Theoretical investigation on radiation tolerance of M(n＋1)AXn phases

Ternary Mn＋1AXn phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, Mn＋1AXn materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different Mn＋1AXn（MAX） phases in terms of electronic structure, including the density of states（DOS） and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds,thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between Mn＋1ACn and Mn＋1ANn due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti3AlC2 to Ti2AlC （Ti3AlC2 and Ti2AlC have the same chemical elements）, can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other Mn＋1AXn phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors.

Extraordinary radiation tolerance of a Ni nanocrystal-decorated carbon nanotube network encapsulated in amorphous carbon

Nanostructured materials with abundant defect sinks show good radiation tolerance due to their efficient absorption of irradiation-induced interstitials and vacancies.However,the poor thermal stability and limited size of such nanomaterials severely limit their practical applications.Herein,we report a novel flexible free-standing network-structured hybrid consisting of amorphous carbon encapsulated nickel nanocrystals anchored on a single-wall carbon nanotube scaffold with excellent radiation tolerance up to 5 dpa at 673 K and exceptional thermal stability up to 1073 K.The nano-scale Ni-SWCNT network with abundant Ni-SWCNT interfaces and grain boundaries provides effective sinks and fast transportation channels for defects,which effectively absorb irradiation-induced defects and improved the irradiation tolerance.Furthermore,the formation of a low-energy Ni-C interface and surface thermal grooves significantly reduces the system free energy and increased thermal stability.The amorphous carbon layer produces an external compressive radial stress that inhibits Ni grain boundaries from migrating,which greatly improves the thermal stability of the hybrid by pinning GBs at grooves between grains and facilitates the annihilation of irradiation-induced defects at the sinks.This work provides a new strategy to improve the thermal stability and radiation tolerance of nano-materials used in an irradiation environment.

Development of an ADC radiation tolerance characterization system for the upgrade of the ATLAS LAr calorimeter

ATLAS LAr calorimeter will undergo its Phase-I upgrade during the long shutdown（LS2） in 2018, and a new LAr Trigger Digitizer Board（LTDB） will be designed and installed. Several commercial-off-the-shelf（COTS）multi-channel high-speed ADCs have been selected as possible backups of the radiation tolerant ADC ASICs for the LTDB. To evaluate the radiation tolerance of these backup commercial ADCs, we developed an ADC radiation tolerance characterization system, which includes the ADC boards, data acquisition（DAQ） board, signal generator,external power supplies and a host computer. The ADC board is custom designed for different ADCs, with ADC drivers and clock distribution circuits integrated on board. The Xilinx ZC706 FPGA development board is used as a DAQ board. The data from the ADC are routed to the FPGA through the FMC（FPGA Mezzanine Card）connector, de-serialized and monitored by the FPGA, and then transmitted to the host computer through the Gigabit Ethernet. A software program has been developed with Python, and all the commands are sent to the DAQ board through Gigabit Ethernet by this program. Two ADC boards have been designed for the ADC, ADS52J90 from Texas Instruments and AD9249 from Analog Devices respectively. TID tests for both ADCs have been performed at BNL, and an SEE test for the ADS52J90 has been performed at Massachusetts General Hospital（MGH）. Test results have been analyzed and presented. The test results demonstrate that this test system is very versatile, and works well for the radiation tolerance characterization of commercial multi-channel high-speed ADCs for the upgrade of the ATLAS LAr calorimeter. It is applicable to other collider physics experiments where radiation tolerance is required as well.

A Novel Radiation Tolerant SOI Isolation Structure

A novel radiation tolerant SOI isolation structure,consisting of thin SiO2/polysilicon/field SiO2 multilayers,is proposed. A device with this structure does not show obvious changes in subthreshold characteristics and leakage current,indicating a superior radiation tolerance to traditional LOCOS.

Enhancement of radiosensitization by metal-based nanoparticles in cancer radiation therapy

Radiation therapy performs an important function in cancer treatment. However, resistance of tumor cells to radiation therapy still remains a serious concern, so the study of radiosensitizers has emerged as a persistent hotspot in radiation oncology. Along with the rapid advancement of nanotechnology in recent years, the potential value of nanoparticles as novel radiosensitizers has been discovered. This review summarizes the latest experimental findings both in vitro and in vivo and attempts to highlight the underlying mechanisms of response in nanoparticle radiosensitization.

RADIOTHERAPEUTIC TOLERANCE OF THE RECONS-TRUCTIVE FLAPS FOLLOWING RADICAL EXCISION OF ORO-MAXILLOFACIAL CANCERS

Objectire To evaluate the radiation tolerance of the reconstructive flaPs used following radicalexcision of oro - maxillofacial tumors. methods The survival and radiation response of 88 flaps (preoperative 14and postoperative 74) in 82 patients were reviewed. Results The survival rate of 14 flaps done on preradiatedareas was 85.7% (12/14), markedly inferior to that of the flaps receiving postoperative radiation (98.6%, 73/74). Therate of radiation response of the flaps (35.1%) was signofcantly lower than that of the normal oral mucosasurrounding the flap (83.8%, P<0.01). Conclusion The good radiation tolerability of the transplants followingtumors excision pointed to the salety of its postoperative radiotherapy.

