37406246 radioactivity radioisotopes

7/30/2019 37406246 Radioactivity Radioisotopes

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Dr Saurabh

Samdariya


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I. IntroductionII. Historical aspects

III. Sources

IV. Ionising radiations

V. Decay constant

VI. activity

VII. half life

VIII. radioactive seriesIX. radioactive equilibrium

X. modes of radioactive decay

XI. Introduction to radioisotopes

XII. radioisotopes in clinical medicine


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the property of an element wherein atom gives off

radiation in terms of particle, electromagneticradiation or both in order to achieve stability is

called as radioactivity & the process is called as

radioactive decay/disintegration.

Total 118 elements discovered till now

Most of them are stable


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Naturally occuring radioactive elements

Uranium

grouped into 3 series Actinium

Thorium

U238 4.51 x 109

yr Pb206

U235 7.13 x 108 yr Pb207

Th23 21.39 x 1010 yr

Pb208


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HISTORICAL ASPECTS


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William

ConradRoentgen

Discoveryof x

Rays - 1895

Nobel prize-1901


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Ernest Rutherford

Discovery of alpha

particles

(1897)


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Sir Joseph john

Thomson

Discovery of electrons

Nobel prize-1906


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Paul ulrich vilard

Discovery of

gamma rays-1900


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Sir James Chadwick

Discovery of neutron

Nobel prize-1932


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1.naturally occuring-Radon

Pottasium

Carbon-14

2. manmade - Medical uses

Consumer products( smoke

detectors)

Fall out from nuclear testing

Emissions (nuclear plants)


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POSITIVECHARGE

PROTONS

NEUTRALCHARGE

NEUTRONS

NUCLEUS

NEGATIVE CHARGE

ELECTRONS

ATOM

Most of the atoms mass.

NUCLEUS ELECTRONS

PROTONS NEUTRONS NEGATIVE CHARGE

POSITIVECHARGE

NEUTRALCHARGE

ATOM

QUARKSAtomic Number

equals the # of...

equal in a

neutral atom


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Atomic Mass Unit (amu)is defined as exactly 1/12 of the mass of the atom

of Carbon-12. It is a very small number.

Isotopes An atom of an element that has the same atomic number butdifferent mass number is called an isotope.

Ions When an atom loses or gains electrons, the species formed is calledan ion and carries a net charge

The atomic massof an element is the average of the isotopic masses,

weighted according to the naturally occurring abundances of the isotopesof the element.

The molecular weight is the sum of amu for all elements, in the molecule,

times Avogadros number (a very large number, 6.02*1023), in grams


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Four Primary Types Of Ionising Radiations-

1. Alpha particles

2.Beta particles3.Gamma rays (or photons)

4.X-Rays (or photons)

5.Neutrons


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Composed of two protons and twoneutrons

Particle radiation (largest and mostmassive of all the ionizing particles)

Least penetrating of all ionizing radiationand can be shielded by a few inches ofair, penetrating power can be stopped by

a piece of paper or the outer layer ofskin.

It has a very short range and it has greatdestructive power within its short range.


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Alpha emission ctdIt is not suitable forradiation therapy since

its range is less than atenth of a millimeterinside the body.

Its main radiation hazardcomes when it is ingestedinto the body it ispositioned for maximumdamage when in contact

with fast-growingmembranes and livingcells

BETA RADIATION


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BETA RADIATION

Particle radiation Beta particles are just electrons from the nucleusThe high energy electrons have greater range ofpenetration than alpha particles, but still much less than

gamma rays. The radiation hazard from betas isgreatest if they are ingested. can be shielded by several inches of plastic, thin

plywood and sheet metal. Can penetrate up to 1/4 in. into the tissue

G di i i


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Gamma radioactivity

is composed of

electromagnetic rays; hasno mass

distinguished from x-raysonly by the fact that itcomes from the nucleus

Most gamma rays aresomewhat higher in energythan x-rays and therefore

are very penetrating.

