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NRSB RMT study materials
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NRSB RMT practice questions

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Question 1Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

In radon measurement, what does the term 'working level' (WL) describe?

  1. The rate at which radon enters a building from soil
  2. The concentration of radon gas itself in indoor air
  3. The potential alpha energy concentration from short-lived radon progeny Correct answer.
  4. The total gamma dose rate measured at a detector

Explanation

The working level is defined as any combination of short-lived radon progeny in one liter of air that yields 1.3 x 10^5 MeV of potential alpha energy. It describes progeny energy concentration, not the parent radon gas concentration. Radon gas is expressed in activity concentration such as Bq/m3 or pCi/L.

Question 2Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon measurement result is reported as 4.0 pCi/L. What is the approximate equivalent in becquerels per cubic meter?

  1. 14.8 Bq/m3
  2. 0.11 Bq/m3
  3. 148 Bq/m3 Correct answer.
  4. 370 Bq/m3

Explanation

One picocurie per liter equals 37 becquerels per cubic meter, so 4.0 pCi/L x 37 = 148 Bq/m3. This conversion factor is standard in radon reporting. The reverse conversion divides by 37.

Question 3Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Which short-lived radon decay product is the alpha emitter most often used to detect progeny during a grab-sample measurement?

  1. Radon-222
  2. Lead-214
  3. Polonium-218 Correct answer.
  4. Bismuth-214

Explanation

Polonium-218 is an alpha-emitting progeny nuclide, so alpha counting of a filtered grab sample detects it directly. Lead-214 and bismuth-214 are beta and gamma emitters. Radon-222 itself is the parent gas and is not a short-lived progeny nuclide.

Question 4Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

What is the primary purpose of placing a radon detector in the lowest livable level of a home?

  1. To shorten the required exposure period
  2. To reduce the effect of humidity on the detector
  3. To measure the highest likely radon concentration occupants are exposed to Correct answer.
  4. To avoid interference from outdoor air

Explanation

Radon is denser than air and tends to accumulate in lower levels, so testing the lowest livable level captures the highest likely occupant exposure. Protocols specify this placement to represent worst-case living conditions. Outdoor air, exposure length, and humidity are separate considerations.

Question 5Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A charcoal canister is deployed for a short-term radon test. Which condition most limits its usefulness?

  1. An open window during deployment
  2. High indoor humidity and temperature fluctuations Correct answer.
  3. Use of a forced-air furnace
  4. The presence of a smoke detector nearby

Explanation

Charcoal canisters rely on adsorption, which is sensitive to humidity and temperature, so these conditions can bias results. Protocols limit deployment when humidity is very high. Nearby smoke detectors, furnaces, and open windows are addressed by other placement rules but are not the primary limitation of the charcoal method itself.

Question 6Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

During a short-term radon test, which action by the occupant would most likely invalidate the result?

  1. Operating the home's heating and cooling normally
  2. Running a bathroom exhaust fan briefly
  3. Closing interior doors between rooms
  4. Leaving windows open for most of the test period Correct answer.

Explanation

Closed-house conditions are required for short-term tests, so prolonged open windows during the test would invalidate results by diluting indoor radon. Normal HVAC operation and brief exhaust use are permitted under closed-house conditions. Closing interior doors is a normal part of the protocol.

Question 7Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon test is conducted in a home's basement that is not currently used as living space. According to typical protocols, where should the primary detector be placed?

  1. In the attic to check for stack effect
  2. In the basement regardless of use
  3. On the main floor near the kitchen
  4. In the lowest level that is regularly occupied as living space Correct answer.

Explanation

Protocols call for testing the lowest level that is regularly occupied, since that is where occupants receive exposure. An unfinished or unused basement may still warrant testing, but the primary living-area measurement follows occupancy. The attic and kitchen are not representative of the lowest livable space.

Question 8Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Which detector type integrates radon exposure over time by recording alpha tracks in a plastic film?

