Novel device to study double-alpha decay at the FRS Ion Catcher Varga, L.; Wilsenach, H.; Hall, O. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2024, Letnik:
1063
Journal Article
Recenzirano
Odprti dostop
A novel system has been developed to detect simultaneous double-alpha emission from purified and weightless sources. The system includes the collection of 224Ra low-energy recoils in purified helium ...buffer gas from the decay of 228Th. The recoil products are thermalized and collected in a cryogenic buffer gas cell and extracted into an RF-ion guide for mass selection. The mass-separated ions are implanted at low kinetic energy into a thin carbon foil placed between two large-area double-sided silicon strip detectors to observe correlated alpha-particle emission. The apparatus is described in detail, including insights into its experimental performance.
The multinucleon transfer (MNT) reaction approach was successfully employed for the first time to measure the isomeric ratios (IRs) of 211Po isomer (25/2+) and its ground state (9/2+) at the IGISOL ...facility using a 945 MeV 136Xe beam impinged on 209Bi and natPb targets. The dominant production of isomers compared to the corresponding ground states was consistently revealed in the α-decay spectra. Deduced IR of 211Po populated through the 136Xe+natPb reaction was found to have an enhancement of ≈1.8-times than that observed for the 136Xe+209Bi. State-of-the-art Langevin-type model calculations have been utilized to estimate the spin distribution of an MNT residue. The computations qualitatively corroborate with the considerable increase in the IRs of 211Po produced from 136Xe+natPb compared to 136Xe+209Bi. Theoretical investigations indicate a weak dependence of target spin on the IRs. The enhancement of the 211Po isomer in the 136Xe+natPb over 136Xe+209Bi can be attributed to the different proton (p)-transfer production routes. Estimations demonstrate an increment in the angular momentum transfer, favorable for isomer production, with increasing projectile energy. Comparative analysis reveals the two entrance channel parameters, projectile mass and p-transfer channels, strongly influencing the population of the high-spin isomer of 211Po (25/2+). This letter reports the first experimental and theoretical study on the IRs of nuclei formed from two different p-transfer channels via two independent MNT reactions.
We lack significant nuclear physics input to understand the rapid-neutron capture (r-)process fully. The r-process is the source of half the elements heavier than iron and the only way to produce the ...long-lived actinides we find on earth. This process’s key nuclear physics inputs are nuclear masses, cross-sections of (n,
γ
) and (
γ
,n), and decay half-lives and branching ratios of neutron-rich isotopes. However, there is currently no method to directly measure neutron-induced reaction rates on short-lived nuclides, so there is no experimental data for the primary nuclear reaction that drives the r-process. We show here a conceptual design of a novel approach to access this information experimentally. The idea is to form a target of short-lived isotopes by confining them as ions in a radio-frequency (RF) trap. Next, they are irradiated with an intense neutron flux, and the reaction products are identified by mass spectrometry. The chosen method is a two-stage process in the presence of high neutron fluxes. The first process is neutron-induced fission in a thin actinide foil to create fission fragments. These fragments are slowed down in a cryogenic stopping cell before being filtered through a radio frequency quadrupole (RFQ) system. The RFQ system selects fission fragments of a specific atomic mass number
A
and confines them to a small volume in an RF trap, where they are irradiated for a second time in a controlled manner. The resultant
A
+1 isotopes are mass-selectively transported to a multiple-reflection time-of-flight mass spectrometer, where the reaction products are identified and counted.
We present the first measurements of the double ratio of the polarization-transfer components (Px′/Pz′)p/(Px′/Pz′)s for knock-out protons from the s and p shells in C12 measured by the C12(e→,e′p→) ...reaction in quasi-elastic kinematics. The data are compared to theoretical predictions in the relativistic distorted-wave impulse approximation. Our results show that the differences between s- and p-shell protons, observed when compared at the same initial momentum (missing momentum), largely disappear when the comparison is done at the same proton virtuality. We observe no difference in medium modifications between protons from the s and p shells with the same virtuality in spite of the large differences in the respective nuclear densities.
We present measurements of the polarization-transfer components in the H2(e→,e′p→) reaction, covering a previously unexplored kinematic region with large positive (anti-parallel) missing momentum, ...pmiss, up to 220MeV/c, and Q2=0.65(GeV/c)2. These measurements, performed at the Mainz Microtron (MAMI), were motivated by theoretical calculations which predict small final-state interaction (FSI) effects in these kinematics, making them favorable for searching for medium modifications of bound nucleons in nuclei. We find in this kinematic region that the measured polarization-transfer components Px and Pz and their ratio agree with the theoretical calculations, which use free-proton form factors. Using this, we establish upper limits on possible medium effects that modify the bound proton's form factor ratio GE/GM at the level of a few percent. We also compare the measured polarization-transfer components and their ratio for 2H to those of a free (moving) proton. We find that the universal behavior of 2H, 4He and 12C in the double ratio (Px/Pz)A(Px/Pz)H1 is maintained in the positive missing-momentum region.
We measured the ratio Px/Pz of the transverse to longitudinal components of polarization transferred from electrons to bound protons in C12 by the C12(e→,e′p→) process at the Mainz Microtron (MAMI). ...We observed consistent deviations from unity of this ratio normalized to the free-proton ratio, (Px/Pz)C12/(Px/Pz)H1, for both s- and p-shell knocked out protons, even though they are embedded in averaged local densities that differ by about a factor of two. The dependence of the double ratio on proton virtuality is similar to the one for knocked out protons from H2 and He4, suggesting a universal behavior. It further implies no dependence on average local nuclear density.
