NukeWorker Forum
Career Path => Training, Tests & Education => Topic started by: JenCrabtree on May 14, 2020, 05:01
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Hello Everyone!!! Hope all is well. I have another question:
I looked online about QF charts. I noticed that some have the Thermo Neutron as 5 and some has them as 3. Which one do I believe?
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Depends on who is giving the test....I've always used 3.
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Not sure about a Thermo Neutron, but a thermal neutron would be 3.
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Quality factor is closely related to linear energy transfer (LET). They both depend on the energy of the Neutron. So using a rounded off number lilke 2, 3 or 5 is assuming your neutron is at that exact speed (energy level).
US NRC values:
Ave Neutron Energy (in MeV), Q
Thermal, 2
0.0001, 2
0.001, 2
0.01, 2.5
0.1, 7.5
0.5, 11
1.0, 11
2.5, 9
5.0, 8
10, 6.5
100, 4
But wait, there's more!
Up until 1986, the international commissions, NCRP and the NRC all agreed on approximate Q values. Then, the joint ICRU/ICRP task force concluded that enough new biological data was at hand to allow a recalculation of approximate Q values for common field conditions. Not to be outdone, the NCRP followed suit in a 1987 document (Report 91) by recommending a new set of approximate Q values. In 1990, the ICRP abandoned the term Q in favor of wR. In 1991, new 10 CFR 20 regulations went into effect for U.S. NRC licensees. These regulations continued the old NRC Q values completely unchanged.
The weighting factors multiplied by total lifetime fatal cancer risk give the probability of dying by a cancer starting in the respective organs. But the more recent ICRP factors use a cancer risk of 5 x 10-4 /rem while the other organization’s factors were based on a lifetime fatal cancer risk of 1 x 10-4 /rem.
There are different organizations (NRC, DOE, ICRP, NCRP). Some stick with the 'old' ways, and some adapt to new methodology.
The NRC likes the old way. The old way is "Quality Factor (QF) and the NRC never changed. They use QF=2 for a 'slow' neutron.The old NUF material said 2 for a Thermal Neutron, because its NRC based.
The NCRP uses QF=5
The new way is to call it a Radiation Weight factor.
The 2007 ICRP uses "Weighting Factor" WR=2.5 It averages the absorbed dose over a tissue or organ rather than at a point.
In the DOE Core study guide, 1.06 - RADIOACTIVITY AND RADIOACTIVE DECAY, Table 7, under Quality factor it says:
"Slow" Neutron, 10 keV QF = 3
Which is really just 2.5 rounded off.
so...
Depends on who is giving the test....
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Quality factor is closely related to linear energy transfer (LET). They both depend on the energy of the Neutron. So using a rounded off number lilke 2, 3 or 5 is assuming your neutron is at that exact speed (energy level).
Hmmm... don't have a citation for this but as I remember it from a Health Physics magazine a few decades ago energies over 15 Mev were relativistic and exposure had more to do with secondary interactions. This made the design of space ships and extra vehicular space suits a balance of attenuating soft gamma and x-ray and producing an increase in dose from secondary radiation from high energy particulates including lower energy neutrons.
My [2cents] from a shaky old memory. Over 15 mev outside of an accelerator or space is not likely. Yes I know this is not helpful to the OP and I am just bloviating out of boredom, time to Zoom the family. The take away is the uselessness of some of the theory that we expect technicians to know especially with conflicting data. Alas one must regurgitate the information the testers want to see as stated by "hamsamich".
:old:
[coffee]
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Thanks everyone!! You all have been very helpful.
Hope everyone has a great weekend!!!!
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Hmmm... don't have a citation for this but as I remember it from a Health Physics magazine a few decades ago energies over 15 Mev were relativistic and exposure had more to do with secondary interactions.
You mean 13 TeV, not 15 Mev.
eV > KeV > MeV > GeV > TeV > PeV > EeV
A relativistic neutron is a neutron which moves with a relativistic speed; that is, a speed comparable to the speed of light.
Neutrons are relativistic when their kinetic energy is comparable to or greater than the energy corresponding to their rest mass. In other words, a neutron is relativistic when its total mass-energy (rest mass + kinetic energy) is at least twice its rest mass. This condition implies that the neutron's speed is close to the speed of light. This requires the particle to move at 86% or more of the speed of light.
Such relativistic neutron are generated in the Relativistic Heavy Ion Collider (RHIC) & Large Hadron Collider (LHC), as well as naturally occurring in cosmic radiation.
For example, at the Large Hadron Collider operating with a collision energy of 13 TeV, a relativistic neutron has a mass-energy 6,927 times greater than its rest mass and travels at 99.999998958% of the speed of light.
At the RHIC, The projectiles typically travel at a speed of 99.995% of the speed of light. For Au + Au collisions, the center-of-mass energy is typically 200 GeV per nucleon-pair, and was as low as 7.7 GeV per nucleon-pair. (Because its so heavy, it can go slower). Run-9 achieved center-of-mass energy of 500 GeV on 12 February 2009.
Cosmic Rays range from GeV to EeV
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You mean 13 TeV, not 15 Mev.
eV > KeV > MeV > GeV > TeV > PeV > EeV
A relativistic neutron is a neutron which moves with a relativistic speed; that is, a speed comparable to the speed of light.
Neutrons are relativistic when their kinetic energy is comparable to or greater than the energy corresponding to their rest mass. In other words, a neutron is relativistic when its total mass-energy (rest mass + kinetic energy) is at least twice its rest mass. This condition implies that the neutron's speed is close to the speed of light. This requires the particle to move at 86% or more of the speed of light.
Such relativistic neutron are generated in the Relativistic Heavy Ion Collider (RHIC) & Large Hadron Collider (LHC), as well as naturally occurring in cosmic radiation.
For example, at the Large Hadron Collider operating with a collision energy of 13 TeV, a relativistic neutron has a mass-energy 6,927 times greater than its rest mass and travels at 99.999998958% of the speed of light.
At the RHIC, The projectiles typically travel at a speed of 99.995% of the speed of light. For Au + Au collisions, the center-of-mass energy is typically 200 GeV per nucleon-pair, and was as low as 7.7 GeV per nucleon-pair. (Because its so heavy, it can go slower). Run-9 achieved center-of-mass energy of 500 GeV on 12 February 2009.
Cosmic Rays range from GeV to EeV
this is why scientists are the worst people for making a definitive decision -> there's never enough data,....
meanwhile world's collide, cats sleep with dogs, women and children die and whole societies collapse,...
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Has anybody noticed that personal neutron dosimetry seems to measure neutron dose lower than neutron radiacs.
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Has anybody noticed that personal neutron dosimetry seems to measure neutron dose lower than neutron radiacs.
yep, that's pert much on purpose and the nature of the beast,....
neutron "dose" is highly dependent on energy, handheld meters are calibrated to allow over compenstation,....
dosimetry does not (over compensate),....
it's only common sense ( and that ALARA crap) to use work controls which produce a lower legal dose record,...
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yep, that's pert much on purpose and the nature of the beast,....
neutron "dose" is highly dependent on energy, handheld meters are calibrated to allow over compenstation,....
dosimetry does not (over compensate),....
it's only common sense ( and that ALARA crap) to use work controls which produce a lower legal dose record,...
Agree and another way to put it is field work uses conservative controls and measurements for risk assessment. More accurate measurements are done by engineers, Health Physicists and dosimetry personnel reporting legal exposure to regulators.
My [2cents] being bored at home.
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The same holds true for gamma instrumentation/EPD/TLD (excuse me... DLR) ratios.