dr. mohammed alnafea [email protected] radioactivity radioactivity

Dr. Mohammed AlnafeaDr. Mohammed [email protected]@ksu.edu.sa

RADIOACTIVITY RADIOACTIVITY

Objectives & learning Objectives & learning outcomeoutcome

Be the end of this lecture student will be able to:

1. Explain the definition of radioactivity, physical half-life and decay process

Do all the calculations of half-lives and activity measurements

Identify the differences between Alpha, Beta & gamma radiation in term of the type of radiation and penetration power.

Explain the principle of radiation detection and use the specific unit of radiation measurements.

2 2nd lecture RAD 311

History of Radiopharmacy

Medicinal applications since the discovery of Radioactivity

Early 1900’sLimited understanding of Radioactivity

and dose


1912 — George de Hevesy1912 — George de Hevesy

Father of the “radiotracer” experiment.

Used a lead (Pb) radioisotope to prove the recycling of meat by his landlady.

Received the Nobel Prize in chemistry in 1943 for his concept of “radiotracers”


Early use of radiotracers in medicineEarly use of radiotracers in medicine

1926: Hermann Blumgart, MD injected 1-6 mCi of “Radium C” to monitor blood flow (1st clinical use of a radiotracer)

1937: John Lawrence, MD used phosphorus-32 (P-32) to treat leukemia (1st use of artificial radioactivity to treat patients)

1937: Technetium discovered by E. Segre and C. Perrier


Early Uses continuedEarly Uses continued1939: Joe Hamilton, MD used radioiodine (I-131) for

diagnosis

1939: Charles Pecher, MD used strontium-89 (Sr-89) for treatment of bone metastases.

1946: Samuel Seidlin, MD used I-131 to completely cure all metastases associated with thyroid cancer. This was the first and remains the only true “magic bullet”.

1960: Powell Richards developed the Mo-99/Tc-99m generator

1963: Paul Harper, MD injected Tc-99m pertechnetate for human brain tumor imaging


What is aWhat is a radiopharmaceuticalradiopharmaceutical? ?

A radioactive compound used for the diagnosis and therapeutic treatment of human diseases.

Radionuclide + Pharmaceutical

Part 1:Part 1: Characteristics of a Characteristics of a RadiopharmaceuticalRadiopharmaceutical


Radioactive MaterialsRadioactive Materials

Unstable nuclides Combination of neutron and protons

Emits particles and energy to become a more stable isotope

N →

↑

Z

Chart of the Nuclides


Radiation decay emissionsRadiation decay emissions

Alpha ( or 4He2+)

Beta ( or e-)Positron ()Gamma ()Neutrons (n)

92nd lecture RAD 311

RadioactivityRadioactivity In 1896 Henri Becquerel -> find that the photographic

plate had been darkened in the part nearest to uranium compounds. He called this phenomenon radioactivity.

Radioactivity (radioactive decay) is the spontaneous break up (decay) of atoms.

Marie Curie (student of Becquerel) examined the radioactivity of uranium compound and she discovered that:

1. All uranium compounds are radioactive 2. Impure uranium sulphide contains two other

elements which are more radioactive than uranium. 3. Marie named these elements radium & polonium. 4. Radium is about two million times more radioactive

than uranium.102nd lecture RAD 311

Electromagnetic RadiationX-ray and -rays

Same properties, differ in origin

X-rays – electronic transitions-rays – nuclear decay

X rays occur when an excited electron emits a X rays occur when an excited electron emits a photon as it relaxes photon as it relaxes

- rays occur when an excited nucleus emits a - rays occur when an excited nucleus emits a photon as it relaxesphoton as it relaxes


Alpha, Beta & gamma radiation

When the radioactive atoms break up, they release energy and lose three kinds of radiation (Alpha, Beta & gamma radiation).

Alpha & Beta are particles where as gamma-rays are electromagnetic wave with the greatest penetrating power.


Interactions of EmissionsInteractions of Emissions Alpha ( or 4He)

High energy over short linear range

Charged 2+ Beta (- or e-)

Various energy, random motion

negative Gamma ()

No mass, hv

Positron (+)Energy >1022 MeV, random

motionAnihilation (2 511 MeV

~180°)Negative

Neutrons (n)No charge, light elements


14

Definition:Definition:A = dN / dt =A = dN / dt =x N x N

where N is the where N is the numbernumber of radioactive of radioactive atoms present at time t, dN the atoms present at time t, dN the expectation value of the number of expectation value of the number of nuclear transitions in time interval dt, nuclear transitions in time interval dt, and and the physical transformation the physical transformation constant (decay constant).constant (decay constant).

