RADIOACTIVITY for Nuclear Chemistry Course for second year student

1. Dr. Mohammed Alnafea
alnafea@ksu.edu.sa
RADIOACTIVITY

2. Objectives & learning outcome
 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

3. History of Radiopharmacy
 Medicinal applications since the discovery of
Radioactivity
 Early 1900’s
 Limited understanding of Radioactivity and
dose
3 2nd lecture RAD 311

4. 1912 — 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”
4 2nd lecture RAD 311

5. Early 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
5 2nd lecture RAD 311

6. Early Uses continued
 1939: 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
6 2nd lecture RAD 311

7. What is a radiopharmaceutical?
 A radioactive compound used for the
diagnosis and therapeutic treatment of
human diseases.
Radionuclide + Pharmaceutical
Part 1: Characteristics of a
Radiopharmaceutical
7 2nd lecture RAD 311

8. Radioactive Materials
 Unstable nuclides
 Combination of neutron and protons
 Emits particles and energy to become a
more stable isotope
N →
↑
Z
Chart of the Nuclides
8 2nd lecture RAD 311

9. Radiation decay emissions
 Alpha (a or 4He2+)
 Beta (b- or e-)
 Positron (b+)
 Gamma (g)
 Neutrons (n)
9
2nd lecture RAD 311

10. Radioactivity
 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.
10
2nd lecture RAD 311

11. Electromagnetic Radiation
 X-ray and g-rays
 Same properties, differ in origin
 X-rays – electronic transitions
 g-rays – nuclear decay
 X rays occur when an excited electron emits a photon
as it relaxes
 g- rays occur when an excited nucleus emits a photon
as it relaxes
11 2nd lecture RAD 311

12. 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.
12
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13. Interactions of Emissions
 Alpha (a or 4He)
 High energy over short linear
range
 Charged 2+
 Beta (b- or e-)
 Various energy, random
motion
 negative
 Gamma (g)
 No mass, hv
 Positron (b+)
 Energy >1022 MeV, random
motion
 Anihilation (2 511 MeV ~180°)
 Negative
 Neutrons (n)
 No charge, light elements
13 2nd lecture RAD 311

14. 14
Definition: A = dN / dt = l x N
where N is the number of radioactive atoms
present at time t, dN the expectation value of the
number of nuclear transitions in time interval dt,
and l the physical transformation constant (decay
constant).
Activity, A
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15. Half Life and Activity
 Radioactive decay
is a statistical
phenomenon
 t1/2
l= decay constant
 Activity
 The amount of
radioactive material
15
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16. Measured Activity
 In practicality, activity (A)
is used instead of the
number of atoms (N).
 A=AOe-lt
 Units
 Curie
 3.7 Exp10 decay/s
 1 g Ra
 Becquerel
 1 decay/s

17. Half Life and decay constant
Half-life is time needed to decrease
nuclides by 50%
Relationship between t1/2 and l
N/No=1/2=e-lt
ln(1/2)=-lt1/2
ln 2= lt1/2
t1/2=(ln 2)/l
17 2nd lecture RAD 311

18. Equations
 Nt=Noe-lt
N=number of nuclei, l= decay constant,
t=time
Also works for A (activity) or C
(counts)
 At=Aoe-lt, Ct=Coe-lt
18 2nd lecture RAD 311

19. Applications in Nuclear
Medicine
 Imaging
 Gamma or positron emitting isotopes
 99mTc, 111In, 18F, 11C, 64Cu
 Visualization of a biological process
 Cancer, myocardial perfusion agents
 Therapy
 Particle emitters
 Alpha, beta, conversion/auger
electrons
 188Re, 166Ho, 89Sr, 90Y, 212Bi, 225Ac, 131I
 Treatment of disease
 Cancer, restenosis, hyperthyroidism
19
2nd lecture RAD 311

20. Ideal Nuclear Properties for
Imagining Agents
 Reasonable energy emissions.
 Radiation must be able to penetrate several layers
of tissue.
 No particle emission (Gamma only)
 Isomeric transition, positron (b+), electron capture
 High abundance or “Yield”
 Effective half life
 Cost
20 2nd lecture RAD 311

21. Ideal Characteristics of a
Radiopharmaceutical
 Nuclear Properties
 Wide Availability
 Effective Half life (Radio and biological)
 High target to non target ratio
 Simple preparation
 Biological stability
 Cost
21 2nd lecture RAD 311

22. Gamma Isotopes
Radionuclide T1/2 g (%)
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)
22 2nd lecture RAD 311

23. Radioactive Decay Kinetics
Outline
 Radioactive decay
kinetics
 Basic decay
equations
 Utilization of
equations
 Mixtures
 Equilibrium
 Branching
 Natural radiation
 Dating
23
2nd lecture RAD 311

24. Basic decay equations
 The radioactive process is a subatomic change within the
atom
 The 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=lDt
Probability of not decaying: 1-p=1- lDt
24 2nd lecture RAD 311

25. Units of Radioactivity
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25
 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.

26. Standard International Radiation
Protection Units
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26
 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

27. Unit Analysis
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27
BASE UNIT CONVERSION TABLE
Unit Unit Conversion
1 Bq 2.7 x 10-11 Ci
1 Ci 3.7 x 1010 Bq
1 Bq 1 dis/sec
1 dis/sec 2.7 x 10-11 Ci
1 Ci 3.7 x 1010 dis/sec

28. Unit Analysis (Con’t.)
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28
BASE UNIT CONVERSION TABLE
Unit Unit Conversion
1 rem 0.01 Sv
1 Sv 100 rem
1 rad 0.01 Gy
1 Gy 100 rad
1 R 2.58 x 10-4 C/kg
1 meter 3.28 ft (39.37in)

29. Radiation Dose Units
Exposure:
Roentgens (R) or Coulomb/Kg
A 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.
29 2nd lecture RAD 311

30. Radiation in Medicine
Procedure Effective dose
(mSv)
Chest x-ray 0.04
Abdominal x-ray 1.5
Lumbar spine x-ray 2.4
Intravenous
Pyelography
4.6
Abdominal CT scan 7.2
Chest CT scan 8.3
Brain CT scan 1.8
Tc-99 bone scan 3.6
Tc-99 lung scan 1.0
I-123 thyroid scan 4.4
30
2nd lecture RAD 311

31. Detecting and Measuring Radiation
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31
 Instruments
 Locate contamination - GM Survey Meter (Geiger
counter)
 Measure exposure rate - Ion Chamber
 Personal Dosimeters - measure doses to staff
 Radiation Badge - Film/TLD
 Self reading dosimeter (analog & digital)

32. 2nd lecture RAD 311
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35. INSTRUMENTATION IN NUCLEAR
MEDICINE
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35
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)

36. Summary
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 second
2nd lecture RAD 311

37. 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

38. Student Homework
next 2 slides
38 2nd lecture RAD 311

39. Q1:Half-life calculation
Using Nt=Noe-lt
 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?
39 2nd lecture RAD 311

40. Q2: Half-life calculation
A=lN
 A 0.150 g sample of 248Cm has a alpha activity of 0.636
mCi.What is the half-life of 248Cm?
40 2nd lecture RAD 311