ABHP PART II EXAMINATION COVER SHEET

July 22, 1996

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Identification number: ____________________

Signature: _____________________________

Mark (X) the questions you have answered and are submitting for grading.

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Remember to indicate on each answer sheet your identification number, the question number, and the number of pages for each; e.g.,

ID #1859, Question 4, page 2 of 3

ID #1859, Question 6, page 1 of 1

Have you taken a certification preparation or refresher course prior to taking this examination?
( ) Yes
( ) No

If so, which format was involved?
( )Intensive, one or two weeks
( )Multi-week, one or two classes per week?

QUESTION 1

Current knowledge of the lifetime risk of a fatal cancer attributable to ionizing radiation is based largely on Japanese A-bomb survivor data. ICRP risk coefficients (Publication 60) have been increased from a nominal fatality probability coefficient of 1.25x10 -2/Sv to 4x10 -2/Sv for a worker population and to 5x10 -2/Sv for members of the general public.

POINTS

12 A. List three reasons for this increase in the risk coefficient. Number your responses. Only the first three numbered responses will be graded.

12 B. List three factors that significantly contribute to the uncertainty of a specific risk calculation based on these current values. Number your responses. Only the first three numbered responses will be graded.

6 C. The following are equations for the risk of death, , as a function of radiation dose equivalent, d, in sievert (Sv) where:
yo is the age-specific background risk of death due to a specific cancer
f(d) is a linear or linear-quadratic function of dose and
g(B) is an excess risk function that depends on gender, attained age, etc.

yo is the age-specific background risk of death due to a specific cancer
f(d) is a linear or linear-quadratic function of dose and
g(B) is an excess risk function that depends on gender, attained age, etc.
A. yd = yo [1+ f(d) g(B)]
B. yd = [1+ f(d)g(B)]
C. yd = yo + f(d) g(B)
D. yd = yo f(d) [1+ f(d) g(B)]
Which of these equations is commonly referred to as the relative risk model?

15 D. NCRP 95 reports that 125,000,000 people in the United States use natural gas for cooking and each receive an average annual effective dose equivalent of 0.004 mSv. Assuming a linear, non-threshold risk model, calculate the expected number of fatal cancers that can be attributed to cooking with gas for a one year period in the United States.

5 E. Which organ has the highest probability of radiation induced cancer as the result of exposure to airborne radon progeny?

QUESTION 2

You are a health physicist at a nuclear installation and your supervisor directs you to measure a long-lived contamination smear with a GM counter. During a 10 minute count interval a total of 1000 counts was recorded while a 1 hour background measurement yielded 2,340 counts.

POINTS

15 A. What is the net sample counting rate and the standard deviation of the net counting rate? Show all work.

10 B. What are the standard deviation and the relative probable error of the 10-minute sample count? Show all work.

10 C. Match the statistical concept or method with the description and/or application that best applies.

  1. Chauvenet's Criteria
  2. "t" Test
  3. Chi-Square Test
  4. Poisson Distribution
  5. Gaussian Distribution

A. Indicates the probability that a difference between two counts is not due to chance.

B. Evaluates counter behavior.

C. Evaluates for rejection of data.

D. Represents a distribution of counting data which is symmetrical about the mean count value.

E. A special case of the binomial distribution applicable when the measured event has a low probability of occurring.

F. Quantifies uncertainty in radioactivity measurement.

15 D. After your supervisor presents your results to the resident inspector, you are directed to recount the sample. What would be the optimum division of counting time between the background and the sample to minimize the resulting errors, if you are given only 2 hours to complete the counts? Show all work.

QUESTION 3

The figure shows five traces labeled A through E for a fixed filter Constant Air Monitor (CAM). Each represents a physically possible combination of a fixed or varying concentration of a single nuclide collected on the filter, with negligible self absorption. The CAM trace starts at a background level, increases as the airborne activity is collected, and then continues after all activity in the sampled air is gone.

