Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of 82Zr and 84Nb were measured for the first time with an uncertainty of ∼10 keV, and the masses of ...79Y, 81Zr, and 83Nb were re-determined with a higher precision. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low α separation energies for neutron-deficient Mo and Tc isotopes, making the formation of Zr–Nb cycle in the rp-process unlikely. The new proton separation energy of 83Nb was determined to be 490(400) keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the p-nucleus 84Sr relative to the neutron-deficient molybdenum isotopes in the previous νp-process simulations.
Direct mass measurements of
78Kr projectile fragments have been performed in the recently commissioned storage ring CSRe employing the isochronous mass spectrometry method. A new data-analysis ...technique has been developed to correct the drifts in the revolution frequencies caused by instabilities of the magnetic fields in the CSRe, thus yielding a mass resolving power of
R
=
m
/
Δ
m
≈
1.7
×
10
5
(sigma). Masses for
45V,
47Cr,
49Mn and
51Fe nuclei are determined with a relative mass precision of
δ
m
/
m
≈
2
×
10
−
7
(sigma) which is an improvement by a factor of
∼
2
compared to the literature values.
Using a novel method of isochronous mass spectrometry, the masses of ^{62}Ge, ^{64}As, ^{66}Se, and ^{70}Kr are measured for the first time, and the masses of ^{58}Zn, ^{61}Ga, ^{63}Ge, ^{65}As, ...^{67}Se, ^{71}Kr, and ^{75}Sr are redetermined with improved accuracy. The new masses allow us to derive residual proton-neutron interactions (δV_{pn}) in the N=Z nuclei, which are found to decrease (increase) with increasing mass A for even-even (odd-odd) nuclei beyond Z=28. This bifurcation of δV_{pn} cannot be reproduced by the available mass models, nor is it consistent with expectations of a pseudo-SU(4) symmetry restoration in the fp shell. We performed ab initio calculations with a chiral three-nucleon force (3NF) included, which indicate the enhancement of the T=1 pn pairing over the T=0 pn pairing in this mass region, leading to the opposite evolving trends of δV_{pn} in even-even and odd-odd nuclei.
Abstract
X-ray bursts are among the brightest stellar objects frequently observed in the sky by space-based telescopes. A type-I X-ray burst is understood as a violent thermonuclear explosion on the ...surface of a neutron star, accreting matter from a companion star in a binary system. The bursts are powered by a nuclear reaction sequence known as the rapid proton capture process (rp process), which involves hundreds of exotic neutron-deficient nuclides. At so-called waiting-point nuclides, the process stalls until a slower β
+
decay enables a bypass. One of the handful of rp process waiting-point nuclides is
64
Ge, which plays a decisive role in matter flow and therefore the produced X-ray flux. Here we report precision measurements of the masses of
63
Ge,
64,65
As and
66,67
Se—the relevant nuclear masses around the waiting-point
64
Ge—and use them as inputs for X-ray burst model calculations. We obtain the X-ray burst light curve to constrain the neutron-star compactness, and suggest that the distance to the X-ray burster GS 1826–24 needs to be increased by about 6.5% to match astronomical observations. The nucleosynthesis results affect the thermal structure of accreting neutron stars, which will subsequently modify the calculations of associated observables.
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•Dhaka pumping is limiting access to safe drinking water in surrounding rural areas.•Large vertical hydraulic gradients were observed ∼30km away from pumping center.•Modeled vertical ...recharge between shallow and deep aquifers was 0.21m/yr.•Estimated vertical movement of high arsenic water from shallow aquifers is 2–5cm/yr.
Sandy aquifers deposited >12,000years ago, some as shallow as 30m, have provided a reliable supply of low-arsenic (As) drinking water in rural Bangladesh. This study concerns the potential risk of contaminating these aquifers in areas surrounding the city of Dhaka where hydraulic heads in aquifers >150m deep have dropped by 70m in a few decades due to municipal pumping. Water levels measured continuously from 2012 to 2014 in 12 deep (>150m), 3 intermediate (90–150m) and 6 shallow (<90m) community wells, 1 shallow private well, and 1 river piezometer show that the resulting drawdown cone extends 15–35km east of Dhaka. Water levels in 4 low-As community wells within the 62–147m depth range closest to Dhaka were inaccessible by suction for up to a third of the year. Lateral hydraulic gradients in the deep aquifer system ranged from 1.7×10−4 to 3.7×10−4 indicating flow towards Dhaka throughout 2012–2014. Vertical recharge on the edge of the drawdown cone was estimated at 0.21±0.06m/yr. The data suggest that continued municipal pumping in Dhaka could eventually contaminate some relatively shallow community wells.
