T. Izumikawa

High-resolution measurement of the time-modulated orbital electron capture and of the β+ decay of hydrogen-like 142Pm60+ ions

Abstract The periodic time modulations, found recently in the two-body orbital electron capture (EC) decay of both, hydrogen-like 140Pr58+ and 142Pm60+ ions, with periods near to 7 s and amplitudes of about 20%, were re-investigated for the case of 142Pm60+ by using a 245 MHz resonator cavity with a much improved sensitivity and time resolution. We observed that the exponential EC decay is modulated with a period T = 7.11 ( 11 ) s , in accordance with a modulation period T = 7.12 ( 11 ) s as obtained from simultaneous observations with a capacitive pick-up, employed also in the previous experiments. The modulation amplitudes amount to a R = 0.107 ( 24 ) and a P = 0.134 ( 27 ) for the 245 MHz resonator and the capacitive pick-up, respectively. These new results corroborate for both detectors exactly our previous findings of modulation periods near to 7 s , though with distinctly smaller amplitudes. Also the three-body β + decays have been analyzed. For a supposed modulation period near to 7 s we found an amplitude a = 0.027 ( 27 ) , compatible with a = 0 and in agreement with the preliminary result a = 0.030 ( 30 ) of our previous experiment. These observations could point at weak interaction as origin of the observed 7 s -modulation of the EC decay. Furthermore, the data suggest that interference terms occur in the two-body EC decay, although the neutrinos are not directly observed.

Examining the exotic structure of the proton-rich nucleus {sup 23}Al

The longitudinal momentum distribution (P{sub //}) of fragments after one-proton removal from {sup 23}Al and reaction cross sections ({sigma}{sub R}) for {sup 23,24}Al on a carbon target at 74A MeV have been measured. The {sup 23,24}Al ions were produced through projectile fragmentation of 135A MeV {sup 28}Si primary beam using the RIPS fragment separator at RIKEN. P{sub parallel} is measured by a direct time-of-flight (TOF) technique, while {sigma}{sub R} is determined using a transmission method. An enhancement in {sigma}{sub R} is observed for {sup 23}Al compared with {sup 24}Al. The P{sub parallel} for {sup 22}Mg fragments from {sup 23}Al breakup has been obtained for the first time. FWHM of the distributions has been determined to be 232 {+-} 28 MeV/c. The experimental data are discussed by using the Few-Body Glauber model. Analysis of P{sub //} demonstrates a dominant d-wave configuration for the valence proton in ground state of {sup 23}Al, indicating that {sup 23}Al is not a proton halo nucleus.

Between atomic and nuclear physics: radioactive decays of highly-charged ions

Highly charged radioactive ions can be stored for extended periods of time in storage rings which allows for precision measurements of their decay modes. The straightforward motivation for performing such studies is that fully ionised nuclei or few-electron ions can be viewed as clean quantum-mechanical systems, in which the interactions of the many electrons can be either excluded or treated precisely. Thus, the influence of the electron shell on the decay probability can be investigated. Another important motivation is stellar nucleosynthesis, which proceeds at high temperatures and the involved atoms are therefore highly ionised. Presented here is a compact review of the relevant experiments conducted at heavy-ion storage rings. Furthermore, we outline the perspectives for future experiments at new-generation storage-ring facilities.

A Map for the Future: Measuring Radiation Levels in Fukushima, Japan

After the cataclysmic explosion in the Fukushima Daiichi Nuclear Power Station triggered by the Great East Japan Earthquake of March 2011, more than 100,000 citizens living within 20km of the nuclear power station were evacuated. These residents were not allowed to return home for more than a year, until April 2012, when the Japanese government began to lift the evacuation order for some areas. As local governments contemplate strategies to revive these communities, a lingering question remains: how safe is it to live here? Answering this question is difficult for a number of reasons. Our project aims to provide data to allow individuals and communities to make their own assessments. The Radioisotope Center (RC) in Niigata University has built a vehicle-mounted radiation monitoring system consisting of a real-time GPS receiver, a dosimeter, and a laptop. This tool allows government officials in the affected municipalities to continuously measure airborne radiation levels. RC has partnered with the Institute for Digital Research and Education (IDRE) from the University of California, Los Angeles (UCLA) to develop a public web-based interface to this data to inform citizens about radiation levels in their communities. Both of these tools enable gathering and making data available to the general public more easily, and allow the public to make informed decisions about the safety of the decontaminated zones in the absence of widely-accepted standards.