  1. Charcoal liquid scintillation detector
  2. Continuous radon monitor
  3. Alpha-track detector Correct answer.
  4. Electret ion chamber

Explanation

Alpha-track detectors use a plastic film in which alpha particles from radon and progeny leave etchable tracks, giving a time-integrated measurement over months. Charcoal detectors are short-term adsorbers. Electret chambers measure charge reduction, and continuous monitors record real-time counts.

Question 9Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

An electret ion chamber radon measurement works by measuring which quantity?

  1. The reduction in voltage of a charged electret Correct answer.
  2. The number of alpha tracks in a plastic film
  3. The mass of charcoal after exposure
  4. The gamma spectrum of bismuth-214

Explanation

In an electret ion chamber, radon and progeny ionize air inside the chamber, which discharges the electret; the voltage drop is proportional to integrated radon exposure. Alpha-track counting, charcoal mass change, and gamma spectroscopy are different methods.

Question 10Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Why is a minimum deployment period of several days specified for many short-term radon tests?

  1. To average out short-term fluctuations in radon concentration Correct answer.
  2. To satisfy manufacturer warranty terms
  3. To ensure the detector is fully discharged
  4. To allow the detector to reach thermal equilibrium

Explanation

Indoor radon varies diurnally and with weather, so a multi-day exposure averages these fluctuations and gives a more representative result. Thermal equilibrium, warranty terms, and discharge are not the reason for the minimum period.

Question 11Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A continuous radon monitor records hourly readings during a test. What is the main advantage of this over a passive integrating device?

  1. It eliminates the need for closed-house conditions
  2. It provides time-resolved data to detect unusual patterns or interference Correct answer.
  3. It requires no calibration
  4. It measures progeny potential alpha energy directly

Explanation

Continuous monitors produce hourly data, allowing the tester to review patterns and identify anomalies such as tampering or unusual ventilation. They do not remove closed-house requirements, do not directly measure progeny potential alpha energy, and do require calibration.

Question 12Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon measurement result from a short-term test is 6 pCi/L. What is the generally recommended follow-up action?

  1. Immediately retest in the attic
  2. Report the result and close the file
  3. Confirm with a second short-term test or a long-term test Correct answer.
  4. No action; the result is below the action level

Explanation

Results at or above the action level of 4 pCi/L call for follow-up, typically a second short-term test or a long-term test to confirm. A single elevated short-term result is not treated as definitive. Retesting in the attic and closing the file are not appropriate responses.

Question 13Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

What is the EPA action level for radon in homes?

  1. 0.4 pCi/L
  2. 2 pCi/L
  3. 4 pCi/L Correct answer.
  4. 20 pCi/L

Explanation

The EPA action level is 4 pCi/L, at which mitigation is recommended. The 2 pCi/L figure is a consideration level, and 0.4 and 20 pCi/L are not the action level. This threshold drives follow-up testing and mitigation decisions.

Question 14Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Which factor most strongly determines whether a short-term or long-term radon test is chosen?

  1. The color of the detector housing
  2. The size of the home
  3. The time available and the need for a representative annual average Correct answer.
  4. The number of occupants

Explanation

Short-term tests are chosen when quick results are needed, while long-term tests better represent the annual average because they span seasonal variation. Home size, detector appearance, and occupant count are not the deciding factors.

Question 15Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

What is the purpose of the closed-house condition that begins 12 hours before a short-term radon test?

  1. To eliminate all radon progeny from the air
  2. To prevent the detector from overheating
  3. To stabilize indoor radon concentrations near typical occupied conditions Correct answer.
  4. To allow the detector to calibrate itself

Explanation

Closed-house conditions prior to and during a short-term test stabilize radon concentrations so the result reflects normal occupied conditions. They do not prevent overheating, remove progeny, or serve calibration.

Question 16Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A quality assurance program requires duplicate measurements. What is the primary purpose of deploying duplicate detectors?