Abstract
A novel isochronous mass spectrometry, termed as
$$B\rho $$
B
ρ
-defined IMS, has been established at the experimental cooler-storage ring CSRe in Lanzhou. Its potential has been studied ...through high precision mass measurements of
$$^{58}$$
58
Ni projectile fragments. Two time-of-flight detectors were installed in one of the straight sections of CSRe, thus enabling simultaneous measurements of the velocity and the revolution time of each stored short-lived ion. This allows for calculating the magnetic rigidity
$$B\rho $$
B
ρ
and the orbit length
C
of each ion. The accurate
$$B\rho (C)$$
B
ρ
(
C
)
function has been constructed, which is a universal calibration curve used to deduce the masses of the stored nuclides. The sensitivity to single stored ions, fast measurement time, and background-free characteristics of the method are ideally suited to address nuclides with very short lifetimes and smallest production yields. In the limiting case of just a single particle, the achieved mass resolving power allows one to determine its mass-over-charge ratio
m
/
q
with a remarkable precision of merely
$$\sim 5$$
∼
5
keV. Masses of
$$T_z=-3/2$$
T
z
=
-
3
/
2
fp
-shell nuclides are re-determined with high accuracy, and the validity of the isospin multiplet mass equation is tested up to the heaviest isospin quartet with
$$A=55$$
A
=
55
. The new masses are also used to investigate the mirror symmetry of empirical residual proton-neutron interactions.
In the isochronous mass spectrometry (IMS) performed at storage rings, masses of short-lived nuclides are determined through precision measurements of their mean revolution times. However, the ...distribution of revolution times could be seriously deteriorated by instabilities of the ring’s magnetic fields. This becomes a significant obstacle for the particle identifications and mass determinations. A data analysis method is described in this paper which is able to largely remove the uncertainties caused by the magnetic field instabilities in the particle identifications and the mean revolution times. We show that this method is very effective for the IMS experiments even when the magnetic fields of a storage ring vary slowly up to a level of ΔB∕B∼10−4.
Isochronous mass spectrometry (IMS) in storage rings is a powerful tool for mass measurements of exotic nuclei with very short half-lives down to several tens of microseconds, using a multicomponent ...secondary beam separated in-flight without cooling. However, the inevitable momentum spread of secondary ions limits the precision of nuclear masses determined by using IMS. Therefore, the momentum measurement in addition to the revolution period of stored ions is crucial to reduce the influence of the momentum spread on the standard deviation of the revolution period, which would lead to a much improved mass resolving power of IMS. One of the proposals to upgrade IMS is that the velocity of secondary ions could be directly measured by using two time-of-flight (double TOF) detectors installed in a straight section of a storage ring. In this paper, we outline the principle of IMS with double TOF detectors and the method to correct the momentum spread of stored ions.
The hot compression tests of underwater vehicle metal material TC17 titanium alloy at deformation temperature of 800 ~ 950 °C and strain rate of 0,01 ~ 10 s-1 were carried out by Thermecmaster-Z ...thermal simulator. The hot deformation behavior of TC17 ferroalloy was studied. The effects of strain rate and deformation temperature on the high temperature forming of TC17 titanium alloy were analyzed. The multiple linear regression constitutive model of TC17 titanium alloy was established. The results show that the flow stress of TC17 alloy decreases with the increase of deformation temperature and increases with the increase of strain rate. The theoretical value of peak stress obtained by the multiple linear regression constitutive model of TC17 alloy is in good agreement with the experimental results, and the correlation is 97,25%. The model has high prediction accuracy.
Isochronous Mass Spectrometry (IMS) in heavy-ion storage rings is an excellent experimental method for precision mass measurements of exotic nuclei. In the IMS, the storage ring is tuned in a special ...isochronous ion-optical mode. Thus, the mass-over-charge ratios of the stored ions are directly reflected by their respective revolution times in first order. However, the inevitable momentum spread of secondary ions increases the peak widths in the measured spectra and consequently limits the achieved mass precision. In order to achieve a higher mass resolving power, the ring aperture was reduced to 60 mm by applying a mechanical slit system at the dispersive straight section. The momentum acceptance was reduced as well as better isochronous conditions were achieved. The results showed a significant improvement of the mass resolving power reaching 5.2×105, though at the cost of about 40% ion loss.
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