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Question 1

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Which radiation detection instrument is MOST appropriate for measuring low-energy beta emitters such as H-3 and C-14 in liquid samples?

Ion chamber survey meter

Sodium iodide gamma spectrometer

Geiger-Mueller detector

Liquid scintillation counter

to track

2026 Statistics

Key Facts: CHP Exam

150

Part I Questions

ABHP

3 + 6 hours

Exam Time (Part I + II)

ABHP

~63%

Part I Passing Score

ABHP

6 years

Experience Required

ABHP

4 years

Renewal Period

ABHP

The CHP exam is a two-part certification. Part I consists of 150 multiple-choice questions over 3 hours covering health physics fundamentals. Part II is a 6-hour applied exam with 6 mandatory core questions and 4 elective problems. Candidates need a bachelor's degree plus 6 years of professional health physics experience. The ABHP has certified health physicists since 1960.

Sample CHP Practice Questions

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1Which radiation detection instrument is MOST appropriate for measuring low-energy beta emitters such as H-3 and C-14 in liquid samples?

A.Ion chamber survey meter

B.Sodium iodide gamma spectrometer

C.Geiger-Mueller detector

D.Liquid scintillation counter

Explanation: A liquid scintillation counter (LSC) is the instrument of choice for measuring low-energy beta emitters like tritium (H-3, max beta energy 18.6 keV) and carbon-14 (C-14, max beta energy 156 keV). These low-energy betas cannot penetrate the window of a GM tube or the crystal housing of a NaI detector. In LSC, the radioactive sample is dissolved directly in a scintillation cocktail, allowing intimate contact between the beta particles and the scintillating medium for efficient detection.

2What is the primary advantage of a high-purity germanium (HPGe) detector over a sodium iodide (NaI) detector for gamma spectroscopy?

A.Higher detection efficiency

B.Superior energy resolution

C.No cooling required

D.Lower cost and simpler operation

Explanation: HPGe detectors provide significantly better energy resolution compared to NaI(Tl) detectors, typically achieving resolutions of 0.1-0.3% versus 6-8% for NaI at 662 keV. This superior resolution allows HPGe detectors to distinguish between closely spaced gamma-ray energies, making them essential for identifying and quantifying multiple radionuclides in complex mixtures. However, HPGe detectors require liquid nitrogen or electromechanical cooling, are more expensive, and generally have lower intrinsic detection efficiency than NaI detectors of comparable size.

3A Geiger-Mueller detector reads 500 counts per minute at a known dose rate of 2 mR/hr. After exposure to a much higher radiation field, the instrument reads zero. What is the MOST likely cause?

A.The detector has experienced saturation or dead-time paralysis

B.The instrument is functioning correctly and the field is zero

C.The radioactive source has completely decayed

D.The battery has failed

Explanation: When a GM detector is exposed to a very high radiation field, the count rate can exceed the detector's resolving time, causing the instrument to read zero or near zero — a phenomenon known as dead-time paralysis or detector saturation. The detector cannot recover between ionization events, and the continuous discharge prevents individual pulses from being registered. This is an extremely dangerous situation because the operator may incorrectly believe the area is safe. Health physicists must always approach unknown fields cautiously and start with the highest range on their instruments.

4Which type of radiation detector operates on the principle of collecting charge carriers produced by ionization in a gas-filled volume?

A.Ionization chamber

B.Thermoluminescent dosimeter

C.Film badge

D.Scintillation detector

Explanation: An ionization chamber collects ions produced when radiation interacts with gas molecules in a defined volume. An applied voltage separates the positive ions and electrons before they can recombine, and the resulting current is proportional to the radiation exposure rate. Ionization chambers operate in the ion saturation region of the gas detector curve and provide accurate exposure or dose-rate measurements. Scintillation detectors use light emission from crystal interactions, TLDs trap electrons in a crystal lattice, and film badges rely on photographic emulsion darkening.

