Nuclear Sciences Defs Only

A unit of measurement equal to 1/12 the mass of a Carbon 12 atom (1.6605402 x 10–24 grams).

Sub-atomic particle that makes up an atom, has a mass of 0.00055 AMU, a negative charge, and is located outside the nucleus in probability shells (orbits).

Amount of kinetic energy (eV) gained by an electron when accelerated through an electric potential difference of 1 volt

A basic substance that cannot be broken down into any simpler substance after it is isolated from a compound, but can be combined with other elements to form compounds.

A nucleus of the same element (same number of protons) with a different number of neutrons.

Sub-atomic particle that makes up an atom, has a mass of 1.00866 AMU, a neutral charge, and is located in the nucleus.

Any particle that is part of the nucleus of an atom, neutrons and protons

Any atom containing a unique combination of neutrons and protons in the nucleus.

Sub-atomic particle that makes up an atom, has a mass of 1.00727 AMU, a positive charge, and is located in the nucleus.

The energy equivalent of the mass defect (MeV). Represents the amount of energy that is released when an atom is formed from its component protons and neutrons. Also, represents the amount of energy that must be supplied to the atom to completely separate it into its individual protons and neutrons.

Average energy required to remove a nucleon from the nucleus.

The attractive or repulsive force that exist between two objects due to their electrical charge.

The splitting of an atoms nucleus resulting from an energy input (excitation energy) into the nucleus greater than the nuclear forces holding the nucleus together.

The difference in mass between a nucleus and the sum of the masses of the individual protons and neutrons in the nucleus (AMU).

The conversion factor equating mass to energy

The strong attractive force in a nucleus between to adjacent nucleons.

The inherent ability of an atom to resist changing its atomic structure or energy level.

The process by which an unstable nucleus spontaneously transmutes from one form to another to reach a more stable state.

The unstable nucleus of an atom immediately following the absorption of a neutron.

The new nucleus present after the decay event.

A process involving the decay of a daughter product of radioactive decay, which may result in transformation to another daughter product that decays, etc.

The probability per unit time that a decay event will occur within a radioactive sample

The rate at which the atoms of a sample of radioactive material disintegrates.

The interaction between a neutron and nucleus of an atom resulting in the neutron transforming some of its kinetic energy to the nucleus with all kinetic energy shared between the neutron and nucleus and total KE conserved.

Any condition that results in an atom being electrically charged or at an energy level above its ground state energy.

Highly excited radionuclides that are the result of a fission event and generally initiate a decay chain with beta decay.

Any electron that is not electrically bound to an atom’s nucleus.

A type of electromagnetic radiation emitted from an unstable nucleus allowing the nucleus to give off energy and return to a stable ground state

The normal energy level of an atom when it is electrically neutral and not influenced by any outside energy inputs.

The time required for a radioactive sample to decay to one half of its original value.

The interaction between a neutron and nucleus of an atom resulting in some of the kinetic energy being transferred from the neutron to the nucleus and causing excitation of the nucleus such that it returns to ground state by gamma emission. KE is not conserved.

An atom or a group of atoms that has acquired a net electric charge by gaining or losing one or more electrons.

Any process that causes an atom or group of atoms to have a net electric charge resulting from losing or gaining one or more electrons

The energy required to remove one or more electrons from an atom

The interaction between a neutron and nucleus resulting in capture of the neutron with enough energy to cause the resulting excited nucleus to split into two fission fragments and the release of neutrons and radiation.

The original nucleus that decays

The interaction between a neutron and nucleus resulting in capture of the neutron and excitation of the nucleus such that it returns to ground state by gamma emission.

The process by which an unstable nucleus spontaneously transmutes from one form to another to reach a more stable state.

Any fission event that occurs independent of neutron induced fission. Generally occurs in radioisotopes with atomic numbers of 92 and above.

Any of the radionuclides with atomic numbers greater than 92.

A bundle of energy (photon) emitted from the electron shell of an excited atom.