POINTS

10 A. The trace which represents the presence of a short term "puff" release of a long-lived radionuclide with no additional releases during the sampling period is:

A.
B.
C.
D.
E.		 Trace A
Trace B
Trace C
Trace D
Trace E

10 B. The trace which represents the presence of a nuclide with a half-life of approximately 20 minutes is:

A.
B.
C.
D.
E.		 Trace A
Trace B
Trace C
Trace D
Trace E

10 C. The trace which represents the presence of an exponentially increasing concentration of a long-lived radionuclide is:

A.
B.
C.
D.
E.		 Trace A
Trace B
Trace C
Trace D
Trace E

20 D. Using the following information calculate the average airborne radioactive material concentration (in µCi/cc) during the release period for the trace labeled as "B":

GIVEN:

QUESTION 4

GIVEN For the photons of interest:

Material µ/p Etr = Eab
(MeV)		 µab/p
(cm2/g)		 Range
(cm)
muscle 0.0626 0.588 0.0294 0.5
bone 0.0604 0.588 0.0283 0.3

µ/p = mass attenuation coefficient
p (muscle) = 1.0 g/cm3
p (bone) = 1.65 g/cm3
Etr = average energy transferred to electronic motion per interaction
Eab = average energy absorbed per interaction
µab/r = mass energy absorption coefficient
Range = the maximum range of the electrons set in motion by photons in the material

POINTS:

5 A. 1. Define kerma.
5 2. Define absorbed dose.
4 3. What condition must exist for absorbed dose to be approximately equal to kerma?
4 4. What is the purpose of a build-up cap on an ionization chamber?
B. Consider the case of a narrow beam of the above photons incident at right angles to a slab phantom consisting of 1 cm of muscle followed by 1 cm of bone. The kerma at the surface of the muscle is 100 J/kg. Show all work.
8 1. What is the kerma 1 cm deep in the muscle?
8 2. By what factor does the kerma change in the bone at the muscle/bone interface?
8 3. What is the ratio of the kerma 1 cm deep in bone to that at 0 cm in bone?
8 C. At what point (depth) in the phantom is the largest absorbed dose? Explain your reasoning.

QUESTION 5

Neutron activation will be used to determine the neutron absorption cross sections of two materials in a sample. Sample activation counting data for post-irradiation times are shown in the figure.

GIVEN

Sample mass = 100 grams
Uniform neutron fluence rate throughout the sample volume = phi = 1.7 x 1012 n/sec-cm2
Target for production of the long lived component = 15 weight%, atomic weight 14
Target for production of the short lived component = 85 weight%, atomic weight 26
Decay curve provided in Figure (extrapolated decay curves are provided).
Assume irradiation is long enough for saturation to be reached
Detector efficiency for the long lived product = 45%

POINTS

10 A. Explain, in general, how you would determine an estimate of the activation product half-lives of the two materials comprising the sample from the graph provided.
10 B. Estimate the half-life and initial activity of the longer-lived component.Show all work and state any assumptions.
20 C. Calculate the microscopic absorption cross section of the target which produces the long lived component. Assume an initial count rate of 9.0E+7 cpm for this part only. Show all work.
10 D. List any 5 factors that need to be considered when evaluating materials for use as neutron shielding. Number your responses. Only the first 5 numbered responses will be graded.

Sample Activation Levels


QUESTION 6

A processing facility discharges a single radionuclide from a process to a liquid effluent stream. Before releasing the effluent to the environment, the stream is to be treated with an ion exchange column.

GIVEN

The radionuclide being discharged is a gamma emitter. It emits a 1.0 MeV gamma per disintegration, and has a radiological half-life of 15 days.

The gamma ray constant for this isotope is 1.55 R-m2/(Ci-hr).
The concentration of the radionuclide in the column is 0.015 Ci/meter.

