QUESTION 9

You are a Health Physicist at a nuclear power plant. The Spent Fuel Pool (SFP) requires fuel consolidation to expand storage capacity and accommodate future spent fuel. Two floor plates on the bottom of the Spent Fuel Pool must be removed. An underwater diver is required to remove these floor plates. The job duration is estimated to be 20 minutes. Spent fuel bundles have been moved to a remote location in the SFP. Radiation surveys of the SFP floor show a small fixed hot spot on the SFP floor in the vicinity of the floor plates.

GIVEN

Hot spot: 600 rem/h (gamma) at 1 foot from hot spot, measured underwater.
Distance from hot spot to floor plates = 3 feet

Tenth value layer for water : 60 cm (includes buildup factor)
Diver dose of record for current year: 2500 mrem

Average energy : 1.0 MeV

Reference Man:
3H beta: 18.6 keV max (100%) Total mass = 70 kg
5.7 keV average Soft tissue mass = 60 kg
3H radiological half-life: 4490 days Water content = 42 kg
3H biological half-life: 10 days

1.6E 12 ergs per eV

POINTS

25 A. Determine the dose equivalent rate at the floor plates. Show all work.
B. Determine the maximum stay time for the male diver to remove the floor plates assuming he is allowed to receive the maximum allowable legal exposure (without invoking a planned special exposure). For section B only , assume that the gamma dose equivalent rate at the floor plates is 5 rem/h. Show all work.
C. Identify five controls which could be applied to ensure the diver remains below regulatory limits. Number your responses. Only the first five numbered responses will be graded.
10 D. 1. A survey after the dive found skin contamination on the diverµs upper legs from a leak in his suit. List and briefly explain 5 actions that you would take upon discovery of the contamination. Number your responses. Only the first five numbered responses will be graded.
10 2. Bioassay was ordered for the diver. The bladder was voided following completion of the dive, and a urine sample was collected from the diver two hours later. A urine tritium concentration of 1E-2 µCi/ml was measured. Is this measurement valid for dosimetric purposes? Explain your answer.
20 3. Calculate the diver's committed effective dose equivalent (CEDE) assuming no intervention to artificially reduce the tritium concentration stated in D.2 above. Show all work and state all assumptions.

QUESTION 10

A plutonium fire occurs in an inerted glove box as a result of air leakage into the glove box. The glove box contains 500 grams of 239Pu in the form of a fine powder and combustible solvents. The fire burns for 20 minutes immediately causing a breach of the integrity of the glove box and the smoke fills the surrounding room. Normal ventilation is automatically secured and emergency room ventilation starts due to the high airborne radioactivity in the room. The emergency ventilation is exhausted to the atmosphere via a single-stage high efficiency particulate air (HEPA) filter through a 10 meter high stack.

GIVEN

Room dimensions: 6m x 6m x 3m
T½ 239Pu = 24,100 yrs.
Emergency ventilation flow: 7 m3/min.
HEPA filter maximum penetration: 0.05%
DAC 239Pu: 2 x 10-12 µCi/cc
Wind speed: 7 m/s
Stability class C
Graphs of y and z vs distance from Meteorology and Atomic Energy, 1968.

Where: Q'= release rate u=wind speed z=elevation h=stack height
X=concentration y = cross-wind distance

POINTS

10 A. How many curies of 239Pu are contained in the glove box? Show all work.
30 B. Assume 50 Curies of 239Pu are initially present in the glove box. Estimate the 239Pu concentration in air in Ci m-3 in the room 20 minutes after the start of the fire. Assume complete combustion and release of the plutonium at a constant rate. Show all work.
30 C. Assuming an air concentration of 3 10-4 µCi/cm3 in the room when the fire ceases, how much time must elapse before entry can be permitted for an inspection team wearing pressure demand SCBAs (i.e., how long until the room air concentration, expressed as a multiple of DAC, is less than the protection factor for the SCBA). Assume removal by the emergency ventilation flow only. Show all work.
30 D. Emergency ventilation is exhausted to the atmosphere via a single stage high efficiency particulate air (HEPA) filter through a 10 meter high stack. Assuming a constant air concentration of 3 x 10-4µCi/cm3 in the room, what is the air concentration at ground level at the site boundary (on the plume centerline) , which is 1000 m downwind? Show all work.