5What is the minimum detectable activity (MDA) of a counting system primarily dependent upon?

A.The energy of the emitted radiation only

B.The physical half-life of the radionuclide

C.The activity of the sample being measured

D.The background count rate and counting time

Explanation: The minimum detectable activity (MDA) is primarily determined by the background count rate, the counting time, and the detector efficiency. A higher background count rate increases the statistical fluctuations that the true signal must exceed, raising the MDA. Longer counting times reduce statistical uncertainty and lower the MDA. The Currie equation (MDA = 2.71 + 4.65 * sqrt(background counts)) quantifies this relationship. While detector efficiency and emission energy also affect MDA, the background and counting time are the dominant factors in the calculation.

6A contamination survey using a pancake GM probe shows 1,200 cpm gross and a background of 200 cpm. If the detector efficiency is 10% and the probe active area is 20 cm², what is the surface activity in dpm/100 cm²?

A.5,000 dpm/100 cm²

B.50,000 dpm/100 cm²

C.10,000 dpm/100 cm²

D.100,000 dpm/100 cm²

Explanation: First, subtract background: 1,200 - 200 = 1,000 cpm net. Convert to dpm using the 10% efficiency: 1,000 / 0.10 = 10,000 dpm over the 20 cm² probe area. Normalize to 100 cm²: 10,000 × (100/20) = 50,000 dpm/100 cm². This standardized surface activity unit (dpm/100 cm²) is used in 10 CFR 835 and NRC guidance to express removable and total surface contamination levels for comparison against regulatory limits.

7Which instrument is BEST suited for performing alpha contamination surveys on flat surfaces?

A.Pressurized ionization chamber

B.High-range gamma survey meter

C.Gas proportional detector with thin window

D.Sodium iodide scintillation detector

Explanation: A gas proportional detector with a thin window (or a zinc sulfide scintillation detector) is best suited for alpha contamination surveys on flat surfaces. Alpha particles have very short range in air (a few centimeters) and cannot penetrate thick detector windows. Gas proportional counters with thin Mylar windows allow alpha particles to enter the detection volume. NaI detectors are designed for gamma radiation, and ion chambers and high-range gamma meters lack the sensitivity and alpha discrimination capability needed for surface contamination surveys.

8What is the purpose of performing a chi-squared test on a set of repeated radiation measurements?

A.To identify the specific radionuclide present

B.To determine the half-life of a radionuclide

C.To calculate the dose rate at a distance

D.To verify that the instrument is responding in a statistically consistent manner

Explanation: The chi-squared test is used to evaluate whether the variation in a series of repeated measurements is consistent with the expected Poisson distribution of radioactive decay. If the chi-squared value falls within the acceptable range, it confirms the instrument is performing reliably and the variability is due to the random nature of radioactive decay rather than instrument malfunction. This is a critical quality control check for radiation detection systems. Values outside the expected range indicate potential problems such as electronic noise, detector instability, or external interference.

9When calibrating a portable radiation survey meter, what is the MOST important parameter to verify?

A.That the battery indicator light is green

B.That the instrument was manufactured within the last year

C.That the instrument reads within ±20% of the true dose rate across its usable range

D.That the instrument reads within the manufacturer's color specifications

Explanation: The primary goal of survey meter calibration is to verify that the instrument reads within ±20% (or ±10% in some programs) of the conventionally true dose rate at multiple points across its usable range. ANSI N323A standards require calibration at two points on each scale that are used. Calibration must be performed using traceable sources, and the results must be documented. Battery checks and visual inspections are part of routine operability checks but are not the core purpose of calibration. Manufacturing date alone does not determine instrument accuracy.

10Which counting geometry provides the highest detection efficiency for a given sample?

