Radiation Electromagnetic radiation Ionizing radiation –capable of separating molecules into cations and anions –e.g. X-rays Non-ionizing radiation –doesn’t normally disassociate molecules –e.g. radio frequency (RF) rays

Atomic reminders Nucleus of an atom contains 1 or more protons, and 0 or more neutrons Neutrons and protons have essentially equal mass, but proton has positive charge while neutron is electrically neutral Elemental identity of an atom is determined by the number of protons (atomic number) –Why?

Atomic reminders (cont’d) Common form of an element has a certain mass number = protons + neutrons Other forms (isotopes) have the same number protons, but different numbers of neutrons These are often unstable and prone to decay

Radioactive Decay Unstable isotopes decay spontaneously, emitting various combinations of particles and energy Some of these decay processes change either the isotope or the elemental identity of the atom The rate of decay is characteristic of the starting isotope, and described by half-life

Decay Examples 6 C 14  7 N 14 + e + - –A neutron turns into a proton, an electron & an antineutrino 92 U 238  2 He Th 234

Radioactive Half-life Different nuclides (isotopes) are distinguished by different decay constants ( ) Radioactive Half-life  the length of time required for half of the atoms in the sample to decay Decay is exponential: N t = N 0 e - t So 0.5*N 0 = N 0 e - t,  t 1/2 = -ln(0.5)/

Types of Ionizing Radiation Alpha –Nuclei of He atom (2 neutrons & 2 protons) –Heavy (6.642x10 -4 g) and slow (10 4 miles/s) –Lots of interactions with energy transfer ( K ion pairs/cm air) –Travel only 1-8 cm in air, less in solids (like skin) –Most hazardous to humans from inside

Types of Ionizing Radiation Beta –Electrons emitted from nucleus, charged (usually negative) –Light (9.130x g) and fast (SOL: 3x10 8 m/s) –Fewer interactions (< 200 ion pairs/cm air) –Travel several meters in air, several cm through human skin –Can cause damage under skin, eyes

Types of Ionizing Radiation Gamma –Electromagnetic ray (photon), neutral charge –Frequency characteristic of nuclide –Massless and fast (SOL) –Lower production of ion pairs than  &  –Different penetration for different materials: 5 cm in lead 50 cm in water 50,000 cm in air

Types of Ionizing Radiation X-Ray –Electromagnetic ray (photon), neutral charge –Frequency in X-ray portion of spectrum (generally lower energy than  ) –Massless and fast (SOL) –Lower production of ion pairs than  &  –Penetration varies with energy

Types of Ionizing Radiation Neutron –1/4 mass of  –Variable energy –Tissue penetration of 1-10 cm

Radiation Measurement Geiger Counter –tube of readily ionized gas exposed to source –ions produced attracted to charged wire and produce electrical pulse Scintillation Counter: –Detector materials emit light when struck by radioactive emission –Photo tube detects light

Dosimeters Thermoluminescence Detector –Lithium fluoride exposed to radiation results in electrons raised to higher energy states (where they tend to remain for a period of time) –“Relax” with heat and measure emitted light Film Badge –Photographic film develops with exposure –Assess degree of exposure of film as f(t)

Radiation Units Activity Absorbed Dose Dose Equivalent Exposure

Activity The transformation (disintegration) rate of a radioactive substance –Curie (Ci) –Becquerel (Bq) - S.I. Unit 1 Bq = 1 disintegration per second (dps) 1 Ci = 3.7 x dps = 3.7 x Bq

Absorbed Dose A physical quantity which represents the energy imparted by radiation onto an absorbing material. –RAD (radiation absorbed dose): A unit of dose as energy per unit exposed mass 1 RAD = 100 ergs/g = 0.01 joules/g Doesn’t differentiate different types of radiation –Gray (Gy) - SI Unit 1 Gy = 1 joule per kilogram = 100 rads

Dose Equivalent An expression of dose in terms of its biological effect. Takes account of the fact that, for a given absorbed dose, a radiation of one type and/or energy may give rise to a greater biological effect than a radiation of another type and/or energy. REM (Radiation Exposed Man): –REM = RAD * QF –QF = Quality Factor (10 for , for ,  & x-ray)

Dose Equivalent (cont’d) QF is used to compare the biological damage producing potential of various types of radiation, given equal absorbed doses. The effectiveness of radiation in producing damage is related to the energy loss of the radiation per unit path length. –REM –SIEVERT (Sv) - S.I. Unit 1 Sv = 100 REMs

Exposure A quantity that expresses the ability of radiation to ionize air and thereby create electric charges which can be collected and measured –Roentgen (R) 1 R = 2.58 x q/kg of air

Exposure Limits Regulated by NRC (10 CFR) Not to exceed 0.1 rem/yr excluding –background radiation –medical radiation (including voluntary participation in research studies) Not to exceed 0.02 REM/hr (unrestricted) Can apply for authorization up to 0.5 REM/yr –Demonstration of need

Health Effects Long-term, low dose Short-term, high dose Various studies available, e.g. – /overview.htmlhttp:// /overview.html Hiroshima and Nagasaki survivors widely studied, e.g. – cdas.or.jp/HICARE/en/index.htmlhttp:// cdas.or.jp/HICARE/en/index.html What happened at Hiroshima?Hiroshima