Activity, A

2nd lecture RAD 311

Half Life and ActivityHalf Life and Activity

Radioactive decay is a statistical phenomenon

t1/2

decay constantActivity

The amount of radioactive material


Measured ActivityMeasured Activity

In practicality, activity (A) is used instead of the number of atoms (N).

A=AOe-t

UnitsCurie

3.7 Exp10 decay/s1 g Ra

Becquerel1 decay/s

Half Life and decay Half Life and decay constantconstant

Half-life is time needed to decrease nuclides by 50%

Relationship between t1/2 and

N/No=1/2=e-t

ln(1/2)=-t1/2

ln 2= t1/2

t1/2=(ln 2)/


EquationsEquations

Nt=Noe-t

N=number of nuclei, = decay constant, t=time

Also works for A (activity) or C (counts)At=Aoe-t, Ct=Coe-t


Applications in Nuclear Applications in Nuclear MedicineMedicine

ImagingGamma or positron emitting

isotopes99mTc, 111In, 18F, 11C, 64Cu

Visualization of a biological processCancer, myocardial perfusion agents

TherapyParticle emittersAlpha, beta, conversion/auger

electrons188Re, 166Ho, 89Sr, 90Y, 212Bi, 225Ac, 131I

Treatment of diseaseCancer, restenosis, hyperthyroidism


Ideal Nuclear Properties for Ideal Nuclear Properties for Imagining AgentsImagining Agents

Reasonable energy emissions.Radiation must be able to penetrate several

layers of tissue.No particle emission (Gamma only)

Isomeric transition, positron (+), electron capture

High abundance or “Yield”Effective half lifeCost


Ideal Characteristics of a Ideal Characteristics of a RadiopharmaceuticalRadiopharmaceutical

Nuclear PropertiesWide Availability Effective Half life (Radio and biological)High target to non target ratioSimple preparationBiological stabilityCost


Gamma IsotopesGamma Isotopes

RadionuclideRadionuclide TT1/21/2 (%) (%)Tc-99m 6.02 hr 140 KeV (89)Tl-201 73 hr 167 KeV (9.4)In-111 2.21 d 171(90),

245(94)Ga-67 78 hr 93 (40), 184 (20),

300(17)I-123 13.2 hr 159(83)I-131 8d 284(6), 364(81),

637(7)Xe-133 5.3 d 81(37)


Radioactive Decay KineticsRadioactive Decay Kinetics

Outline Radioactive decay

kinetics Basic decay

equations Utilization of

equations Mixtures Equilibrium Branching

Natural radiation Dating


Basic decay equationsBasic decay equationsThe radioactive process is a subatomic change

within the atomThe probability of disintegration of a particular atom

of a radioactive element in a specific time interval is independent of its past history and present circumstances

The probability of disintegration depends only on the length of the time interval.

Probability of decay: p=t

Probability of not decaying: 1-p=1- t


Units of RadioactivityUnits of Radioactivity


Curie (Ci) = 2.22 E12 disintegration per minutes (dpm) or 3.7Exp10 disintegration per seconds (dps).

Becquerel (Bq) = 1 dps.

Maximum Dose/year = 5 REM or 50 mSv.

Maximum Dose/year for Declared Pregnant Woman & Minors= 0.5 REM or 5 mSv.

Standard International Radiation Standard International Radiation Protection UnitsProtection Units


Becquerel (Bq) for Curie 1 Ci = 3.7 x 1010 Bq

Gray (Gy) for rad 1 Gy = 100 rad

Sievert (Sv) for rem 1 Sv = 100 rem

Unit AnalysisUnit Analysis


BASE UNIT CONVERSION TABLE

UnitUnit Unit ConversionUnit Conversion1 Bq 2.7 x 10-11 Ci1 Ci 3.7 x 1010 Bq

1 Bq 1 dis/sec1 dis/sec 2.7 x 10-11 Ci1 Ci 3.7 x 1010 dis/sec

Unit Analysis (Con’t.)Unit Analysis (Con’t.)


