Particle Pairs Tab

The Particle Pairs tab is the first tab that should be filled out when setting up a new calculation. It defines the reaction particle pairs – the two particles that fuse to form, or result from the decay of, the compound nucleus.

Tip

Always start here. AZURE2 uses the particle pair information to automatically calculate allowed channels in the Levels and Channels tab and to populate options in the Segments tab.

Managing Particle Pairs

Click the + button in the lower-left corner to add a new particle pair.
Select a pair and click - to delete it.
Double-click an existing pair to edit it.

Each particle pair is automatically assigned a numerical key (displayed on the far left), which is referenced when creating segments.

Important

The first particle pair must always be of type (Particle, Particle). After the first, pairs may be defined in any order.

Particle Pair Types

AZURE2 supports three types of particle pairs:

Type	Description
(Particle, Particle)	Standard nuclear reaction pair (e.g., p + ¹⁴N). Must be the first pair defined.
(Particle, Gamma)	Radiative capture pair for gamma-ray transitions to bound states. Some fields are auto-populated and cannot be edited. Gamma-ray decays are limited to bound states.
(Beta Decay)	Beta-delayed particle emission pair. Some fields are auto-populated.

Add Particle Pair Dialog

When adding or editing a particle pair, a dialog window appears with the following fields:

Particle Properties

For both the light and heavy particle:

Spin (J): The spin of the particle. Half-integer values should be entered as decimals (e.g., 0.5 for spin-1/2).
Parity: The parity of the particle, selected from the drop-down menu: + or -.
Proton Number (Z): The number of protons in the particle.
Mass (M): The mass number of the particle.

Pair Properties

Excitation Energy: The excitation energy of the heavy particle (in MeV). This is non-zero for transitions to excited states rather than the ground state.
Separation Energy: The energy required to separate the compound system (in its ground state) into the constituent particle pair (in MeV).
Channel Radius: The R-matrix channel radius (in fm). Different particle pairs need not share the same radius. A useful estimate is:

\[R = R_0 \times (A_p^{1/3} + A_t^{1/3})\]

Warning

The channel radius is a model parameter, not a physical nuclear radius. Always test the sensitivity of your results to the channel radius by re-running the calculation with different values. The channel radius cannot currently be used as a fit parameter.
External Capture Multipolarities: For (Particle, Gamma) pairs only. Select E1 and/or E2 multipolarities. The code automatically determines the allowed intrinsic and angular momentum combinations based on the defined resonances.