Figure A.2 Meteorology and Atomic Energy : y versus distance

Figure A.3 Meteorology and Atomic Energy : z versus distance

QUESTION 11

A patient with a thyroid condition is given 131I therapy. The patient receives an oral dose of 100 mCi of 131I. Assume that 30% of 131I is taken up instantaneously by the thyroid and that131I is distributed uniformly in the thyroid. The patient has an unusual thyroid iodine retention rate so the published 131I dose conversion factor cannot be used.

GIVEN:

131I T½ = 8.05 days
Biological T½ in thyroid = 90 days
Thyroid mass = 20 grams
Ave. 131I beta energy = 190 keV
1 eV = 1.6 x 10-19 J

POINTS:

30 A. Using the above information, calculate the absorbed dose to the patientµs thyroid over the first year after the procedure.
B. Regarding patient room preparation by the hospital radiation protection staff:
20 1. State four radiation protection concerns in room prepartation. Number your responses. Only the first four numbered responses will be graded.
20 2. Describe four specific measures that could be taken in room preparation. Number your responses. Only the first four numbered responses will be graded.
20 C. What radiation protection measures/controls should be implemented for the protection of the hospital staff? List four. Number your responses. Only the first four numbered responses will be graded.
10 D. What radiation protection concerns would you have regarding allowing this individual to resume activities as a Radiation Worker at a nuclear power facility ? List two concerns. Number your responses. Only the first two numbered responses will be graded.

QUESTION 12

As the Medical Physicist in a diagnostic medical facility, you are asked to provide advice regarding reduction of breast dose and assistance in establishing a mammographic quality assurance program.

GIVEN

The following information pertains to an anterior-posterior (AP) chest x-ray examination:

Maximum dose equivalent in tissue at midfield position of skin entrance = 300 µSv

Organ Weighting Factor ICRP 26 Fractional Mean Organ Dose Equivalent resulting from Maximum Entrance Dose Equivalent
(mSv/mSv entrance dose)
Gonads
Breast
Bone marrow (red)
Lung
Thyroid
Bone surfaces
Remainder:








Stomach
PancreasSpleen
Esophagus
Liver
Kidneys
0.25
0.15
0.12
0.12
0.03
0.03

0.06
0.06
0.06
0.06
0.06
0.06
0
0.75
0.1
0.4
0.2
0.15

0.4
0.4
0.4
0.4
0.4
0.2
All other organ doses are negligible.

f-factor (exposure in air to dose in tissue conversion) = 0.927 cGy/2.58x 10- 4 C kg-1

POINTS

20 A. Determine the effective dose equivalent (HE) in µSv for an AP chest x-ray examination using the given information. Show all work.
10 B. Suggest a simple modification to the chest x-ray examination which would deliver a greatly reduced mean organ dose equivalent to the breast compared to taking an AP chest x-ray.
10 C. An advantage of reporting (HE) from diagnostic x-ray examinations rather than simply monitoring the skin entrance exposure, is the ability to more accurately express overall patient risk. List two practical disadvantages in the use of (HE). Number your responses. Only the first two numbered responses will be graded.
15 D. The radiation oncologists at this facility inquire about using the (HE) concept for informing patients about doses from radiation therapy. Is it appropriate to use this concept in radiotherapy risk assessment and communication (yes or no)?. Justify your answer.
15 E. NCRP Report Number 85, MAMMOGRAPHY -- A USERµS GUIDE, and the Mammography Quality Control Manual - Medical Physicist's Section from the American College of Radiology's Mammography Quality Control Standards are common medical health physics references. These references acknowledge that the average glandular dose to the breast from mammography can be determined from the incident exposure in air using a conversion factor, DgN . This quantity depends on six factors at most. List three of these six factors. Number your responses. Only the first three numbered responses will be graded.
10 F. A consultant determines that the average glandular dose,DgN , to an average patient at your mammographic facility is 1.07 mGy. Calculate the average glandular dose conversion factor, DgN (in mGy/2.58 x 10- 4 C kg - 1), if the incident exposure in air needed to produce a proper density image is 1.8 x 10- 4 C kg - 1. Show all work.
20 G. List five typical quality assurance tests that a medical health physicist would perform on mammographic x-ray equipment (such as those tests described in the Mammography Quality Control Manual - Medical Physicist's Section from the American College of Radiology). Number your responses. Only the first five numbered responses will be graded.

