We have investigated the basic operation of a composite detector comprising of elements arranged in the shape of an U-shaped rectangular well. Considering an isotropic scattering of gamma-rays and partial energy absorptions in up to four detector modules, expressions for the addback factor and the peak-to-total ratio have been obtained in terms of only one probability amplitude. We have compared the performance of two U-shaped detectors having different geometries and observed negligible gain in addback due to the longer arms. For completeness, comparisons have been made with composite detectors like the two element stacked detector and the two level pyramidal detector, both being embedded inside the U-shaped detector. Our pen-on-paper approach could be used to understand the operation of modern arrays having detector elements arranged in various sophisticated ways.

We report the investigation of the module-wise absorptions of a sixteen element composite detector arranged in the shape of a four level pyramid. Using the simplifying assumptions of the isotropic scattering of gamma-rays, equal absorption probabilities of successive gamma scatterings inside the detector, and up to fourth order interactions of gamma-rays, the gamma-ray absorptions in each module of the composite detector are studied. This basic study gives us a quantitative estimate of the contribution of each module to the full energy peak efficiency during the addback mode. Predictions have been compared with that of the four element stacked detector.

A didactic approach has been presented for the understanding of operation of the stacked or series combination of gamma-ray detectors. Assuming isotropic scattering of gamma-rays, we have obtained expressions for the addback factor in terms of only one probability. Using the experimental data of the HHS spectrometer, we have predicted the addback factor for various stacked detectors. This generalised technique could be used to predict the performance parameters of a stacked detector with any number of elements. Other than simulation studies, we present an intuitive way of understanding the operation of series detectors.

We have presented a probabilistic formalism for predicting the response of the series and parallel combination of gamma-ray detectors arranged in the form of a matrix. Assuming isotropic scattering of incident gamma-rays and considering up to four detector hit events, we have obtained expressions for the addback factor and the peak-to-total ratio (in the addback mode) in terms of only one probability. Using the experimental data of the HHS spectrometer, we have predicted the addback factor for four composite detectors. Predicted values of addback factor and fold distribution show a reasonable agreement with the experimental ones for the clover detector.

We have investigated the operation of a composite detector comprising of elements arranged in the shape of a well. A probabilistic formalism is introduced in terms of only one probability amplitude. Considering up to four detector hit events, gamma-ray absorptions and gamma-ray scatterings both inside and outside the composite detector are studied. Our results show that there are three groups of modules based on the values of the peak-to-background ratio of a module.

A probabilistic approach has been presented for modeling the spectrometer for INTEGRAL satellite (SPI). We have considered the isotropic scattering of gamma-rays inside the detector, as well as the equal absorption probabilities of successive gamma scatterings inside the detector. Expressions are obtained for the addback factor and the peak-to-total ratio in terms of two parameters. Results have been compared with experimental data.

In a recent paper, an experimentally validated first principle approach has been introduced for modeling a composite detector consisting of several high-purity germanium detector modules having hexagonal shapes [JINST 7, P07006 (2012)]. In the present paper, a similar modeling approach has been applied for clover-type detectors having square shapes. The performance parameters like addback factor and peak-to-total ratio could be understood in terms of the probability of full energy peak absorption of gamma-ray after multiple detector interaction (α). We suggest a simple formalism for calculating α for clover-type detectors with various geometries.

We present a phenomenological approach of understanding the operation of the Clover germanium detector. Using the simplifying assumptions of the isotropic scattering of gamma-rays, equal absorption probabilities of successive gamma scatterings inside the detector, and up to fourth order interactions of gamma-rays, we have obtained expressions for performance parameters like the addback factor and the peak-to-total ratio in terms of the probability of full energy peak absorption of gamma-ray after single detector interaction. Results have been compared with available experimental data.

In modern gamma-ray spectroscopy experiments, various shapes and sizes of detectors are being used. In this paper, for the first time in literature, we have used a first principle approach to model composite detector consisting of triangular shaped detector modules, using a probabilistic method similar to our previously published work [JINST 7 (2012) P07006], where the emphasis was on the hexagonal shape of the detector modules. Expressions for the addback factor and peak-to-total ratio have been obtained in terms of the probability of full energy peak absorption of the gamma-ray after single detector interaction and the ratio of covered lateral surface area to total lateral surface area of the composite detector. Our work could provide insight in developing new detectors for gamma-ray spectroscopy.

