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DOE-STD-1128-98
Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities
Experience has shown that 20% over very low energy to 1.25 MeV is more
realistic. This specification applies to a specific window selection (e.g., below 0.05
MeV, the electron equilibrium cap or beta shield must be removed).
According to ANSI N317 (ANSI, 1980a), the response of neutron survey
instruments for neutron energies in the range of thermal to 10 MeV shall
approximate the dose equivalents given in that standard for instruments that are
designed for dose equivalent rate measurements. The angular response for neutron
instruments should be within 15% in a 2B steradian frontal direction for 252Cf
energy neutrons or equivalent. The operating range is to be from 0 to at least
2000 mrem/h.
ANSI N42.17A (ANSI, 1988b) has a broader scope than ANSI N317 (ANSI,
1980a) but the criteria in it apply to portable survey instruments. Additional
criteria include geotropism (maximum change of 6% from reference reading for all
orientations), temperature shock, mechanical shock, vibration, and ambient
pressure (maximum change of 15% from reference reading for the latter four
criteria). Some differences exist between ANSI N42.17A and ANSI N317. In
most cases, the criteria for ANSI N42.17A are more applicable because these
criteria are based on substantial testing, which was sponsored by DOE. In ANSI
N42.17A, precision is tied into a measurement level; for example, it quotes a
precision of 15% at <500 cpm and 10% at >500 cpm. Also, with the advent of
liquid crystal displays and other digital readouts, "response time" is defined as the
time it takes for the reading to move from 10% to 90% of the equilibrium or
steady-state reading. Another significant difference in the standard is that the
battery lifetime specification is 100 hours instead of the 200 hours mentioned in
ANSI N317.
For direct alpha contamination surveys, the use of audible signals (headphones or
speaker) greatly facilitates the detection of "hot spots."
IEC Publication 325 (IEC, 1981) provides additional guidance on the uniformity of
probe response for alpha and beta contamination meters. Surface sensitivity
measurements are also discussed in this standard.
3.5.2.2 Performance Criteria for Fixed Monitoring Instruments
Airborne contamination monitors, surface contamination monitors, photon and
neutron area monitors, and emergency instrumentation are fixed monitoring
instruments subject to the following standard performance criteria.
3-19


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