BARC OCES/DGFS flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Binding energy per nucleon

The total nuclear binding energy divided by the mass number A; it peaks near 8.8 MeV at Fe-56, so fission of heavy nuclei and fusion of light nuclei both release energy.

Half-life

The time for half of a radionuclide sample to decay; related to the decay constant by T½ = ln2/λ, and independent of the initial amount or chemical state.

Becquerel

The SI unit of radioactivity equal to one nuclear transformation per second; 1 curie equals 3.7×10^10 becquerels, the activity of one gram of radium-226.

Four-factor formula

The infinite multiplication factor of a thermal reactor, k∞ = η·f·p·ε, the product of reproduction factor, thermal utilization, resonance escape probability, and fast fission factor.

Delayed neutrons

Neutrons emitted by fission products seconds to minutes after fission; they constitute about 0.65% of U-235 fission neutrons and make reactor control possible below prompt critical.

Moderating ratio

The slowing-down power of a moderator divided by its macroscopic absorption cross-section (ξ·Σs/Σa); a high value indicates efficient thermalization with little neutron loss.

Equivalent dose

Absorbed dose multiplied by the radiation weighting factor w_R (1 for gamma and beta, 20 for alpha); expressed in sieverts and reflecting biological harm.

Carnot efficiency

The maximum efficiency of a heat engine operating between hot and cold reservoirs, η = 1 − T_C/T_L with absolute temperatures; no real cycle can exceed it.

Euler buckling load

The critical axial load for a slender column, P_cr = π²EI/(K·L)², where K depends on end conditions: 1 pinned-pinned, 0.5 fixed-fixed, 0.7 fixed-pinned, 2 fixed-free.

Reynolds number

The dimensionless ratio ρvD/μ that predicts flow regime; in a pipe, flow is generally laminar below Re ≈ 2000 and turbulent above about 4000.

Thevenin theorem

Any linear two-terminal network can be replaced by a voltage source V_th in series with R_th, where V_th is the open-circuit voltage and R_th the resistance seen with sources made inactive.

Mohr's circle

A graphical construction giving principal stresses σ1,2 = (σx+σy)/2 ± √[((σx−σy)/2)² + τxy²] and maximum shear stress (σ1−σ2)/2 for a plane stress state.

Bernoulli equation

For steady, incompressible, inviscid flow along a streamline, p/ρg + v²/2g + z is constant; it expresses conservation of energy in fluid motion.

Back emf

The voltage induced in a motor armature opposing the supply, E_b = V − I_a·R_a; it limits armature current and falls as the motor speeds up or the field weakens.

Steady-flow energy equation

For a control volume at steady state, Q − W = Σṁ_out·h_out − Σṁ_in·h_in when kinetic and potential energy changes are neglected; the first law for open systems.

Gibbs free energy

ΔG = ΔH − TΔS; a process at constant temperature and pressure is spontaneous when ΔG is negative, and equilibrium corresponds to ΔG = 0.

Arrhenius equation

The temperature dependence of a rate constant, k = A·e^(−Ea/RT); a plot of ln k versus 1/T is linear with slope −Ea/R.

Henderson–Hasselbalch equation

For a buffer, pH = pKa + log([A⁻]/[HA]); it predicts pH from the acid dissociation constant and the ratio of conjugate base to weak acid concentrations.

Beer–Lambert law

Absorbance A = ε·c·l, proportional to molar absorptivity, concentration, and path length; linear only for dilute solutions and monochromatic light.

Pauli exclusion principle

No two electrons in an atom may share the same four quantum numbers, so each orbital holds at most two electrons with opposite spins.

First-order reaction half-life

For a first-order reaction, t½ = ln2/k, independent of initial concentration; concentration decays as C = C0·e^(−kt).

Ideal gas molar volume

At 273.15 K and 1 bar, one mole of an ideal gas occupies about 22.7 litres (22.4 L at 1 atm), from PV = nRT with R = 8.314 J/mol·K.

Enthalpy

H = U + PV; at constant pressure the change in enthalpy equals the heat exchanged, ΔH = q_p, making it the natural quantity for chemical reactions in open vessels.

Successive percentage change

Two successive changes of a% and b% produce a net change of a + b + ab/100 percent, with signs preserving increases and decreases.

Compound interest formula

A = P(1 + r/n)^(nt), where P is principal, r the annual rate, n the compounding frequency per year, and t the time in years.

Work-rate formula

If A alone finishes a job in x days and B alone in y days, working together they take xy/(x+y) days; rates add reciprocally.

Relative speed

For two bodies moving in the same direction, relative speed is the difference; in opposite directions it is the sum; a train of length l crossing a platform L takes (L+l)/speed.

Combination formula

nCr = n!/[r!(n−r)!], the number of ways to choose r items from n without regard to order; symmetry gives nCr = nC(n−r).

Average speed for equal distances

When equal distances are covered at speeds u and v, average speed is the harmonic mean 2uv/(u+v), not the arithmetic mean (u+v)/2.

Syllogism validity rule

A conclusion follows only if it is true in every possible Venn arrangement of the premises; particular statements do not imply existence beyond what the premises state.

Number series strategy

Test differences, ratios, squares and cubes, and alternating sub-series before assuming one rule; the odd term is the one that breaks the rule the others satisfy.

Simple versus compound interest

Simple interest is P·r·t; compound interest is P(1+r/n)^(nt). For two years at rate r, the compound excess over simple interest is P(r/100)².