# Activity-mass relationships for uranium and natural thorium.

**Citation:** 49 CFR 173.434  
**Type / status:** regulation / current  
**Agency:** Pipeline and Hazardous Materials Safety Administration  
**Effective:** 2026-08-18  
**Published:** Not stated

The table of activity-mass relationships for uranium and natural thorium are as follows:

Thorium and uranium enrichment 1 (Wt% 235 U present) Specific activity TBq/gram Grams/Tbq Ci/gram Grams/Ci 0.45 (depleted) 1.9 × 10−8 5.4 × 107 5.0 × 10−7 2.0 × 106 0.72 (natural) 2.6 × 10−8 3.8 × 107 7.1 × 10−

## Document text

The table of activity-mass relationships for uranium and natural thorium are as follows:

Thorium and uranium enrichment 1 (Wt% 235 U present) Specific activity TBq/gram Grams/Tbq Ci/gram Grams/Ci 0.45 (depleted) 1.9 × 10−8 5.4 × 107 5.0 × 10−7 2.0 × 106 0.72 (natural) 2.6 × 10−8 3.8 × 107 7.1 × 10−7 1.4 × 106 1.0 2.8 × 10−8 3.6 × 107 7.6 × 10−7 1.3 × 106 1.5 3.7 × 10−8 2.7 × 107 1.0 × 10−6 1.0 × 106 5.0 1.0 × 10−7 1.0 × 107 2.7 × 10−6 3.7 × 105 10.0 1.8 × 10−7 5.6 × 106 4.8 × 10−6 2.1 × 105 20.0 3.7 × 10−7 2.7 × 106 1.0 × 10−5 1.0 × 105 35.0 7.4 × 10−7 1.4 × 106 2.0 × 10−5 5.0 × 104 50.0 9.3 × 10−7 1.1 × 106 2.5 × 10−5 4.0 × 104 90.0 2.1 × 10−6 4.7 × 105 5.8 × 10−5 1.7 × 104 93.0 2.6 × 10−6 3.9 × 105 7.0 × 10−5 1.4 × 104 95.0 3.4 × 10−6 3.0 × 105 9.1 × 10−5 1.1 × 104 Natural thorium 8.1 × 10−9 1.2 × 108 2.2 × 10−7 4.6 × 106 1 The figures for uranium include representative values for the activity of uranium-234 which is concentrated during the enrichment process. The activity for thorium includes the equilibrium concentration of thorium-228.

[Amdt. 173-244, 60 FR 50307, Sept. 28, 1995, as amended by 63 FR 52849, Oct. 1, 1998]

## Provenance

- Official: Yes
- Source: <https://www.ecfr.gov/on/2026-08-18/title-49/section-173.434>
- Source ID: `ecfr`
- SHA-256: `b4df1847d1d5199a68d78e1a112cdce952b73f705de18c2212fbd2ee82382d02`
- Retrieved: 2026-08-20T05:46:04.092Z
- Exported: 2026-08-22T15:30:53.842Z
- Document slug: `49-cfr-173-434`

### Source metadata

```json
{
  "cfrTitle": 49,
  "part": "173",
  "section": "173.434",
  "subpart": "Subpart I—Class 7 (Radioactive) Materials",
  "corpusVersion": "2026-08-18",
  "jurisdiction": "US"
}
```