The ion exchange system is to have a decontamination factor of 0.99 for this radionuclide. The column will consist of a vertical column 0.5 meters in diameter and 9 meters in height above the floor.
Density of air = 1.293E 3 g/cm3
Density of lead = 11.36 g/cm3

Build-Up Factors
Relaxation Lengths Build-Up Factor Relaxation Lengths Build-Up Factor
1
2
3
4
5		 1.36
1.7
2.02
2.33
2.62		 6
7
8
9
10		 2.9
3.17
3.44
3.7
3.96

Interaction Coefficients (cm2/g)
Energy (MeV) Air Lead
µ/p µab/p µ/p µab/p
1.0 0.0636 0.0279 0.0701 0.0364

POINTS

15 A. What is the unshielded exposure rate at a point 12 meters horizontally from the column and 1 meter above the floor? Ignore scatter from the floor and ceiling, ignore attenuation in the column and its contents. Show all work.
15 B. You are considering installation of a 2-cm thick lead sleeve over the column. By what factor will exposure rates be reduced by the addition of the shielding ? Do not use rules of thumb. Show all work.
10 C. Explain why the equation I=Ioe -µx does not apply in relation to photon shielding for broad beam conditions or for very thick materials? Describe the physical process involved.
10 D. You want to extend the range of an uncompensated GM process monitor by a factor of 10 through the use of lead shielding. The GM monitor was calibrated using a precision source of the same radionuclide being processed. Explain how the lead shielding affects the response of the shielded GM detector.

QUESTION 7

You are asked to design the shielding for an electron accelerator facility with the facility information given below. Use the figures copied from the NCRP 51 (1977), Radiation Protection Design Guidelines for 0.1-100 MeV Particle Accelerator Facilities, attached.

GIVEN

Electron beam kinetic energy = 20 MeV
Peak current = 1 A
Beam pulse length = 1 µs
Beam pulse frequency = 10 Hz

The target is a tungsten beam dump.
Z, tungsten = 74
Z, copper = 29

Five figures from NCRP 51 (attached)

POINTS

50 A. Assume that the dose equivalent rate in an office, which is at 90° from the beam line and 5 meters from the target (perpendicular distance from the beam line), needs to be no greater than 0.5 mrem/h. Calculate the minimum thickness required for the concrete wall (density is 2.35 g/cm3) between the target and the office.
20 B. Assume that in part A the required transmission factor is 10-4 and the existing concrete wall is 2.5 feet. Calculate the additional lead thickness required to complement the concrete wall.
10 C. What would be the neutron dose yields (higher or lower) if copper is used as the target, instead of tungsten? State two reasons. Number your responses; only the first two responses will be graded.
20 D. In estimating the shielding for the scattered x-ray radiation, the reflection coefficient a (albedo factor) can be used. List four parameters that may affect the reflection coefficient. Number your responses; only the first four responses will be graded.

E.1. X-Ray Emission Rates from High-Z Targets



E.6 Equivalent Incident Electron Energies


Equivalent electron energy for analysis of transmission of x-rays emitted in the 90° direction from very thick high-Z targets, as a function of the incident electron energy. The x-ray spectrum at 90° is lower in energy than the specrum at 90°. This lower-energy radiation can be described in terms of an incident electron energy that would in effect produce x-rays with similar transmission characteristics in the 0° direction. Transmission curves or tenth-value layer curves applicable to the lower energy selected from this graph may be used in the calculation of shielding thicknesses for the 90° beam. The same procedure would be a conservative approach for x-rays from low-Z targets, and for x-rays emitted in the 190° direction.
Referrences: (1) Burrill (1968); (2) and Seltzer (1970); (3) McCall and Nelson (1974); and (4) Saxon (1964).


E.8 Broad-Beam Transmission Through Concrete of X Rays
Produced by 0.5- to 176-Mev Electrons


Transmission of thick-target x rays through ordinary concrete (density 2.35 g/cm-3), under broad-beam conditions. Energy designations on each curve (0.5 to 176 MeV) refer to the monoenergetic electron energy incident on the thick x-ray producing target. Curves represent transmission in dose-equivalent index ration. (See Appendix E-12 for basis for interpolating between curves.) Curves derived from (1) Miller and Kennedy (1956); (2) Kirn and Kennedy (1954); (3) Karzmark and Capone (1968); and (4) NCRP Report No. 34 (NCRP, 1970a) and NCRP Report No. 49 (NCRP, 1976).


