Nuclear Radiation
Radioactivity This is the process by which unstable isotopes emit material. The instability in the atom is the result of an unstable nucleus trying to become more stable. A radioisotope is defines as the nuclei of an unstable isotope Example: C-14 radioactive dating process
Radiation Is defined as the material and/ or energy that are emitted from an unstable isotope. Examples: AAlpha – this is a Helium ion He Beta – changes a neutron into a proton or a proton into a neutron Gamma – is not a particle – it is energy (ray) 0 0
Energy In terms of the energy associated with each type of radiation: Increasing energy Good news…………………………Bad news
Penetrating Ability Depending upon its energy, different types of radiation are stopped by different materials Good News………………………Bad news
Radioactive Decay The next step in the process of becoming more stable
Nuclear Chemistry deals with the nuclei of atoms breaking apart. Atoms are continually undergoing decay. When studying nuclear chemistry, there is a typical format used to represent specific isotopes.nuclei Atoms Copyright © Cengage Learning. All rights reserved 7
The nuclear reactions that we will cover in chemistry class can be categorized as either an emission reaction or a bombardment reaction. Emission reactions: These are decay reactions, in which an unstable isotope decays into another element/isotope and releases a particle. The particles we will covering include: 4 2 Alpha particle – helium nucleus 0 -1 Beta particle – electron 0 0 Gamma emission 1 1 p Proton 1 0 n Neutron Copyright © Cengage Learning. All rights reserved 8
9 First type of Radioactive Decay – Alpha Particle Production Alpha particle – helium nucleus Examples Net effect is loss of 4 in mass number and loss of 2 in atomic number.
Where A is the parent isotope (the atom being broken apart) B is the daughter isotope or the isotope formed.parent isotope daughter isotope When an element is broken down in alpha decay it loses two neutrons and two (2) protons. This means that the name of the element will change as well, moving back two (2) places on the periodic table.element Copyright © Cengage Learning. All rights reserved 10
Nuclear equations are typically written in the format shown below. Alpha decay follows the form: Copyright © Cengage Learning. All rights reserved 11
Alpha decay is not very penetrating because the He atoms capture electrons before traveling very far. However it is very damaging because the alpha particles can knock atoms off of molecules.molecules Alpha decay is the most common in elements with an atomic number greater than 83.
Copyright © Cengage Learning. All rights reserved 13 Second type of Radioactive Decay – Beta Particle Production Beta particle – electron Examples Net effect is to change a neutron to a proton.
Beta negative decay follows the form: The beta emission increases the atomic number by one (1) by adding one (1) proton. At the same time, one (1) neutron is lost so the mass of the daughter isotope is the same as the parent isotope.atomic number neutron Copyright © Cengage Learning. All rights reserved 14
Beta negative decay is more penetrating than alpha decay because the particles are smaller, but less penetrating than gamma decay. Beta electrons can penetrate through about one (1) cm of flesh before they are brought to a halt because of electrostatic forces.electrostatic forces Beta decay is most common in elements with a high neutron to proton ratio.
Gamma emission Am Z A 0 0 + A Z B (Isotopes are moving from an excited state (m) to ground state) Copyright © Cengage Learning. All rights reserved 16 Third type of Radioactive Decay – Gamma Production
Gamma decay follows the form: In gamma emission, neither the atomic number or the mass number is changed. A high energy gamma ray is given off when the parent isotope falls into a lower energy state. Gamma radiation is the most penetrating of all. These photons can pass through the body and cause damage by ionizing all the molecules in their way Copyright © Cengage Learning. All rights reserved 17
Copyright © Cengage Learning. All rights reserved 18 Fourth type of Radioactive Decay – Positron Production Positron – particle with same mass as an electron but with a positive charge Example Net effect is to change a proton to a neutron.
Positron emission (also called Beta positive decay) follows the form: Copyright © Cengage Learning. All rights reserved 19 In this reaction a positron is emitted. A positron is exactly like an electron in mass and charge force except with a positive charge. It is formed when a proton breaks into a neutron with mass and no charge and this positron with no mass and the positive charge. Positron emission is most common in lighter elements with a low neutron to proton ratio.
20 Fifth type of Radioactive Decay – Electron Capture Process in which one of the inner- orbital electrons is captured by the nucleus.
Electron capture follows the form: 21 In this reaction a nucleus captures one (1) of its own atom's inner shell electrons which reduces the atomic number by one. This captured electron joins with a proton in the nucleus to form a neutron. Electron capture is common in larger elements with a low neutron to proton ratio.
Transuranium Elements Elements with atomic numbers greater than 92 which have been synthesized.
Bombardment reactions These are reactions that result from the addition of a particle to an isotope, which results in the formation of a new element/isotope and occasionally another particle. Isotopes can be bombarded with any of the following particles: 4 2 0 -1 0 0 1 1 p 1 0 n 23
Bombardment reactions Alpha bombardment A Z X A+4 Z+2 Y Beta bombardment A Z X A Z-1 Y Gamma bombardment A Z X Am Z X Proton bombardment A Z X p A+1 Z+1 Y Neutron bombardment A Z X n A+1 Z X 24
25 Concept Check Transformation If the bombardment of Am-243 with alpha particles leads to the emission of a neutron, which nuclide is formed in this nuclear transformation process? The correct answer is d. Since a neutron is emitted, the mass number goes up by 3 (not 4) and the atomic number goes up by 2 (from 95 to 97).