What is Radioactive Material per DOT? The Definition Explained

Why This Definition Matters

Understanding the DOT definition of radioactive material is foundational. Get it wrong, and you might over-classify something that doesn't need Class 7 shipping—wasting time and money. Or worse, you might under-classify something that does, creating a compliance violation and potential safety issue.

I have seen it where a shipment is over-regulated because the radioactive material did not exceed BOTH the ALEC and the ACEM. Remember: if it doesn't exceed both, it does not meet the definition of radioactive material per DOT.

This definition is the starting point for every radioactive shipment. Before you can determine package type, labels, or shipping papers, you must first answer: “Is this material even regulated as radioactive under DOT?”

Who Needs to Know This

This applies to anyone who:

• Determines whether a material requires Class 7 shipping
• Works with materials that contain any level of radioactivity
• Prepares or reviews radioactive material shipments
• Receives materials that may or may not be radioactive
• Manages radioactive material programs at their facility

The DOT Definition: 49 CFR 173.403

The definition lives in 49 CFR 173.403. Here's what it actually says (paraphrased for clarity):

Radioactive material means any material containing radionuclides where both:

1. The activity concentration exceeds the values in Table 4 of 49 CFR 173.436, AND
2. The total activity exceeds the values in Table 4 of 49 CFR 173.436

This is a two-part test. Your material must exceed BOTH thresholds to be regulated. If it's below either threshold, it's not DOT radioactive material.

The Two Thresholds Explained

Activity Concentration Exempt for Materials (ACEM) - Bq/g or Ci/g

This measures how “concentrated” the radioactivity is per unit mass. The exempt concentrations vary by radionuclide—some nuclides are more hazardous than others, so they have lower thresholds.

Activity Limit Exempt for Consignments (ALEC) - Bq or Ci

This measures the absolute amount of radioactivity present in the consignment. Even if the concentration is high, a tiny amount may be exempt. The exempt quantities also vary by radionuclide.

Finding the Exempt Values: 49 CFR 173.436

The exempt concentration and exempt quantity values are found in Table 4 of 49 CFR 173.436. This table lists values for hundreds of radionuclides.

For example (representative values—always verify current regulations):

Working Through an Example

Let's say you have a sample containing Co-60:

• Sample mass: 100 grams
• Total activity: 800 Bq of Co-60

Step 1: Calculate activity concentration

800 Bq ÷ 100 g = 8 Bq/g

Step 2: Compare to exempt concentration (ACEM)

Co-60 exempt concentration = 10 Bq/g
Your concentration (8 Bq/g) is BELOW the exempt concentration.

Result: This material is NOT radioactive material per DOT, regardless of total activity. You don't need to check the second threshold—failing either test means it's exempt.

What About Mixtures of Radionuclides?

When you have multiple radionuclides in a single material, the calculation gets more complex. You must use the “sum of fractions” approach:

For each radionuclide, calculate:

(Activity concentration ÷ Exempt concentration)

Sum these fractions. If the sum exceeds 1, the mixture exceeds the exempt concentration threshold.

Do the same for total activity:

(Total activity ÷ Exempt quantity)

Sum these fractions. If the sum exceeds 1, the mixture exceeds the exempt quantity threshold.

DOT vs. NRC: Different Definitions

This is a critical distinction that trips people up:

A material can be:

• NRC-licensed but not DOT-regulated (below DOT thresholds)
• DOT-regulated but not NRC-licensed (naturally occurring materials above DOT thresholds)
• Both (most common scenario for radioactive shipments)

It is possible to confuse the DOT definition of RAM with the NRC definition. When shipping RAM, always use the DOT definition as the NRC definition refers to material licensing.

Naturally Occurring Radioactive Materials (NORM)

NORM presents an interesting case. Materials like certain ores, scales, or soils may contain naturally occurring radionuclides (like Ra-226 or K-40). These are evaluated against the same DOT thresholds.

If the activity concentration and total activity exceed the 49 CFR 173.436 values, the material IS radioactive material per DOT—even though it's “natural” and may not be NRC-licensed.

For shipping NORM (naturally occurring radioactive material), it can get tricky as there is also TENORM (Technologically Enhanced Naturally Occurring Radioactive Material) which can be confusing for classifying. There is an exclusion in 173.401(b)(4) for NORM but be aware that any concentration of NORM byproduct material from extracting ores, oil, or other materials, can be considered TENORM. Radioactive shippers must have strong documentation if they are taking the exceptions for NORM.

How RadShip.com Helps

RadShip.com simplifies this definition check:

• RAMcalc – Enter your nuclides and activities, and the calculator automatically checks against exempt values. No manual table lookups required.
• Mixture handling – RAMcalc performs sum-of-fractions calculations for multi-nuclide materials using Mixture Mode.
• Consignment tracking – Add other packages in your consignment to ensure accurate ALEC calculations.
• Clear output – Tells you definitively whether your material is DOT-regulated.

Hazard communication is the whole premise for why we classify radioactive material accurately. We do not want to overregulate or underregulate hazardous material shipments. Both can cause confusion, more time and money, and in some cases put emergency response personnel at risk.

Try it free for 7 days.

Common Questions

If my radioactive material does not meet the DOT/IATA definition, can I just ship it as a normal package?

Yes! Although it is recommended to take proper care to package it to prevent damage. If your material is below both the ACEM and ALEC thresholds, it is not regulated as Class 7 radioactive material and can be shipped as an ordinary package.

If my material is below exempt values, can I still ship it as radioactive?

No. According to PHMSA Interpretation 09-0260, you may not voluntarily classify material as Class 7 if it doesn't meet the defining criteria. Proper classification is a shipper responsibility under 49 CFR 171.8—and that means classifying based on what the material actually is, not being overly conservative.

What if I can't find my radionuclide in Table 4?

49 CFR 173.436 includes values for “unknown” or unlisted radionuclides. These are conservative (low) values that ensure safety when the specific nuclide isn't identified.

Does decay change whether something is regulated?

Absolutely. Radioactive decay reduces activity over time. Something that's regulated today may fall below thresholds after sufficient decay. Always use current activity values.

What about instruments containing radioactive sources?

The same definition applies. If the source in the instrument exceeds both thresholds, the instrument contains radioactive material per DOT. However, instruments often qualify for “excepted package” shipping under UN2911.

Summary: Your Definition Checklist

Before classifying a shipment, confirm:

• ☐ Identify all radionuclides present
• ☐ Determine activity concentration for each (Bq/g)
• ☐ Determine total activity for each (Bq)
• ☐ Look up exempt values in 49 CFR 173.436 (or use RAMcalc)
• ☐ For single nuclides: compare directly to ACEM and ALEC values
• ☐ For mixtures: calculate sum of fractions
• ☐ If BOTH thresholds exceeded → DOT radioactive material
• ☐ If EITHER threshold NOT exceeded → NOT DOT radioactive material

Regulatory References

DOT Requirements:

• 49 CFR 173.403 – Definitions (including radioactive material)
• 49 CFR 173.436 – Table of activity values (ACEM and ALEC)
• 49 CFR 173.401 – Scope and exemptions

NRC Requirements:

• 10 CFR 20.1003 – Definitions
• 10 CFR 30 – Rules of General Applicability to Domestic Licensing

IATA (Air Transport):

• IATA Dangerous Goods Regulations, Section 2.7 – Class 7 definitions (aligns with DOT for most purposes)