QUESTION 13

Management at your institution expects you, the Radiation Safety Officer, to be the institutionµs expert about the biological effects and exposure criteria for radiofrequency (RF) and extremely low-frequency (ELF) electromagnetic radiation. Several workers, concerned by newspaper articles they have read, ask you questions about these types of electromagnetic radiation.

POINTS:

30 A. Define the following terms:
1. Electric Field Strength
2. Magnetic Field Strength
3. Poynting Vector
10 B. Provide an example of ELF electromagnetic radiation.
20 C. Sketch a spatial graph of a plane, sinusoidal electromagnetic wave. Your drawing must show how the two oscillating fields relate to each other and to the direction of propagation of the wave. Label your sketch.
20 D. Some workers are concerned about electromagnetic radiation that video display terminals (VDTs) emit. List two sources of electromagnetic radiation in VDTs and describe the radiation. Number your responses. Only the first two numbered responses will be graded.
20 E. According to NCRP Report 86, which biological effect of RF electromagnetic radiation is the primary basis for establishing RF electromagnetic radiation exposure criteria?

QUESTION 14

As the RSO at a university you are asked to estimate the dose to the tissue of an animal which has been injected with a beta-emitting radioisotope. You are also concerned about the possible dose to the hands of a person taking samples of the labeled tissue after the animal has been sacrificed. Potential for external exposures resulting from bremsstrahlung production must also be evaluated.

GIVEN

The animal and the organs in question have dimensions much greater than the range of the beta particles.

32P 33P
Number of betas/decay 1 1
Emax (MeV) 1.71 0.249
Eavg(MeV) 0.695 0.0766
Half-life (days) 14.3 25.4
Approximate half-value layer
for absorption (mg cm- 2)
150 6

1 eV=1.6 x 10-19 J

Beta particle range in mg cm2 = 412 E(1.265 - 0.954 ln E)
E=beta maximum energy, MeV

Bremsstrahlung production: f=3.5x10-4 ZE
f= fraction of energy converted to photons
Z= atomic number of absorber
E= electron energy in MeV

Biological half-life of phosphorus (P) in soft tissue is about 19 days

Atomic number: H=1 N=7
O=8
tissue=7.1
Si=14
Photon attenuation in air at 0.7 MeV
mass energy absorption coefficient = 2.93 m2 kg-1
mass attenuation coefficient = 7.56 m2 kg-1

POINTS

35 A. For an organ with an initial 32P concentration of 5.0107 Bq kg-1 calculate the dose in Gy to the organ in a live animal for a 10 day period. State your assumptions and show all work.
25 B. 1. If the beta dose rate to the tissue inside an organ containing uniformly dispersed 32P is 0.5 Gy hr-1, what is the shallow dose to the fingers of a person holding the organ for 10 minutes while taking tissue samples and wearing gloves with a thickness of 10 mg cm2?
2. What is the shallow dose to the fingers if the radioisotope is 33P?
State your assumptions and show all work.
10 C. Attenuation of the 32P beta particles is approximately exponential for absorber thicknesses less than the range. What characteristic of beta decay accounts for this?
30 D. Calculate the bremsstrahlung dose rate in air at 30 cm from a 0.050 kg block of tissue containing 5.0x107 Bq kg-1 of 32P. Assume that the bremsstrahlung production is from beta particles with the average energy and that the photons also have an energy equal to the average beta particle energy. State your assumptions and show all work.


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