Dr. Mohammed Alnafea RADIOACTIVITY RADIOACTIVITY

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

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

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

Early use of radiotracers in medicine 1926: Hermann Blumgart, MD injected 1-6 mCi of “Radium C” to monitor blood flow (1 st clinical use of a radiotracer) 1937: John Lawrence, MD used phosphorus-32 (P- 32) to treat leukemia (1 st use of artificial radioactivity to treat patients) 1937: Technetium discovered by E. Segre and C. Perrier 5 2nd lecture RAD 311

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

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

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

Radiation decay emissions Alpha (  or 4 He 2+ ) Beta (   or e - ) Positron (   ) Gamma (  ) Neutrons (n) 9 2nd lecture RAD 311

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

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

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 2nd lecture RAD 311

Interactions of Emissions Alpha (  or 4 He) 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 motion Anihilation (2 511 MeV ~180°) Negative Neutrons (n) No charge, light elements 13 2nd lecture RAD 311

14 Definition:A = dN / dt =x N Definition:A = dN / dt =  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 the physical transformation constant (decay constant). Activity, A 2nd lecture RAD 311

Half Life and Activity Radioactive decay is a statistical phenomenon t 1/2  decay constant Activity The amount of radioactive material 15 2nd lecture RAD 311

Measured Activity In practicality, activity (A) is used instead of the number of atoms (N). A=A O e - t Units Curie 3.7 Exp10 decay/s 1 g Ra Becquerel 1 decay/s

Half Life and decay constant Half-life is time needed to decrease nuclides by 50% Relationship between t 1/2 and N/N o =1/2=e - t ln(1/2)=- t 1/2 ln 2= t 1/2 t 1/2 =(ln 2)/ 17 2nd lecture RAD 311

Equations N t =N o e - t N=number of nuclei, = decay constant, t=time Also works for A (activity) or C (counts) A t =A o e - t, C t =C o e - t 18 2nd lecture RAD 311

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

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 (  + ), electron capture High abundance or “Yield” Effective half life Cost 20 2nd lecture RAD 311

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

Gamma Isotopes RadionuclideT 1/2  (%) Tc-99m 6.02 hr140 KeV (89) Tl hr167 KeV (9.4) In d171(90), 245(94) Ga-6778 hr93 (40), 184 (20), 300(17) I hr159(83) I-1318d284(6), 364(81), 637(7) Xe d81(37) 22 2nd lecture RAD 311

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

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= t Probability of not decaying: 1-p=1- t 24 2nd lecture RAD 311

Units of Radioactivity 2nd lecture RAD 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 Protection Units 2nd lecture RAD Becquerel (Bq) for Curie 1 Ci = 3.7 x Bq Gray (Gy) for rad 1 Gy = 100 rad Sievert (Sv) for rem 1 Sv = 100 rem

Unit Analysis 2nd lecture RAD BASE UNIT CONVERSION TABLE UnitUnit Conversion Unit Unit Conversion 1 Bq 2.7 x Ci 1 Ci3.7 x Bq 1 Bq1 dis/sec 1 dis/sec2.7 x Ci 1 Ci3.7 x dis/sec

Unit Analysis (Con’t.) 2nd lecture RAD 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 C/kg 1 meter 3.28 ft (39.37in)

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

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 nd lecture RAD 311

Detecting and Measuring Radiation 2nd lecture RAD Instruments Instruments Locate contamination - GM Survey Meter (Geiger counter) Locate contamination - GM Survey Meter (Geiger counter) Measure exposure rate - Ion Chamber Measure exposure rate - Ion Chamber Personal Dosimeters - measure doses to staff Personal Dosimeters - measure doses to staff Radiation Badge - Film/TLD Radiation Badge - Film/TLD Self reading dosimeter (analog & digital) Self reading dosimeter (analog & digital)

2nd lecture RAD

2nd lecture RAD

2nd lecture RAD

INSTRUMENTATION IN NUCLEAR MEDICINE 2nd lecture RAD 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)

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 radioactive decays per second 2nd lecture RAD 311

Summary of Units 2nd lecture RAD 311

Student Homework next 2 slides 38 2nd lecture RAD 311

Q1:Half-life calculation Using N t =N o e - t 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

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