Low Energy Photon Spectrometer Research Articles

Examination of nuclear chirality with a magnetic moment measurement of the I=9 isomeric state in Cs128

The $g$ factor of the isomeric $I={9}^{+}$ bandhead of the yrast states in $^{128}\mathrm{Cs}$ is obtained from the time differential perturbed angular distribution measurement performed with the electromagnet at IPN Orsay. An external magnetic field of 2.146 T at the target position was attained with GAMIPE reaction chamber surrounded by four high-purity germanium detectors, of which two were low-energy photon spectrometer type. The results are in accordance with $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}^{\ensuremath{-}1}\phantom{\rule{4pt}{0ex}}I={9}^{+}$ bandhead assignment and are discussed in the context of chiral interpretation of the $^{128}\mathrm{Cs}$ nucleus as a composition of the odd proton, odd neutron, and even-even core with their angular momentum vectors. The obtained $g$-factor value was compared with predictions of the particle-rotor model. The experimental $g$ factor corresponds to the nonchiral geometry of the isomeric bandhead. This observation indicates the existence of the chiral critical frequency in $^{128}\mathrm{Cs}$ and may explain the absence of the chiral doublet members for $I<13\ensuremath{\hbar}$.

Different manifestations of triaxial shapes of the positive and negative parity bands in Os187

The excited states of $^{187}\mathrm{Os}$ have been studied via $^{186}\mathrm{W}(^{4}\mathrm{He},3n)^{187}\mathrm{Os}$ reaction at a beam energy of 36 MeV. The $\ensuremath{\gamma}$ rays were detected using the Indian National Gamma Array at the Variable Energy Cyclotron Centre having seven Compton-suppressed clover high-purity germanium (HPGe) detectors and one low-energy photon spectrometer (LEPS) detector with a digital data acquisition system. The level scheme of $^{187}\mathrm{Os}$ has been extended substantially up to $\ensuremath{\approx}$3.86 MeV of excitation energy and $37/2\phantom{\rule{0.16em}{0ex}}\ensuremath{\hbar}$ of spin with the placement of more than 90 new $\ensuremath{\gamma}$ rays. All known bands have been extended and new band structures have been identified. The results show evidence of triaxial shapes for different configurations of $^{187}\mathrm{Os}$ and different manifestations of nonaxial shape have been observed in the same nucleus. A comparison of the observed band crossing frequency in $^{187}\mathrm{Os}$ with neighboring nuclei gives evidence of a deformed shell gap at $N=110$. The experimental results are well explained using total Routhian surface calculations.

Alignment effects in the medium-spin level structure of Se78

The excited states of $^{78}\mathrm{Se}$ were populated using the $^{76}\mathrm{Ge}(\ensuremath{\alpha},2n)$ fusion evaporation reaction. The deexcited gamma rays were detected using the Indian National Gamma Array (INGA) spectrometer comprising clover and low-energy photon spectrometer (LEPS) detectors. The ground state band of $^{78}\mathrm{Se}$ has been extended up to ${E}_{x}$ = 8.5 MeV and $J$ = $16\ensuremath{\hbar}$; this excitation regime is very close to the $\ensuremath{\pi}(1{g}_{9/2}^{2})$ crossing frequency. Several newly observed in-band and intraband transitions belonging to the other bands of $^{78}\mathrm{Se}$ have also been placed in the level scheme based on their coincidence relationships. From the newly identified $E1$ transitions, an enhancement in the $B(E1)$/$B(E2)$ values with spin has been observed which indicates the onset of octupole correlations in the band structure built on the ${3}^{\ensuremath{-}}$, 2508-keV state. Persistence of triaxial shape up to the highest observed spin of the ground state band has been observed and the feature of successive $1{g}_{9/2}^{2}$ quasiparticle alignments due to protons and neutrons has been unveiled. The consequences arising due to the occurrence of the neutron $1{g}_{9/2}$ quasiparticle alignments in the other observed correlated band structures are also presented. The results are interpreted in terms of total Routhian surface (TRS) calculations and the level structure systematic of the neighboring nuclei.

