# Song et al. (2025) — The measurement of 99Tc β-decay spectrum and implications for g_A

## Citation

Song, J.W., Ramalho, M., Lee, M.K., et al. (2025). The measurement of the ⁹⁹Tc β-decay spectrum and its implications for the effective value of weak axial coupling. *arXiv:2506.17544*.

## Key Results

| Model | g_A^eff | sNME [fm³] | χ²_ν | p-value |
|---|---|---|---|---|
| glekpn (CloseCVC) | 1.1 | 0.0674 | 1.106 | 0.12 |
| jj45pnb (CloseCVC) | 1.0 | 0.0681 | 1.244 | 0.004 |
| MQPM (CloseCVC) | 1.0 | 0.0651 | 1.644 | <0.0001 |
| **glekpn (FarCVC)** | **1.2** | **−0.0698** | **1.066** | **0.22** |
| jj45pnb (FarCVC) | 1.0 | −0.0669 | 1.097 | 0.14 |
| MQPM (FarCVC) | 1.0 | −0.0683 | 1.095 | 0.14 |

## Methodology

- **Detector**: MMC with 4π gold absorber, energy threshold 10 keV
- **Nuclear models**: glekpn, jj45pnb (NSM), MQPM
- **sNME treatment**: ESSM (sNME as fit parameter) — two solutions per g_A (closeCVC and farCVC)
- **Fit range**: 10–41 keV and 50–280 keV (excluding Gd X-ray region)

## Key Findings

1. **Contradicts Paulsen et al. (2024)**: The enhanced g_A value (1.526) is not supported when using proper ESSM treatment
2. **Quenched g_A**: Best fit is g_A^eff = 1.0–1.2 with farCVC sNME
3. **Best model**: glekpn with g_A^eff = 1.2, sNME = −0.0698 fm³, χ²_ν = 1.066

## Implications

- Resolves the inconsistency between first-forbidden and higher-forbidden nonunique transitions
- Supports quenched g_A consistent with Suhonen's review values
- Demonstrates the importance of proper sNME treatment in SSM analysis

## References

- [[Shape Factor C(W, g_A)]]
- [[SSM — Spectrum Shape Method]]
- [[ESSM — Enhanced Spectrum Shape Method]]
- [[Paulsen et al. (2024)]]
- [[Ramalho & Suhonen (2024)]]