Single Escape Peaks Research Articles

Variation in cosmic ray flux during Solar Eclipse on 21 June, 2020 at Jaipur, India

Variation in gamma ray flux was recorded during the Annular Solar Eclipse on 21 June, 2020 at Jaipur, India where 88.3% of the solar disk was eclipsed. Two Sodium Iodide NaI (Tl) scintillation detectors were employed for the experiment and flux was recorded in the energy range 300 keV to 2 MeV. The first detector employed to record data for the duration of 3 h and 30 min records a sizeable enhancement at the characteristic energy 1460 keV and the corresponding single escape peak at 949 keV. No substantial variation in the radiations was noticed by the detector employed for recording data for 20 critical minutes during the peak of the eclipse.

Measurement of HFETR reactor power by improved 16N gamma spectrum analysis method

To increase redundancy and diversity of the reactor power measurement, a system for the measurement of reactor power can be established based on neutron activation analysis using 16O(n,p)16N reaction. In this work, gamma spectrums from the coolant of HFETR core are continuously detected by 16N monitor with NaI(Tl) detector and the count rates in the spectrum range of 4.5 MeV-7.5 MeV are obtained. Meanwhile, the overlapping peaks in the given spectrum range are decomposed with Levenberg-Marquardt method during the operation of HFETR. The results confirm that the count rates of full-energy peak, single-escape peak and double-escape peak of 6.13 MeV gamma spectrums is proportionate to the increased reactor power measured by other monitors such as compensated ionization chamber and thermal power. It is possible to achieve the absolute nuclear power measurement by adopting the count rate of 16N 6.13 MeV peak, detection efficiency of detector and 16N source term.

Experimental measurements of Doppler broadening of escape peaks in HPGe detectors

Single-escape, double-escape, and annihilation peak widths from eleven spectra taken with differing HPGe coaxial detectors and differing primary gamma sources were measured. For each of these, the Doppler broadening component of the peak width was derived. Significant Doppler broadening was observed only in the single escape peak and in the annihilation peak width. Averaged values and their uncertainties useful for modeling each type of peak width in nuclear radiation spectra are presented.

Analysis of the effects of pair production for the suppressed clover detector

Full energy peak, single escape peak and double escape peak areas have been extracted for an escape suppressed clover detector. Results have been obtained for the single crystal and addback modes of operation as well as the active and passive suppression cases at several gamma energies. We have compared the ratio of single escape peak areas in addback mode with that of single crystal mode to study if the single escape peak gains or loses counts due to addback mode. Detailed analysis has been performed for quantifying the advantages of using addback mode and active suppression. Comparison is made for different types of clover detectors with different volumes.

A Mathematical Approach to Determine Escape Peak Efficiencies of High-Purity Germanium Cylindrical Detectors for Prompt Gamma Neutron Activation Analysis

Determining single-escape (SE), double-escape (DE), and full-energy (FE) peak efficiencies is helpful in prompt gamma-ray neutron activation analysis, in which identifying complicated gamma peaks as well as quantifying spectra is crucial. The FE peak efficiency was measured at the National Institute of Standards and Technology for a closed-end, n-type high-purity germanium (HPGe) cylindrical detector using standard point sources, whereas SE and DE peak efficiencies and the SE-to-DE peak ratio for the HPGe detector were calculated using compact analytical expressions.

A Pulse Shape Analysis technique for the MAJORANA experiment

In order to achieve background count rates sufficiently low so as to allow the observation of rare events such as neutrinoless double beta (0νββ) decay, background suppression techniques are routinely employed. In this paper we present details of a novel Pulse Shape Analysis algorithm, which allows single-site events such as 0νββ decay to be distinguished from multi-site background events in germanium detectors. The algorithm, which is based on the event-by-event χ 2 fitting of experimental signals to a basis data set of unique single-site pulse shapes, has been developed through simulation studies and tested experimentally using a Broad Energy Germanium detector. It is found experimentally that the technique is able to successfully identify and reject 99% of multi-site events in the single escape peak associated with the gamma decay of 208Tl, whilst maintaining a survival probability of 98% for neutrinoless double-beta-decay-like double escape peak events.

Precise Monte Carlo simulation of gamma-ray response functions for an NaI(Tl) detector

Three widely used methods to calculate the response functions for NaI(Tl) detectors were investigated. The methods were Berger–Seltzer's method (Nucl. Instrum. Methods 104 (1972) 317), general Monte Carlo (MC) programs, such as EGS4 (The EGS4 code system, Stanford Linear Accelerator Center, 1985) and MCNP4B (MCNP—a general Monte Carlo N-particle transport code, Los Alamos National Laboratory Report, LA-12625-M, 1997), and special MC programs. The pulse height spectra in a 3″×3″ NaI(Tl) detector due to several gamma-ray sources have been measured to verify the calculated results of these methods. The energies of the sources ranged from 0.4118 to 7.11 MeV. The spectra generated by Berger–Seltzer's method and the general MC programs did not agree well with the experimental data. PETRANS 1.0, the special MC program developed in house, was fairly accurate since it also considered the scintillation efficiency and the single escape peak shift.