  1. To assess measurement precision Correct answer.
  2. To measure two different rooms at once
  3. To increase the detector's sensitivity
  4. To reduce the required exposure time

Explanation

Duplicate detectors are deployed side by side to evaluate precision, since their results should agree within expected limits. They do not measure different rooms, increase sensitivity, or shorten exposure time.

Question 17Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A spike or blank measurement in a radon QA program is used primarily to check which aspect of the measurement?

  1. Occupant behavior during the test
  2. Building construction type
  3. Outdoor radon levels
  4. Detector bias and background Correct answer.

Explanation

Spikes and blanks check detector bias and background by introducing a known or zero exposure. They are not designed to assess occupant behavior, construction type, or outdoor radon levels.

Question 18Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Why must a radon detector be placed away from exterior walls, drafts, and heat sources?

  1. To avoid localized conditions that bias the measurement Correct answer.
  2. To keep the detector within its temperature range only
  3. To prevent the detector from being stolen
  4. To reduce the required number of detectors

Explanation

Drafts, exterior walls, and heat sources create localized concentration and temperature differences that can bias results, so placement avoids them. The concern is measurement representativeness, not theft or detector count.

Question 19Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon test is performed in a room where a sump pump runs frequently and the sump is open. What is the most appropriate action?

  1. Test as-is and note the condition, since an open sump may affect radon entry Correct answer.
  2. Seal the sump permanently before testing
  3. Move the detector to the attic
  4. Cancel the test because sumps always invalidate results

Explanation

An open sump can be a radon entry pathway and may affect results, so the condition should be documented and the test conducted under normal conditions. Permanently sealing it changes the building before testing, and moving to the attic misrepresents exposure.

Question 20Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Which unit is used to express the concentration of radon gas in air?

  1. Grams per liter
  2. Working level months
  3. Millisieverts per year
  4. Becquerels per cubic meter Correct answer.

Explanation

Radon gas concentration in air is expressed in activity per volume, such as becquerels per cubic meter or picocuries per liter. Millisieverts per year expresses dose, working level months expresses progeny exposure, and grams per liter is a mass concentration.

Question 21Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A long-term alpha-track test is deployed for one year. What is the main advantage of this duration?

  1. It avoids the need for closed-house conditions entirely
  2. It captures seasonal variation and gives a better annual average Correct answer.
  3. It eliminates the need for follow-up testing
  4. It measures only winter concentrations

Explanation

A year-long test spans seasonal changes, producing a more representative annual average than a short-term test. It does not remove the need for follow-up decisions and is not limited to winter. Closed-house conditions are less critical for long-term tests but are not the stated advantage.

Question 22Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

What does a working level month (WLM) represent?

  1. Cumulative exposure to radon progeny potential alpha energy over time Correct answer.
  2. The total gamma dose from a building
  3. The instantaneous radon gas concentration
  4. The annual radon entry rate

Explanation

A working level month is the cumulative exposure equivalent to one working level sustained for one working month of 170 hours. It combines progeny potential alpha energy with exposure time. It is not an instantaneous gas concentration, gamma dose, or entry rate.

Question 23Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A tester finds that a charcoal canister was exposed for 7 days instead of the intended 2 days. How should this be handled?

  1. Report the result without comment
  2. Extrapolate the result to 2 days
  3. Average the result with a second canister
  4. Discard the result because the exposure period is outside the method's valid range Correct answer.

Explanation

Charcoal canisters are validated for short exposure periods, and exceeding that period can cause saturation or desorption, making the result unreliable. The correct response is to discard and repeat the test rather than report, average, or extrapolate.

Question 24Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Which statement best describes the relationship between radon gas and its short-lived progeny in a measurement context?

  1. Progeny are only produced outdoors
  2. Progeny are the solid decay products that carry most of the potential alpha energy Correct answer.
  3. Progeny are stable and do not decay
  4. Progeny are the same as radon gas and are measured identically

Explanation

Short-lived progeny such as polonium-218, lead-214, and bismuth-214 are solid decay products that carry most of the potential alpha energy of concern. They are distinct from radon gas and are not stable. They form indoors as well as outdoors.