The number of atoms of a given isotope in a unit volume. Atomic density uses the symbol “N” as a designation, and the units are atoms per cubic centimeter.

Unit of measurement, where 1 barn is equal to 1 ´ 10‑24 square centimeters

The minimum amount of energy required for fission to occur in a specific fuel type.

A neutron born more than 1 ´ 10‑14 seconds after a fission event.

The delayed energy released by decay of the fission fragments after reactor shutdown.

A neutron that has a kinetic energy greater than 0.1 MeV.

A fuel type that will fission due to the binding energy of an incident neutron.

A neutron reaction in which an incident neutron is absorbed by a target nucleus, resulting in the splitting of the target nucleus into two new atoms, some neutrons, and gamma rays.

A neutron emitted as a direct result of the fission process.

Any particle created as the result of a fission event.

A fuel type that requires kinetic energy in addition to binding energy of an incident neutron for fission to occur.

A neutron that has a kinetic energy between 0.1 MeV and 1 eV

A measure of the probability that a given interaction will occur between a single target nucleus and an incident neutron. The effective area presented by the target nucleus to the incident neutron, for a particular reaction.

The average distance a neutron travels before an interaction occurs.

The probability that a given interaction will occur between a target nucleus and neutron (barns or cm2).

A neutron that is emitted within 10-14 seconds of a fission event and is a direct result of the fission process (fission neutron).

A neutron that has a kinetic energy less than 1 eV.

A neutron that is produced independently of neutron induced fission.

Any fission that results in the production of three fission fragments.

A neutron that is in thermal equilibrium with its surroundings.

The condition of the reactor where the number of neutrons produced by fission in one generation equals the number of neutrons produced by fission in the previous generation (keff = 1) (r = 0).

The factor by which the number of neutrons produced by fission in one generation must be multiplied to determine the number of neutrons produced by fission in the next generation.

The ratio of fast neutrons produced from all fission events divided by fast neutrons produced by thermal fission events.

The ratio of the number of fast neutrons that start to slow down divided by the number of fast neutrons produced from all fissions.

The time from the birth of one generation of neutrons to the time of the birth of the next generation of neutrons.

The fractional change in fission neutron population per generation, or the measure of the departure of a reactor from criticality

The ratio of fast neutrons produced by thermal fission events divided by the number of thermal neutrons absorbed in the fuel.

The ratio of fast neutrons that become thermal divided by the number of fast neutrons that start to slow down.

Used to describe the processes that occur during the neutron life cycle.

The condition in which the number of neutrons produced by fission in one generation is less than the number of neutrons produced by fission in the previous generation (keff < 1) (negative r).

The condition in which the number of neutrons produced by fission in one generation is greater than the number of neutrons produced by fission in the previous generation (keff > 1) (positive r).

The ratio of the number of thermal neutrons absorbed in the core divided by the number of fast neutrons that become thermal.

The ratio of the number of thermal neutrons absorbed in fuel divided by the number of thermal neutrons absorbed in the core.

The weighted average of the decay constants for the six groups of delayed neutron precursors in the reactor core (sec–1).

The weighted average of the effective delayed neutron fraction for all fissile nuclides in the reactor core. equals the number of fissions caused by delayed neutrons divided by the total number of fissions caused by fission neutrons.

The average time between the absorption of a neutron which causes fission and the absorption of resultant neutrons

A reactivity unit related to a dollar of reactivity, where one cent is one-hundredth of a dollar

The weighted average of the delayed neutron fractions for all fissile/fissionable nuclides in the reactor core

A neutron born approximately 12.7 seconds after a fission event

The fraction of neutrons born delayed from fission of a particular nuclide. b equals the number of neutrons born delayed divided by the total number of neutrons born from fission of a particular nuclide.

The total time from the fission event to absorption of a delayed neutron born from a delayed neutron precursor resulting from that fission event. » 12.7 seconds

The decay constant for a delayed neutron precursor. It is the probability that a nucleus will decay per unit time (sec–1).

