A semi-empirical relation which can be used to determine the total attenuation cross sections of samples containing H, C, N and O in the energy range 145–1332 keV has been derived based on the total attenuation cross sections of several sugars, amino acids and fatty acids. The cross sections have been measured by performing transmission experiments in a narrow beam good geometry set-up by employing a high-resolution hyperpure germanium detector at seven energies of biological importance such as 145.4 keV, 279.2 keV, 514 keV, 661.6 keV, 1115.5 keV, 1173.2 keV and 1332.1 keV. The semi-empirical relation can reproduce the experimental values within 1–2%. The total attenuation cross sections of five elements carbon, aluminium, titanium, copper and zirconium measured in the same experimental set-up at the energies mentioned above have been used in a new matrix method to evaluate the effective atomic numbers and the effective electron densities of samples such as cholesterol, fatty acids, sugars and amino acids containing H, C, N and O atoms from their effective atomic cross sections. The effective atomic cross sections are the total attenuation cross sections divided by the total number of atoms of all types in a particular sample. Further, a quantity called the effective atomic weight was defined as the ratio of the molecular weight of a sample to the total number of atoms of all types in it. The variation of the effective atomic number was systematically studied with respect to the effective atomic weight and a new semi-empirical relation for Zeff has been evolved. It is felt that this relation can be very useful to determine the effective atomic number of any sample having H, C, N and O atoms in the energy range 145–1332 keV irrespective of its chemical structure.

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We report here a simple Compton scattering experiment which may be carried out in graduate and undergraduate laboratories to determine the rest mass energy of the electron. In the present experiment, we have measured the energies of the Compton scattered gamma rays with a NaI(Tl) gamma ray spectrometer coupled to a 1 K multichannel analyzer at five scattering angles of θ = 30 • , 50 • , 60 • , 70 • and 80 • using a 137 Cs radioactive gamma source and a suitable aluminum absorber. The rest mass energy of the electron is determined as the reciprocal of the slope of the plot of parameter S versus (1 − cos θ ). The obtained value is found to agree with the standard value.

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In this work, we have made an effort to determine whether the effective atomic numbers of H-, C-, N-and O-based composite materials would indeed remain a constant over the energy grid of 280-1200 keV wherein incoherent scattering dominates their interaction with photons. For this purpose, the differential incoherent scattering cross-sections of Be, C, Mg, Al, Ca and Ti were measured for three scattering angles 60 • , 80 • and 100 • at 279.1, 661.6 and 1115.5 keV using which an expression for the effective atomic number was derived. The differential incoherent scattering cross-sections of the composite materials of interest measured at these three angles in the same set-up and substituted in this expression would yield their effective atomic number at the three energies. Results obtained in this manner for bakelite, nylon, epoxy, teflon, perspex and some sugars, fatty acids as well as amino acids agreed to within 2% of some of the other available values. It was also observed that for each of these samples, Z eff was almost a constant at the three energies which unambiguously justified the conclusions drawn by other authors earlier [Manjunathaguru and Umesh, J. Phys. B: At. Mol. Opt. Phys. 39, 3969 (2006); Manohara et al, Nucl. Instrum. Methods B266, 3906 (2008); Manohara et al Phys. Med. Biol. 53, M377 (2008)] based on total interaction cross-sections in the energy grid of interest.

One of the most recognized and widely used treatment modality in cancer is radiation therapy which depends on the radiosensitivity of tumour tissue. Over the past few years there has been lot of interest in the use of formulations to enhance radiotherapeutic effects, especially using metallic (mainly gold) based nanoparticles. Our goal here is to fabricate nanoparticles (NPs) that can be delivered to tumor tissue to increase its radiosensitivity. This would increase efficiency of radiation absorption by the tumor tissue and reduce radiation doses delivered during radiotherapy. This could potentially decrease radiation exposure related side effects to patients. We have achieved this by synthesizing nanoparticles of high Z elements such as gold, silver and a more efficient bimetallic silver-gold size ranging from 3nm to 72nm using chemical reduction and hydrothermal method. The synthesized metallic nanoparticles were characterised using Ultraviolet (UV)-Visible Spectroscopy, Fluorescence spectroscopy and Dynamic Light Scattering. The metallic nanoparticles showed radiosensitizing activity in colloidal form by absorbing radiations when irradiated by 60 Co source which emits two gamma rays of energy 1173keV and 1332keV. Based on our results, we are of the opinion that such radio-sensitizing agent if injected into the tumour tissue would increase radiation absorption and enhance treatment effect with lower therapeutic radiation dosage.

The total interaction cross sections (σt) of some sugars and amino acids and five elements: lithium, carbon, oxygen, aluminium and calcium have been measured for 6.4 keV, 13.95 keV, 14.4 keV, 17.74 keV, 24.14 keV, 30.8 keV, 35 keV, 59.54 keV, 81 keV, 122 keV and 136 keV photons in a narrow beam good geometry set up, by using high resolution detectors such as a Si-PIN diode detector and a high purity germanium detector. The σt values have been used in a matrix method to evaluate the effective atomic numbers Zeff of the samples from their effective atomic cross sections σa. The effective atomic cross section of a sample σa is the total interaction cross section divided by the total number of atoms of all types in it. Further, a quantity called the effective atomic weight Aeff of a sample was defined as the ratio of the molecular weight A to the total number of atoms of all types in it. The variation of Zeff was systematically studied with respect to Aeff as well as σa at each experimental energy separately and new semi-empirical relations for Zeff have been evolved. It is felt that these relations can be very convenient for determining the effective atomic number of any sample having H, C, N and O atoms in the energy range 6.4 keV–136 keV irrespective of its chemical structure.