Electron spectrometer for electric monopole (E0) transition studies in nuclei

The study of electric monopole (E0) transitions between two 0+ states is important because the monopole strength carries vital information about the nuclear structure due to its direct link with the mean squared charge radius r2 and quadrupole deformation parameter β. Therefore, the measurement of internal conversion electrons (ICE) or internal pair formation (IPF) is crucial for E0 transition studies. Transitions between 0+ states do not change angular momentum. Hence, single-photon emission is forbidden, but can decay by conversion electrons or pair formation and two-photon emission which is mostly negligible. In order to implement E0 studies at iThemba LABS, an electron spectrometer that uses a solenoidal magnetic field acting as a lens and a Si(Li) detector has been refurbished and characterized using calibration sources of ICE. Figures of merit have been extracted and compared with simulations. The spectrometer coupled with an array of LaBr3:Ce detectors and Low Energy Photon Spectrometers (LEPS) was successfully implemented for in-beam experiments. Measurements of internal conversion coefficients (ICC) and monopole strengths extracted from in-beam measurements of 72As, 72Ge, and 72Se are presented.

Investigation of α -induced reactions on Sb isotopes relevant to the astrophysical γ process

The aim of the present work is to measure the $^{121}$Sb($\alpha,\gamma$)$^{125}$I, $^{121}$Sb($\alpha$,n)$^{124}$I, and $^{123}$Sb($\alpha$,n)$^{126}$I reaction cross sections. The $\alpha$-induced reactions on natural and enriched antimony targets were investigated using the activation technique. The ($\alpha$,$\gamma$) cross sections of $^{121}$Sb were measured and are reported for first time. To determine the cross section of the $^{121}$Sb($\alpha$,$\gamma$)$^{125}$I, $^{121}$Sb($\alpha$,n)$^{124}$I, and $^{123}$Sb($\alpha$,n)$^{126}$I reactions, the yields of $\gamma$-rays following the $\beta$-decay of the reaction products were measured. For the measurement of the lowest cross sections, the characteristic X-rays were counted with a LEPS (Low Energy Photon Spectrometer) detector. The cross section of the $^{121}$Sb($\alpha$,$\gamma$)$^{125}$I, $^{121}$Sb($\alpha$,n)$^{124}$I and $^{123}$Sb($\alpha$,n)$^{126}$I reactions were measured with high precision in an energy range between 9.74 MeV to 15.48 MeV, close to the astrophysically relevant energy window. The results are compared with the predictions of statistical model calculations. The ($\alpha$,n) data show that the $\alpha$ widths are predicted well for these reactions. The ($\alpha$,$\gamma$) results are overestimated by the calculations but this is due to the applied neutron- and $\gamma$ widths. Relevant for the astrophysical reaction rate is the $\alpha$ width used in the calculations.While for other reactions the $\alpha$ widths seem to have been overestimated and their energy dependence was not described well in the measured energy range, this is not the case for the reactions studied here. The result is consistent with the proposal that additional reaction channels, such as Coulomb excitation, may have led to the discrepancies found in other reactions.

Alpha-induced reactions on selenium between 11 and 15 MeV

The production of 77,79,85,85mKr and 77Br via the reaction Se() was investigated between and 15 MeV using the activation technique. The irradiation of natural selenium targets on aluminum backings was conducted at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany. The spectroscopic analysis of the reaction products was performed using a high-purity germanium detector located at PTB and a low energy photon spectrometer detector at the Goethe University Frankfurt, Germany. Thick-target yields were determined. The corresponding energy-dependent production cross sections of 77,79,85,85mKr and 77Br were calculated from the thick-target yields. Good agreement between experimental data and theoretical predictions using the TALYS-1.6 code was found.

Characterisation of a composite LEPS

A low energy photon spectrometer (LEPS), which is a composite planar HPGe, has been characterised experimentally. It has been shown that beyond 200 keV, effect of image charges deteriorates the efficiency of the detector in its addback mode. Data have been corrected on event-by-event basis resulting in improvement of the performance.

Lifetime measurements and decay spectroscopy of132I

The low-lying states of odd-odd 132 I, the 3p-3h nucleus with respect to the doubly magic 132 Sn, have been characterized from decay spectroscopy. The neutron rich Iodine and Tellurium isotopes have been produced as fission product of alpha-induced fission of 235 U and radiochemically separated. The life-time of the first excited state of 132 I have been precisely measured using LaBr3(Ce) scintillators from the decay of 132 Te. The IT decay of the high spin isomer (8 - ) in 132 I has been measured with a Low Energy Photon Spectrometer (LEPS) of segmented planar Ge detector.

