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In this paper, the average energy of the $\gamma$ -photon ( $E_{\mathrm {a},\mathrm{ph}}$ ) is calculated and the correlation between $\log E_{\mathrm{a},\mathrm{ph}}$ and the logarithm of the synchrotron peak frequency ( $\log\nu_{\mathrm{p}}$ ) is discussed for a sample of 620 BL Lac objects. The results show that there exists a positive correlation between the $\gamma$ -photon energy and the synchrotron peak frequency for BL Lac objects, which implies that the $\gamma$ -ray emissions are related to the low-energy emissions of radio to X-ray bands, and the high energetic $\gamma$ -ray emissions are only partially from the synchrotron self-Compton process (SSC) for BL Lac objects.

Monte Carlo N-particle (MCNP) code has been used to simulate the transport of gamma photon rays of different energies (22, 31, 59.5 and 81 keV) to estimate the iron content in solutions. In this study, MCNP simulation results are compared with experiment and XCOM theoretical data. The simulation shows that the obtained results are in good agreement with experimental data, and better than the theoretical XCOM values. The study indicates that MCNP simulation is an excellent tool to estimate the iron concentration in the blood samples. The MCNP code can also be utilized to estimate other trace elements in the blood samples.

Background Intraoperative in situ identification of 18F-FDG-avid tissue sites during radioguided oncologic surgery remains a significant challenge for surgeons. The purpose of our study was to evaluate the 1.5-to-1 ratiometric threshold criteria method versus the three-sigma statistical threshold criteria method for determination of gamma detection probe positivity for intraoperative in situ identification of presumed abnormal 18F-FDG-avid tissue sites in a manner that was independent of the specific type of gamma detection probe used. Methods From among 52 patients undergoing appropriate in situ evaluation of presumed abnormal 18F-FDG-avid tissue sites during 18F-FDG-directed surgery using 6 available gamma detection probe systems, a total of 401 intraoperative gamma detection probe measurement sets of in situ counts per second measurements were cumulatively taken. Results For the 401 intraoperative gamma detection probe measurement sets, probe positivity was successfully met by the 1.5-to-1 ratiometric threshold criteria method in 150/401 instances (37.4%) and by the three-sigma statistical threshold criteria method in 259/401 instances (64.6%) (P

Gamma-ray self-absorption in stainless steel samples has been studied with an experimental method based on fast neutron activation and a Monte Carlo calculation technique adapted to the experimental conditions. A relation between self-absorption and absorption of γ-photons inside stainless steel samples was found. The influence of the γ-ray energy and sample depth have been investigated. Agreement between the two methods has been found.

A sensitive activation technique for the determination of trace levels of oxygen in a wide range of materials is described with particular emphasis on the γ-irradiation facilities at AERE Harwell and experience of the use of the technique over a number of years. Procedures for removing surface oxygen contamination prior to determination of bulk oxygen concentrations are given, together with details of the radiochemical separation procedures used for a wide range of materials, and examples of the results obtained.

A non destructive high energy gamma photon activation technique has been developed for the determination of iodine in a wide range of natural materials. Results are presented and compared with those obtained by independent analytical techniques. Studies of the loss of iodine from soils on heating are also presented. The sensitivity and precision of the technique are discussed and its practical aspects described.

An apparatus ensuring identitical irradiation conditions for three samples and a standard of large volumes is reported. The interference caused by the protons originating from the16O(γ, p)15N reaction is determined. Results show that the secondary rection18O(p, n)18F induced by the protons of the former reaction gives an apparent fluorine content in natural waters of 0.015 μg/g for a maximum gamma photon beam energy of 21 MeV.

The concentration of carbon and oxygen has been measured in various samples of LEC–grown InP and GaAs crystals using gamma photon activation analysis and mass spectrometry. The concentration of these elements was found to be extremely low (0.1–0.3 ppma) contrary to previouslyreported work.