Radiation effects caused by solar proton events will be a common problem for many types of sensors on missions to the inner solar system because of the long cruise phases coupled with the inverse ...square scaling of solar particle events. In support of the BepiColombo and Solar Orbiter missions we have undertaken a comprehensive series of tests to assess the effects on a wide range of sensors. Sensors based on scintillators have been proposed for both missions. In this paper, we report on a series of controlled irradiations on a set of five LaBr3:Ce scintillators. The crystals are 1in. right circular cylinders of LaBr3, packaged in aluminium housings and viewed through BK7 optical windows. Four crystals were exposed to simulated solar proton events over the energy range 60–200MeV having a spectral shape approximating that of the August 1972 solar particle event. Each crystal was exposed to a different total fluence. One crystal was exposed to an integral fluence of 109protonscm−2, a second to 1010protonscm−2, the third to 1011protonscm−2 and the fourth to 1012protonscm−2. The latter corresponds to an absorbed dose in silicon of 1Mrad or in SI units, 10kGy. The fifth crystal served as a reference. The crystals were characterized both before and after the irradiations in terms of energy resolution, light output and background count rate. The key conclusions of the study are that LaBr3 is radiation tolerant showing no measurable degradation effects when exposed to experimentally simulated solar proton flare spectra with fluences up to 1012protonscm−2 (∼1Mrad or 10kGy equivalent in silicon) and integrated above a 60MeV energy threshold. LaBr3 behaves as a generic intermediate mass material showing similar activation yields as CsI(Tl) and Ge above 1010protonscm−2 (∼10krad (100Gy) equivalent in silicon) and significantly less than Ge below this fluence.
Radiation effects caused by solar proton events will be a common problem for many types of sensors on missions to the inner solar system because of the long cruise phases coupled with the inverse ...square scaling of solar particle events. As part of a study in support of the BepiColombo mission to Mercury we have undertaken a comprehensive series of tests to assess these effects on a wide range of sensors. In this paper, we report on the measurements on a large volume coaxial Ge detector which was exposed to simulated solar proton spectra of integrated fluences
8
×
10
8
,
6
×
10
9
and
6
×
10
10
protons
cm
-
2
. After each irradiation the detectors performance was accessed in terms of energy resolution, efficiency and activation. The detector was then annealed and the measurements repeated before the next irradiation. The minimum operational performance criteria were based on the resolution and efficiency requirements necessary to detect and separate specific radioisotope emission lines from a planetary regolith. Specifically that the energy resolution be restored to 5
keV FWHM at 1332
keV and the detection efficiency be degraded to no more than 10% of its pre-irradiation value. The key conclusion of this study is that even after a modest solar proton event the detector requires extensive annealing. After exposure to an event of integral fluence
∼
8
×
10
8
protons
cm
-
2
this amounts to
∼
1
week duration at
100
∘
C
, whereas for a fluence of
∼
6
×
10
10
protons
cm
-
2
, the detector requires 3.5 months of annealing to satisfy the minimum operational performance requirements and 4.5 months to return the energy resolution to
<
3
keV
FWHM at 1332
keV. As a consequence such an instrument will require constant, planned and active management throughout its operational lifetime. The impact on spacecraft operations including resource management therefore needs careful consideration.
Cosmic neutrinos with ultra high energies can be detected acoustically using hydrophones. The detection of these neutrinos may provide crucial information about then GZK mechanism. The flux of these ...neutrinos, however, is expected to be low, so that a detection volume is required more than a order of magnitude larger than what has presently been realized. With a large detection volume and a large number of hydrophones, there is a need for technology that is cheap and easy to deploy. Fiber optics provide a natural way for distributed sensing. In addition, a sensor has been designed and manufactured that can be produced cost-effectively on an industrial scale. Sensitivity measurements show that the sensor is able to reach the required sea-state zero level. For a proper interpretation of the expected bipolar signals, filtering techniques should be applied to remove the effects of the unwanted resonance peaks.