Band structures and intruderπi13/2state in197Tl

The excited states in the odd-$A$ ${}^{197}$Tl nucleus have been studied by populating them using the ${}^{197}$Au($\ensuremath{\alpha}$, 4$n$)${}^{197}$Tl reaction at a beam energy of 48 MeV. The $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence data were taken using a combination of clover, low-energy photon spectrometer (LEPS), and single-crystal high-purity germanium (HPGe) detectors. Precise spin and parity assignments of the excited states have been done through polarization and directional correlation from oriented states (DCO) measurements. A new band structure has been identified and evidence for a possible intruder $\ensuremath{\pi}{i}_{13/2}$ state has been found for the first time. Possible configurations of the observed bands have been discussed. The total Routhian surface calculations have been performed to study the shape of ${}^{197}$Tl for different configurations.

Investigation of α-induced reactions on the p nucleus

Cross sections for the Yb168(α,γ)Hf172 and Yb168(α,n)Hf171 reactions were measured by means of the activation method using α particles with energies between 12.9 MeV and 15.1 MeV. The spectroscopy of the γ rays emitted by the reaction products was performed using three different HPGe detector types, namely clover-type high-purity germanium detectors, a low-energy photon spectrometer detector, and a coaxial high-purity germanium detector. The results were compared to Hauser–Feshbach statistical model calculations. Within certain assumptions, astrophysical conclusions could be drawn concerning the production of the p nucleus Yb168. The data in this work can serve as a contribution to the current very fragmentary experimental data base for charged-particle induced reactions. In addition, the absolute intensity for nine γ-ray transitions following the electron capture decay of Hf171 could be derived.

Improving the effectiveness of a low-energy Compton suppression system

A novel method for collecting and processing coincidence data from a Compton Suppressed Low Energy Photon Spectrometer (LEPS) is presented, greatly simplifying the current setup and extending the suppression abilities of the system. Offline analysis is used, eliminating the need to discard coincidence data when vetoing coincident events with fast-timing electronics. Additional coincident events are identified that are usually missed, and which represent interactions in the active NaI(Tl) shield prior to an interaction in the LEPS detector. By suppressing these events, the Compton Suppression factor was improved by 144% for the 661.66keV decay line in a 137Cs source. The geometry used for this particular Compton suppression system is highly sensitive to these effects, however similar event profiles are expected in all coincidence systems.

Determination of uranium in water by neutron activation and a low energy photon spectrometer

Ground and drinking water samples were analyzed for uranium by neutron activation analysis and a low energy photon spectrometer. Two methods were used: direct irradiation of water and pre-concentration by evaporation. The concentrations varied from 0.1 to 21 µg/l. The lowest detection limit obtained by pre-concentration was 0.01 µg/l while for the direct irradiation of water it was 0.04 µg/l. With these methods, we were able to determine the U concentration in all samples which were submitted for analysis.

Low-spin studies of theπh11/2νh11/2structure in134Pr

Low-spin states built on the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{h}_{11/2}$ configuration in ${}^{134}\mathrm{Pr}$ have been studied using a ${}^{119}\mathrm{Sn}{(}^{19}\mathrm{F},4n)$ fusion-evaporation reaction. A planar low-energy photon spectrometer along with a low-$Z$ target chamber was utilized in an array of five high-purity Ge detectors for the purpose of measuring low-energy $\ensuremath{\gamma}$ rays. A 39.3-keV $\ensuremath{\gamma}$ ray was discovered as a new transition at the bottom of the band. The transition was found to have an $M1$ multipolarity, determined from the internal conversion coefficients evaluated from the missing transition intensity. The new bandhead was assigned and was identified as an isomeric state with a mean lifetime of $\ensuremath{\tau}=4.6(1)\mathrm{ns}.$ This bandhead decays by a 306-keV $\ensuremath{\gamma}$-ray transition that was found to have an $E1$ multipolarity through the analysis of the angular distribution asymmetry.

Lifetime of the 21.8-keV state in98Tc

The lifetime of the 21.8-keV (5{sup +}) state in {sup 98}Tc has been measured to be 3.5(9) ns by direct timing methods, using a BaF{sub 2} scintillator and a low-energy photon spectrometer. This state is of interest because it is expected to decay partially by bound internal conversion when the charge state of the technetium ion is 20 or greater.

Energy levelsin98251Cf populated in the α decayof100255Fm

Gamma-ray spectra of a 20-h {sup 255}Fm source containing {approx}1 mCi activity were measured with a 25% Ge detector and a low-energy photon spectrometer (LEPS). Gamma lines with intensities as low as 1.0x10{sup -6}% per {sup 255}Fm {alpha} decay were observed. Gamma-gamma coincidence spectra of a {sup 255}Fm sample were measured with the GAMMASPHERE array. A comparison of the {gamma}-ray spectrum gated by the Cf K{sub {alpha}} x-ray peak with the {gamma}-singles spectrum provided spins of the excited states in {sup 251}Cf. The {gamma}-ray data, in conjunction with previously measured {sup 250}Cf(d,p) reaction data, allowed us to characterize several single-particle and vibrational states above the N=152 subshell gap.