Question 25Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A home has a radon result of 3.9 pCi/L from a short-term test. What is the most defensible interpretation?

  1. The result is just below the action level but close enough to warrant consideration of confirmatory testing Correct answer.
  2. The result should be rounded up to 4 pCi/L and mitigation ordered
  3. The result proves the home has no radon problem
  4. The home is safely below the action level and needs no further thought

Explanation

A result just below 4 pCi/L is close to the action level, and confirmatory testing is reasonable because short-term results fluctuate. It does not prove the absence of a problem, and rounding up to force mitigation is not justified.

Question 26Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

In radon measurement practice, what does the term 'picocurie per liter' (pCi/L) express?

  1. The total alpha energy released by radon progeny in one liter of air
  2. The number of radon progeny attached to airborne particles per liter
  3. The mass of radon gas dissolved in one liter of water
  4. The number of radon atoms decaying per unit time in one liter of air Correct answer.

Explanation

A picocurie is a unit of radioactivity equal to 2.22 decays per minute, so pCi/L expresses the activity concentration of radon gas per liter of air. It is a decay-rate measure, not a mass or an energy total. This is the unit most commonly reported for residential radon tests in the United States.

Question 27Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon measurement professional is explaining why radon progeny matter even though most test devices report radon gas. Which statement is most accurate?

  1. Progeny are the primary source of the inhaled alpha dose, while the gas measurement serves as a practical proxy Correct answer.
  2. Progeny concentrations are always numerically identical to the gas concentration
  3. Progeny decay only after leaving the lung, so their dose contribution is negligible
  4. Progeny are chemically inert and contribute no measurable radiation dose

Explanation

Short-lived progeny such as polonium-218 and polonium-214 emit the alpha particles that deposit most of the dose in lung tissue. Radon gas is measured because it is easier to sample and because progeny levels generally track the parent gas. The gas result therefore serves as an index of exposure rather than a direct dose measurement.

Question 28Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Which statement describes the correct handling of a charcoal canister after the exposure period ends?

  1. Leave it open in the test room for 24 hours to equilibrate before sealing
  2. Place it in a warm area so the adsorbed radon can redistribute evenly
  3. Open it briefly each day so the laboratory can confirm the exposure occurred
  4. Seal it immediately and record the exact stop time, then ship it promptly for analysis Correct answer.

Explanation

Charcoal adsorbs radon, and once exposure ends the collected radon begins to decay and can also desorb. The canister must be sealed at once, with the stop time documented, and returned quickly to the laboratory. Delays or reopening degrade the result because the adsorbed activity changes.

Question 29Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

An alpha-track detector is deployed for a long-term test. What does the plastic film inside the detector record?

  1. Tracks left by alpha particles that strike and damage the material Correct answer.
  2. Color changes caused by radon gas reacting with the plastic
  3. The total volume of air that diffuses through the detector housing
  4. Electrical charge accumulated on the film surface

Explanation

Alpha particles crossing the plastic create microscopic damage trails that become visible after chemical etching and are counted under magnification. The track density is proportional to integrated radon exposure over the deployment. This makes the device well suited to long exposure periods.

Question 30Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

When placing a radon detector in a room, why is it kept at least about 20 inches above the floor and away from the ceiling?

  1. To keep the detector within reach of the tester during retrieval
  2. To ensure the detector remains warmer than the surrounding air
  3. To sample air in the breathing zone while avoiding stagnant layers near surfaces Correct answer.
  4. To prevent the detector from being exposed to indoor humidity

Explanation

Radon concentration varies with height and with proximity to surfaces where progeny plate out. Placement in the general breathing zone, away from floor and ceiling boundary layers, gives a result more representative of occupant exposure. It also reduces interference from dust and drafts near surfaces.

Question 31Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon test is conducted in a room adjacent to a bathroom with an exhaust fan. What is the most appropriate action for the tester?