BASE UNIT CONVERSION TABLE UnitUnit Unit Unit

ConversionConversion

1 rem 0.01 Sv1 Sv 100 rem1 rad 0.01 Gy1 Gy 100 rad1 R 2.58 x 10-4 C/kg1 meter 3.28 ft (39.37in)

Radiation Dose UnitsRadiation Dose Units

Exposure: Roentgens (R) or Coulomb/KgA measure of the number of ion pairs created in a certain mass

Absorbed Dose: Rad (100 energy/g) of Gray (J/Kg)A measure of the energy deposited into the mass of irradiation

Effective Dose: Rem or Sievert (Sv)Represents the dose that the total body could receive (uniformly) that would give the same cancer risk as various organs getting different doses.


Radiation in Medicine ProcedureProcedure Effective dose Effective dose

(mSv)(mSv)

Chest x-rayChest x-ray 0.040.04

Abdominal x-rayAbdominal x-ray 1.51.5

Lumbar spine x-rayLumbar spine x-ray 2.42.4

Intravenous Intravenous PyelographyPyelography 4.64.6

Abdominal CT scanAbdominal CT scan 7.27.2

Chest CT scanChest CT scan 8.38.3

Brain CT scanBrain CT scan 1.81.8

Tc-99 bone scanTc-99 bone scan 3.63.6

Tc-99 lung scanTc-99 lung scan 1.01.0

I-123 thyroid scanI-123 thyroid scan 4.44.4


Detecting and Measuring Detecting and Measuring RadiationRadiation


InstrumentsInstrumentsLocate contamination - GM Survey Meter Locate contamination - GM Survey Meter

(Geiger counter)(Geiger counter)Measure exposure rate - Ion ChamberMeasure exposure rate - Ion Chamber

Personal Dosimeters - measure doses to staffPersonal Dosimeters - measure doses to staffRadiation Badge - Film/TLDRadiation Badge - Film/TLDSelf reading dosimeter (analog & digital)Self reading dosimeter (analog & digital)

INSTRUMENTATION IN INSTRUMENTATION IN NUCLEAR MEDICINENUCLEAR MEDICINE


Non imaging equipment: •Activity meter• Sample counters• Single- and multi-probe systems

Imaging equipments:• Gamma camera • Single Photon Emission Computed • Tomograph (SPECT)• Positron camera (PET)

SummarySummary

36

• The radioactive decay law in equation form;

• Radioactivity is the number of radioactive decays per unit time;

• The decay constant is defined as the fraction of the initial number of radioactive nuclei which decay in unit time;

• Half Life: The time taken for the number of radioactive nuclei in the sample to reduce by a factor of two;

• Half Life = (0.693)/(Decay Constant);

• The SI Unit of radioactivity is the becquerel (Bq) 1 Bq = one radioactive decay per second;

• The traditional unit of radioactivity is the curie (Ci); 1 Ci = 3.7 x 1010 radioactive decays per second2nd lecture RAD 311

Summary of Units Summary of Units

Quantity Name SI Unit Old Unit activity becquerel (Bq) s-1 curie (Ci)

(1 Bq = 2.7 x 10-11 Ci) specific activity

__ Bq.m-3, Bq.kg-1

Ci.m-3, Ci.kg-1

exposure __ C.kg-1 roentgen (R) (1 R = 2.58 10-4 C.kg-1)

absorbed dose

gray (Gy) J.kg-1 rad (rad) (1 Gy = 100 rad)

equivalent dose

sievert (Sv) J.kg-1 __

effective dose

sievert (Sv) J.kg-1 rem (rem) (1 Sv = 100 rem)

2nd lecture RAD 311

Student HomeworkStudent Homeworknext 2 slidesnext 2 slides


Q1:Half-life calculationQ1:Half-life calculation

Using NUsing Ntt=N=Nooee--tt

For an isotope the initial count rate was 890 Bq. After 180 minutes the count rate was found to be 750 Bq.What is the half-life of the isotope?


Q2: Half-life calculationQ2: Half-life calculation

A=NA 0.150 g sample of 248Cm has a alpha activity of

0.636 mCi.What is the half-life of 248Cm?


dr. mohammed alnafea [email protected] radioactivity radioactivity

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