Experimental investigation of the effect of oxygen on the positron annihilation mechanisms in liquids

Treatment of cancer patients requires high-sensitivity diagnostic techniques. Recently, the Society of Positron Annihilation Spectroscopy (PAS) has been working on hypoxia detection using positron lifetime and hopes to diagnose cancer at its initial phases. The accepted hypothesis for the use of positron as a biomarker of tumor hypoxia is that due to the distance between the blood vessels and the cancerous tissues, the oxygen concentration strongly decreases in cancerous tissues. The point that can put the PAS technique in the category of cancer diagnosis tools is its potential capability for oxygen-sensing in tissues. So, the partial pressure of oxygen in the patient’s tissues can be measured from the Positron Annihilation Lifetime Spectroscopy (PALS). However, before the positron lifetime imaging technique can be established, it is essential to verify the oxygen-sensing capability of the PALS in various chemical environments. In this paper, the mechanisms of positron annihilation in the deionized water and air-bubbled water samples were investigated via systematic experiments by our homemade Doppler Broadening Spectroscopy (DBS) and PALS spectrometer. Three mechanisms for positron annihilation in the investigated liquid samples including oxidation, Positronium conversion, and Positronium inhibition were described. The outcome of this investigation could advance the development of the PALS method for detecting tumors before metastasis, using the J-PET machine, which is still under development at Jagiellonian University.

Experimental investigation of the effect of oxygen on the positron annihilation mechanisms in liquids Keywords:

Positronium , Lifetime , PAS , Tumor , hypoxia