High spin states of $^{37}\mathrm{Ar}$, populated through the $^{27}\mathrm{Al}(^{12}\mathrm{C},np)^{37}\mathrm{Ar}$ reaction with a 40 MeV $^{12}\mathrm{C}$ beam, were studied using the Indian National Gamma Array (INGA) facility. The existing level scheme has been extended up to 10.5 MeV by adding some new levels and transitions. The spins and parities of the new levels were assigned from ${R}_{\mathrm{DCO}}$, ${R}_{\mathrm{ADO}}$, and linear polarization measurements. The spins and parities of the existing levels also were modified or confirmed in the present experiment. The multipole mixing ratios ($\ensuremath{\delta}$) for most of the transitions were measured and compared with the earlier measurements wherever available. Large basis shell model calculations with different particle restrictions in $sd$ and $pf$ orbitals were performed to understand the microscopic origin of these levels. A simple two-level mixing calculation was also performed to extract the amount of multiparticle multihole configuration mixing for a few levels.

We used the 8$\pi$ $\gamma$-ray spectrometer at the TRIUMF-ISAC radiocative ion beam facility to obtain high-precision branching ratios for $^{19}$Ne $\beta^+$ decay to excited states in $^{19}$F. Together with other previous work, our measurements determine the superallowed $1/2^+ \to 1/2^+$ beta branch to the ground state in $^{19}$F to be 99.9878(7)\%, which is three times more precise than known previously. The implications of these measurements for testing a variety of weak interaction symmetries are discussed briefly.

Motivated by the various shapes and configurations of detectors used in modern gamma arrays, for the first time in literature, we have investigated the operation of a composite detector comprising of elements arranged in the shape of a pyramid. A probabilistic formalism is introduced to predict the response of two, three and four level pyramid shaped composite detector in terms of only one probability amplitude. Considering up to four detector hit events, expressions for the addback factor and the peak-to-total ratio have been obtained. The general trend of predicted values of the addback factor, the peak-to-total ratio and the fold distribution match with the available experimental data for other composite detectors. Our novel phenomenological approach could provide a guidance in designing new detectors for gamma-ray spectroscopy.

A Coulomb-excitation reorientation-effect measurement using the TIGRESS γ−ray spectrometer at the TRIUMF/ISAC II facility has permitted the determination of the 〈21+‖E2ˆ‖21+〉 diagonal matrix element in 12C from particle−γ coincidence data and state-of-the-art no-core shell model calculations of the nuclear polarizability. The nuclear polarizability for the ground and first-excited (21+) states in 12C have been calculated using chiral NN N4LO500 and NN+3NF350 interactions, which show convergence and agreement with photo-absorption cross-section data. Predictions show a change in the nuclear polarizability with a substantial increase between the ground state and first excited 21+ state at 4.439 MeV. The polarizability of the 21+ state is introduced into the current and previous Coulomb-excitation reorientation-effect analyses of 12C. Spectroscopic quadrupole moments of QS(21+)=+0.053(44) eb and QS(21+)=+0.08(3) eb are determined, respectively, yielding a weighted average of QS(21+)=+0.071(25) eb, in agreement with recent ab initio calculations. The present measurement confirms that the 21+ state of 12C is oblate and emphasizes the important role played by the nuclear polarizability in Coulomb-excitation studies of light nuclei.

The main source of F-19 in the universe has not yet been clearly identified and this issue represents one of the unanswered questions of stellar modeling. This lack of knowledge can be due to the F-19(alpha, p)Ne-22 reaction cross-section that has proven to be difficult at low energies: direct measurements stop only at about similar to 660 keV, leaving roughly half of the astrophysical relevant energy region (from 200 keV to 1.1 MeV) explored only by R-matrix calculations. In this work, we applied the Trojan Horse Method to the quasi-free three-body Li-6(F-19, p(22)Ne)d reaction performed at E-beam = 6 MeV in order to indirectly study the F-19(alpha, p)Ne-22 reaction in the sub-Coulomb energy region. In this way, we obtained the cross-section and the reaction rate in the temperature region of interest for astrophysics and free from electron screening effects. A brief analysis of the impact of the new measured reaction rate in AGB star nucleosynthesis is also presented.

The abundance of 19F in the universe is strictly related to standard and extramixing processes taking place inside AGB-stars, that are considered to be the most important sites for its production. Nevertheless the way in which it is destroyed is far from being well understood. For this reason we studied the 19F(α,p)22Ne reaction, that is supposed to be the main destruction channel in the Helium-rich part of the star. In this experiment, the reaction has been studied in the energy range of relevance for astrophysics (0÷1 MeV) via the Trojan Horse Method (THM), using the three-body reaction 6Li(19F,p22Ne)d.