A unit of reactivity where one dollar of reactivity is equivalent to the effective delayed neutron fraction . If the reactivity of the core is one dollar, the reactor is prompt critical

The time required for a reactor to double in power. DT is used to estimate reactor period (sec).

The fraction of neutron induced fissions caused by delayed neutrons of a particular nuclide

The percentage of fissions that occur in the reactor for each particular fuel type present

The percentage of fissions that occur in the reactor for each particular fuel type present

The average time required for one-half of the atoms of a material to decay

Represents how long, on the average, a delayed neutron precursor will exist before decaying.

The condition of the reactor reaching criticality on prompt neutrons alone. It will occur when positive reactivity added
is equal to, or greater than, the average effective delayed neutron fraction

The initial rapid decrease in neutron population following a step insertion of negative reactivity

The initial rapid increase in neutron population following a step insertion of positive reactivity

The total time from the fission event to absorption of a prompt neutron born from that fission event. » 1 ´ 10–4 sec

The time, in seconds, required to change reactor power by a factor of e (2.718).

The time (in minutes) required to change reactor power by a factor of 10. Expressed as DPM (decades per minute). It is a measure of the rate of change of reactor power in DPM

The widening and flattening effect on resonance capture probability peaks for epithermal neutrons due to increased kinetic energy of target atoms resulting from increased fuel temperature.

The reactivity coefficient that relates the change in reactivity due to a change in fuel temperature.

The reactivity coefficient that relates the change in reactivity due to a change moderator temperature

Discrete excitation energy levels exist within a nucleus

Reactivity coefficient that relates the change in reactivity due to a change in void fraction

The temperature decrease per unit time usually measured at the vessel skin, steam dome, and recirculation loop

The reactor sustains a chain reaction with a stable neutron count rate and an infinite reactor period

The heat generated in the core from the decay of fission products.

The negative reactivity contributed to the core by the Doppler coefficient when the core void fraction is decreased using recirculation flow.

An estimate, made by the reactor engineers that determines on what rod pattern what rod, and what rod position the reactor is expected to go critical

The temperature rise per unit time usually measured at the vessel skin, steam dome, and recirculation loop

The point during a reactor startup where heat production from fission exceeds ambient heat losses. A further increase
in power will raise the temperature of fuel and moderator

A plot using the inverse count ratio (ICR) following reactivity change events to obtain a conservative estimate of critical rod position. May also be used during fuel loading to monitor for inadvertent criticality. This is sometimes also referred to as an inverse count ratio plot or an inverse count rate ratio plot.

The instantaneous amount of reactivity by which a reactor is sub-critical or would be sub-critical from its present condition assuming all control rods are fully inserted except for the single rod with the highest integral worth and equilibrium xenon removed

______ scattering is the type of scattering reaction where kinetic energy raises the internal energy of the target nucleus.

Any process that causes an atom or group of atoms to have a net electric charge resulting from losing or gaining one or more electrons can be referred to as:

Identify the 4 basic types of Radiation

The difference in mass between a nucleus and the sum of the masses of individual protons and neutrons in the nucleus is called the _______

The splitting of an atom's nucleus resulting from an energy input (excitation energy) into the nucleus greater than the nuclear force holding the nucleus together is called ______

What is the attractive or repulsive force that exists between two objects due to their electrical charge?

At time t = 0, a radioactive sample contains 1x10¹⁰ atoms. After 31 days, the sample contains 3.6x10⁴ atoms. Determine the half life of the sample

When will a reactor respond to a set amount of added reactivity?

The departure from criticality can be used to describe what?

What is the Effective Delayed Neutron Fraction B_eff?

When a reactor has reached an equilibrium in the number of neutrons produced from one generation to another (the reactor is critical k_eff=1), what is the reactivity?

