Nuclear Medicine Area Surveys: 35.70 & 20.1501

A nuclear medicine survey program runs on two engines, and confusing them is where facilities get cited. The first is the end-of-day ambient radiation exposure-rate survey required by 10 CFR 35.70 in areas where written-directive material was prepared or administered. The second is the broader program of radiation and contamination surveys required by 10 CFR 20.1501 and the facility's license conditions. They use different instruments, answer different questions, and carry different action levels — and a defensible program keeps both clearly defined.¹³

The distinction matters because 35.70 is narrower than most people remember. It is specifically an ambient exposure-rate survey, done at the end of each day of use, in areas tied to written-directive (generally therapy) material. Contamination surveys, diagnostic-area surveys, and the everyday frisking that keeps a hot lab clean live under 20.1501 and the license, not under 35.70. This article separates the two engines, gives the instruments, frequencies, and trigger levels for each, works the arithmetic of turning a meter reading into a compliance decision, and ties it back to records and inspection.

Introduction

Surveys are how a radiation safety program sees. Dose limits, ALARA goals, and license conditions are abstractions until someone puts a calibrated instrument in a room and reads a number. That number — a dose rate on a wall, a count rate on a wipe — is the evidence that the program is actually controlling exposure and contamination, not just describing them on paper.

Nuclear medicine is unusual among imaging disciplines because the source is unsealed and mobile. Radiopharmaceuticals are drawn, injected, excreted, spilled, and carried through the department by patients and staff. A fixed X-ray tube stays put; a millicurie of Tc-99m does not. That mobility is exactly why the survey program has to be routine and systematic: contamination and elevated dose rates appear where the workflow takes the material, which is not always where you expect.

The regulatory architecture reflects this. The Nuclear Regulatory Commission and Agreement States require both a specific end-of-day ambient survey for higher-risk written-directive work (35.70) and a general, performance-based survey obligation (20.1501) that the license fleshes out into concrete procedures. Understanding which rule drives which survey is the foundation of a clean program.

Topic Explanation

Engine one: the 35.70 ambient exposure-rate survey

The text of 10 CFR 35.70 is specific. A licensee must survey, with a radiation detection survey instrument, at the end of each day of use, all areas where unsealed byproduct material requiring a written directive was prepared for use or administered. There is an exception: the survey need not be performed in an area where patients or human research subjects are confined when they cannot be released under 10 CFR 35.75. And the record of each survey must be retained under 10 CFR 35.2070.¹²

Three features define its scope:

• It is an ambient dose-rate survey. It measures exposure rate (for example, in mR/h or µSv/h), not removable contamination.
• It is tied to written directives. Written directives are generally required for therapy administrations, so 35.70 principally covers therapy preparation and administration areas.
• It is daily, at end of use. It runs at the end of each day the relevant material was used, not weekly or monthly.

A common misconception is that 35.70 is the whole survey program. It is not. It is the daily ambient check on the highest-risk workflow.

Engine two: the 20.1501 general survey obligation

The broader requirement lives in 10 CFR 20.1501. It requires each licensee to make surveys of areas that may be necessary to comply with Part 20 and that are reasonable under the circumstances to evaluate radiological conditions and potential hazards — including radiation levels and concentrations or quantities of radioactive material. It also requires that instruments used be calibrated and appropriate for the radiation measured.³

This is the engine that drives:

• Contamination (removable and total) surveys of prep areas, hot labs, injection rooms, imaging rooms, and waste storage.
• Ambient dose-rate surveys of diagnostic-use and storage areas not otherwise covered by 35.70.
• Frisking and personnel/area monitoring appropriate to the workflow.

Because 20.1501 is performance-based, the specific what, where, how often, and at-what-level is set by the facility's license conditions, informed by NRC model procedures in NUREG-1556, Volume 9, Revision 3.⁷ For the instrument side of this obligation, see our discussion of the survey meter calibration program and choosing the right radiation survey meter.

A third, event-driven survey: package receipt

Distinct from routine area surveys, 10 CFR 20.1906 governs surveys of incoming packages of radioactive material: monitoring external surfaces for dose rate and wiping for removable contamination, with monitoring performed promptly (within 3 hours if the package is received during working hours), and notification of the carrier and NRC if contamination or radiation levels exceed the limits referenced from the U.S. Department of Transportation regulations.⁶ We cover this workflow in detail in package receipt and wipe testing.

Key Technical Principles

What each survey answers

An ambient dose-rate survey answers "how much external radiation field is present here?" It protects against external exposure to staff and the public and is compared against dose-based design objectives. A contamination survey answers "is there loose radioactive material on this surface that could spread or be taken up?" It protects against contamination spread and internal dose. The two are complementary; a clean dose-rate reading does not prove a surface is free of removable contamination, and vice versa.

