Basic Nuclear and Radiochemistry PDF

Basic Nuclear and Radiochemistry Svetlana Selivanova, PhD and Alan B. Packard, PhD  Outline 1. Historical Background 2. Structure of the Atom 3. Nuclear decay processes 4. Nuclear decay equations 5. Nuclear reactions 1. Historical Background ...

Basic Nuclear and Radiochemistry Svetlana Selivanova, PhD and Alan B. Packard, PhD  Outline 1. Historical Background 2. Structure of the Atom 3. Nuclear decay processes 4. Nuclear decay equations 5. Nuclear reactions 1. Historical Background  Discovery of X-rays An X-ray being taken circa. 1896. Röntgen, circa. 1900 Röntgen's first "medical" X-ray, of his wife's hand, 22 December 1895. Röntgen received the first Wikipedia. Nobel Prize for Physics in 1901 https://www.pastmedicalhistory.co.uk/wilhelm-rontgen-and-the-first-x-ray/  Discovery of radioactivity Henri Becquerel, 1896 1896 – Discovered natural radioactivity when he observed that a photographic plate exposed to a phosphorescent substance produced an image of the phosphorescent substance on the plate. 1900 – Measured the properties of beta particles. 1901 – Observed that when he left a piece of radium in his vest pocket, he was burned by it, which led to the development of radiotherapy for the treatment of cancer. 1903 – Shared the Nobel Prize in Physics with Marie and Pierre Curie. The SI unit for radioactivity is the becquerel, defined as the quantity of radioactive material in Photographic plate fogged which one nucleus decays per second. by exposure a uranium salt.  Discovery of Radium (1898) Isolated by Marie and Pierre Curie in 1898 from pitchblende, a uranium ore Used in luminescent paints (Radium Girls) through the 1960s Marie and Pierre Curie were awarded Nobel prize in 1903 (with Henri Becquerel) The same year Marie Curie received her PhD Curie: A (non-SI) unit of radioactivity equal to the number of atoms in a one g sample of radium-226 that decay in one second. (3.7 x 1010 dps) Image: ttps://commons.wikimedia.org/w/index.php?curid=6267288  First Human Studies Blumgart and Weiss, 1927 Studies on the Velocity of Blood Flow: VII. The Pulmonary Circulation Time in Normal Resting Individuals (J Clin Invest. 1927; 4: 399–425.) Used Radium C (214Bi) to measure arm-to-arm transit time of blood First to use a radiotracer for a diagnostic procedure In honor of this accomplishment, each year the SNMMI Cardiovascular Council presents the Hermann Blumgart Award for outstanding achievement in the field of nuclear cardiology and service to the council.  Invention of the cyclotron - 1934 Ernest O. Lawrence Nobel Prize in Physics - 1939 Stanley Livingston and Ernest Lawrence standing beside the 27” cyclotron Image: https://nara.getarchive.net/media/ms-livingston-and-ernest-lawrence- beside-the-27-inch-cyclotron-built-in-1934-738cbf  First Nuclear Reactor 1938 – Meitner, Strassmann, and Hahn discovered that bombardment of uranium with neutrons produced barium. They proposed that the barium was created by the fission of the uranium nuclei. 1939 – Results from several different research teams showed that multiple neutrons were released during the fission reaction leading to the concept of a nuclear chain reaction 1942 – The first nuclear reactor, Chicago Pile-1, was constructed at the University Chicago Pile-1 of Chicago by Fermi  Tracer Principle George de Hevesy Won the Nobel Prize in Chemistry (1943) for the development of radioactive tracers to study chemical processes in plants and animals by using 212Pb to investigate lead absorption and metabolism in plants. A practical application – He spiked his leftover food with radioactivity to prove that his landlady was recycling leftovers. Used 2H to study water metabolism and 32P to study phosphorus metabolism in the human body. Discovered Hafnium (Hf)  The Discovery of Technetium – 1937 Carlo Perrier and Emilio Segre Isolated from a piece of molybdenum from the Berkeley cyclotron In 1925, Noddack, Berg, and Tacke reported the discovery of element 43, but their results could not be reproduced. Noddack and Tacke did discover rhenium Tacke was the first to propose the concept of fission.  