G di i i


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thick concrete can reduce

the effect of gamma raysto permissible levels.

It is the most usefultype of radiation formedical purposes, but atthe same time it is themost dangerous becauseof its ability to penetratelarge thicknesses of

material

Gamma radioactivity


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Fraction of total no of atoms that decay per unit of

time

Radioactive decay is a stastical phenomenon

No of atom disintegrating per unit time-no ofradioactive atoms present

N N

T

N = No e-t


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Radioactivity of radioactive elements

A = - N

A = Ae- t

units - curiebecqurel(SI)

1 ci =3.7x10 dps

1 Bq = 1 dps=2.7x 10-11 ci

y


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Time required for either the activity or no of radioactive

atom to decay to half of the initial value

N = Noe- t

T1/2 =

.693


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Physical Half-Life

Time (in minutes, hours, days or years) required for the activity of a radioactive material to decrease by one half due

to radioactive decay

Biological Half-Life Time required for the body to eliminate half of the radioactive

material (depends on the chemical form)

Effective Half-Life

The net effect of the combination of the physical & biological

half-lives in removing the radioactive material from the body

Half-lives range from fractions of seconds to millions of years

1 HL = 50% 2 HL = 25% 3 HL = 12.5%


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Avg life time for decay of radioactive atoms

Time period that a hypothetical source would need if it

retained its original activity for the time period and then

suddenly decayed to zero activity to produce the same no

of disintegration as produced over an infinite time period

by the source if it decayed exponentially

ta = 1/

ta = 1.44 t1/2


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Activity per unit mass of radionuclide

Uses -

1.Tracer studies are done using high

sp. activity elements.2.Teletherapy source(Co-60 is preferred

overCs-137)


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parent nuclei daughter nucei

(t1/2)p> (t1/2)d {Transient eq.}

(t1/2)p>>>>>(t1/2)d {Secular eq. }

examples-

- Mo generator producing Tc99m for

diagnostic purposes (transient)

- Ra source in a sealed tube or needle

in order to keep radon gas (secular)


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A = A1 x y2 [ ( 1-e-y2-y1 ) t ]y2-y

1

A2 / A1 = Y2 / Y2-Y1 = T1 / T1-T2

A2 = A1 (1- e-y2

t )


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An unstable releases energy to become morestable(RADIOACTIVE DECAY)

decay

primay decay processes decay

e capture

emission

Secondary decay processes iso metastbleinternal conversion


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3000 known nuclei, but only266 stable ones!

Z > 83 elements not stable!

Tendency forN Z, for smallZ, but N > Z for larger Z.

(due to proton repulsion)

Unusual stability formagic numbers.Z, N = 2, 10, 18, 36, 54

(analogous to electronic shells


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Radioactivity

decays with time


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particles are monoenegertic and have 4 to 8 Mevenergy.

ZXA

Z- 2YA-4 + 2He

4 + Q

Q = Disintegration energy(K.E. of alpha particle

and daughter nuclei)

Ex- elements having high Z (Ra216 Rn222 Po218

U235 Pu239 Am241)


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1.

-

(negatron)

decay- high n/p ratioEx.- H, C, P, Co, Sr, Mo, I,

Cs, Au

0n1 1p1 + -1 0 + + Q

ZX

A

Z- 1Y

A

+ -1

0

+ +Q


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2 . + (positron)decay- low n/p ratio( )

1p

10n

1 + +10 + + Q

Z

XA

Z- 1

YA ++1

0 +

+Q


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Similar to + decay

nucleus captures e- from its orbit (usually K shell )

It increases nuclear mass by .511 Mev

From p to n

Occur for not sufficient energy for b+decay(1.22Mev)

Ex - Na, K, Cr, Co, Ir


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Secondary decay processes-

1. emission

. excitation energy given off by

photon = rays

. fast process

E = EP - ED


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Ionizing Radiation

alpha particle

beta particle

Radioactive Atom

X-ray

gamma ray


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http://upload.wikimedia.org/wikipedia/commons/8/84/IodoAtomico.JPGhttp://upload.wikimedia.org/wikipedia/commons/8/84/IodoAtomico.JPG


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if two atoms of an element are having same atomic no

(p) but differ in their their atomic mass(A) then those two

atoms are called as isotope of each other and if atom is

having property of radioemission it is called as

RADIOISOTOPES.


