Levels and Channels Tab

The Levels and Channels tab is used to enter the compound nucleus level information. It uses the particle pair definitions from the Particle Pairs tab to automatically calculate all allowed R-matrix channels.

Tab Layout

The tab is divided into four frames:

  1. Compound Nucleus Levels (left) – the list of nuclear levels.

  2. Channels in Selected Level (center) – the allowed channels for the currently selected level.

  3. Channel Configuration (top right) – controls to limit the number of R-matrix channels.

  4. Channel Details (bottom right) – detailed information for the selected channel, including the width parameter input field.

Managing Levels

Adding a Level

Click the + button in the lower-left corner. A dialog appears prompting for:

  • Excitation Energy – the excitation energy of the compound nucleus (in MeV).

  • Spin (J) – the total spin. Half-integer values should be given as decimals (e.g., 1.5).

  • Parity – select + or - from the drop-down menu.

After clicking Accept, the new level appears in the list and its allowed channels are automatically calculated from the particle pair information.

Importing Levels from IAEA Database

Click the NDS button to query the IAEA Nuclear Data Services for known level schemes. AZURE2 automatically determines the compound nucleus from the defined particle pairs. The dialog displays retrieved levels with their energies and spin-parities, allowing you to select which levels to import.

Editing a Level

Select a level and double-click to modify it. To delete a level, select it and click the - button.

Level Controls

Include / Exclude

The checkbox in the Include? column controls whether a level participates in the calculation. Uncheck to exclude a level without deleting it.

Fix Energy

The checkbox in the Fix? column prevents the level energy from varying during a fit.

Other Buttons

  • Fix All Widths – fix all channel width parameters at once.

  • Fix All Energies – fix all level energies at once.

  • Export LaTeX – export the level scheme as a LaTeX table for publication.

Channels

When a level is selected, its allowed channels appear in the Channels in Selected Level frame. Each channel is characterized by:

  • The particle pair it belongs to

  • The channel spin (S)

  • The orbital angular momentum (L)

  • For gamma-ray channels: the radiative decay type

Selecting a channel displays its details in the Channel Details frame, where the width parameter can be entered.

Width Parameters

The width parameter entered at the bottom of the Channel Details frame represents:

  • Partial width for unbound levels (channels above the separation energy).

  • ANC (Asymptotic Normalization Coefficient) for bound-state channels (automatically determined by the code).

Tip

Relative interference signs between channels are set by changing the sign of the partial width or ANC.

Fix Width

The Fix? checkbox in the channels list prevents the width parameter from varying during a fit. A width left at zero is automatically held fixed.

Channel Configuration

The Channel Configuration frame (top right) controls which channels are generated:

Maximum Orbital Momentum (L_max)

The maximum orbital angular momentum quantum number. Default is 2. Must be set high enough for all relevant channels to appear.

Maximum Gamma Multipolarity

The maximum electromagnetic multipolarity for gamma-ray channels. Default is 2.

Maximum Multipolarities per Decay

The maximum number of multipolarities to consider per gamma-ray decay. Default is 2.

Warning

The user must carefully check that the channel configuration is set correctly. If the maximum orbital momentum is too low, channels may be missing, leading to incorrect results or crashes. The code requires at least one channel for each particle pair for each \(J^\pi\).

Dummy Levels

Because the number of levels and angular momenta must be truncated, the code only includes those \(J^\pi\) values that are present in the defined levels. To include all necessary hard-sphere phase shifts for scattering and external capture calculations, the user may need to add dummy levels:

  1. Create a level at an arbitrary energy with the missing \(J^\pi\).

  2. Fix its energy.

  3. Set all partial widths to zero.

The effects of including these dummy levels should be investigated for each allowed spin-parity combination.

Gamma-Ray Calculations

For gamma-ray calculations, the user should define a level corresponding to each gamma-ray particle pair defined in the Particle Pairs tab. This allows setting the ANCs and gamma-ray decay widths for each bound state. The energies of these levels must match the excitation energies of the gamma-ray particle pairs.