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Health Safety & Radiation Protection (RAD 453)Course :

حمن بسم الله الّر�حيم الّر�

Chapter 1: Fundamental Radiation Concepts

Omrane KADRI, Ph.D.

okadri@KSU.EDU.SA

Office 2021

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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

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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 theunstable 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.

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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 isotopesIsotopes can be stable or unstable

XAZ

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Definition

1) The Radioactive Atom

max32.14020

4019

MeVCaK

YX AZ

AZ 1

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2) Radioactive Decay Modes

1. Beta (minus) decay

Parent nucleusNeon - 19

DaughterNucleus

Fluorine - 19

+

MeVFNe 22.2199

1910

YX AZ

AZ 1

2. Beta (plus) decay

raysMeVMevraysXTelluriumTeeI 035.0)027.0(12552

12553

)(1 possiblyraysraysXYeX AZ

AZ

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3. Electron Capture

2) Radioactive Decay Modes

4. Gamma decay

5. Alpha decay

XX AZ

AZ

*

HeYX AZ

AZ

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42

PuPu 24094

*24094

< 4cm air, will not penetrateskin. - several mtrs in air, penetratesskin ~ 0.8 cm, use ~ 6 mm plasticshielding.X - penetrating, speak of half-thickness 1/2, use lead shielding.

- more penetrating than X-rays, use lead or concrete shielding.

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3) Decay Equation

Penetrating Distances

A radioactive nuclide decays at a rate proportional to the numberof original nucleii present:

Ndt

dN :where = decay constant

Integrating the above gives the decay equation:t

t eNN 0

e-t term indicates that radioactive atoms decay exponentially

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Activity & Half-life

3) Decay Equation

693.0

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Half life (1/2): The time required for amount of radioactive materialto decrease by one-half:

(Eq.1)(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 secondkilobecquerel (kBq) = 103 BqMegabecquerel (MBq) = 106 BqGigabecquerel (GBq) = 109 BqTerabecquerel (TBq) = 1012Bq

ANTOINE HENRI BECQUEREL

1852-1908

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4) Radioactivity Units

Other unit is the Curie 1 Ci = 3.7 x 1010 Bq = 37 GBq

(Eq.1)(Eq.1) 21/693.0

0011 / tt eAeAtNA

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 willfinally 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&

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5) Interaction With Matter

Example of a range calculation

Q. What is the range, in mm, of a 35S beta particle in perspex?

A. The max. energy of the 35S beta particle is 0.168 MeV• the range of the particle is 0.084 gcm-2

The density () of perspex = 1.2 gcm-3

• the penetration depth in cm (t) is given by t = range /

= 0.084 / 1.2 = 0.07 cm = 0.7 mm

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5) Interaction With Matter

X or -rayphoton

photoelectron

Photoelectric Effect

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5) Interaction With Matter

Compton Effect

X or photon Pair Production

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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 reductionin intensity.

Analogous to half-life - called half-thickness - thickness of absorberrequired 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.

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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 1012 disintegrations per minute (dpm)Typical activities found in a university lab are in the microcurie (Ci) to

millicurie (mCi) range

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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)

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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)

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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 tissueThe 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.

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6) Radiation Units

Other ‘Dose’ Units

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Equivalent dose (HT)Accounts for biological effect per unit dose

radiation weighting absorbed

factor ( WR ) dose (D)

HT = WR x D

The SI unit: sievert (Sv) HT (Sv) = WR x D (Gy)

Traditional (old) unit: rem (roentgen equivalent man)

HT (rem) = WR x D (rad)

1 Sv = 100 rem

6) Radiation Units

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Radiation weighting factors (WR)

Radiation type and energy range

WR

Photons (X-rays and gamma-rays) all energies Electrons, all energies Neutrons <10 keV 10-100 keV >100 kev to 2 MeV 2-20 MeV >20 MeV Protons >20MeV Alpha-particles, fission fragments

1 1 5 10 20 10 5 5 20

6) Radiation Units

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Effective dose (E)

Risk related parameter, taking relative radiosensitivity of each organ and tissue into account

E = ΣT (WT x HT)

WT - tissue weighting factor for organ THT - equivalent dose received by organ or tissue T

The SI unit of effective dose: sievert (Sv)

6) Radiation Units

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Tissue weighting factors (WT)Organ or tissue Tissue weighting

factor (WT)

GonadsRed bone marrowColonLungStomachBladderBreastLiverOesophagusThyroidSkinBone surfaceRemainder

Total

0.20.120.120.120.120.050.050.050.050.050.010.010.05

1.0

6) Radiation Units

Natural sources = 300 mrem Medical = 53 mOccupational = 0.9 mrem Nuclear Fuel = 0.05 mremConsumer products = 5-13 mremMisc. environmental = 0.06 mrem

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From NCRP Report 93

6) Radiation Units

‘Background’ Radiation

Whole body = 5,000 mrem/yearExtremities = 50,000 mrem/yearEye = 15,000 mrem/yearFetus = 500 mrem/gestation period (declared

pregnancy)Minors = 500 mrem/yearRad workers = 100 mrem/year over background

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6) Radiation Units

Occupational Radiation Exposure Limits

Rate – of disintegrationDPMCurieBecquerel (SI)NOT CPM

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Dose - amount of radiation exposed

Roentogen Rad Gray (SI) REM (equivalent) Sievert (SI equivalent)

6) Radiation Units

Review

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