No abstract

Auger electrons emitted after nuclear decay have potential application in targeted cancer therapy. For this purpose it is important to know the Auger electron yield per nuclear decay. In this work we describe a measurement of the ratio of the number of conversion electrons (emitted as part of the nuclear decay process) to the number of Auger electrons (emitted as part of the atomic relaxation process after the nuclear decay) for the case of I. Results are compared with Monte-Carlo type simulations of the relaxation cascade using the BrIccEmis code. Our results indicate that forI the calculations based on rates from the Evaluated Atomic Data Library underestimate the K Auger yields by 20%.

Auger electron emitters (AEEs) are attractive tools in targeted radionuclide therapy to specifically irradiate tumour cells while sparing healthy tissues. However, because of their short range, AEEs need to be brought close to sensitive targets, particularly nuclear DNA, and to a lower extent, cell membrane. Therefore, radioimmunoconjugates (RIC) have been developed for specific tumour cell targeting and transportation to the nucleus. Herein, we assessed, in A-431CEA-luc and SK-OV-31B9 cancer cells that express low and high levels of HER2 receptors, two 111In-RIC consisting of the anti-HER2 antibody trastuzumab conjugated to NLS or TAT peptides for nuclear delivery. We found that NLS and TAT peptides improved the nuclear uptake of 111In-trastuzumab conjugates, but this effect was limited and non-specific. Moreover, it did not result in a drastic decrease of clonogenic survival. Indium-111 also contributed to non-specific cytotoxicity in vitro due to conversion electrons (30% of the cell killing). Comparison with [125I]I-UdR showed that the energy released in the cell nucleus by increasing the RIC’s nuclear uptake or by choosing an AEE that releases more energy per decay should be 5 to 10 times higher to observe a significant therapeutic effect. Therefore, new Auger-based radiopharmaceuticals need to be developed.

The conversion electrons from the decay of the 35.5-keV excited state of 125 Te following the electron capture decay of 125 I have been investigated at high resolution using an electrostatic spectrometer. The penetration parameter λ = −1.2(6) and mixing ratio |δ(E2/M 1)| = 0.015(2) were deduced by fitting to literature values and present data. The shake probability of the conversion electrons is estimated to be 0.5, more than two times larger than the predicted value of 0.2.

The emergence of nuclear collectivity near doubly-magic 132 Sn was explored along the stable, eveneven 124−130 Te isotopes. Preliminary measurements of the B(E2; 4 + 1 → 2 + 1 ) transition strengths are reported from Coulomb excitation experiments primarily aimed at measuring the g factors of the 4 + 1 states. Isotopically enriched Te targets were excited by 198-205 MeV 58 Ni beams. A comparison of transition strengths obtained is made to large-scale shell-model calculations with successes and limitations discussed.