We present measurements of the electron helicity asymmetry in quasi-elastic proton knockout from 2H and 12C nuclei by polarized electrons. This asymmetry depends on the fifth structure function, is ...antisymmetric with respect to the scattering plane, and vanishes in the absence of final-state interactions, and thus it provides a sensitive tool for their study. Our kinematics cover the full range in off-coplanarity angle ϕpq, with a polar angle θpq coverage up to about 8°. The missing energy resolution enabled us to determine the asymmetries for knock-out resulting in different states of the residual 11B system. We find that the helicity asymmetry for p-shell knockout from 12C depends on the final state of the residual system and is relatively large (up to ≈0.16), especially at low missing momentum. It is considerably smaller (up to ≈0.01) for s-shell knockout from both 12C and 2H. The data for 2H are in very good agreement with theoretical calculations, while the predictions for 12C exhibit differences with respect to the data.
Kinetic model simulations of charge carrier transport following irradiation of LiF:Mg,Ti (TLD-100) including Fluorine vacancy/F center creation by the radiation and dose-dependent ...vacancy-interstitial recombination are presented which describe the experimentally measured linear/exponentially saturating optical absorption dose response of the electron trapping centers at 4.0eV, 4.77eV, 5.08eV (F band) and 5.45eV. Linear/exponentially saturating dose response is commonly observed for centers which are not created by the radiation. The creation of Fluorine vacancies by the radiation could therefore be expected to lead to a supralinear dose response of the F center before the onset of saturation. Nonetheless, the dose response is linear from 10Gy to 500Gy and can be fitted with a dose-filling constant β=6.1·10−5Gy−1 corresponding to a 5% and 25% decrease from linearity at 103Gy and 5·103Gy respectively. The model attempts to resolve a central question concerning the mechanisms leading to the linear/exponentially saturating dose response of the F band even though Fluorine vacancies are being continuously created during the irradiation. The electron-trapping characteristics of the created vacancies are assumed to differ somewhat from the vacancies originally present in un-irradiated samples due to differences in their immediate environment. Vacancy-interstitial recombination for separation distances less than a critical distance, dc is demonstrated to be significant for D>500Gy (dc=36Å) and is an important mechanism contributing to the F center saturation at high dose-levels. The kinetic model accurately simulates the experimentally observed F center dose response over the entire investigated dose range of 10–105Gy under the following conditions: (i) The concentration of vacancies initially present is unexpectedly high at ∼1023m−3, possibly due to the highly doped, non-crystalline and hot-pressed nature of the LiF:Mg,Ti samples. (ii) The transition probability, An4o, for electron capture into the initially-present vacancies is ∼40 times greater than An4, the transition probability for the radiation-created vacancies. These two factors marginalize the effect of the created vacancies at low dose resulting in a linear dose response.
We report the first measurements of the transverse (Px and Py) and longitudinal (Pz) components of the polarization transfer to a bound proton in the deuteron via the H2(e→,e′p→) reaction, over a ...wide range of missing momentum. A precise determination of the electron beam polarization reduces the systematic uncertainties on the individual components to a level that enables a detailed comparison to a state-of-the-art calculation of the deuteron using free-proton electromagnetic form factors. We observe very good agreement between the measured and the calculated Px/Pz ratios, but deviations of the individual components. Our results cannot be explained by medium modified electromagnetic form factors. They point to an incomplete description of the nuclear reaction mechanism in the calculation.
A conduction band/valence band kinetic model for thermoluminescence (TL) dose response is described which incorporates both localized and delocalized recombination mechanisms. The model is capable of ...simulating the linear/supralinear behaviour of TL dose response and, as well, the experimentally observed decrease of the supralinearity with decreasing photon energy. These characteristics are observed in the dose response of the various peaks in the glow curve of LiF:Mg,Ti and in other TL materials. In the irradiation stage, the model uses nanodosimetric considerations to describe the electron–hole concentration, ne–h and e-only concentration, ne, filling rates with dose of a spatially correlated trapping center/luminescent center (TC/LC) complex. The linear dose response arises from the dominant role of the geminate/localized recombination at low dose. The supralinearity arises due to the increased relative intensity of delocalized recombination at high dose coupled with a decrease in the efficiency of the competitive processes with increasing dose. The dependence of the supralinearity on photon energy is obtained by adopting different dose-filling-rates of ne–h and ne as a function of photon energy. Specifically, for low dose-levels below ~1–10Gy, ne–h/ne is assumed to increase slowly/linearly with dose and to increase slightly with decreasing photon energy below ~100keV due to the increasing average ionization density of the electron tracks. For levels of dose above ~10Gy, the ratio increases more rapidly in an exponential manner with later entry to maximum values with decreasing photon energy. The demarcation dose of ~1–10Gy separating the linear from the exponentially increasing behaviour of ne–h/ne corresponds to the approximate onset of supralinearity observed for composite peak 5 in LiF:Mg,Ti. This assumed behaviour for ne–h/ne is consistent with the structure/size of electron tracks and the onset and relative importance of intra-track versus inter-track recombination.
•Development of a kinetic model of thermoluminescence dose response was achieved.•The effects of ionization density were included to explain the behaviour of supralinearity with photon energy.•Electron–hole population of spatially correlated defects in irradiation stage was incorporated based on nanodosimetric considerations.
PDF