Electric quadrupole moment of 25Na

The electric quadrupole coupling constant eqQ/h of 25Na (Iπ = 5/2+, T1/2 = 59.6 s), implanted in a TiO2 single crystal, has been measured by use of the β-NMR technique, to determine the electric quadrupole moment Q. As a result, |eqQ/h| = (44 ± 16) kHz and |Q(25Na)| = (1.0 ± 0.4) mb were determined. From the NMR on 25Na in NaCl, the magnetic moment was determined as |µ| = (3.6832 ± 0.0003) µN

Behavior of Boron Implanted in Semiconductor Si

Using β-NMR with 12B nuclei the temperature dependence of the lattice locations of boron implanted in Si is studied. At low temperature almost 100% of the implanted B is in either substitutional site or nonsubstitutional site. Above 260 K, the nonsubstitutional B rapidly becomes undetectable and disappears at a temperature higher than 325 K due to the fast spin-lattice relaxation. Above 450 K, the fraction of substitutional B increases to 100%. These experimental results are consistently explained by the thermal atomic jump and the dissociation of the defect associated with the nonsubstitutional B.

Measurement of the reaction cross section of (18)C and observations of fragments from (17)C and (18)C at 80A MeV

The one- and two-neutron removal reactions from (17)C and (18)C as well as the reaction cross section of (18)C have been studied using a carbon target at 80A MeV. The longitudinal momentum distributions of (15,16)C fragments from (17)C and (16,17)C fragments from (18)C were measured by a direct time-of-flight method. The width of (15)C fragments from (17)C is fairly smaller than that from other C isotopes. The experimental data are discussed within the framework of the Glauber model.

Precise Studies of Nucleon Density Distribution of 6He and 8He

Reaction cross sections (σR) for 6He and 8He have been measured on 9Be, 12C, and 27Al targets at intermediate energies. We deduced the nucleon density distribution of 6He and 8He through our data with the use of modified Glauber calculation. This method is a sensitive probe for dilute nucleon density and we successfully clarified the halo structure of 6He and the neutron skin‐type density distribution of 8He.

The ferroptosis inducer erastin irreversibly inhibits system x c − and synergizes with cisplatin to increase cisplatin’s cytotoxicity in cancer cells

System xc− was recently described as the most upstream node in a novel form of regulated necrotic cell death, called ferroptosis. In this context, the small molecule erastin was reported to target and inhibit system xc−, leading to cysteine starvation, glutathione depletion and consequently ferroptotic cell death. Although the inhibitory effect of erastin towards system xc− is well-documented, nothing is known about its mechanism of action. Therefore, we sought to interrogate in more detail the underlying mechanism of erastin’s pro-ferroptotic effects. When comparing with some well-known inhibitors of system xc−, erastin was the most efficient inhibitor acting at low micromolar concentrations. Notably, only a very short exposure of cells with low erastin concentrations was sufficient to cause a strong and persistent inhibition of system xc−, causing glutathione depletion. These inhibitory effects towards system xc− did not involve cysteine modifications of the transporter. More importantly, short exposure of tumor cells with erastin strongly potentiated the cytotoxic effects of cisplatin to efficiently eradicate tumor cells. Hence, our data suggests that only a very short pre-treatment of erastin suffices to synergize with cisplatin to efficiently induce cancer cell death, findings that might guide us in the design of novel cancer treatment paradigms.

High rate silicon tracker for proton computed tomography

Proton computed tomography (CT) is an imaging technique using a high-energy proton beam penetrating the human body and shows promise for improving the quality of cancer therapy with high-energy particle beams because more accurate electron density distribution measurements and in-situ positioning can be achieved with proton CT. The deterioration of the spatial resolution owing to multiple Coulomb scattering is saved by reconstructing the proton trajectory. We have developed a prototype system for proton CT and demonstrate a precise measurement of electron density and an improvement in spatial resolution. In order to control of the radiation dose and reduce the exposure time for imaging, the precise position detector should work with very high rate (a few MHz). We have developed high speed tracker with large area silicon strip detector, Amplifier-Shaper-Discriminator LSI, which was developed for drift chamber readout at high energy physics experiment, and FPGA. We report the performance of the tracker evaluated with very high intensity proton beam for the cancer therapy.