A neutron that has kinetic energy less than 1 eV is know as a ______

A neutron that has a kinetic energy greater than 0.1 MeV is known as a _______

A fuel type that requires kinetic energy in addition to binding energy of an incident neutron for fission to occur is known as a _____ material

What are the two nuclides present in large amounts in the fuel of some reactors with large resonant peaks that dominate the Doppler Effect?

The time in minutes required to change the reactor power by a factor of 10, expressed in DPM, which is a measure of the rate of change of reactor power is known as the _____

Which electrons have the higher energy, the inner or outer electrons

The energy equivalent of the mass defect is also known as the ______

The name given to the strong attractive force in the nucleus between two adjacent nucleons is known as the ____

The average distance that a neutron travels before an interaction occurs is known as the ____

Given ^A_ZX define A, X, and Z

Given an electrically neutral isotope ₉₂U²³⁵, how many n, p⁺ and e^- are there?

Any fission event that occurs independent of neutron induced fission is known as _______.
Generally, this occurs in radioisotopes with very large atomic numbers.

Any particle that is part of the nucleus (neutrons and protons) is known as a ________

Using the Chart of Nuclides, calculate the mass defect of Nickel-58

The average energy required to remove a nucleon from the nucleus is known as the ____

Define a thermal neutron

The probability of an incident neutron interacting with a target nucleus per unit length of travel of the incident neutron (∑) and in units or cm^-1 is known as the __________, while the measure of the probability that a given interaction will occur between a single target nucleus and an incident neutron is known as the _______ and is represented as (σ). This is defined as the effective area presented by the target nucleus to the incident neutron for a particular reaction (units of barns = 1 x 10^-24cm²)

Given a sample of radioactive element containing 4.8x10²⁴ atoms and a half-life of 1 day, how many atoms remain after 5 days?

Using your chart of nuclides, name the element Xe and determine the number of stable isotopes.

The decay heat produced by a reactor shutdown from full power is initially what % of thermal rated reactor power?

Any fission that results in the production of 3 fission fragments is known as a ______. This is not as common as a regular fission where the nucleus splits into two masses of _____ sizes.

The process where a high energy gamma (>1.02MeV) interacts with the electric field and is converted to mass (electrons and positrons) is known as ______. Mid energy reactions with a photon, where some energy is transferred to the electron, the electron is knocked out and the gamma is scattered is known as ______. The low energy photon reaction, where the total energy of the γ is absorbed by the electron and the electron is ejected is known as ______

What is the cutoff for the time in which a prompt neutron is produced? What is the average time for the production of a delayed neutron?

In the 6 factor formula, the factor f represents which factor. expressed as
f=thermal neutrons absorbed in fuel / thermal neutrons absorbed in core

When a reactor has a k_eff=1 the reactor is ______.

The ratio of fast neutrons that become thermal, divided by the number of fast neutrons that start to slow down is known as the _______, and is expressed as
p=fast neutrons that become thermal/fast neutrons that start to slow down

A control rod withdrawal results in the k_eff of a reactor changing from 0.975 to 0.980, calculate how much reactivity was added to the core, in pcm (percent milli)

What is the widening and flattening effect on resonance capture probability peaks for epithermal neutrons due to increased kinetic energy of target atoms resulting from increased fuel temperature?

What is the name given to the instantaneous amount of reactivity by which a reactor is sub-critical or would be from its present condition assuming all control rods are fully inserted except for the single rod with the highest integral worth and equilibrium Xe removed?

What is the condition where the reactor period is reduced to the prompt neutron component? It is associated with rapid increase in neutron power.

What type of neutron is more likely to cause fast fission in U²³⁸?

What are the 3 factors that effect decay heat after a reactor is shutdown?

The condition in which the number of neutrons produced by fission in one generation is greater than the number of neutrons produced by fission in the previous generation is known as ______.

The factor by which the number of neutrons produced by fission in one generation must be multiplied by to determine the number of neutrons produced by fission in the next generation is know as the _______. In order to have a critical reactor this value must be _______, meaning that the reactor is able to sustain a chain reaction.