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" W
R=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....
