1 Health Safety & Radiation Protection (RAD 453) Course : بسم الله الرّحمن الرّحيم Chapter 1: Fundamental Radiation Concepts Omrane KADRI, Ph.D. Office 2021

2 1) The Radioactive Atom 2) Radioactive Decay Modes 3) The Radioactive Decay Equation 4) Radioactivity Units 5) Interactions of Radiations with Matter 6) Radiation Units Outline

3 1) The Radioactive Atom - All matter is composed of elements and all elements are composed of atoms. - The atom contains a nucleus consisting of protons and neutrons with electrons revolving in circular and elliptical orbits about the nucleus. - Electrons carry a negative charge, protons carry positive charge, and the neutrons have no electrical charge. - An atom normally has one electron in orbit for each proton in the nucleus, leaving the atom electrically neutral.

Radioactivity - a natural and spontaneous process by which the unstable atoms of an element emit or radiate excess energy in the form of particles or waves. After emission the remaining daughter atom can either be a lower energy form of the same element or a completely different element. The emitted particles or waves are called ionising radiation because they have the ability to remove electrons from the atoms of any matter they interact with. 4 1) The Radioactive Atom

Atoms with the same number of protons/electrons have the same physical and chemical properties, these are called elements e.g. all oxygen atoms have 8 protons. Elements are arranged in order of increasing proton number and are characterised with the symbol - Periodic Table Elements can have different numbers of neutrons and these are called isotopes Isotopes can be stable or unstable 5 Definition 1) The Radioactive Atom

6 2) Radioactive Decay Modes 1. Beta (minus) decay Parent nucleus Neon - 19 Daughter Nucleus Fluorine - 19 ++ 2. Beta (plus) decay

7 3. Electron Capture 2) Radioactive Decay Modes 4. Gamma decay 5. Alpha decay

 < 4cm air, will not penetrate skin.  - several mtrs in air, penetrates skin ~ 0.8 cm, use ~ 6 mm plastic shielding. X - penetrating, speak of half- thickness  1/2, use lead shielding.  - more penetrating than X-rays, use lead or concrete shielding. 8 3) Decay Equation Penetrating Distances

A radioactive nuclide decays at a rate proportional to the number of original nucleii present: :where = decay constant Integrating the above gives the decay equation: e - t term indicates that radioactive atoms decay exponentially 9 Activity & Half-life 3) Decay Equation Half life (  1/2 ): The time required for amount of radioactive material to decrease by one-half: (Eq.1)

The disintegration rate of a radioactive nuclide is called its Activity. The unit of activity is the becquerel named after the discoverer of radioactivity. 1 Bq = 1 disintegration per second kilobecquerel (kBq) = 10 3 Bq Megabecquerel (MBq)= 10 6 Bq Gigabecquerel (GBq)= 10 9 Bq Terabecquerel (TBq)= Bq ANTOINE HENRI BECQUEREL ) Radioactivity Units Other unit is the Curie 1 Ci = 3.7 x Bq = 37 GBq (Eq.1) Numbers Rate (Number/time)

 and X-rays interact with matter in 2 major ways: Ionisation: removal of an electron from an atom leaving an ion. Excitation: addition of energy to the atom, giving an excited state. After each ionisation the charged particle will lose energy and will finally be ‘stopped’ - i.e.  radiation has a finite range. Range is measured in gcm -2 R  = E  / 2 gcm -2 R  = E  / 1000 gcm -2 & 11 5) Interaction With Matter

Example of a range calculation Q. What is the range, in mm, of a 35 S beta particle in perspex? A. The max. energy of the 35 S beta particle is MeV the range of the particle is gcm -2 The density (  ) of perspex = 1.2 gcm -3 the penetration depth in cm (t) is given by t = range /  = / 1.2 = 0.07 cm = 0.7 mm 12 5) Interaction With Matter

X or  -ray photon photoelectron Photoelectric Effect 13 5) Interaction With Matter Compton Effect

X or  photon Pair Production 14 5) Interaction With Matter X and  rays are types of electromagnetic radiation. They are not ‘stopped’ by matter but are attenuated. Attenuation depends on energy of radiation, thickness and density of absorber material. Given thickness of absorber produces the same fractional reduction in intensity. Analogous to half-life - called half-thickness - thickness of absorber required to reduce intensity by 1/2.