Solar proton event damage in space-borne Ge detectors Quarati, F.; Brandenburg, S.; Buis, E.-J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2009, Letnik:
610, Številka:
1
Journal Article
Recenzirano
By means of annealing it has been possible to fully restore the spectral performance of Ge detector after exposure to simulated Solar Proton Events (SPE) of integrated fluences up to 6×10
10
...protons/cm
2.
The required annealing time to achieve the restoration of energy resolution, the ratio FWTM/FWHM and detection efficiency to pre-irradiation values is of the order of 25 weeks. However, about half of this time might be considered sufficient to restore the detector within acceptable operational limits for most applications.
The long annealing time required to restore the detection performances opens a question on the actual suitability of Ge detector for inner solar system missions, as BepiColombo and Solar Orbiter, unless enhanced robustness or faster recovering capability can be developed, for instance using specific crystal encapsulation.
In semi-arid areas vegetation is scarce and often dominated by individual shrubs on raised mounds. The processes of formation of these mounds are diverse and still debated. Often, shrub mound ...formation is directly related to the formation of vegetation patterns, thereby assuming that shrub mound formation is driven by biological interactions. We hypothesize that water-related erosion and sedimentation are also important drivers of shrub mound formation in the Northern Negev Desert of Israel. We test this hypothesis by combining field observations with model simulations. We studied shrub mounds in the semi-arid catchment of Sayeret Shaked in the Northern Negev Desert (200
mm annual precipitation). Height and diameter of shrub-canopy and shrub mounds were measured and micro-morphological techniques were used to reconstruct the formation of the shrub mounds. We used landscape evolution model LAPSUS to simulate shrub mound formation at short (single precipitation event) and longer (100
years) timescales at different slope angles. Both field and model results indicate that shrub mounds in Sayeret Shaked are at least partly formed by redeposition of eroded material below the shrubs, and by erosion and lowering of the surrounding crust. Additional model simulations suggest that mounds are formed most under low shrub density and large shrub-canopy diameter. Shrub mound formation increases with slope. In dryer and wetter climates than the studied 200
mm rainfall semi-arid climate zone, shrub mound formation is less likely.
We studied the controls on functional surface cover types in four catchments along a semi-arid to arid precipitation gradient in the northern Negev Desert of Israel. First, we selected four ...functional types, based on their unique water use and redistribution functionality: shrubs, Asphodelus ramosus, other herbaceous plants and surface crusts. We estimated percentage of surface covered by these functional types and by bedrock outcrops and loose surface stones. Additionally data was collected on soil depth, relative elevation, insolation, slope, curvature, and overlain with surface cover maps. Relations between functional types and landscape structure variables were analyzed with descriptive statistics. The landscape structure variables bedrock, relative elevation, soil depth and surface stones explained most of the cover variance in the catchments. In catchments with many bedrock outcrops, functional types were best explained by the landscape structure variables. In catchments with homogeneous soils reaching beyond the root zone, the biological interactions between functional types were more important. Along the precipitation gradient the explanatory power of the biological variables decreased with decreasing precipitation, while the explanatory power of landscape structure variables appeared unrelated. Only in homogeneous semi-arid catchments regular vegetation patterns can develop, in arid and heterogeneous catchments irregular patterns dominate.
Proton irradiation of liquid crystal based adaptive optical devices Buis, E.J.; Berkhout, G.C.G.; Love, G.D. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
2012, 2012-1-00, 20120101, Letnik:
270
Journal Article
Recenzirano
To assess its radiation hardness, a liquid crystal based adaptive optical element has been irradiated using a 60
MeV proton beam. The device with the functionality of an optical beam steerer was ...characterised before, during and after the irradiation. A systematic set of measurements on the transmission and beam deflection angles was carried out. The measurements showed that the transmission decreased only marginally and that its optical performance degraded only after a very high proton fluence
(
10
10
p
/
cm
2
)
. The device showed complete annealing in the functionality as a beam steerer, which leads to the conclusion that the liquid crystal technology for optical devices is not vulnerable to proton irradiation as expected in space.
PDF