A.4π geometry

B.2π geometry

C.Marinelli beaker at 25 cm from detector

D.Point source at 1 meter

Explanation: A 4π geometry, where the detector completely surrounds the sample, provides the highest possible geometric efficiency because radiation emitted in all directions has the opportunity to interact with the detector. This geometry captures nearly all emitted radiation and is approached by liquid scintillation counting (where the sample is immersed in the scintillation cocktail) or well-type detectors. A 2π geometry captures approximately half the emitted radiation, while more distant geometries capture progressively smaller solid angles and yield lower efficiencies.

About the CHP Exam

The CHP (Certified Health Physicist) is the premier professional certification in health physics, granted by the American Board of Health Physics (ABHP). The two-part exam tests competence in radiation protection, dosimetry, shielding, instrumentation, and regulatory compliance. The CHP credential is recognized by the U.S. Nuclear Regulatory Commission (NRC) and is accredited by the Council of Engineering and Scientific Specialty Boards (CESSB).

Questions

150 scored questions

Time Limit

3 hours (Part I); 6 hours (Part II)

Passing Score

~95 correct out of 150 (approximately 63%) on Part I

Exam Fee

$250 (Part I); $750 (Part II) (ABHP)

CHP Exam Content Outline

25%

Measurements and Instrumentation

Selection and use of measuring instruments, interpretation of measurement values, calibration, data quality objectives, and radiation detection methods.

20%

Standards and Requirements

Federal and state regulations (NRC, EPA, DOE), ALARA principles, dose limits, regulatory guidance, and compliance requirements.

20%

Hazards Analysis and Controls

Hazard identification, engineered controls, shielding design, failure analysis, radiological consequence assessment, and control effectiveness.

20%

Operations and Procedures

Standard operating procedures, emergency response, radiation protection program requirements, facility operations, and records management.

15%

Fundamentals and Education

Nuclear physics, radioactive decay, radiation interaction with matter, dosimetry fundamentals, and health physics training and education.

How to Pass the CHP Exam

What You Need to Know

Passing score: ~95 correct out of 150 (approximately 63%) on Part I
Exam length: 150 questions
Time limit: 3 hours (Part I); 6 hours (Part II)
Exam fee: $250 (Part I); $750 (Part II)

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

CHP Study Tips from Top Performers

1Focus on the five domains of practice and allocate study time proportional to their exam weight (Measurements and Instrumentation is the largest at 25%).

2Practice calculation-heavy questions — Part I includes 19-23 calculation problems, and Part II is primarily calculations and short essays.

3Study the ABHP Exam Preparation Guide and review past Part II exams available on the AAHP website.

4Master the NRC regulations (10 CFR Parts 19, 20, 30, 40, 50) as Standards and Requirements accounts for 20% of the exam.

5If you pass Part I, you have 7 years to pass Part II — but start preparing early as Part II requires professional judgment and applied knowledge.

Frequently Asked Questions

What is the CHP exam?

The CHP (Certified Health Physicist) exam is a two-part professional certification exam administered by the American Board of Health Physics (ABHP). Part I is a 150-question multiple-choice exam testing fundamentals, and Part II is a 6-hour applied exam with essay and calculation problems.

How many questions are on the CHP Part I exam?

Part I of the CHP exam contains 150 multiple-choice questions with 5 answer choices each. The exam must be completed in 3 hours.

What is the passing score for the CHP exam?

The Part I passing score is typically around 95 correct answers out of 150 (approximately 63%). The Part II exam is graded on a point system with 50 points per core question.

How much does the CHP exam cost?

Part I costs $250 total ($100 application fee + $150 registration fee). Part II costs $750 total ($250 application fee + $500 registration fee). Fees are non-refundable.

What are the prerequisites for the CHP exam?

Candidates need a bachelor's degree in physical science, biological science, or engineering with at least 20 semester hours in physical science, plus 6 years of professional health physics experience (3 years applied). Advanced degrees can reduce the experience requirement.

Is the CHP recognized by the NRC?

Yes, the CHP credential is recognized by the U.S. Nuclear Regulatory Commission as evidence of professional competence in health physics. Many NRC licensees require or prefer CHP-certified health physicists.