Anchoring ambient action levels to dose limits

Ambient dose-rate action levels are not arbitrary — they derive from the Part 20 dose limits. For unrestricted areas, 10 CFR 20.1301 limits the dose to an individual member of the public to 1 mSv (0.1 rem) in a year and, in 20.1301(a)(2), to 0.02 mSv (2 mrem) in any one hour.⁴ For occupational exposure, 10 CFR 20.1201 sets the annual total effective dose equivalent limit at 50 mSv (5 rem).⁵ These limits, combined with realistic occupancy, set the design objectives that ambient survey readings are measured against.

A worked ambient check: suppose an unrestricted-area wall outside an injection room reads a dose rate of 0.01 mSv/h during active use. First, the instantaneous check: 0.01 mSv/h is below the 0.02 mSv-in-any-one-hour limit for unrestricted areas.⁴ Second, the annual check with occupancy: if the area is occupied a fraction $T$ of the time and the source is present for $H$ hours per year,

For $\dot{D}=0.01\text{mSv/h}$, $H=500\text{h/yr}$ of active use, and $T=0.2$ (a low-occupancy corridor):

This sits right at the public annual limit, signaling that either occupancy, shielding, or workflow needs attention — a survey reading that "passes" the instantaneous test can still fail the annual objective once occupancy is applied.⁴

Elevated ambient readings are exactly what one expects near therapy patients: measurements around hospitalized I-131 therapy patients have reported dose rates on the order of a few µSv/h at 1 m (with one study reporting roughly 6.8 µSv/h at 1 m early after administration), which is precisely why 35.70 mandates the daily ambient survey of therapy areas.⁸

Turning a count rate into a contamination result

Removable contamination surveys convert a wipe (smear) count into an activity per unit area. The core relationship is:

where $A_{\text{removable}}$ is the removable activity on the wipe in disintegrations per minute (dpm), $C_{\text{net}}$ is the net count rate in counts per minute after background subtraction, and $\epsilon$ is the instrument's counting efficiency (counts per disintegration) for the radionuclide of interest. Where the wipe collects only a fraction $f$ of the surface activity, a removal-fraction correction (commonly $f\approx 0.1$) is applied to estimate total surface removable activity.

Worked example: a smear of a 100 cm² area gives a net 150 cpm on a scaler with 15% efficiency for the isotope:

Compared against commonly used trigger levels — roughly 200 dpm/100 cm² for unrestricted areas and 2,000 dpm/100 cm² for restricted areas — a result of 1,000 dpm/100 cm² would exceed a typical unrestricted-area action level but fall below a typical restricted-area level. The binding numbers are those written into the facility's license; these values come from NRC model procedures, not from a fixed number in Part 20.⁷ Because the result depends directly on $\epsilon$, instrument calibration and efficiency determination are not optional niceties — they are what makes the number defensible, as 20.1501 requires. Our overview of minimum detectable activity in contamination surveys covers the counting-statistics side of choosing a defensible detection limit.

Survey program at a glance

Frequencies and trigger levels in this table are representative; the binding requirements are the facility's license conditions and applicable NRC or Agreement State rules.³⁷

Clinical Impact

Protecting staff, patients, and the public

The survey program is the day-to-day mechanism that keeps occupational and public doses within limits and as low as reasonably achievable. Detecting a contaminated bench or an elevated dose rate early prevents the spread of contamination onto hands, clothing, and equipment — the pathway to internal dose and to tracking activity out of controlled areas. In therapy work, the daily ambient survey verifies that dose rates around treatment and preparation areas are what the shielding and workflow assumed. Measured dose rates around I-131 therapy patients confirm that these areas genuinely need daily attention.⁸

Catching problems before they become events

Routine surveys are an early-warning system. A gradually rising background in the hot lab, a recurring hot spot near a waste container, or a dose rate that no longer matches the shielding assumption are all signals a survey program surfaces before they become a reportable contamination event or an overexposure. This is the same logic that underlies decontamination discipline; see nuclear medicine decontamination best practices.

Inspection readiness

Surveys are among the first records an inspector reviews. Missing end-of-day therapy-area surveys, surveys with no instrument calibration behind them, or trigger levels that do not match the license are common findings. A survey program that clearly maps each survey to its rule, uses calibrated instruments, and retains records under 10 CFR 35.2070 and the license is a program that inspects well.

