Neutrons Flashcards
Describe nucleons
Protons: positive 1 charge. Approx 1 amu.
Neutrons: neutral charge. Also approx 1 amu.
Located in nucleus
Describe electrons
Negative 1 charge.
Approx 1/1835 the mass of protons and neutrons.
Orbits around the nucleus.
What is an amu?
6.022x10^23 amu = 1 gram.
What is Atomic Number (Z)?
Number of protons in an atom.
Defines the specific element.
What is Neutron number (N)?
Number of neutrons in a nucleus.
Mass number - Atomic number
What is Mass Number (A)?
Total number of nucleons in a nucleus.
What is a nuclide?
All atoms containing unique combinations of protons and neutrons.
A specific nuclide has a specific number of neutrons as well as a specific number of protons.
What is an Isotope?
Varying nuclides of a particular element (same number of protons) with different numbers of neutrons.
3 forces that act on a nucleus
Electrostatic: strong (long range) repulsive between protons.
Gravitational: nucleons have mass and therefore gravity -> negligible.
Nuclear: strong (short range) attractive force. Holds nucleus together.
How does Neutron/Proton Ratio affect the stability of a nucleus?
Atoms with a higher Binding Energy per nucleons are more stable. As the Atomic number rises (above ~60) the BE/A decreases, and as such, larger (heavier) nuclei tend to be less stable. That also means that the Neutron/Proton ratio rises as more neutrons are required to overcome the repulsive force of the many protons in the nucleus.
Relationship between Mass Defect and Binding Energy.
Mass defect = mass lost to energy to “bind” an atom together.
Delta m=931.5 MeV.
Calculate Mass Defect
Delta m= {Z[m(p)+m(e)]+m(n)}-m(atom)
Calculate Binding Energy per Nucleon
BE/A
What is Elastic Scattering?
Collision in which KE is conserved.
KE in equals KE out.
Nucleus is not excited, just moves faster, and neutron loses KE equal to the amount transferred to the nucleus.
What is Inelastic Scattering?
KE is not conserved. Some KE of neutron is transferred to excitation energy of the nucleus. The nucleus then emits a neutron with lower KE and it also emits a gamma to lower back to ground state. KE out is lower than KE in due to emission of a gamma (energy).
What is Radioactive Capture?
A nucleus absorbs a neutron, becomes excited, and then emits a gamma to decay down to ground state.
What is Particle Ejection?
A nucleus absorbs a neutron and then becomes excited. The excited nucleus then emits a particle (alpha or proton) and a slightly smaller atom.
Ex: 5B10+n->(5B11)*->3Li7+2a4
(Can be looked at as the atom “splits” into smaller particles/atoms, however, this is not the same as fission)
Describe Fission
A heavy nucleus absorbs a neutron and splits into 2 smaller atoms [much larger than particles (alphas and protons)] in conjunction with 2-3 neutrons and gammas.
Define Excitation Energy
Energy that a nucleus contains above ground state energy.
Define Critical Energy
Energy required to be absorbed by a nucleus above ground state in order to cause that particular nucleus to fission.
Define Fissile Material
Material that will fission when absorbing neutrons of any energy level (BE)
Define Fissionable Material
Material that will fission if the nucleus absorbs a neutron with enough binding energy to over come the critical energy of the nucleus. Thermal neutrons (or neutrons of lower energy levels) may not have enough energy to cause the nucleus to reach critical energy.