The observational F-19 abundance in stellar environments systematically exceeds the predicted one, thus representing one of the unsolved challenges for stellar modeling. It is therefore clear that further investigation is needed in this field. In this work, we focus our attention on the measurement of the F-19(alpha, p)Ne-22 reaction in the astrophysical energy range, between 0.2 and 0.8. MeV (far below the Coulomb barrier, 3.8MeV), as it represents the main destruction channel in He-rich environments. The lowest energy at which this reaction has been studied with direct measurements is similar to 0.66. MeV, covering only the upper tail of the Gamow window, causing the reactionrate evaluation to be based on extrapolation. To investigate lower energies, the F-19(alpha, p) Ne-22 reaction has been studied by means of the Trojan horse method, applied to the quasi-free Li-6(F-19, p(22)Ne) H-2 reaction at E-beam = 6 MeV. The indirect cross section of the F-19(alpha, p)Ne-22 reaction at energies. less than or similar to 1 MeV was extracted, fully covering the astrophysical region of interest and overlapping. existing direct data for normalization. Several resonances have been detected for the first time inside the Gamow window. The reaction rate has been calculated, showing an increase up to a factor of 4 with respect to the literature at astrophysical temperatures. This might lead to potential major astrophysical implications.

Learning how F-19 is produced and destructed in AGB-stars is crucial. Fluorine abundance is in fact important, given that it is strongly tied to standard and extra-mixing processes taking place in AGB-stars. This kind of objects are considered to be the main sources of fluorine in galactic environment, in which experimental abundances are far overestimated. For this reason the reaction F-19(alpha,p)Ne-22, that represents the main destruction channel in He-rich environment, was studied at energies corresponding to T similar to 2.10(8) K. Such reaction has been studied with direct method at E-beam = 1100 keV for alpha particles impinging on a fluorine target, corresponding to E-C.M. similar to 900 keV, still far from the Gamow window, placed at 390 divided by 800 keV, below the Coulomb barrier (3.81 MeV). An experiment was performed at Rujer Boskovic Institut (Zagreb), applying the Trojan Horse Method. With this experimental procedure we were able to select the quasi-free contribution coming from 6Li(F-19,p Ne-22)H-2 at E-beam = 6 MeV at kinematically useful angles. We measured the F-19(alpha,p)Ne-22 at 0 MeV <= E-C.M <= 0.9 MeV, extracting the two body cross-section in absolute units at energies of astrophysical interest.

Learning how 19F is produced and destructed in AGB-stars is crucial. Fluorine abundance is in fact important, given that it is strongly tied to standard and extra-mixing processes taking place in AGB-stars. This kind of objects are considered to be the main sources of fluorine in galactic environment, in which experimental abundances are far overestimated. For this reason the reaction 19F(α, p)22Ne, that represents the main destruction channel in He-rich environment, was studied at energies corresponding to T∼2·108 K. Such reaction has been studied with direct method at Ebeam = 1100 keV for alpha particles impinging on a fluorine target, corresponding to EC.M. ∼ 900 keV, still far from the Gamow window, placed at 390÷800 keV, below the Coulomb barrier (3.81 MeV). An experiment was performed at Rujer Boskovic Institut (Zagreb), applying the Trojan Horse Method. With this experimental procedure we were able to select the quasi-free contribution coming from 6Li(19F,p 22Ne)2H at Ebeam = 6 MeV at kinematically useful angles. We measured the 19F(α, p)22Ne at 0 MeV ≤ EC.M ≤ 0.9 MeV, extracting the two body cross-section in absolute units at energies of astrophysical interest.

19F experimental abundances is overestimated in respect to the theoretical one: it is therefore clear that further investigations are needed. We focused on the 19F(α, p)22 Ne reaction, representing the main destruction channel in He-rich environments. The lowest energy at which this reaction has been studied with direct methods is EC.M. ≈ 0.91 MeV, while the Gamow region is between 0.39 ÷ 0.8 MeV, far below the Coulomb barrier (3.8 MeV). For this reason, an experiment at Rudjer Boskovic Institute (Zagreb) was performed, applying the Trojan Horse Method. Following this method we selected the quasi-free contribution coming from 6Li(19F,p22 Ne)2 H at Ebeam=6 MeV at kinematically favourable angles, and the cross section at energies 0 < EC.M. < 1.4 MeV was extracted in arbitrary units, covering the astrophysical region of interest.