E.12 Dose-Equivalent Index Tenth-Value Layers for
Broad-Beam X-rays in concrete


Dose-equivent index tenth-value layers in ordinary concrete (density 2.35g/cm-3) for thick target x-rays under broad-beam conditions, as a function of the energy of electrons incident on the thick target. The dotted curve refers to the first tenth-value layer; the solid curve refers to subsequent or "equilibrium" tenth-value layers. Both curves are empirically drawn through data points derived from the following references: (1) Miller and Kennedy (1956); (2) Kirn and Kennedy (1954); (3) Karzmark and Capone (1968); and (4) NCRP Report No. 34 (NCRP, 1970a), (5) Maruyama et al. (1971). Studies by Lokan et al. (1972) on light Ilmenite-loaded concrete (density 2.89 g/cm-3) are in reasonable agreement with the solid curve above, on a mass thickness basis (g cm-2).


E.14 Dose-Equivalent Index Tenth-Value Layers for
Broad-Beam X Rays in Lead


Dose-equivent index tenth-value layers in ordinary lead (density 11.3 g/cm-3) for thick target x-rays under broad-beam conditions, as a function of the energy of electrons incident on the thick target. The dotted curve refers to the first tenth-value layer; the solid curve refers to subsequent or "equilibrium" tenth-value layers. Both curves are empirically drawn through data points derived from the following references: (1) Miller and Kennedy (1956); (2) Maruyama et al. (1971); (3) ICRP Publication No. 4 (ICRP, 1964); and (4) NCRP Report No. 34 (NCRP, 1970a). The empirical curve is not extended into the 10- to 100-MeV region because of uncertainties in the available data.

QUESTION 8

You are approached by a local Realtor who asks you for a consultation on a problem with a radon measurement in a house. A radon expert hired by a potential home buyer took an air sample in an unfinished basement next to the uncovered sump. The sample time was about 5 minutes and the measured radon concentration, based upon laboratory analysis of the sample taken in the house, was reported as 19 pCi/l.

GIVEN

Lifetime Risk of Lung-Cancer Mortality, excess risk: 350 deaths/106 person-WLM (for lifetime exposure)
Average life expectancy: 70 years
Residential Occupancy Factor: 0.5

POINTS

5 A. Select the best definition for working level from the following.
A. Any combination of the short-lived radon daughters in 1 liter of air that results in the ultimate emission of 1.3x105 MeV of potential alpha energy.
B. Any combination of radon and its short-lived daughters in 1 liter of air that results in the ultimate emission of 1.3x105 MeV of potential alpha energy.
C. 4 pCi/l of the short-lived radon daughters as measured at ambient temperature and pressure.
D. Any concentration of radon and its short-lived daughters that results in a Committed Effective Dose Equivalent of 0.1 rem/y.
E. Any concentration of the short-lived daughters that results in a Committed Dose Equivalent of 50 rem/y to the bronchial epithelium.
15 B. Would you recommend remediation based upon the measurement described in the introduction to this problem? Provide 2 justifications for your answer. Number your responses. Only the first two numbered responses will be graded.
25 C. The Realtor wants your assessment of the potential health effects of the 19 pCi/l concentration. Assume the measurement is a long-term average value. What is the excess risk of cancer death attributable to this level of radon? Assume that the radon progeny to radon activity ratio is 0.5. Show all work; state all assumptions.
15 D. List three potential sources of radon in the home and two appropriate remediation measures for each. Number your responses. Only the first three numbered responses will be graded.
20 E. List three potential sources of radon in the home and two appropriate remediation measures for each. Number your responses. Only the first three numbered responses will be graded.
1. Define unattached fraction.
2. The figure below represents the variation of mean dose to the tracheobronchial region of the lung with percent of unattached fraction. Explain the reason for the increase in dose with the percent increase in unattached fraction.
10 F. Estimation of health risk from radon is based primarily on studies of radon exposures to miners. Describe two factors (cautions) that should be considered in applying miner data to residential situations. Number your responses. Only the first two numbered responses will be graded.
10 G. Which of the following statements best describes the action recommended by the Environmental Protection Agency when the average, long-term radon concentration in a living area is determined to be 10 pCi/l?
A. This level is among the highest ever found in homes; immediate action is warranted to reduce radon concentration.
B. This level is average for homes; however remedial action should be taken within a few years to make the exposure as low as reasonably achievable.
C. Fix your home; take action to remediate the radon problem.
D. Perform additional measurements.
E. No action is recommended.


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