99Mo/99mTc generator Richards, Green and Tucker, 1958 Outgrowth of the development of the 132Te/1321 generator at BNL in the mid-50s 99mTc was identified as an impurity coming from 99Mo The 99Mo/99mTc generator was never patented by BNL Now used in more than 15 million procedures every year in the US First imaging study with 99mTc (Tc-sulfur colloid; Harper, Lathrop & Richards, 1964) https://www.bnl.gov/newsroom/news.php?a=213162  The Challenge of Tc Chemistry Technetium was unknown prior to 1937, and there are no stable isotopes Technetium chemistry was largely unexplored until the late 1970s Technetium exists in oxidation states from +7 to -1, and its chemistry is complex Technetium is eluted from the generator as TcO4- TcO4- is useful only for imaging the thyroid and gastric mucosa It’s difficult to get TcO4- into a more useful oxidation state Prior to 1970 there were very few 99mTc radiopharmaceuticals Primarily aggregates such as Tc-sulfur colloid More than 10 years after the invention of the 99Mo/99mTc generator, the full potential of the 99Mo/99mTc generator had yet to be realized.  Development of the 99mTc “Instant Kit” Eckelman & Richards, 1970 99mTcO - 4 + SnCl2 + “L”  “Tc-L” >95% yield, >95% purity, sterile, pyrogen-free, < 1 min J Nucl Med. 1970: 11; 761  Synthesis of [18F]FDG Electrophilic synthesis (using F2): Ido, T., et al. (1978) J Label Compd Radiopharm, 14: 175-183. Nucleophilic synthesis (using F-) Currently used method First human studies with [18F]FDG Kuhl, Alavi, et al. 1976 (UPenn) Used [18F]FDG produced at BNL and flown to Philadelphia in a small plane 2. Structure of the atom Bohr Model of the Atom https://www.texasgateway.org/resource/bohr-model  It's Not Quite that Simple The nucleus isn't a simple ball Electron orbitals are complicated The nucleus is comprised of a mix of neutrons (neutral) and protons (positively charged) The ratio between neutrons and protons determines the stability of the nucleus. The electrons occupy distinct orbitals with rules about: How many electrons can be in an orbital How the orbitals are filled How electrons can move between the orbitals The interplay between these properties gives rise to nuclear decay phenomena https://science.howstuffworks.com/life/cellular-microscopic/bohr-model.htm  Atomic symbols Mass number A (number of protons plus neutrons) 18 9F Chemical element Atomic number Z (number of protons)  Chart of the Nuclides Karlsruhe Nuclide Chart – New 10th edition 2018, EPJ Nuclear Sciences & Technologies 5:6, 2019  Chart of the Nuclides – A Closer Look Isotopes Isotones Atomic Number (Z) Nuclide – An atom having a specific mass number (A) and atomic number (Z) Radionuclide – A nuclide that is radioactive Isotopes – Same Z, different N Isotones – Same N, different Z Neutron Number (N) Isobar – Same Z + N https://www.nndc.bnl.gov/nudat2/ 3. Nuclear decay processes  Nuclear Stability More than 3,000 nuclides have been identified, and most of them are unstable The stability of a nuclide is determined by several factors. One important factor is the N/Z ratio, the ratio of the number of neutrons to the atomic number. Radionuclides with excess neutrons tend to decay by β- emission Essentially, a neutron is converted to a proton resulting in a more stable nucleus 99Tc (Z = 43) → 99Ru (Z = 44) + β- Radionuclides with too few neutrons tend to decay by β+ emission or ε Essentially, a proton is converted to a neutron resulting in a more stable nucleus. 