The isotope shown here is Dysprosium The lecturer can point out that not decay is mentioned but transition - this is due to the fact that the isotope remains from the same element. Just some internal energy is lost and emitted in the form of electromagnetic radiation.
ATOMIC NUCLEUS AND RADIOACTIVITY E.H.ANNEX Medical Physicist Batra Hospital and Medical Research Centre New Delhi 62
1896 – Henry Becquerel – studied phosphorescence with Uranyl sulfate – discovered the Uranium Radioactivity. Nobel Prize in Physics – 1903 for discovery of radioactivity Becquerel investigated whether there was any connection between X-rays and naturally occurring phosphorescence. He had inherited from his father a supply of uranium salts, which phosphoresce on exposure to light. When the salts were placed near to a photographic plate covered with opaque paper, the plate was discovered to be fogged. The phenomenon was found to be common to all the uranium salts studied and was concluded to be a property of the uranium atom. Later, Becquerel showed that the rays emitted by uranium, which for a long time were named after their discoverer (‘Becquerel rays’), caused gases to ionize and that they differed from X-rays in that they could be deflected by electric or magnetic fields.
From 1896 on – Marie and Pierre Curie pursued the study of ‘Becquerel rays’)
They studied radioactive materials, In 1898 they deduced a logical explanation: that the pitchblende contained traces of some unknown radioactive component which was far more radioactive than uranium; thus on December 26 th 1898 Marie Curie announced the existence of this new substance.
Over several years of unceasing labour they refined several tons of pitchblende, progressively concentrating the radioactive components, then two new chemical elements. The first they named polonium after Marie's native country, and the other was named radium from its intense radioactivity.
As the nuclei get bigger, some of the nucleons get so far apart, the strong nuclear force isn’t effective due to its short range
But the electrostatic repulsions between the protons is a long range force and keeps pushing the protons apart
Nuclear Energy Our everyday life units for energy and mass are not suitable for atoms. The atomic mass unit (unified mass unit): 1u = 1.66 x10 27 kg Mass of a hydrogen atom is 1.0078 u The energy unit is the electronvolt (eV). 1eV = 1.60 10 19 J 1Mev = 1.60 10 13 J E (1 u) = mc 2 = 931 MeV
When the atomic nucleus undergoes spontaneous transformation, called radioactive decay , radiation is emitted
If the daughter nucleus is stable, this spontaneous transformation ends
If the daughter is unstable, the process continues until a stable nuclide is reached
Most radio nuclides decay in one or more of the following ways: (a) alpha decay, (b) beta-minus emission, (c) beta-plus (positron) emission, (d) electron capture, or (e) isomeric transition. (f) internal conversion
Types of Radioactivity particles: electrons : photons (more energetic than x-rays) penetrate! Easily Stopped Stopped by metal particles: nucleii Radioactive sources B field into screen detector
Alpha ( ) decay is the spontaneous emission of an alpha particle (identical to a helium nucleus) from the nucleus
Typically occurs with heavy nuclides (A > 150) and is often followed by gamma and characteristic x-ray emission
-decay Emission of an -particle or 4 He nucleus (2 neutrons, 2 protons) This is the preferred decay mode of nuclei heavier than 209 Bi with a proton/neutron ratio along the valley of stability The parent decreases its mass number by 4, atomic number by 2
-decay Emission of an electron (and an antineutrino) during conversion of a neutron into a proton The mass number does not change, the atomic number increases by 1. Example: 87 Rb -> 87 Sr + e – + This is the preferred decay mode of nuclei with excess neutrons compared to the valley of stability
-decay and electron capture Emission of a positron (and a neutrino) or capture of an inner-shell electron during conversion of a proton into a neutron The mass number does not change, the atomic number decreases by 1. Examples: 40 K -> 40 Ar + e + + 50 V+ e – -> 50 Ti + + These are the preferred decay modes of nuclei with excess protons compared to the valley of stability
Sometimes when a nucleus decays, the product is not stable either(radioactive isotope) and it will decay. The series of disintegration until a stable nuclide is reached is called a decay series. 235 U decaying into 207 Pb is a well-known one another is thorium series that starts with 232 Th and ends with 208 Pb.
The Decay Constant N/ t N(t) N number of radionuclides at some moment of time t N number of nuclei that decay in a time interval t decay constant N 0 initial number of nuclei T 1/2 half-life e = 2.718 N = N t N(t) = N 0 e t N 0 /2 = N 0 e T 1/2 T 1/2 = 0.693/
If the half life of the parent is longer than that of the daughter,then after a certain time a condition of equilibrium will be achieved ,that is the ratio of the daughter activity to the parent activity will become constant . In addition the decay rate of the nuclide is then governed by the half life or disintegration rate of the parent
First accomplished by Rutherford in 1919, even though alchemists tried for hundreds of years.
Transmutation of lead into gold was achieved by Glenn Seaborg, who succeeded in transmuting a small quantity of lead in 1980. He also first isolated plutonium for the atomic bomb and discovered/”created” many elements. (NY Times, Feb 1999)
There is an earlier report (1972) in which Soviet physicists at a nuclear research facility in Siberia accidentally discovered a reaction for turning lead into gold when they found the lead shielding of an experimental reactor had changed to gold.
Accomplished with particle accelerators like the Stanford Linear Accelerator (SLAC)