
- 22. 2222 Ionizing Radiation (cont’d)Ionizing Radiation (cont’d) There are 2 types of ionizing radiation:There are 2 types of ionizing radiation: electromagnetic waveselectromagnetic waves sub-atomic particlessub-atomic particles Typically, particles are parts of atomsTypically, particles are parts of atoms alpha (helium nucleus)alpha (helium nucleus) beta (electron)beta (electron) positron (positive anti-electron)positron (positive anti-electron) neutron (component of nucleus)neutron (component of nucleus)
- 23. 2323 ““Radioactive” versusRadioactive” versus “Radiation”“Radiation” The terms “radioactive” and “radiation” areThe terms “radioactive” and “radiation” are often confusedoften confused By keeping the following relationship inBy keeping the following relationship in mind, these two terms can bemind, these two terms can be distinguished:distinguished: Radioactive atoms emit radiationRadioactive atoms emit radiation Radioactive atoms emit radiationRadioactive atoms emit radiation
- 24. 2424 RadiationRadiation is particles or waves ofis particles or waves of energy emitted from unstable atomsenergy emitted from unstable atoms Radioactive ContaminationRadioactive Contamination isis radioactive material usually in anyradioactive material usually in any location you do not want itlocation you do not want it Radiation vs. RadioactiveRadiation vs. Radioactive ContaminationContamination
- 25. 2525 RF µwave infrared visible uv x-rayγ-ray cosmic low energylow energy high energyhigh energy ionizing radiationionizing radiationnon-ionizingnon-ionizing Electromagnetic SpectrumElectromagnetic Spectrum
- 27. 2727 ALPHA PARTICLEALPHA PARTICLE EMISION OF TWO PROTONS AND TWO NEUTRONSEMISION OF TWO PROTONS AND TWO NEUTRONS FROM THE NUCLEUSFROM THE NUCLEUS 238238 9292UU-------------->>234234 9090Th +Th +44 22He (Alpha)He (Alpha)
- 29. 2929 BETA RADIATIONBETA RADIATION EMISION OF AN ELECTRON OR A POSITRONEMISION OF AN ELECTRON OR A POSITRON FROM A NUCLEUSFROM A NUCLEUS
- 30. 3030 MECHANISUM OF BETAMECHANISUM OF BETA EMISSIONEMISSION ELECTRON EMISSIONELECTRON EMISSION 00 11 nn 11 11 P + -P + -11 00 e + ve + v POSITRON EMISSIONPOSITRON EMISSION
- 31. 3131 Phosphorous –32 beta spectrum 0.5 1.0 1.50 E = 0.70 MeV Beta particle energy,MeV Emax = 1.71 MeV R E L A T I V E N U M B E R
- 32. 3232 ELECTRON EMISSIONELECTRON EMISSION AN EXAMPLEAN EXAMPLE 3232 1515PP 3232 1616S +S + 00 -1-1 e + 1.71 MeVe + 1.71 MeV POSITRON EMISSIONPOSITRON EMISSION AN EXAMPLEAN EXAMPLE 2222 1111NaNa 2222 1010Ne +Ne + 00 11e + ve + v
- 33. 3333 ORBITAL ELECTRON CAPTUREORBITAL ELECTRON CAPTURE INSTEAD OF CONVERTING A PROTON TO AINSTEAD OF CONVERTING A PROTON TO A NEUTRON AND A POSITRON,IN SOMENEUTRON AND A POSITRON,IN SOME RADIOACTIVE TRANSFORMATION ONE OFRADIOACTIVE TRANSFORMATION ONE OF THE EXTRA- NUCLEAR ELECTRON ISTHE EXTRA- NUCLEAR ELECTRON IS CAPTURED BY THE NUCLEUS, AND UNITSCAPTURED BY THE NUCLEUS, AND UNITS WITH AN INTRA-NUCLEAR PROTRON TOWITH AN INTRA-NUCLEAR PROTRON TO FORM A NEUTRON ACCORDING TO THEFORM A NEUTRON ACCORDING TO THE FOLLOWING EQUATIONFOLLOWING EQUATION 00 -1-1 e +e + 11 11 HH 11 00 n +vn +v
- 35. 3535 Gamma Rays
- 36. 3636 22 Na Ec 10.2% e + 89.8% , 0.544 MeV Gamma , 1.277 MeV 22 Ne Sodium-22 decay scheme
- 37. 3737 Neutrons
- 38. 3838 NEUTRON RADIATIONNEUTRON RADIATION CAN MAKE THE MATERIAL THROUGHCAN MAKE THE MATERIAL THROUGH WHICH THEY PASS RADIOACTIVE BY BEINGWHICH THEY PASS RADIOACTIVE BY BEING ABSORBED BY NUCLEI ( THIS PROCESS ISABSORBED BY NUCLEI ( THIS PROCESS IS CALLED NEUTRON ACTIVATION)CALLED NEUTRON ACTIVATION) HAS NO CHARGEHAS NO CHARGE CAN CAUSE SIGNIFICANT CELL DAMAGE BYCAN CAUSE SIGNIFICANT CELL DAMAGE BY INDIRECT IONISATION AND OTHERINDIRECT IONISATION AND OTHER PROCESSESPROCESSES CAN CAUSE FISSION IN HEAVY ISOTOPESCAN CAUSE FISSION IN HEAVY ISOTOPES SUCH ASSUCH AS 235235 U ORU OR 239239 PuPu
- 42. 4242 ALPHA RADIATION is stopped by your skin; it is only a hazard when inside your body
- 43. 4343 BETA RADIATION can penetrate the skin; therefore, it can be a skin or eye hazard
- 44. 4444 X- and GAMMA RADIATION can penetrate into your body delivering a deep dose
- 45. 4545 NEUTRONS are very penetrating; therefore, they can affect all organs
Editor's Notes
- When atoms throw off energy in an attempt to re-balance themselves that process is called decay. Half-life is the time it takes for half of the nuclei in a substance to undergo radioactive decay. Decay is a random process. Background radiation fluctuates up and down all day long. Important to take background readings of the entire port. Radionuclides found in nature typically have long half-lives; medical radionuclides typically have short half-lives. Uranium (natural) – long half-life of 4.5 billion years Medical nuclides – short half-lives – Carbon 11 has a half-life of 20 minutes - that’s why for some medical radionuclides it literally has to be made down the hall from the person receiving it, otherwise the material would be rendered useless. 6X half-life for a substance to be decayed down to 1%
- If you were to inadvertantly wander through the tunnel of the VACIS or an x-ray machine while it was scanning, you would be irradiated. However, once the source of x-rays is turned off - you would no longer be irradiated. However, if you were to get a radioactive substance (powder, liquid, etc.) “on” you - you would be contaminated. In other words, that source of contamination “goes with you” no matter where you (and can contaminate others as well) until you are decontaminated.