Practical Optimization Tips

• Separate the two engines on paper. Write your survey procedure so it is explicit which surveys satisfy 35.70 (daily ambient, written-directive areas) and which satisfy 20.1501 (general radiation and contamination). Auditors should not have to guess.
• Match instruments to the question. Use an ion chamber or appropriate dose-rate meter for ambient surveys and an efficient contamination monitor or scaler for wipes. One instrument rarely does both well.
• Keep calibration current and efficiencies documented. Because contamination results scale inversely with efficiency, an out-of-calibration instrument or an undocumented efficiency undermines every wipe result. This is a 20.1501 requirement, not a nicety.
• Put trigger levels in writing and match the license. State your removable-contamination action levels and ambient investigation levels explicitly, and confirm they match your license conditions rather than a remembered rule of thumb.
• Map the survey to the workflow. Survey where the material actually goes — injection chairs, uptake rooms, restrooms used by therapy patients, waste storage — not just the obvious hot lab bench.
• Record contemporaneously and retain. Log surveys as they are done, with instrument, background, result, and action taken, and retain them under 10 CFR 35.2070 and the license.
• Investigate and document exceedances. When a reading exceeds an action level, decontaminate or shield, re-survey, and document the investigation and resolution — the paper trail is as important as the fix.

Regulatory Considerations

The survey program is governed by a specific medical-use rule (35.70), a general protection rule (20.1501), and the facility's license, all administered by the NRC or an Agreement State. For radioactive material — which is what nuclear medicine uses — the jurisdiction is the NRC in non-Agreement States and the state's radiation-control program in Agreement States. Of the states DRPS serves, Washington DC and Delaware are direct-NRC (non-Agreement) jurisdictions for radioactive material, while Florida, Maryland, Virginia, California, Nevada, Pennsylvania, New York, and New Jersey administer their own Agreement State programs. A licensee must confirm which authority issues and inspects its license and follow that program's version of these requirements.¹³

The specific obligations are: the end-of-day ambient exposure-rate survey of written-directive areas under 10 CFR 35.70, with records retained under 10 CFR 35.2070; the general survey obligation and instrument-calibration requirement under 10 CFR 20.1501; the dose limits that anchor action levels under 10 CFR 20.1201 (occupational) and 20.1301 (public); and the package-receipt survey under 10 CFR 20.1906. NRC model procedures and licensing guidance in NUREG-1556, Volume 9, Revision 3 translate these into concrete survey procedures and the trigger levels most facilities adopt into their license conditions.^1234567 The survey program should be integrated with the facility's recordkeeping obligations — see NRC Part 35 recordkeeping requirements — and with the occupational dose-limit framework in NRC occupational dose limits under Part 20.

DRPS helps facilities build and audit this program through radiation safety officer support, radioactive material license support, and medical physics consulting.

Frequently Asked Questions (FAQs)

What does 10 CFR 35.70 actually require?

Section 35.70 requires a licensee to survey, with a radiation detection survey instrument, at the end of each day of use, all areas where unsealed byproduct material requiring a written directive was prepared for use or administered. It is an ambient radiation exposure-rate survey, and the record must be retained under 10 CFR 35.2070. The survey does not need to be done in an area where a patient who cannot yet be released is confined.

Is 35.70 the same as a contamination survey?

No. Section 35.70 is specifically an ambient radiation exposure-rate survey, measuring dose rate, not removable contamination. The requirement to survey for contamination, and to survey areas of diagnostic use, flows from 10 CFR 20.1501, which requires surveys reasonable to evaluate radiological conditions, plus the facility's license conditions. Most programs run both an ambient dose-rate survey and a removable-contamination survey.

Does a diagnostic-only clinic have to do the 35.70 end-of-day survey?

The 35.70 end-of-day ambient survey is tied to unsealed material requiring a written directive, which generally means therapy administrations. A clinic performing only diagnostic studies without written directives is still subject to 10 CFR 20.1501 surveys and its license conditions, which typically call for routine ambient and contamination surveys, but the specific 35.70 daily written-directive-area survey may not apply. Read your license.

What survey trigger levels should we use?

Removable-contamination trigger levels are not fixed in 10 CFR Part 20 for routine areas; they come from the facility's license conditions and NRC model procedures. Commonly used values are on the order of 200 dpm per 100 square centimeters for unrestricted areas and 2,000 dpm per 100 square centimeters for restricted areas, but the binding numbers are those written into your license. Ambient dose-rate action levels are anchored to the public dose limit in unrestricted areas.

How do we convert a survey meter reading into contamination?

Removable contamination in disintegrations per minute equals the net count rate divided by the instrument's counting efficiency for the radionuclide. If the wipe collected only a fraction of the surface activity, that removal fraction is applied as well. The result is compared, per 100 square centimeters wiped, against the license trigger level. Instruments must be calibrated, as required by 10 CFR 20.1501.

