Performance of the low pressure MWPCs for f ission fragments under a high background

Two couples of low pressure multi-wire proportional chambers (MWPC) were located in the target chamber to detect fission fragments in a hypernuclei producing experiment at Thomas Jefferson National Laboratory (Jlab). In the experiment, a continuous wave (CW) electron beam was applied to form hypernuclei by electromagnetic interaction. In the target chamber, the high energy (1.853 GeV) and high intensity (500 nA) primary electron beam caused a high particle background, which influenced the detection of the fission fragments. This report described the design of the MWPCs and studied the fission-fragment detecting performance of them under such a high background. The efficiency of the MWPCs was given with the help of a high resolution kaon spectrometer. At the same time, the background particles were discussed with a Monte Carlo code based on GEANT4.     

The Nd–Mn exchange interaction,low temperature specific heat and magnetism of Nd2/3Ca1/3MnO3

The low temperature specific heat and magnetic characteristics of Nd_2/3Ca_1/3MnO₃ perovskite are studied in a wide range of magnetic fields (up to 9 T). Temperature dependent specific heat data show a broadened Schottky-like anomaly below 20 K caused by splitting of the Nd³⁺ ions ground-state doublet in the effective molecular field H_ex, determined by exchange interaction between Nd and Mn spin systems supplemented by an applied external magnetic field. Existence of the splitting at zero magnetic field and expressed field dependence is the evidence of a strong exchange coupling between Nd and Mn magnetic subsystems. The Nd-ions magnetic ordering leads to an additional contribution to the magnetic moment of the system below 30 K, producing anomalies of the magnetic loss and field-cooled and zero-field-cooled magnetizations. The observed broadened Schottky-like anomalies are fitted for each applied magnetic field by the sum of three Schottky functions. Applied magnetic field extends the anomaly region and shifts it to higher temperatures. Splitting of the higher crystal field Kramers doublets gives an additional contribution to the heat capacity in magnetic fields. The ground state doublet g-factors g_|| and g_⊥ were estimated to be 3.4 and 2.2, respectively, and H_ex was estimated to be 9 T. The Nd³⁺ ions magnetic moment estimated from the magnetization data agrees with the value obtained from the specific heat data.     

Magnetic properties of novel FeSe(Te) superconductors

Magnetization studies were carried out for the novel FeSe_1−xTe_x superconductors (0≤x≤1$0\le x\le 1$) to investigate a behavior of the intrinsic magnetic susceptibility χ$\chi$ in the normal state. The magnetic susceptibility was found to increase gradually with Te content. The temperature dependencies of the magnetic susceptibility χ$\chi$ and its anisotropy Δχ=_χ∥−_χ⊥$\mathrm{\Delta }\chi ={\chi }_{\parallel }-{\chi }_{\perp }$ were measured for FeSe in the temperature range 4.2–300 K, and a growth of susceptibility with temperature was revealed. For FeTe a substantial increase of χ$\chi$ under pressure was found. Ab initio calculations of the band structure and magnetic susceptibility have shown, that FeSe_1−xTe_x systems are close to magnetic instability with dominating enhanced spin paramagnetism. The calculated paramagnetic susceptibility exhibits a strong dependence on the unit cell volume V   and especially the height of chalcogen species from the Fe plane. With appropriate values of these parameters the calculations have reproduced the experimental data on χ(T)$\chi (T)$ and χ(P)$\chi (P)$ for FeSe and FeTe, respectively.