  1. Move the detector into the bathroom to capture the local concentration
  2. Operate the fan normally and note its use, since the closed-house condition does not require turning off intermittent exhaust fans Correct answer.
  3. Turn the fan off for the entire test and seal the bathroom door
  4. Extend the test to 30 days because an exhaust fan is present

Explanation

Closed-house conditions require windows and exterior doors to remain closed, but intermittent exhaust fans used in normal fashion are permitted and should be documented. The goal is to represent ordinary occupied conditions, not to eliminate every ventilation device. Sealing rooms or relocating detectors would distort the result.

Question 32Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon test report lists a result of 2.1 pCi/L from a short-term test in a living area. What is the most defensible interpretation?

  1. The result proves the basement has no radon entry pathway
  2. The result is below the action level, though seasonal variation means a retest or long-term test can still be informative Correct answer.
  3. The measurement should be discarded because it is below 4 pCi/L
  4. The home is guaranteed to remain below the action level indefinitely

Explanation

A short-term result below the action level indicates the measured concentration during that period was low, but radon varies with season, weather, and operation of the home. Additional testing can confirm the finding but is not mandatory at that level. No single short-term test guarantees future concentrations.

Question 33Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Which condition during a short-term radon test would most likely produce a falsely low result?

  1. The tester places the detector in an interior room on the lowest livable level
  2. The tester leaves a window open in the test room throughout the deployment Correct answer.
  3. The tester documents the detector serial number on the chain-of-custody form
  4. The tester records the start and stop times accurately

Explanation

Open windows increase air exchange with outdoor air, which dilutes indoor radon and biases the result low. Closed-house conditions exist precisely to prevent this during short-term testing. Accurate documentation and proper placement do not bias the concentration downward.

Question 34Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon test is being planned for a two-story home with a finished basement used as a family room. Where should the primary detector be placed?

  1. Outside the home, to establish an outdoor reference concentration
  2. In the attached garage, because it is at grade level
  3. On the second floor, because that is where bedrooms are located
  4. In the finished basement, since it is the lowest level suitable for occupancy Correct answer.

Explanation

Placement guidance calls for the lowest level of the home that is suitable for occupancy, because radon entering from soil tends to be most concentrated there. A finished basement used as living space qualifies. Outdoor or garage measurements do not represent occupant exposure.

Question 35Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A continuous radon monitor is used for a short-term test. What does the tester do with the hourly data at the end of the test?

  1. Average only the hours when the home was occupied
  2. Discard the first and last 24 hours and report the remaining maximum
  3. Review the pattern for signs of tampering or unusual ventilation and report the average over the deployment Correct answer.
  4. Report only the single highest hourly value as the result

Explanation

Hourly data allow the tester to check for sudden drops that suggest opened windows or other interference, and to confirm the device operated throughout. The reported result is the average concentration over the test period, not an extreme value. The pattern supports quality assurance rather than replacing the average.

Question 36Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Which statement best explains why short-term radon tests are commonly run for at least 48 hours?

  1. Detectors are manufactured to activate only after two days of exposure
  2. Laboratory analysis cannot begin until 48 hours have elapsed
  3. Radon gas requires 48 hours to diffuse into a detector's sampling chamber
  4. Radon concentrations fluctuate hourly, so a multi-day average smooths short-term variation Correct answer.

Explanation

Radon levels vary with weather, pressure, and ventilation on time scales of hours. Averaging over at least two days reduces the influence of transient extremes and gives a more representative result. The minimum is about measurement stability, not device activation or shipping.

Question 37Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A quality assurance program includes periodic calibration checks of a continuous monitor. What is the main purpose of these checks?

  1. To confirm the instrument's response remains traceable to a known radon standard over time Correct answer.
  2. To satisfy the requirement that every test be duplicated
  3. To determine the radon concentration in the building where the monitor is stored
  4. To measure the progeny-to-gas ratio in the test room

Explanation

Calibration establishes that the monitor's reported concentration matches a known reference activity. Periodic checks detect drift so that reported results remain accurate and defensible. They are about instrument performance, not about characterizing the storage location or duplicating tests.