There are specific units for the amount of radiation you receive in a given time and for the total amount of exposure you are subjected to. 15 6) Radiation Units Kerma (R) Dose (Gy) × Q = Sievert

This is the amount of radioactivity in a sample (the amount of radioactivity = activity)  A commonly-used unit for measuring activity is the curie(Ci)  1 curie is equal to 2.2 x disintegrations per minute (dpm)  Typical activities found in a university lab are in the microcurie (  Ci) to millicurie (mCi) range 16 6) Radiation Units What is a Curie (Ci)? What is a Becquerel (Bq)?  The amount of radioactive material which decays at a rate of one disintegratration per second (dps)  This is the SI unit of radioactive material or activity

 CPM is the counts per minute that a detector “sees”  DPM are the actual disintegrations (release of energy) by a radioactive sample [disintegrations per minute] Since detectors aren’t 100% efficient... DPM = CPM / Detector Efficiency (the detector efficiency for the specific radioisotope, that is) 17 6) Radiation Units CPM & DPM

Dose is the amount of radiation you were actually exposed to:  Roentgen - This can only be used to describe an amount of gamma and X-rays, and only in air. One roentgen is equal to depositing in dry air enough energy to cause 2.58E-4 coulombs per kg. It is a measure of the ionizations of the molecules in a mass of air. (NOT a or b particles) 18 6) Radiation Units Radiation Dose vs Rate  REM - The most common used unit for measuring radiation dose in people is the rem  REM = Roentgen equivalent for man, a roentgen (an international unit of X- or gamma-radiation) adjusted for the atomic makeup of the human body  Since the rem is a relatively large unit, it is more common to use the millirem (mrem), which is 1/1000th of a rem

 Rad (Radiation Absorbed Dose)- this is the amount of exposure to any type of material from any type of radiation measured in Joules/kg tissue  The Gray is the absorbed dose that corresponds to the transfer of 1 joule to 1 kg of material (SI unit). Does not relate to biological effects. 19 6) Radiation Units Other ‘Dose’ Units

20 Equivalent dose (HT) Accounts for biological effect per unit dose radiation weighting absorbed factor ( W R ) dose (D) H T = W R x D The SI unit: sievert (Sv) H T (Sv) = W R x D (Gy) Traditional (old) unit: rem (roentgen equivalent man) H T (rem) = W R x D (rad) 1 Sv = 100 rem 6) Radiation Units

21 Radiation weighting factors (W R ) 6) Radiation Units

22 Effective dose (E) Risk related parameter, taking relative radiosensitivity of each organ and tissue into account E = Σ T (W T x H T ) W T - tissue weighting factor for organ T H T - equivalent dose received by organ or tissue T The SI unit of effective dose: sievert (Sv) 6) Radiation Units

23 Tissue weighting factors (W T ) 6) Radiation Units

 Natural sources = 300 mrem Medical = 53 m  Occupational = 0.9 mrem Nuclear Fuel = 0.05 mrem  Consumer products = 5-13 mrem  Misc. environmental = 0.06 mrem 24 From NCRP Report 93 6) Radiation Units ‘Background’ Radiation

 Whole body = 5,000 mrem/year  Extremities = 50,000 mrem/year  Eye = 15,000 mrem/year  Fetus = 500 mrem/gestation period (declared pregnancy)  Minors = 500 mrem/year  Rad workers = 100 mrem/year over background 25 6) Radiation Units Occupational Radiation Exposure Limits

Rate – of disintegration  DPM  Curie  Becquerel (SI)  NOT CPM 26 Dose - amount of radiation exposed  Roentogen  Rad  Gray (SI)  REM (equivalent)  Sievert (SI equivalent) 6) Radiation Units Review

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