Towards the end of 2017, a new beam line was commissioned at the Laboratorio Nacional de Espectrometría de Masas con Aceleradores (LEMA) at Instituto de Física of the Universidad Nacional Autónoma de ...México (IFUNAM). Initially, LEMA was a 1 MV tandetron accelerator just dedicated to Accelerator Mass Spectrometry (AMS); nowadays, the new line adopted the main characteristics of the AMS system in a natural way: i.e., it has a high precision measurement of the beam energy and a very high and stable current (tens of μ A) depending of charge state of each isotope. The precise low energy limit around 400 keV opens a window to study reactions in the region of interest for Astrophysics. At the same time, the LEMA beam-line allows to develop experiments combining nuclear reactions with AMS, as well the developing of all of kind of Ion Beam Analysis (IBA) studies. In this work the main characteristics of the line, the ancillary systems and the perspectives for low energy measurements for nuclear studies and applications are described.
This article reports the characterization of two High Purity Germanium detectors performed by extracting and comparing their efficiencies using experimental data and Monte Carlo simulations. The ...efficiencies were calculated for pointlike γ-ray sources as well as for extended calibration sources. Characteristics of the detectors such as energy linearity, energy resolution and full energy peak efficiencies are reported from measurements performed on surface laboratories. The detectors will be deployed in a γ-ray assay facility that will be located in the first underground laboratory in Mexico, Laboratorio Subterr'aneo de Mineral del Chico (LABChico), in the Comarca Minera UNESCO Global Geopark 1.
This work presents results of experiments aimed to measure total L X-ray production cross sections due to the impact of 1.335 MeV to 1.835 MeV protons on Sr, Y, Zr, Nb, and Mo, which were contrasted ...with previously published experimental data and theoretical predictions of the ECPPSR model and a universal fit recently proposed. Two atomic parameters databases were also used, as well as a correction due to multiple ionization (MI) of outer atomic shells. The measured cross sections are higher than all measured and theoretical values, being better described by the ECPSSR model with MI adjustments. However, when uncertainties of the used atomic parameters are considered, it is seen that it is impossible to determine the accuracy of the models with regard to the experimental values.
Abstract
We produced monoisotopic targets of
13
C and
28,29
Si with 10
15−16
atoms/cm
2
areal density by ion implantation in different matrices at the Accelerator Mass Spectrometry (AMS) facility in ...Mexico. The tandem accelerator terminal voltage was set at the lowest achievable value (200 kV) that yield beams with energy of 435 keV. It is possible to do ion implantation at lower energies in our facility through the use of molecular beams, so in this work we looked for, and successfully found, bound positively charged molecular beams, although with very low intensity. We inject 235 keV
C
6
−
molecules into the charge of exchange canal (argon) of our tandem accelerator and detected the survival fraction of C
2
,
3
,
4
molecules in 1
+
and 2
+
charge states or above. Our results showed that some molecules remain bound, with one or more electrons missing, after being forced through a low density gas stripper at relatively high energy. In the production process of negative molecular fluxes in the Source of Negative Ions by Cesium Sputtering (SNICS) we found an odd-even effect in their intensity that we understand as the coupling between the fragment size distribution of a dynamic fragmentation of graphite by cesium impact and the electron affinity of the molecules with n-carbon atoms. The availability of these kind of high energy molecular beams opens the door for discovery both in the study of the physics of negative and positive molecular ions.
The combination of the activation method and accelerator mass spectrometry (AMS) has grown to be an important resource to measure nuclear reaction cross sections, especially when these are very ...small. The activation method refers to the production of long-lived radioisotopes by nuclear reactions induced by charged particles, neutrons, or γ-rays. The ultrasensitivity achieved by AMS allows the detection of even a very small number of such long-lived radioactive products. Several reviews of this topic have been published recently and our goal in this work is to continue with the review effort by including some of our own publications, as well as a few more.
The 5.5 MV CN-Van de Graaff (VDG) accelerator was first installed and operated in the early 50's at Rice University (Houston, TX) and it was donated to IFUNAM (“Instituto de Física, Universidad ...Nacional Autónoma de México”) in 1984 and started a new life in 1988. At the end of 2017, the ion source was severely damaged. Several power supplies were destroyed. In this article we describe the process of restoring the VDG terminal. A number of power supplies were redesigned, built, tested and mounted in the Terminal. As a result of the work carried out during most of 2019, the VDG accelerator is now operational and we show data from the Rutherford Backscattering (RBS) analysis of a platinum coated silicon slab using the first proton and α beams. Electronic diagrams of all supplies in their new configuration are provided for the benefit of this kind of RF-Ion sources users still numerous.
We describe the use of the 4tt CHIMERA charged particle detector as a large efficiency y-ray detector. The CsI(Tl) stage of the CHIMERA telescope is used to detect and identify y-rays. The high ...detection efficiency and the sufficient energy resolution guaranteed by CsI(Tl) allows us to use the detector for the study of rare decays. Two examples are reported: the low probability gamma decay (<10%) of the Pygmy resonance of a radioactive nucleus as the 68Ni; the measurement of the gamma decay probability of excited levels of 12C as the Hoyle state at 7.65 (∼10−4) MeV and the 3- level at 9.64 MeV (∼107), both important for the Carbon production in stars. Future experiments made possible at INFN-LNS by the availability of the new fragment separator FRAISE are also outlined.
The World Health Organisation (WHO) presents an upper limit for lead in drinking water of 10 parts per billion ppb. Typically, to reach this level of sensitivity, expensive metrology is required. To ...increase the sensitivity range of low-cost devices, this paper explores the prospects of using a volume reduction technique of a boiled water sample doped with Lead-210 (
210
Pb), as a means to increase the solute’s concentration.
210
Pb is a radioactive lead isotope and its concentration in a water sample can be measured with e.g. High Purity Germanium (HPGe) detectors at the Boulby Underground Germanium Suite. Concentrations close to the WHO limit have not been examined. This paper presents a measurement of the volume reduction technique retaining
99
±
(
9
)
% of
210
Pb starting from a concentration of
1.9
×
10
-
6
ppb before reduction and resulting in
2.63
×
10
-
4
ppb after reduction. This work also applies the volume reduction technique to London tap water and reports the radioassay results from gamma counting in HPGe detectors. Among other radio-isotopes,
40
K,
210
Pb,
131
I and
177
Lu were identified at measured concentrations of
2.83
×
10
3
ppb,
2.55
×
10
-
7
ppb,
5.06
×
10
-
10
ppb and
5.84
×
10
-
10
ppb in the London tap water sample. This technique retained
90
±
50
%
of
40
K. Stable lead was inferred from the same water sample at a measured concentration of 0.012 ppb, prior to reduction.
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