Question 38Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon measurement business needs to decide how to handle a detector that was dropped and shows a cracked housing before deployment. What is the appropriate action?

  1. Deploy it anyway and note the damage on the report
  2. Deploy it in an outdoor location as a control
  3. Tape the crack and deploy it as a duplicate
  4. Remove it from service and document the damage rather than deploying it Correct answer.

Explanation

A compromised housing can allow uncontrolled air exchange or alter the diffusion barrier, so the device no longer meets its design specifications. Equipment that may not perform as intended should be removed from service and the action documented. Deploying it, even with a note, produces a result of unknown validity.

Question 39Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon test result from a workplace is being compared with occupational exposure concepts. What does one working level (WL) represent?

  1. The alpha dose delivered to the lung over one year of exposure
  2. The number of radon atoms decaying per minute in one cubic meter of air
  3. Any combination of short-lived radon progeny in one liter of air that releases 1.3 x 10^5 MeV of alpha energy Correct answer.
  4. A radon gas concentration of exactly 4 pCi/L in equilibrium with its progeny

Explanation

The working level is defined by the potential alpha energy concentration of short-lived progeny, specifically 1.3 x 10^5 MeV per liter of air. It is a progeny-based quantity, not a direct gas concentration. Working level months combine this with exposure duration.

Question 40Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A charcoal canister test is planned for a weekend, but the occupant plans to run a whole-house fan for several hours. How should the tester respond?

  1. Explain that the fan must not be operated during the test because it changes normal closed-house conditions Correct answer.
  2. Place a second canister next to the fan to capture the effect
  3. Allow the fan because closed-house conditions apply only to windows and doors
  4. Reschedule the test to a 90-day alpha-track deployment automatically

Explanation

Whole-house and window fans substantially increase air exchange and can depress radon concentrations, so they are not operated during short-term tests. The tester should ensure the occupant understands the closed-house requirements before deployment. A second canister does not correct the altered test conditions.

Question 41Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A homeowner asks whether a radon test can be performed in a home that has been vacant for months with windows open. What is the best response?

  1. The home must remain open to represent vacant conditions
  2. The home should be closed up for at least 12 hours before the test begins Correct answer.
  3. The test can begin immediately because vacancy reduces radon entry
  4. The test should be run outdoors first to establish a baseline

Explanation

Closed-house conditions begin at least 12 hours before a short-term test so that indoor concentrations reflect the building rather than recent outdoor air exchange. A long-vacant, ventilated home would otherwise give an artificially low result. The tester should confirm the closed-house period before deployment.

Question 42Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Which factor would most likely cause a radon test result to be rejected by a laboratory or quality assurance reviewer?

  1. The detector was placed on an interior wall in a basement room
  2. The exposure duration was shorter than the minimum specified for that device Correct answer.
  3. The report was issued within a week of device return
  4. The occupant kept interior doors open during the test

Explanation

Each device type has a specified exposure window, and a deployment outside that window cannot yield a valid result under the protocol. Interior placement and open interior doors are consistent with normal conditions. Prompt reporting is desirable and not a cause for rejection.

Question 43Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon measurement provider is asked to test a home where a radon mitigation system was installed last year. What is the most appropriate testing approach?

  1. Turn the system off for the entire test to measure the underlying soil gas
  2. Skip testing because mitigation guarantees the action level is met
  3. Test only the soil beneath the slab through a suction point
  4. Test as usual with the system operating, since the goal is to verify the post-mitigation concentration Correct answer.

Explanation

Post-mitigation testing verifies that the installed system is keeping indoor concentrations low under normal operating conditions. Turning the system off would measure something other than the living environment the occupants experience. Mitigation does not eliminate the need for verification testing.

Question 44Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A tester is comparing a short-term charcoal canister result with a long-term alpha-track result from the same home. Which explanation best accounts for a substantial difference?

