alpha-decay-q-value

name	alpha-decay-q-value
description	Use this skill when calculating Q-alpha values from measured alpha energies and updating the Q field (cols 65-74) and DQ field (cols 75-76) in ENSDF P records. Uses exact kinematic formula Q = E_alpha * A/(A-4). Applies to single files or chains of alpha-decay datasets.

Alpha Decay Q-Value Calculation and P Record Update

ENSDF 80-column data record and field definitions, structural rules, column positions, and uncertainty notation: .github/agents/ENSDF-Agent.agent.md. Spot-check policy: .github/copilot-instructions.md.

Purpose

Compute $Q_\alpha$ from the measured alpha energy $E_\alpha$ and populate the Q and DQ fields in the parent P record of each ENSDF alpha-decay dataset.

Formula

$$Q_\alpha = E_\alpha \times \frac{A_\text{parent}}{A_\text{parent} - 4}$$

$$\delta Q_\alpha = \delta E_\alpha \times \frac{A_\text{parent}}{A_\text{parent} - 4}$$

Round both to the nearest integer (keV precision).

P Record Field Layout

Field	Columns (1-based)	Width
Q (Q-value)	65–74	10 chars, left-justified
DQ (uncertainty)	75–76	2 chars, left-justified

Input Sources

• $E_\alpha$ and $\delta E_\alpha$: from the A record (cols 10–19, 20–21) or from the QP$From E|a= comment line.
• $A_\text{parent}$: mass number of the parent nuclide (from NUCID in the P record).

Workflow

Step 1: Read $E_\alpha$ and $\delta E_\alpha$

From the cP QP$ comment line (preferred, as it identifies the g.s.-to-g.s. transition):

219NP cP QP$From E|a=9015 keV {I16} g.s. to g.s. transition ...

Extract 9015 and 16.

Or directly from the daughter A record (cols 10–19 and 20–21).

Step 2: Identify $A_\text{parent}$

Read cols 1–3 of the P record NUCID. For 219NP P ..., $A = 219$.

Step 3: Compute and Round

Q  = round(Ea * A / (A - 4))
DQ = round(DEa * A / (A - 4))

Step 4: Write into P Record

• Cols 65–74 (index 64–73): str(Q).ljust(10)
• Cols 75–76 (index 74–75): str(DQ).ljust(2)
• Verify total line length = 80 chars.

new_line = s[:64] + str(Q).ljust(10) + str(DQ).ljust(2) + s[76:80] + '\n'

Step 5: Validate

Run ruler on the modified P record line:

python .github/scripts/ensdf_1line_ruler.py --line "modified line here"

Example

Parent	$A$	$E_\alpha$ (keV)	$\delta E_\alpha$	$Q_\alpha$	$\delta Q$
219NP	219	9015	16	9183	16
215PA	215	8087	12	8240	12
211AC	211	7451	9	7595	9
207FR	207	6762	8	6895	8

Common Errors

Error	Cause	Fix
Q copied from $E_\alpha$ directly	Forgot kinematic factor	Always apply $A/(A-4)$
DQ wrong	Used wrong $A$ or forgot to round	Recompute with correct $A$
Line length ≠ 80	s[76:80] truncated	Ensure source line is .ljust(80) before slicing

Notes

• For an alpha-decay chain, process each file independently; each file has its own $A_\text{parent}$.
• The P record Q field represents $Q_\alpha$ for the parent decay (g.s. to g.s.).
• Do not confuse with the daughter L-record energy (always 0 for g.s.).