News and Discussions > Site News
HP Essay question.
Rennhack:
Today is October 3rd, 2004. You are an ALARA engineer in a pre-job briefing. You have been informed that a NDE tech has dropped his source through a grate in the floor in the Rx Building. It has landed on a 3 inch valve with that sits one and a half feet behind a half inch wall of lead which has manipulator arms. You are familiar with the valve. It is shielded because inside it is 10 grams of Cobalt 60. You also know that it is about a ten min. journey from the air lock.
The Rx is at 50% power. Remote detectors tell you there is a neutron field in that area reading 30 mRad/hr. The source certificate the NDE tech hands you states that on September 11th, 2001 his Ir-192 source had an activity of 1.4 Curies.
An operator in the room tells you that he is familiar with the remote manipulators in that location, because he uses them on a regular basis to operate the valve. He estimates that he can retrieve the source, and deposit it back in its shielded container in fifteen minutes.
What would the total man rem exposure for this job be?
wave_theory:
Zero. Job cancelled when I calculate Ir-192 source activity. NDE tech fired.
Rennhack:
--- Quote ---Zero. Job cancelled when you calculate Ir-192 source activity. NDE tech fired.
--- End quote ---
Wrong. 667 mRem is hardly a job stopper.
--- Quote ---MeV & Yield for Ir-192
0.316 0.87
0.486 0.52
0.308 0.32
0.295 0.3
6CEN = 6 Rem/hr @ 1 foot
667 mRem/.25 hr @ 18 inches
(Still not taking into account the shield.)
--- End quote ---
HVL for Pb
0.5 MeV = .38 cm
1.0 MeV = .86 cm
1.5 MeV = 1.2 cm
2.0 MeV = 1.3 cm
I=IO(.5)n
Need more help? I thought 'yous-guys' were smarty-pants.
maxparity:
Mr. Rennhack,
I agree with you that some of "uss guise" wear trousers of at least a fair degree of intellect("smarty pants").Being that as it is or is not, I will suggest to you sir that if the given data you put out is indeed the data to be used in your little brain teaser,then before you offer up your massive intellect to help us lesser gifted than yourself,you may consider decay-correcting your source prior to using it in the rest of your calculations.Although I had to make an assumption as to the deposition time of the Cobalt in the valve as it was not given,I have that answer directly in front of me in case you encounter any further difficulties.Have a great day and Karma to all.
Rennhack:
When I said
--- Quote ---“Need more help? I thought 'yous-guys' were smarty-pants.”
--- End quote ---
I was only trying to stimulate interest in the question, to challenge others, I was not trying to be a smart ass, or offend you.
As for decay correction...I only gave an example, not the answer... I was showing that the exposure was not great. (Hence, I neither decay corrected, nor took into account the shielding.)
It is a question to help those that wish to exercise their minds the ability to do so. No one is required by law to try to answer the question. Attitudes should be left at the door.
FYI:
Strong Gamma-rays from Decay of Ir-192
This table was derived from ENSDF as of September 1993.
Gamma-ray
energy(keV) Intensity(%) Decay mode / Half-life
-------------------------------------------------------
56.68 -- IT 1.45 M
295.96 -- B- 1.45 M
316.51 -- B- 1.45 M
612.47 -- B- 1.45 M
-------------------------------------------------------
155.16 -- IT 241 Y
-------------------------------------------------------
205.8 3.3 EC 73.831 D
308.46 30. B- 73.831 D
316.51 82.8 B- 73.831 D
374.49 0.72 EC 73.831 D
468.07 47.8 B- 73.831 D
484.58 3.18 EC 73.831 D
-------------------------------------------------------
Navigation
[0] Message Index
[#] Next page
Go to full version