18F (Z = 9) → 18O (Z = 8) + β+ Another factor determining stability is the "energy" of the nucleus. A nucleus with excess energy can release that energy in the form of a γ ray. 99mTc → 99Tc + γ (140 keV)  β- emission Neutron-rich radionuclides often decay by β- emission. In addition to the β- particle, an antineutrino (𝜈)ҧ is also emitted. Essentially, a neutron is converted into a proton n → p+ + β- + 𝜈ҧ Note that: 1. In β- decay, Z increases by 1 and N decreases by 1. 2. In this case, two β- particles are emitted 3. Decay is not to the ground state – γ rays are also emitted 4. The total energy of the transition (Q) is 970.8 keV regardless of the path Drawing by Kays666 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=14714921  β- particles are not monoenergetic The decay energy is shared between the β- particle and the antineutrino Note that: 1. Very few β- particles are emitted at the maximum energy. 2. The mean β- energy is approximately 1/3 the maximum energy.  β+ (positron) emission Neutron-deficient radionuclides often decay by β+ emission. In addition to the β+ particle, a neutrino (ν) is also emitted. Essentially, a proton is converted into a neutron p + → n + β+ + ν Note that: 1. In β+ decay, Z decreases by 1 and N increases by 1 1.02 MeV 2. 18F also decays by electron capture (ε) 3% of the time. 3. 1.02 MeV is necessary for the production of the positron 4. The total energy of the transition (Q) is 1.655 MeV regardless of the path Ermert J., Neumaier B. (2019) "The Radiopharmaceutical Chemistry of Fluorine-18: Nucleophilic Fluorinations." In: Lewis J., Windhorst A., Zeglis B. (eds) Radiopharmaceutical Chemistry.  β+ emission is not monoenergetic The decay energy is shared between the β+ particle and the neutrino (ν) Note that, as with β- decay: 1. Very few β+ particles are emitted at the maximum energy. 2. The mean β+ energy is approximately 1/3 the maximum energy. http://199.116.233.101/index.php/PET_Decay (Wikipedia)  Electron Capture Decay (ε) Neutron-deficient radionuclides can also decay by electron capture. Lighter atoms tend to decay by β+ while heavier atoms tend to decay by ε. Those in the middle decay via both routes. As with β+ decay, a proton is converted into a neutron, except that with electron capture, an orbital electron is "captured" by the nucleus p+ + e- → n + ν + energy Note that: 1. In ε decay, as in β+ decay, Z decreases by 1 and N increases by 1 2. Decay is not necessarily to the ground state – γ rays may also be emitted 3. The total energy of the transition (Q) is the sum of the two emission energies.  Isomeric Transition (IT) Not all nuclear decay processes produce the daughter in the ground state. The resulting higher energy states are referred to as isomeric states. The half-lives of isomeric states vary from picoseconds to years. Isomeric states with longer half-lives are described as metastable. The decay from one excited state to a lower energy state or the ground state is referred to as an isomeric transition. The isomeric transition may result in: The emission of a γ ray or The energy may be transferred to an orbital electron and emitted in the form of a conversion electron.  An Example of Isomeric Transition Metastable 99mTc decays to 99Tc with the emission of 3 γ rays γ1 – 7.1 x 10-9% γ2 – 89% γ3 – 0.02% The "missing" energy (e.g., 11% for γ2) is emitted in the form of conversion electrons  Multiple Decay Modes Often Occur in the Same Nucleus The branching ratio (B.R.) is the fraction of decays that occur via a particular pathway Jalilian, Iran J Nucl Med. 2017; 25(1):1-10  α Emission Alpha-emitters are primarily heavy elements (e.g., U) that must lose mass to become more stable. Alpha decay is often a chain in which the daughter is also radioactive and may decay by  or - emission. Alpha decay is monoenergetic. Alpha particles are highly energetic (typically 4-8 MeV) and deposit their energy within a short distance (