RESUMO
The DAMA/LIBRA collaboration has reported the observation of an annual modulation in the event rate that has been attributed to dark matter interactions over the last two decades. However, even though tremendous efforts to detect similar dark matter interactions were pursued, no definitive evidence has been observed to corroborate the DAMA/LIBRA signal. Many studies assuming various dark matter models have attempted to reconcile DAMA/LIBRA's modulation signals and null results from other experiments, however no clear conclusion can be drawn. Apart from the dark matter hypothesis, several studies have examined the possibility that the modulation is induced by variations in detector's environment or their specific analysis methods. In particular, a recent study presents a possible cause of the annual modulation from an analysis method adopted by the DAMA/LIBRA experiment in which the observed annual modulation could be reproduced by a slowly varying time-dependent background. Here, we study the COSINE-100 data using an analysis method similar to the one adopted by the DAMA/LIBRA experiment and observe a significant annual modulation, however the modulation phase is almost opposite to that of the DAMA/LIBRA data. Assuming the same background composition for COSINE-100 and DAMA/LIBRA, simulated experiments for the DAMA/LIBRA without dark matter signals also provide significant annual modulation with an amplitude similar to DAMA/LIBRA with opposite phase. Even though this observation does not directly explain the DAMA/LIBRA results directly, this interesting phenomenon motivates more profound studies of the time-dependent DAMA/LIBRA background data.
RESUMO
We present new constraints on dark matter interactions using 1.7 years of COSINE-100 data. The COSINE-100 experiment, consisting of 106 kg of tallium-doped sodium iodide [NaI(Tl)] target material, is aimed to test DAMA's claim of dark matter observation using the same NaI(Tl) detectors. Improved event selection requirements, a more precise understanding of the detector background, and the use of a larger dataset considerably enhance the COSINE-100 sensitivity for dark matter detection. No signal consistent with the dark matter interaction is identified and rules out model-dependent dark matter interpretations of the DAMA signals in the specific context of standard halo model with the same NaI(Tl) target for various interaction hypotheses.
RESUMO
Accelerator Based Neutron Sources (ABNS) have been studied for their utility in materials research as well as for boron neutron captured therapy. By making significant efforts to study the (p,n) and (d,n) nuclear reactions, the specifications of the accelerator system have been determined. In this paper, we compare the design results for two types of radio frequency quadrupole (RFQ) accelerators to provide proton and deuteron beams, respectively. Both systems consist of an electron cyclotron resonance (ECR) ion source, a low-energy beam transport system, an RFQ accelerator, a medium-energy beam transport system, a Be target, and a moderator system. In order to achieve a compact accelerator system at a reasonable cost, different requirements must be applied to the design of RFQ accelerators. The proton RFQ has been designed with an operation frequency of 352 MHz, up to 4 MeV acceleration, 10 mA beam intensity, and a continuous-wave (CW) operation mode to achieve 0.84 × 109 n/(s/cm2) of neutron production. However, the deuteron RFQ has been designed with an operation frequency of 200 MHz, up to 2.5 MeV acceleration, 15 mA of beam intensity, and a CW operation mode to achieve 1.02 × 109 n/(s/cm2) of neutron production. In this paper, we describe the merit of the deuteron based neutron source by comparing two types of the RFQ accelerators for proton and deuteron beams including the common system of the ECR ion source and Be target in detail.