Monte Carlo calculations of the response features for NaI detectors

The response features for sodium iodide detector for a monoenergetic gamma-ray source are calculated because of the importance of this type of detector in industry and research. The response features calculated are: full energy peak, single scattered escape, single escape peak, double scattered escape, double escape peak, besides single scatter, double scatter and triple scatter continua. These features are compared for different sizes and geometric efficiencies of the detector. The Monte Carlo simulation provides the weighting factors of the previously mentioned eight features of the response for the Nal detector that are necessary for response function generation for that type of detectors.

Gamma-ray escape peak characteristics of radiation-damaged reverse-electrode germanium coaxial detectors

A comparison of the characteristics of full-energy gamma-ray peaks and their corresponding escape peaks when high energy photons interact in radiation damaged reverse-electrode (n-type) germanium coaxial detectors is presented. Coaxial detector geometry is the dominant factor, causing charge collection to be dramatically better for interactions occurring near the outer periphery of the detector as well as increasing of the probability of escape events occurring in this region. It follows that the resolution of escape peaks is better than that of ordinary gamma-ray peaks. This is experimentally verified. A nearly identical but undamaged detector exhibited significant Doppler broadening of single escape peaks. Because double escape events preferentially occur at outer radii, energy shifts of double escape reflect extremely small amounts of charge trapping in undamaged detectors.

Optimization of a Compton-suppression system by escape-peak ratio

Abstract A Compton-suppression system consisting of an HPGe central detector surrounded by eight BGO scintillators in an annular geometry was assembled. This system is dedicated to in-beam γ-ray measurements. The ratios of full-energy to single-escape peak and full-energy to double-escape peak, at γ-rays of 2754, 4443, and 6139 keV, were used to derived associated suppression factors in order to optimize detection conditions of the system. The suppression factors derived both from the escape peak ratios and the corresponding peak-to-Compton ratios of the γ-ray spectra are compared and discussed. This optimization technique may be of great significance for analyzing complicated spectra, where high-energy γ-rays are considered for analytical use.

On the use of the single escape peak in Ge(Li) spectroscopy

The single escape (SE) peak in a Ge(Li) detector is shown to be wider than either a double escape or a full energy peak of the same pulse height. The extra width arises from Doppler broadening of the annihilation energy and is determined by the electron momentum distribution in germanium. In addition the centroid of an SE peak in a coaxial detector is Doppler shifted to higher energies because of the positron's mobility in the electric field in the detector. These effects necessitate caution in the use of SE peaks in energy measurements and system linearity tests, and in extraction of Fano factor or nuclear lifetime from linewidth measurements.

On the decay of cobalt 60

The gamma spectrum from Cobalt 60 decay has been investigated with a 40 cc Ge(Li) detector. A peak at 822 keV is shown to be not a gamma transition but a single escape peak and an upper limit of 10 is given to the branching ratio of the 2158 keV level.

Studies of Detection Efficiencies and Operating Characteristics of Ge(Li) Detectors

The rapidly expanding use of Ge(Li) detectors in all fields of gamma-ray spectroscopy has led to a need for information from which experimenters may effectively select the best detector for their special needs. This is necessitated because of the large variety of detector sizes and configurations which are currently available and the lack of standardization of sizes. Several criteria should be considered in the selection of a detector for a specific application. Among these are: 1) detection efficiency, 2) charge collection efficiency, which gives rise to abnormal peak broadening as a function of gamma-ray energy as well as to asymmetric peak shapes, 3) timing characteristics for coincidence applications, and 4) energy resolution which is one of the measures of the ability to identify a weak gamma-ray in the presence of strong higher-energy gamma rays. We have measured these characteristics for several planar and open-ended and five-sided coaxial detectors. Absolute full-energy peak, double-escape peak and single-escape peak efficiencies were obtained for gamma-ray energies from 30 keV to 11 MeV. For planar devices, the effects of thickness and cross-sectional area of the depleted volume have been investigated. Some studies have been made of the problems involved in measuring gamma-ray intensities. These include measurements of the counter "edge effects" by a comparison of the efficiency curves obtained at different source-detector distances. Other studies involve random and real coincidence summing effects which are countingrate and geometry-dependent effects.

The calibration of a Ge(Li) gamma-ray spectrometer for energy and relative intensity measurements

Two aspects of Ge(Li) gamma-ray spectrometry are discussed. The non-linearity of an amplifier-analyzer system was measured using a precision pulser and was checked with gamma-ray standards. The overall accuracy was 2 parts in 10 4. The relative detection efficiency of gamma-ray full-energy peaks was determined using sources with well measured relative gamma-ray emission rates. Two Ge(Li) detectors with active volumes of 3 cm 2×0.5 cm and 4 cm 2×0.5 cm were calibrated in the energy range 80—3200 keV. An overall accuracy of 5% in the energy region from 500–3200 keV and an accuracy of 10% over the entire range was obtained. The relative areas of the single escape peak and double escape peak to the full energy peak as a function of energy are included. The relative intensities of the 569.6, 1063.6 and 1771 keV gamma-rays following the decay of 207Bi were measured.