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DIAGNOSIS THERAPY

in vitro in vivo internal external

Systemic sources tele radio


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14C

3H

125I

201Tl123I

111In

67Ga

81Rb-81mKr

others

+ emitters

for PET

18F, 11C,13N,15O

86Y, 124I

68Ge-68Ga

82Sr-82Rb

131I,90Y153Sm,186Re

188W-188Re

166Ho,177Lu,

Others

a-emitters:225Ac-213Bi

211At,223Ra

149Tb

e--emitters:125I

sealed sourcesand

applicators:

192Ir,

182Ta,

137Cs

Others

needles for

brachytherapy:

103Pd,

125I

microspheres

90Sr or 90Y,

others

60Co

Gamma

Knife

137Cs

blood

cell

irradi-ation


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Radioactive traccers which emmit gamma rays

within the body are given by injection inhalation or

orally

Radioactive tracers are short lived isotopes linked

to chemical compounds which permit speciic

physiological processes to be scrutinised

Emitted gamma rays are detected by gamma

camera & build image from the point from whichradiationis emitted.image is enhanced by computer

& viewed on monitor..

thus a organ can be viewed from

several angles


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now a days PET & PETCT are also used instead of gamma

camera.. They detects positrons emitted from

radionucleides

FUNCTIONAL imaging

Mean effffective dose is 4.6 mSv per diagnostic procedure

Advantage over routine x ray imaging-

1.both bone & soft issue can be imaged successfully

2.functional status of organ is determined


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2 forms

teletherapy/EBRT

(external RNT)

brachytherapy

(internal RNT)


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http://upload.wikimedia.org/wikipedia/commons/8/84/IodoAtomico.JPG


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The imaged property is the distribution of radionuclide-

labeled agents injected in the body: radiopharmaceuticals

Produce functional images of tracer concentrations relatedto pathophysiological Process

Radioisotope- An unstable isotope of an element thatdecays or disintegrates spontaneously, emitting radiation

Radioactive decay of radioisotopes leads to the emission of-, -, -, and x radiation depending on the radionuclideinvolved


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The range of-, -particles is small

for in vivo imaging using external

Radioisotope imaging is restricted to the use of radionuclides emitting photons with energies > 50 keV


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Anger camera (1960s)

Radioisotope imaging is restricted to the useof radio nuclides emitting photons

with energies > 50 keV

Lead collimator (incidence orientationselection)

Scintillation camera of NaI (sodium iodide) Photomultipliers (PMT)


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Static planar scintigraphy

Dynamic planar scintigraphy

Emission Computed Tomography (ECT)

Single Photon Computed Tomography (SPECT) Positron Emission Tomography (PET


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Single Photon Computed Tomography (SPECT) Same principle of Gamma camera but with 2 or 3 rotating

cameras to record projection data more efficiently

In CT we know the position of the emitting source and thedetection point; in SPECT only the detection point

In CT absorption is the essence of the imaging process; inSPECT attenuation degrades the images

Attenuation must be compensated for (single scan-line of

photons to estimate transmission coefficient)


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Gated SPECT particularly useful in cardiacperfusion studies

Some systems with slip ring technology


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Radiotracer produces positrons, which areannihilated within around 1mm from their origin

After annihilation 2 -ray photons are emittedalong a Line Of Response (LOR)

Electronic coincidence detectors (12ns), which

eliminates lead collimators and allows higherefficiency

In PET it is easier to correct for attenuation


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AUGER electron emitters for therapy


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+ emitters

for

in vivo dosimetry

Scintigraphic abdominal


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images 5 & 24 h p.i.

