Radiation Protection Course

Radiation Protection Service

Radiation Protection Course

Background Physics

Michael Watt

Contents

• Atomic Structure

• Types of Radiation

• Attenuation & Shielding

• Activity & Half Life

Nucleus

Electrons

-ve charge

Atomic Structure 1

Atomic Structure 2

Proton +ve

Neutrons

Atomic Structure 3

Carbon 12

C12

6

Atomic Number - No. protons

Atomic Mass -no. protons and neutrons

Carbon 12

Definition of Isotope

Atom protons fixed – number of neutrons can vary to form different isotopes.

Example carbon has 2 stable isotopes 126C, 13

6C

To be stable number of N and P must be about equal

Stability Curve

p=nNo..ofProtons

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

Carbon 14

C14

6

Atomic Number - No. protons

Atomic Mass -no. protons and neutrons

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

-VE or +VE

Alpha(2n+2p)

Smoke detectors

Beta(electron or positron)

Biological work

Gamma &

X-ray(electromagnetic radiation)

Some biological work (I-125) and Medical imaging

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.

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 Americium 241 (& γ) 5.4 MeV

Beta 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

ActivityNew UnitBecquerel

1 disintegration per second.

Old UnitCurie

Based on number of disintegrations from 1 g of radium-226. 3.7 x 1010 dps.

Specific Activity

Measure of the activity per unit mass or volume

Bq/g or Bq/ml

Half Life ( T1/2 )

1 half life

1 half life

1 half life

Time

Half Life

• Fluorine-18 110 min• Phosphorus-32 14.3 d• Phosphorus-33 25.6 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