  1. Charcoal canisters systematically overstate radon by a factor of two
  2. The two device types measure entirely different gases
  3. Alpha-track detectors cannot measure concentrations below 4 pCi/L
  4. The tests integrate different time periods, and seasonal variation can shift radon levels considerably Correct answer.

Explanation

Both device types measure radon gas, but over very different periods, so seasonal and weather-driven variation can produce different averages. The long-term result is generally the better estimate of the annual average. Neither device type has the fixed biases described.

Question 45Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon test is conducted in a room where the detector is placed directly above a floor register supplying heated air. What is the primary concern?

  1. The register will add radon to the air and inflate the result
  2. The detector will overheat and stop recording entirely
  3. Air movement and temperature from the register can disturb the sampling environment and bias the result Correct answer.
  4. The detector will record the supply air temperature rather than radon

Explanation

Placement guidance calls for keeping detectors away from drafts, heat sources, and strong air movement because these affect the local concentration sampled by the device. The concern is bias in the measurement, not device failure or radon production by the register.

Question 46Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

Which statement correctly describes the relationship between radon concentration and the duration of a long-term alpha-track test?

  1. Track density is independent of the radon concentration present
  2. Track density reflects only the concentration during the final week of exposure
  3. Track density decreases as exposure time increases
  4. The accumulated track density reflects the integral of concentration over the exposure period Correct answer.

Explanation

Alpha-track detectors accumulate damage trails continuously, so track density is proportional to the time-integrated concentration. Longer exposure therefore produces more tracks for a given average concentration. This integration is what makes the device suitable for estimating annual averages.

Question 47Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A radon test is being set up in a home with a crawl space and no basement. Where should the detector be placed?

  1. In the attic, which has the best ventilation
  2. In the attached garage adjacent to the crawl space
  3. Inside the crawl space itself
  4. On the lowest level of the home that is suitable for occupancy Correct answer.

Explanation

Placement guidance specifies the lowest level suitable for occupancy, which in a home without a basement is typically the first floor. Crawl spaces, attics, and garages are not occupied living space and do not represent occupant exposure. Testing those areas would not answer the question the test is meant to address.

Question 48Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A quality assurance reviewer notices that a batch of detectors from one lot reads consistently higher than a set of known-value reference devices. What does this most likely indicate?

  1. That radon concentrations increased during the test period
  2. A calibration or lot-related bias that should be investigated before results are reported Correct answer.
  3. That the reference devices are faulty in every case
  4. Normal random variation that requires no action

Explanation

A consistent offset across a lot relative to known values points to a systematic bias rather than random scatter. The reviewer should investigate calibration, background, and lot performance before releasing affected results. Consistent direction and magnitude distinguish bias from ordinary variability.

Question 49Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

What is the purpose of recording the start and stop date and time on a radon detector's chain-of-custody record?

  1. To document the exact exposure interval so the result can be interpreted and audited Correct answer.
  2. To calculate the detector's purchase price
  3. To establish the building's construction date
  4. To determine which technician performed the laboratory analysis

Explanation

The exposure interval defines the period over which the measurement applies and is essential for validating the test against the device's specified duration. It also supports traceability if the result is later questioned. The record is not used for pricing, analysis staffing, or building age.

Question 50Radon measurement fundamentals and testing practice (RMT content domain; weights not published by NRSB)

A short-term radon test in a bedroom returns 8 pCi/L. The occupant wants to know what the result means for the household. Which response is most appropriate?

  1. The result should be halved to account for detector uncertainty
  2. The result can be ignored because short-term tests are never reliable
  3. The home must be evacuated immediately by regulation
  4. The result is above the action level and follow-up testing or mitigation evaluation is warranted Correct answer.

Explanation

A short-term result above the action level indicates a need for confirmation and consideration of mitigation. Standard practice is to follow up with a second short-term test or a long-term test before making a mitigation decision. Panic evacuation and arbitrary adjustment of results are not part of the process.