Performance Criteria for Fixed Monitoring Instruments

DOE-STD-1128-98

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 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.

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