affected by

carcinoid with

extensive hepatic and

paraaortal metastases

Patients:

3 patients with metastases of

carcinoid tumor (histologicallyconfirmed)

. No therapy with unlabeled

somatostatin > 4 weeks

Age: 46 67 years, male

All were candidates for a

possible 90Y-DOTATOC therapy


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PhysicalRadionuclide Half-Life Use__________________Americium-241 432 yrs Smoke Detectors

Bismuth-213 46 min TAT(targeted alpha therapy)

Cesium-137 30 yrs Food Irradiator

Cobalt-60 5.27 yrs EBRT,sterilising

Cromium-51 28 days label RBC & quantify GI protein loss

Dysprosium-165 2hr aggregated OH in synovectomy

Erbium-169 9.4 days arthritis pain-synovial joints

Holmium-166 26 hr liver tumors(,Rx)

Hydrogen-3 12 yrs Exit Signs

Iridium-192 74 days Industrial Radiography,BT wires


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Physical

Radionuclide Half-Life UseIodine-125 60 days Brachtherapy(prostate,brain)

- DVT leg, GFR kidney

Radioimmunoassys

Iodine-131 8 days Imaging & treating throid cancer,- abnormal liver function ,

renal blood flow

urinary tract obstruction

Iron-59 46 days Study Fe metabolism in spleen

Lutetium-177 6.7 days Rx of small endocrine tumors

Molybdenum-99 66 hr PARENT in generator for Tc99m

Palladium-103 17 days prostate ca-BT permanent seed implant


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Physical

Radionuclide Half-Life Use______________________Phosphorus-32 14 days Rx of Polycythemia vera

Plutonium-239 24,000 yrs Nuclear Weapon

Pottasium-42 12 hr Detemination of exchangeable

pottasium in coronary blood flow

Radon-222 4 days Environmental Level

Rhenium-186 3.8 days pain reief in bone caner

Rhenium-188 17 hr -iradiate coronary arteries from

an angioplasty baloon

Samarium-153 47 hr pain relief in metastatic bone 20

Selenium-75 120 days study production of digestive

enzymes (Selenomethionine)


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Physical

Radionuclide Half-Life Use______________Sodium-24 15 hrs study electrolytes in body

Strontium-89 50 days relief from pain of prostate

& bone cancerStrontium-90 29 yrs Eye Therapy Device

Technetium-99m 6 hrs Diagnostic Imaging

(skeleton,myocardium,lung)

Xenon-133 5 days lung ventilation studiesYtterbium-169 32 days CSF studies

Ytterbium-177 1.9 hrs progenitor ofLu-177


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Physical

Radionuclide Half-Life Use_________________________

Fluorine-18 PET(brain,heart physiology,pathology)

Cobalt-57 272 days marker to estimate organ size

Gallium-67 78 hr tumor imaging, localisation of

inflammatory leison(infective)

Gallium-68 68 min positron emitter(PET)

Iodine-123 13 hr of thyroid function .

Thallium-20173 hr of CAD , MI


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allow to separate chemically short-lived radioactive daughter nuclei with

good characteristics for medical

imaging from long-lived radioactive

parent nuclei. Typical techniques used

are chromatographic absorption,

distillation or phase separation

This method is in particular applied forthe separation of the rather short-lived99Tcm (T1/2=6 h) from the long lived

99Mo

(T1/2=2.7 d).

Milking cow analogy


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Applying the radioactivedecay law the growth of

activity of the daughter

nuclei A2 with respect of

the initial activity of themother nucleusA1

0can

be expressed in terms of

their respective decay

constants 2 and 2 with

2 >> 1:


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52-year old female breast cancer

ANT POST


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Phosphorus-32

Rhenium-186

Samarium-153

Strontium-89

Rhenium-188


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Gadolinium enhanced

SPECT imageRadioisotope

cisternography


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37406246 radioactivity radioisotopes

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