- Alpha ( ) particles are helium nuclei (4He). They consist of 2 protons + 2 neutrons, forming a very stable atom. -particles are quite heavy particles (atomic mass = 4), i.e. 4 times the mass of the hydrogen nucleus. The electrical charge is + 2. Usually -particles are emitted from heavy atoms, with high energy of several MeV (Mega = million electronvolt). If -particles penetrate matter they cause heavy ionization, loose their energy fast and are stopped by few centimeters of air or millimeters of solid material (e.g. one sheet of paper). In biological tissue they create a lot of damage by killing many cells in a small volume.
- Beta () radiation consists of electrons emitted from the nucleus. Normally electrons are negatively charged. If they are positively charged they are called “positrons”. The mass of the electron is much (~1/8000th) smaller than that of alphas, therefore ionization is much weaker, penetration through matter much deeper. Betas penetrate meters of air and centimeters of solid material. They are stopped by some cm of plastic (e.g. plexiglass), or few mm of glass (goggles). Note: Never handle any Beta sources without eye protection - goggles!!
- Gamma () radiation is a kind of electromagnetic radiation, similar to light or radiowaves, only with much higher energy. It has no mass and no charge. Gamma “particles” are called “photons”. Ionization of matter by -radiation is very weak, penetration through matter very deep and dependent on the energy. The higher the energy, the deeper the penetration through matter. For low energetic -radiation (up to ~ 0.5 MeV) high-Z materials (lead) provide better shielding. For higher energies only the product of density and thickness counts. High energy -radiation can penetrate kilometers of air, meters of water or concrete. Typical shielding materials are several 10 cm of lead or up to 1 m of concrete. -radiation completely penetrates the body, causing a deep dose. X-rays have physically the same nature as gamma rays, i.e. they are electromagnetic radiation. However, while -rays are emitted from the nucleus of the atom, X-rays are generated in the shell, by electrons moving from a higher to a lower energy level (“characteristic X-rays”). X-rays can also emerge when charged particles are slowed down, called “Bremsstrahlung”
- Neutron radiation exists in nature only as part of cosmic radiation impinging on the earth from outer space. Neutrons are mostly produced in nuclear reactors and accelerators. Only a few man-made “Trans-uranium” elements (e.g. Pu, Americium, Californium) undergo “spontaneous fission” and emit neutrons. Neutrons have no charge and mass 1 (same as protons). They give up their energy by bouncing on other nuclei, like billiard balls. If a neutron hits a proton, all the energy from the neutron may be transferred to the proton, which will then transfer it to the surrounding matter (“indirect ionization”). Hydrogen (consisting of protons), e.g. in form of water or plastics, is therefore the most efficient shielding material for neutrons.
- Shielding alpha and beta particles Due to the fact that alpha and beta particles deposit so much energy over such a short distance they are very easy to shield. Alpha particles require little or no shielding as they travel only a very short distance in air. For beta-emitting radioisotopes, low atomic number material such as plastic is recommended. Plastic will adequately shield the betas and keep bremsstrahlung production to a minimum. The thickness of the shield will depend on the range of the beta in the chosen material. A 3/8" plexiglass shield is recommended when working with P-32.
- Due to their weak penetration -radiation is not dangerous in view of external exposure, - particles are stopped in the outmost layer of the skin. However, if -emitting radionuclides are incorporated in the body, e.g. inhaled in the lung, they can be very dangerous and destroy the inner organs. Shielding of -radiation is very easy, a plastic wrapper or piece of paper is sufficient to completely stop all -particles. They will not penetrate clothing or goggles. Note: always carefully avoid incorporation of - emitting radionuclides !!
- Beta radiation penetrates the skin up to a few cm of tissue. It can heavily damage (burn) the skin and is particularly dangerous for the eye. Note: never touch beta sources with your fingers, always use tweezers or tongs and wear goggles to protect your eyes !!
- The intensity of -radiation decreases with the square of the distance from the source (“1/R2 law”). So if you retreat from the source from 10 cm to 1 m the intensity and your exposure will decrease by a factor of 100 ! NOTE: never take a gamma source in your fingers, use at least tongs or tweezers of some length ! The first few centimeters make a lot of difference !
- Neutrons penetrate through the body like gammas, leading to a deep dose. It takes several meters of concrete or metals to stop neutrons, but only some 10 cm of water, paraffin or plastic (hydrogen). Best shielding for fast neutrons is first to slow them down in a moderator containing hydrogen, e.g. water of paraffine, then to absorb them by some particular elements, such as boron or cadmium.