Who is responsible for the survey program?

The Radiation Safety Officer owns the survey program: defining what is surveyed, how often, with which calibrated instruments, and at what action levels, and ensuring records are kept. Technologists typically perform routine surveys, and a medical physicist or health physicist supports instrument calibration, trigger-level derivation, and program review. The RSO is accountable for compliance with 35.70, 20.1501, and the license.

Key Takeaways

• Two engines, not one. The daily ambient exposure-rate survey of written-directive areas (35.70) and the general radiation and contamination survey program (20.1501) are separate obligations with different instruments and action levels.¹³
• 35.70 is narrow and specific. It is an end-of-each-day ambient dose-rate survey, tied to written-directive (generally therapy) material, with records under 35.2070.¹²
• Contamination surveys live under 20.1501 and the license. So do diagnostic-area surveys, frisking, and the trigger levels most programs use.³⁷
• Action levels trace to dose limits. Ambient objectives derive from the 2-mrem-in-any-hour and 1-mSv/yr public limits and the 50-mSv/yr occupational limit.⁴⁵
• The arithmetic depends on calibration. Contamination in dpm is net cpm divided by efficiency, so instrument calibration is what makes a wipe result defensible.³
• Records make it real. Contemporaneous logs, calibrated instruments, and retained records under 35.2070 and the license are what turn a survey into compliance.²⁷

Conclusion

A nuclear medicine survey program is not a single checklist item; it is two coordinated obligations that together keep exposure and contamination under control. The 35.70 daily ambient survey watches the highest-risk therapy workflow, while the 20.1501 program — shaped by the license and NRC model procedures — covers contamination, diagnostic areas, and everyday monitoring. Keeping the two clearly separated, mapping each survey to its rule and its calibrated instrument, and anchoring action levels to the underlying dose limits produces a program that protects people and withstands inspection.

The Radiation Safety Officer and supporting medical physicist should treat surveys as the program's sensory system. When the instruments are calibrated, the trigger levels match the license, the surveys follow the material through the workflow, and the records are retained, the survey program does exactly what it is meant to do: catch problems while they are small and prove, on paper, that the facility is in control.

How DRPS Can Help

Diagnostic Radiation Physics Services helps nuclear medicine and radiopharmaceutical therapy programs design and audit survey programs that satisfy both 10 CFR 35.70 and 10 CFR 20.1501. That includes writing survey procedures that map each survey to its rule, deriving defensible removable-contamination and ambient action levels, supporting instrument calibration and efficiency determination, reviewing records for inspection readiness, and integrating the survey program with the license and the broader radiation safety program through radiation safety officer support, radioactive material license support, and medical physics consulting.

DRPS supports facilities across our service locations, including Florida, Maryland, Virginia, Washington DC, California, Nevada, New York, Pennsylvania, New Jersey, and Delaware.

Related Resources

• Survey meter calibration program
• Choosing the right radiation survey meter
• Minimum detectable activity in contamination surveys
• Package receipt and wipe testing
• NRC Part 35 recordkeeping requirements
• NRC occupational dose limits under Part 20
• Radiation Safety Officer consulting
• Radioactive material license support

References

1. U.S. Nuclear Regulatory Commission. 10 CFR 35.70: Surveys of ambient radiation exposure rate. ecfr.gov
2. U.S. Nuclear Regulatory Commission. 10 CFR 35.2070: Records of surveys for ambient radiation exposure rate. ecfr.gov
3. U.S. Nuclear Regulatory Commission. 10 CFR 20.1501: General (surveys and monitoring). ecfr.gov
4. U.S. Nuclear Regulatory Commission. 10 CFR 20.1301: Dose limits for individual members of the public. ecfr.gov
5. U.S. Nuclear Regulatory Commission. 10 CFR 20.1201: Occupational dose limits for adults. ecfr.gov
6. U.S. Nuclear Regulatory Commission. 10 CFR 20.1906: Procedures for receiving and opening packages. ecfr.gov
7. U.S. Nuclear Regulatory Commission. NUREG-1556, Volume 9, Revision 3: Consolidated Guidance About Materials Licenses — Program-Specific Guidance About Medical Use Licenses. 2019. nrc.gov
8. Alkhorayef M, Sulieman A, Mohamed-Ahmed M, et al. Staff and ambient radiation dose resulting from therapeutic nuclear medicine procedures. Appl Radiat Isot. 2018;141:270-274. doi:10.1016/j.apradiso.2018.07.014. doi.org