Direct Penetrating Radiation at LANL

Overview

Direct Penetrating Radiation Overview

Naturally occurring external penetrating radiation originates from terrestrial and cosmic sources in the form of gamma rays, neutral particles, and charged particles. Human-made radiation consists of the same types of radiation.

To evaluate natural and human-made direct penetrating radiation (DPR) in our ambient environment, the Laboratory's environmental monitoring program uses thermoluminescent dosimeters (TLDs). Because the doses from natural background terrestrial and cosmic sources are much larger than those from human-made sources, it is extremely difficult to distinguish human-made sources from the natural background. In fact, the annual variation in natural background is much larger than the entire LANL contribution.

Most terrestrial DPR comes from naturally occurring ⁴⁰K, radionuclides in the thorium and uranium decay chains, and radionuclides deposited as a result of nuclear atmospheric testing
(e.g., ⁹⁰Sr and ¹³⁷Cs). Terrestrial radiation varies daily, seasonally, and geographically. These levels can vary from 15% to 25% at a given location because of changes in soil moisture and snow cover that reduces or blocks the radiation (NCRP 1975). Different soil types also affect radiation levels. Placement of the dosimeters is important because dosimeters that are placed in a narrow canyon will receive terrestrial radiation from the walls and the floor of the canyon and will show higher exposures than dosimeters placed on a flat surface where no walls are nearby.

Cosmic radiation doses increase with increasing elevation because there is less atmosphere to attenuate the radiation. At sea level, the dose from cosmic radiation is between 25 and 30 mrem/yr. Because of our elevation, we in Los Alamos receive about 70 mrem/yr dose from cosmic sources. Different locations in the region range in elevation from about 1.7 km (1.1 mi) at Española to 2.7 km (1.7 mi) at the Pajarito Ski Hill, resulting in a corresponding range of 50 to 90 mrem/yr from cosmic radiation. Cosmic radiation can vary ±10% because of solar modulations (NCRP 1987). The fluctuations of terrestrial and cosmic radiation sources make it difficult to detect an increase in radiation levels from LANL sources, which are typically much smaller than the magnitude of the natural fluctuations.

Terrestrial exposure rates for Los Alamos National Laboratory areas have been mapped along side a contour map of the site, click here to view.

Network

Direct Penetrating Radiation Monitoring Network

In an attempt to evaluate the impact from Laboratory operations, TLDs are placed around the Laboratory and in the surrounding communities. This network of dosimeters is divided into three groups: off-site (regional), off-site perimeter, and on-site.

The regional group has several locations ranging from approximately 7 to 60 km (4 to 38 mi) from the Laboratory boundary. These regional stations are located in the neighboring communities of Española, El Rancho, Santa Fe, San Ildefonso Pueblo, and Santa Clara Pueblo.

The off-site perimeter group has about 15 locations within 4 km (2.5 mi) of the Laboratory boundary (see Figure 4-13 1975 ESR). These stations are placed in residential areas surrounding the Laboratory and in locations where people work.

The on-site locations are within Laboratory boundaries, generally around operations that may produce ionizing radiation. Many of these stations are located near TA-54 (waste characterization, packaging, disposal, and other operations) and TA-53 LANSCE.

The environmental TLDs we use are the standard LANL dosimeters known as "Model 8823." After exposure to radiation, the TLD chips are collected, then heated in a laboratory to measure the energy stored in the crystal. This stored energy is released in the form of light that is proportional to the amount of radiation absorbed by the TLD.

Stations

DPRNET Monitoring Stations

The DPRNET monitoring equipment is or has been sited at over 250 locations in northern New Mexico since the program's inception. The locations are selected according to the criteria in LA-UR-00-1168.

DPRNET Station Locations and Operating Dates

Data

Direct Environmental Penetrating Radiation Data

LANL monitors DPR at more than 100 stations in the environment of Los Alamos County and its nearby communities.

Data are included in the annual Environmental Surveillance Reports (ESRs), as well as a description of the monitoring program. Each yearly ESR discusses the particular stations where a dose from LANL is measurable above the natural radioactivity background dose of 25 to 50 mrem per quarter.

• Quarterly Dose Summaries 1999-2006
• Annual Dose Summaries 1974-1998

News

Direct Penetrating Radiation Program Updates

Calendar Year 2007 Program Changes
We continue to monitor at 90 stations as follows.

• Population centers - In addition to Los Alamos and White Rock, we continue to monitor at Espanola, Santa Fe, San Ildefonso Pueblo, Santa Clara Pueblo, and El Rancho.
• AIRNET Stations - We monitor for DPR at all 40 active AIRNET stations.
• LANSCE - The Los Alamos Neutron Science Center, LANSCE, is monitored by a ring of eight stations (numbers 19, 64, 65, 114, 115, 123, 124, 125).
• MDA G - Material Disposal Area (MDA) G is monitored by a ring of 33 stations, numbered 601 through 652.

Summary
We continue to monitor for DPR at 40 AIRNET stations and about 50 additional locations, including the locations where a public dose of more than 5 mrem/year is credible. We welcome your comments and questions concerning other locations.

Albedo TLDs

Albedo Dosimeters for Environmental Neutron Monitoring

The Consent Decree between the Department of Energy and the Concerned Citizen's for Nuclear Safety required that seven albedo TLDs be placed on the north, south, and east sides of TA-18. The albedo TLDs were operated for a period of five years, from 1997-Q2 through 2002-Q1.

• Results of External Radiation Monitoring Dosimeters