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Radiation Stay Time Calculator

Calculate maximum allowable work time in a radiation field based on dose rate and dose limit

Field guide: Understanding the Inverse Square Law in Radiation Protection

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Free radiation stay-time dose screen for radiation workers, RSOs, and ALARA coordinators who need a local arithmetic prompt from an entered external dose rate, selected 10 CFR 20 source row or local dose budget, accumulated-dose prompt, and optional task-duration prompt. The screen preserves simple dose = rate x time math, shows duration rows, and keeps source warnings visible for constant-dose-rate assumptions, mR/R-to-mrem approximations, survey quality, dosimetry records, declared-pregnancy context, public-dose context, radiation work permits, ALARA review, and RSO review. The output is not entry authorization, radiation work permit approval, dose-record update, dosimetry assignment, ALARA completion, public-dose demonstration, declared-pregnancy clearance, planned special exposure approval, or legal compliance verification.

Pro Tip: Use this screen after the task dose budget has been set by the current radiation protection program, not to set that budget by itself. If dose rate changes as the worker moves, break the job into segments and total the dose for each segment. Confirm the dose-rate row with calibrated surveys, reconcile prior dose from official records, and keep worker rotation, alarms, access control, and work authorization in the RSO or health physics procedure.

Review inverse-square dose-rate prompts before stay-time arithmetic

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Review shielded dose-rate prompts before stay-time arithmetic

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Review source-activity dose-rate prompts before survey confirmation

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Screen whether the area needs RSO posting review

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How It Works

  1. Enter a Dose-Rate Prompt

    Enter the measured dose-rate row at the work position in mR/hr, R/hr, mSv/hr, or μSv/hr. Use a calibrated survey and current procedure context; if the row is estimated from distance or source activity, treat it as a pre-survey prompt only.

  2. Select a Source Row or Local Budget

    Select a 10 CFR 20 source row or enter a local dose-budget prompt that has already been established by RSO procedure, ALARA review, or the work planning process. Enter prior accumulated dose from the official record, not from memory.

  3. Review Arithmetic and Warnings

    Review remaining-budget and duration-dose prompts, then resolve the listed source gaps. Field use still requires current dose records, calibrated surveys, RWP or procedure checks, dosimetry, access control, alarms where applicable, and qualified RSO or health physics review.

Assumptions

  • Dose rate is assumed constant throughout the duration prompt (no change in source position, distance, shielding, or worker location during the task).
  • Dose is calculated as Rate x Time with no correction for dose rate fluctuations.
  • The dose-budget prompt entered is reduced by any prior accumulated dose prompt the user enters.
  • Whole-body dose (TEDE) is the default metric. Extremity and lens dose limits are not separately calculated.

Limitations

  • Does not model variable dose rates during a task. Use segment-based calculations for complex time-motion scenarios.
  • Does not track cumulative dose across multiple entries or tasks. Use official dosimetry records for prior accumulated dose.
  • Does not distinguish between deep dose equivalent (DDE) and shallow dose equivalent (SDE).
  • Does not calculate internal dose from airborne contamination or ingestion. This is an external dose tool only.

References

  1. 10 CFR 20.1201 - Occupational Dose Limits for Adults
  2. 10 CFR 20.1003 and 20.1101 - Definitions, radiation protection programs, and ALARA source context
  3. 10 CFR 20.1201, 20.1208, and 20.1301 - Occupational, embryo/fetus, and public dose-limit source rows
  4. 10 CFR 20.1501, 20.1502, and 20.2106 - Surveys, individual monitoring, and monitoring-record context
  5. NRC Regulatory Guide 8.29 - Occupational radiation risk instruction source context
  6. ANSI N43.3 - General Radiation Safety: Installations Using Non-Medical X-Ray and Sealed Gamma-Ray Sources

Frequently Asked Questions

Under 10 CFR 20.1201, the occupational dose limit for the whole body (total effective dose equivalent, or TEDE) is 5 rem (50 mSv) per year. The limit for any individual organ or tissue is 50 rem (500 mSv) per year. The lens of the eye limit is 15 rem (150 mSv) per year. The skin and extremity limit is 50 rem (500 mSv) per year. Most facilities set administrative control levels at 10 to 20 percent of these regulatory limits to provide margin and demonstrate ALARA.
An administrative dose limit or action level is a dose threshold set by the facility radiation protection program, typically below a regulatory ceiling. Examples vary by site and license condition. The app can accept the value as a local prompt, but it cannot verify that the value is current, task-specific, or authorized for the worker.
If the dose rate changes during the task, calculate the dose for each segment separately and add the segment doses. The screen does not perform a full time-motion study or verify worker position. Real-time alarming dosimeters and surveys can support the procedure, but alarm settings and dose records are controlled outside the app.
ALARA stands for As Low As Reasonably Achievable. It is part of a radiation protection program under 10 CFR 20.1101. Stay-time arithmetic is one input to ALARA planning, but a complete review also depends on source records, surveys, distance, shielding, tooling, worker training, dose records, procedures, supervision, and RSO review.
Always use the dose rate at the actual work position where the worker's body (specifically the torso) will be during the task. Contact dose rates on a source container or pipe surface are useful for handling precautions but do not represent whole-body exposure during a task performed at arm's length. Survey the area at the positions where workers will stand, kneel, or reach during the job. If the work position varies, use the highest dose rate in the range of positions.
Electronic personal dosimeters can display real-time dose and dose rate and may alarm under the facility procedure. Alarm setpoints, required dosimetry, record dose, response actions, and worker instructions are procedure and RSO decisions. This screen does not set or enforce alarms.
Disclaimer: This screen provides preliminary dose = rate x time arithmetic from values you enter. Actual exposure depends on worker position, dose-rate variability, survey quality, source condition, shielding, access control, dosimetry, and task execution. It does not replace the radiation protection program, RWP process, calibrated surveys, official dose records, or RSO/qualified health physics review.

Guides for this job

Safety

Understanding the Inverse Square Law in Radiation Protection

How the inverse square law applies to radiation safety, with worked examples, source-boundary warnings, 10 CFR 20 threshold context, and survey/RSO review gaps.

Read Guide →
Safety

Radioactive Decay Activity Arithmetic and Review Boundaries

Decay equation prompts, half-life source rows, certificate and inventory boundaries, dose-rate survey limits, transport/waste caveats, and RSO-review gaps.

Read Guide →
Safety

ALARA Stay-Time Arithmetic and Review Boundaries

How to review stay-time arithmetic, apply 10 CFR 20 dose-limit source context, document radiation work permits, and keep occupational dose records separate from calculator prompts.

Read Guide →
Safety

Radiation Area Posting Threshold Context per 10 CFR 20

Complete posting requirements for Radiation Areas, High Radiation Areas, and Very High Radiation Areas. Includes sign specifications, access controls, and exceptions per 10 CFR 20.1902-1903.

Read Guide →

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