The variations in long term TLD measurements of environmental background radiation at locations in southeastern New York state and northern New Jersey.

The variations of the measured dose rate in air should be recognized especially where background radiation is used as a comparative benchmark to assess radiation surveillance and environmental remediation work. In this note, the natural variations of the combined gamma and cosmic-ray background air-dose rate as measured by lithium fluoride thermoluminescence dosimeters are reported. The dosimeters were deployed monthly at locations within 150 km of the Environmental Measurements Laboratory in New York City. Urban and suburban stations were established with simultaneous indoor and outdoor measurements at some locations. Measurements were obtained over 10 to 18 years. The mean air-dose rates from the six outdoor and four indoor stations vary from 50.8 to 123.1 nGy h{sup -1}. The range of the annual dose rates expressed as a percent-difference of the minimum and maximum is 5.3 to 18.0%. Commonly, 1-mo deviations from the long term mean of about {+-}10 to {+-}25% are observed. An abrupt decrease in the annual dose rate at one of the measurement sites was attributed to a minor relocation of a dosimeter. Structural shielding factors for the first and second floors of a residence are reported. The ground level location of a dosimeter inside another residence apparently resultedmore » in a very high shielding factor. Finally, a gradual decrease of the dose rate at most of the stations is shown to exist (approximately -0.3 nGy h{sup -1} y{sup -1} for the outdoor stations). Plausible causes of this trend are briefly discussed. 24 refs., 6 figs., 2 tabs.« less