Details

Autor(en) / Beteiligte

• Willms, R S
• Dogruel, D
• Myers, R
• Farrell, R

Titel

A new solid state tritium surface monitor

Ort / Verlag

United States

Erscheinungsjahr

2004

Link zum Volltext

Quelle

Taylor & Francis Journals Auto-Holdings Collection

Beschreibungen/Notizen

• Traditionally the amount of tritium on a surface is determined by swiping the surface with a material such as filter paper and counting the removed tritium by scintillation. While effective, this method can be time consuming, can alter the surface and only measures removable tritium. For a given application each of these considerations may or may not be a disadvantage. A solid state monitor, on the other hand, has the potential to provide rapid analysis, not alter the surface and measure all tritium on a surface. This allure has promoted open wall ion chamber and PIN diode-based tritium surface monitor development, and these techniques have enjoyed certain success. Recently the first tests were performed with an avalanche photodiode (APD) for surface tritium measurement. The tritium surface concentration is determined by placing the APD within a few millimeters of the surface of interest. Beta decay from the surface tritium impacts the APD resulting in amplified current through the diode. Analysis of this signal with a multi-channel analyzer enables counting of beta decay events and determination of the beta energy spectrum. While quite similar in concept to PIN diode based measurements, side-by-side testing showed that the APD provided substantially better counting efficiency. Considerations included count rate, background, sensitivity, stability and effect of ambient light. An important factor in the U.S. for a tritium surface monitor is the ability to measure concentrations down to the 'free release' limit, i.e., the concentration below which items can be removed from radiological control areas. The two limits being used are 10,000 disintegrations per min (dpm)/100 cm{sup 2} and 1,000 dpm/100 cm{sup 2}. Present tests show that the APD is capable of measuring down to 1,000 dpm/100 cm{sup 2} in reasonable count times. Data from this promising technique will be presented in this paper.