Nuclear physics, radioactivity Flashcards
Give the definition of isotopes!
Isotopes are the variants of a chemical element with a given atomic number whose mass numbers are different.
List the isotopes of hydrogen with their mass number and the constituents of their nuclei!
Hydrogen, mass number 1, 1 proton
Deuterium, 2, 1 proton+1 neutron
Tritium, 3, 1 proton+2 neutron
What is the mass defect of nuclei?
The mass defect equals the difference between the mass of a nucleus and the total mass of its constituents (Z: the number of protons and A-Z: the number of neutrons, where Z and A are the atomic number and the mass number of the nucleus, respectively):
Delta m = (Z m proton + [A-Z] m neutron) - m atom where Delta m is the mass defect, m proton, m neutron and m atom are the masses of a free, unbound proton, a free, unbound neutron and the given atomic nucleus, respectively.
What is the relationship between the total binding energy (Delta E) and the mass defect (Delta m) of a given nucleus?
Delta E=Delta m c2, according to Einstein’s mass-energy equivalence principle (c is the speed of light in vacuum).
Describe how the binding energy per nucleon changes as a function of mass number.
Binding energy per nucleon has a maximum at nuclei with mass numbers 55-60 (i.e. Fe).
What are the properties of nuclear force (their range, strength and direction)?
Nuclear forces have limited range, their effect is negligible at a distance of more than a single nucleon and they are independent of charge. They are very powerful attractive forces whose magnitude exceeds that of electrostatic forces.
On what kind of energy level does a nucleon reside in a nucleus compared to the energy of a free particle?
A bound nucleon has negative potential energy compared to a free particle.
List the types of radioactive radiation and characterize the particles constituting them!
Alpha radiation consists of helium nuclei. Negative beta radiation (Beta-) is composed of electrons, whereas positive beta radiation (Beta+) consists of positrons. Gamma radiation is an electromagnetic radiation consisting of high energy photons.
What is the direction of changes in the atomic number and the mass number of nuclei during alpha decay, both types of beta decay, electron capture and gamma decay?
Alpha decay -4, -2
Beta - decay: 0, +1
Beta + decay and EC: 0, -1
Gamma decay: 0, 0
Why is the spectrum of beta decay continuous?
Besides an electron (or a positron) an antineutrino (or a neutrino) is also emitted, and the energy released during the decay is shared randomly between the two particles.
What is electron capture and what does it produce?
Some nuclei are capable of capturing an electron residing on the K shell decreasing their atomic number by one. The vacancy generated this way on the K shell is filled by an electron from a higher shell. This transition generates characteristic X-ray and/or an Auger electron.
Give the equation describing the number of undecayed nuclei as a function of time (i.e. the law of radioactive decay) .
N = N0e^ -lambda t
N0: number of radioactive nuclei at t=0,
N: number of undecayed radioactive nuclei at the time of investigation,
Lambda: decay constant,
t: time.
What is the physical meaning of the radioactive decay constant?
Radioactive decay constant is equal to the inverse first power of the mean lifetime of a radioactive nucleus.
What is the relationship between the radioactive decay constant () and the half life (T)?
T = ln2/lambda
ln 2: the natural logarithm of 2.
Define biological half life.
Biological half life is the time period during which half of the initial quantity of the radioactive isotope leaves the living system undecayed due to metabolism, secretion or excretion.
