Radiation Protection Course Radiation Protection Service

Radiation Protection Course Background Physics Michael Watt

Contents Atomic Structure Types of Radiation Attenuation & Shielding Activity & Half Life

Atomic Structure 1 Nucleus Electrons -ve charge

Atomic Structure 2 Proton +ve

Atomic Structure 3 Neutrons

no. protons and neutrons Carbon 12 Atomic Mass - no. protons and neutrons C 12 6 Atomic Number - No. protons

Carbon 12

Definition of Isotope Atom protons fixed – number of neutrons can vary to form different isotopes. Example carbon has 2 stable isotopes 126C, 136C To be stable number of N and P must be about equal

Stability Curve p=n No..of Protons No. of Neutrons

Definition of Radioactive Isotope This occurs when the ratio of Neutrons to protons is too great or too small, and the atom spontaneously attempts to become stable Example carbon has five radioactive isotopes C-10, C-11, C-14, C-15, C-16

no. protons and neutrons Carbon 14 Atomic Mass - no. protons and neutrons C 14 6 Atomic Number - No. protons

Ion An atom or molecule which has lost or gained one or more electrons An ion will have a positive or negative electrical charge

Ionisation

Types of ionising radiation Alpha (2n+2p) Smoke detectors Beta (electron or positron) Biological work Gamma & X-ray (electromagnetic radiation) Some biological work (I-125) and Medical imaging -VE or +VE

Sources of Ionising Radiation Alpha Americium 241 (& γ) Radon 222 Polonium 210 Beta Tritium (Hydrogen-3) Carbon-14 Sulphur-35 Phosphorus-32/33 Gamma Iodine-125 Cobalt-60 (& β) Fluorine-18

X-Rays Produced by accelerating electrons from a cathode onto an anode inside an evacuated glass tube. Less than 1 % of energy converted to x- rays, rest to heat. X-rays have the same physical properties as gamma photons.

Attenuation paper perspex lead

Energy of Ionising radiation The energy of Alpha, Beta and Gamma radiations is measured in ELECTRON VOLTS eV, normally keV and MeV 1eV = 1.6 x 10-19 J Higher energy = more penetrating (for a given type of radiation)

Alpha Beta Gamma Americium 241 (& γ) 5.4 MeV Tritium (Hydrogen-3) Carbon-14 Sulphur-35 Phosphorus-32 Phosphorus-33 18.6 keV 157 keV 167 keV 1710 keV 250 keV Gamma Iodine-125 Cobalt-60 Fluorine-18 36 keV 1.17 MeV & 1.33 MeV

Shielding Materials Alpha particles – Paper, dead layer of skin Beta particles – 1 cm perspex or tissue Gamma Photons – dense material such as lead or DU

Activity New Unit Old Unit Becquerel 1 disintegration per second. Curie Based on number of disintegrations from 1 g of radium-226. 3.7 x 1010 dps.

Measure of the activity per unit mass or volume Specific Activity Measure of the activity per unit mass or volume Bq/g or Bq/ml

Half Life ( T1/2 ) Time 1 half life 1 half life 1 half life

Half Life Fluorine-18 110 min Phosphorus-32 14.3 d Iodine-125 59.9 d Sulphur-35 87.5 d Cobalt-60 5.3 y Tritium (Hydrogen-3) 12.3 y Carbon-14 5730 y

Radiation Dose Gray (Gy) – absorbed dose. Defined as 1 Joule of energy absorbed per kilogramme of material. Sievert (Sv)– Unit of equivalent dose and effective dose 100 rad = 1 Gray ( 100 rem = 1 Sv) 1mrad = 10 µGray ( 1 mrem = 10 µSv)

Next… Short video: Working Safely with Radioactivity