Robotic stereotactic irradiation and reirradiation for spinal metastases： safety and efficacy assessment

Background Spine is the most common site of bone metastases in patients with cancer.Conventional external beam radiotherapy lacks precision to allow delivery of large fraction radiation but simultaneously limit the dose to spinal cord.The purpose of this study was to evaluate the safety and efficacy of CyberKnife（R） radiation therapy for spinal metastases.Methods Seventy-three lesions in 62 patients treated with CyberKnife radiotherapy from September 2006 to June 2010 for spinal metastases were retrospectively reviewed.Thirteen tumors in 12 patients had received prior radiation.Patients were followed clinically and radiographically for at least 12 months or until death.In all patients,the spinal cord and thecal sac were contoured for dose-volume constraints,and maximum doses to 0.1,0.5,1,2,and 5-ml volumes were analyzed.Results Using the CyberKnife System,20-48 Gy in one to five fractions for unirradiated patients,and 21-38 Gy in one to five fractions for the previously irradiatied patients,were delivered.Median 2-Gy normalized Biological Equvaient Dose （nBED） of unirradiated targets and irradiated targets were 49.6 Gy10/2 （range,31.25-74.8 Gy10/2） and 46.9 Gy10/2 （range,29.8-66 Gy10/2）,respectively.With a median follow-up of 9.4 months （range,2.5-45 months）,twenty-nine patients （46.7％） were alive,whereas the others died of progressive disease.Fifty-six patients （93.3％） reported complete or partial reduction of pain after CyberKnife radiotherapy at one-month follow-up,17 patients （28.3％） reported some degree of pain relief after first fraction of the treatment course.Two patients experienced local recurrence at fifth and ninth months postradiotherapy.Median maximum nBED for spinal cord and thecal sac of naive targets were 68.6 Gy2/2 （range,8.3-154.5Gy2/2） and 83.5 Gy2/2 （range,10.5-180.5 Gy2/2）,respectively.Median maximum nBED for spinal cord and thecal sac for the re-irradiated targets were 58.6 Gy2/2 （range,17.7-140 Gy2/2） and 70.5 Gy2/2 （range,21.7-141.3 Gy2/2）,respectively.No patient developed radiation related myelopathy during the follow-up period.Conclusion Cyberknife radiotherapy is clinically effective and safe for spinal metastases,even in previously irradiated patients.

Atomic scale structure dominated FCC and B2 responses to He ion irradiation in eutectic high-entropy alloy AlCoCrFeNi_(2.1)

Radiation-tolerant materials are widely desired in nuclear reactors. High-entropy alloys(HEAs) exhibiting superior mechanical performance and swelling tolerance are being considered as next-generation nuclear structural materials. However, an understanding of HEAs irradiation tolerance at an atomic scale is still lacking. In this study, the atomic scale irradiation response of AlCoCrFeNi_(2.1), composed of face-centered cubic(FCC) phase and B2 phase, has been systematically investigated at 298 and 723 K. The bubble volume ratio of the B2 phase is much larger than that of the FCC phase under the same irradiation conditions, and hence, the FCC phase has superior swelling tolerance than the B2 phase. Also, order-disorder transformation occurred in both L12and B2 phases. The different irradiation responses between the FCC and B2 phases, depend firstly on composition and secondly on crystal structure. The higher compositional complexity and complicated atomic-level lattice environment of the FCC phase contribute to better radiation performance than B2 phase. The results pave a way for exploring radiation-tolerant structural high-entropy alloys.

Defect properties in a VTaCrW equiatomic high entropy alloy(HEA)with the body centered cubic(bcc)structure

We report first-principles results of the point defect properties in a V-Ta-Cr-W high-entropy alloy(HEA)with the body-centered cubic(bcc)structure.Different from the widely-investigated face-centered cubic(fcc)HEAs,the local lattice distortion is more pronounced in bcc ones,which has a strong influence on the defect properties and defect evolution under irradiation.Due to the large size of Ta,the exchange between vacancies and Ta exhibits lower energy barriers.On the other hand,interstitial dumbbells containing V and Cr possess lower formation energies.These defect energetics predicts an enrichment of V and Cr and a depletion of Ta andWin the vicinity of defect sinks.Besides,we find that interstitial dumbbells favor the[110]orientation in the HEA,instead of[111]direction in most nonmagnetic bcc metals,which helps to slow down interstitial diffusion significantly.Consequently,the distribution of migration energies for vacancies and interstitials exhibit much larger overlap regions in the bcc HEA compared to fcc HEAs,leading to the good irradiation resistance by enhancing defect recombination.Our results suggest that HEAs with the bcc structure may bear excellent irradiation tolerance due to the particular defect properties.

Review on helium behaviors in nanochannel tungsten film

Tungsten(W)as plasma facing material(PFM)needs to face an unprecedented harsh environment in the fusion reactor,which puts forward high requirements for its radiation tolerance.Among the many challenges,the rapid accumulation of helium(He)atoms to form numerous bubbles or even“fuzzy”nanostructure leads to swelling and embrittlement of W matrix and seriously shorten its service life,which is one of the most serious problems faced by PFM-W at present.In this review,we summarize the recent works on the nanochannel W films with high surface-to-volume ratio deposited by magnetron sputter-ing,and the behaviors of He in the nanochannel W films at different fusion-related irradiation environment.Experimental and simulation results showed that the nanochannel W films have better radiation tolerance performance in managing He behaviors than that of commercial bulk W.