High Sensitive Measurements of 137Cs and Other Radionuclides in Environmental Samples Using Germanium Detectors

Three types of high-purity germanium (HPGe) detector systems for low-level radioactivity measurement were constructed in the laboratory near sea level. An anti-Compton system was set up by combining a large volume HPGe (rel. eff. 115%) with a well type NaI(Tl). The detection limit (D.L.) of 137Cs of an ashed oyster sample for the anti-Compton mode of 115% Ge was 0.023 Bq/sample for 8·104 s counting, whereas 0.035 Bq/sample for the normal mode. Under similar measuring conditions, D.L. of 137Cs for a medium volume HPGe (rel. eff. 51%) was 0.042 Bq/sample. A low-background Ge-LEPS (Low Energy Photon Spectrometer) was sufficiently sensitive for low level measurements of 210Pb, 234Th and other low energy gamma-emitters. The detection limit for 210Pb in the sample shape of 60 mm diameter by 2 mm thick was about 0.05 Bq/sample for 5.0·105 s background counting. Using this LEPS, it was found that 210Pb behaves similarly to 7Be in both air and precipitation (snowfall).

Measurement of gamma-ray intensities of 231Th using semiconductor detectors

Nuclide 231Th was yielded by the 232Th(n, 2n) reaction with neutron irradiation in the Kyoto University Reactor (KUR). Moreover, the thorium was purified chemically. Gamma-ray spectra of thorium have been measured using low-energy photon spectrometers and a high-purity germanium detector. Relative γ-ray intensities ranging from 25 to 352 keV in the decay of 231Th have been determined with satisfactory accuracy. The results are in very good agreement with those of earlier studies. We observe two new γ-rays at 77.69 and 177.66 keV, whose intensities are found to be (0.063±0.010)% and (0.00095±0.00020)%, respectively, relative to that of 84.21 keV taken as 100%. Absolute intensity of 84.21 keV γ-ray which is the most prominent one from the decay of 231Th and that of 185.739 keV following the decay of 235U are also determined from the secular equilibrium for 235U– 231Th. The results obtained in two cases are (6.60±0.25)% and (58±2)%, respectively.

Systematization of efficiency correction for gamma-ray disk sources with semiconductor detectors

Full energy peak efficiency correction for disk sources has been systematically studied using the mapping method with two high-purity germanium detectors and two low-energy photon spectrometers. The following are found using only single-line (i.e., no coincidence summing loses) γ-rays: (1) The efficiency distributions on a plane parallel to the entrance window of semiconductor detectors is in perfect accord with Gaussian curves inside the circumference of the cylindrical Ge crystal, however, they deviate from the curves outside the circumference. (2) The width parameters of the Gaussian function fitted to the efficiency distributions have a systematic relationship with γ-ray energy. (3) The mapping method is of practical use and has satisfactory accuracy.

Specific radioactivity of europium-152 in roof tiles exposed to atomic bomb radiation in Nagasaki.

Specific radioactivities of residual europium (Eu)-152 were measured in six roof tile samples exposed to the Nagasaki atomic bomb at two locations. The ground distances of the two locations from the hypocenter are 1020 m and 1060 m. In order to obtain reliable data, Eu-enriched samples (from 207 to 855 mg) were prepared by separating Eu from each roof tile sample (from 1 to 2 kg). For the major aliquot of the Eu-enriched sample, residual radioactivity of 152Eu was measured using a low-energy photon spectrometer. For the minor aliquot of the Eu-enriched sample, Eu content was determined by neutron activation analysis. Results of the specific radioactivity (152Eu/Eu, Bq mg-1) corrected to the time of bombing were in a range from 0.080 to 0.446. Although the measured values showed some scattering, they are moderately consistent with the calculated values by the DS86 methodology, i.e. the average ratio of the calculated to measured values is 1.3 +/- 0.8.

Natural Background in Ge(Li) Spectrometers

The natural background activity of a Ge(Li) spectrometer was measured and background reduction was evaluated. Twenty lines were observed in the energy spectrum, extending from 20 to 1000 keV. Background reduction, achieved by shielding geometry improvements for low energy photon spectrometer, is presented. Continuum counting rate for 13 % relative-efficiency Ge(Li) detector decreased from 4.9 c/min keV at 120 keV to less than 0.1 c/min keV at 900 keV in a 50 mm lead shield.