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
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 2 π
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.
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