Instrument Description

The Colorado Inner Radiation Belt Experiment, or CIRBE, was launched on April 15th, 2023, into a sun-synchronous orbit with a 97.4o degree inclination and a 509 kilometer altitude. CIRBE is partitioned into two sections: a spacecraft bus (XB1 from Blue Canyon Technologies), and its only science payload, Relativistic Electron Proton Telescope integrated little experiment-2, or REPTile-2.

REPTile-2 is a 10x10x15 cm energetic particle telescope. It includes four 1.5 mm thick silicon detectors (‘D1’ through ‘D4’) separated into inner areas (diameter 20 mm) and outer rings (diameter 40 mm), which are known as guard rings (‘G’). These detectors were obtained from Micron Semiconductors, UK. In front of the silicon detectors there is a beryllium window with a diameter of 20 mm and a thickness of 0.3 mm that block <~200 keV electrons and <~6 MeV protons from reaching the silicon detectors. In front of the beryllium window, a collimator is used to prevent particles from outside the telescope’s field of view of ~51o from entering the detector stack.

Khoo, L.-Y., Li, X., Selesnick, R. S., Schiller, Q., Zhang, K., Zhao, H., et al. (2022). On the challenges of measuring energetic particles in the inner belt: A Geant4 simulation of an energetic particle detector instrument, REPTile-2. Journal of Geophysical Research: Space Physics, 127, e2021JA030249. https://doi.org/10.1029/2021JA030249

REPTile-2 has a high energy resolution and is capable of measuring electrons from ~0.25-6 MeV and protons from ~6.5-100 MeV via the 120 total energy channels used to measure these particles at different energies. Protons and electrons are each dedicated 60 channels, with 50 of those measuring range particles and 10 of them measuring penetrating particles. It also has an extremely high time resolution capable of distinguishing events occurring merely 400 nanoseconds after each other.

For more information about REPTile-2: here

Logic Information

REPTile-2 records an event when a particle enters the detector stack and deposits energy on one or more detectors. The instrument uses a system of logic to determine which events are considered valid and to categorize valid events into one of four categories corresponding to what kind of particle is being measured: range protons (RNGp), penetrating protons (PENp), range electrons (RNGe), and penetrating electrons (PENe).

Valid events are events that deposit an amount of energy that is above a certain threshold (TD) on the first detector (D1) and do not deposit an amount of energy that is above another threshold (TG) on the guard rings (G). TD and TG are set at 100 keV and 671 keV, respectively. This means that if an event deposits more than 100 keV on D1 and less than 671 keV on G, it is considered to be a valid event.

Events are further classified via the use of two slant equations. The first slant equation, D12s, is true if the energy deposited on D1 divided by 2.8 MeV plus the energy deposited on D2 divided by 4.2 MeV is greater than 1. If D12s is not true then the event is an electron. The event is further classified as either a range or a penetrating electron by whether or not TD is deposited on D4; if TD is deposited on D4, the event is a penetrating electron (PENe), and if not, the event is a range electron (RNGe).

The second slant equation, D34s, is true if the amount of energy deposited on D3 divided by 13.5 MeV plus the amount of energy deposited on D4 divided by 30 MeV is greater than 1. If both D12s and D34s are true and TD has not been deposited on D4, the event is classified as a range proton (RNGp). If only D12s is true and TD has been deposited on D4, the event is classified as a penetrating proton (PENe).

The logic equations are summarized in the table below taken from: Khoo, L.-Y., Li, X., Selesnick, R. S., Schiller, Q., Zhang, K., Zhao, H., et al. (2022). On the challenges of measuring energetic particles in the inner belt: A Geant4 simulation of an energetic particle detector instrument, REPTile-2. Journal of Geophysical Research: Space Physics, 127, e2021JA030249. https://doi.org/10.1029/2021JA030249.

Energy Channel Information

Each of the four categories is dedicated a range of energy channels, with each channel corresponding to a certain particle energy. The particle type, channel energies, and geometric factor times energy channel width (GdE) for each channel as calculated by the bowtie method are shown in the table below.

Channel NumberParticle TypeEnergy (MeV)GdE (cm2sr MeV)
1RNGp6.80.0392272444479054
2RNGp6.80.0410347259093529
3RNGp6.90.0413182507919513
4RNGp70.043823614357862
5RNGp7.10.0506866384362174
6RNGp7.20.0518894733226866
7RNGp7.30.0569562796589815
8RNGp7.50.0720184011053454
9RNGp7.60.0698009920443771
10RNGp7.70.0754675359633083
11RNGp7.90.0776797680914494
12RNGp8.10.0838597832119609
13RNGp8.20.0862950938748381
14RNGp8.40.10190163290902
15RNGp8.60.0998505287432661
16RNGp8.90.121482935529745
17RNGp9.10.125365793689071
18RNGp9.40.136192429199833
19RNGp9.60.138826261654679
20RNGp9.90.149855188681277
21RNGp10.20.161971246127969
22RNGp10.60.178305325456198
23RNGp10.90.180748486870869
24RNGp11.30.188379176521905
25RNGp11.70.20600782158654
26RNGp12.10.218832723432197
27RNGp12.60.234544446932618
28RNGp13.10.26588330108469
29RNGp13.60.254699883086223
30RNGp14.10.267324019322415
31RNGp14.70.290400499253022
32RNGp15.30.30497435535352
33RNGp160.350671678121021
34RNGp16.70.341609611569272
35RNGp17.40.335591504245762
36RNGp18.20.355100677038051
37RNGp190.355539287991945
38RNGp19.80.375758786843855
39RNGp20.80.414962626539929
40RNGp21.70.412125823391869
41RNGp22.70.427594167581035
42RNGp23.80.451653146373649
43RNGp24.90.433352598042547
44RNGp26.10.441347501542973
45RNGp27.40.49000872334778
46RNGp28.70.505489489225791
47RNGp30.10.466614938381014
48RNGp31.60.4057175118402
49RNGp33.10.527043656420538
50RNGp34.50.179635941840052
51PENp95.13.6262936568183
52PENp32.30.318290237272177
53PENp34.60.382979559546845
54PENp37.20.719428002135456
55PENp39.41.17338020904926
56PENp48.84.09986951288032
57PENp54.76.79403446819182
58PENp63.411.9634539965272
59PENp76.921.5241923999758
60PENp132.6182.665006223793
61RNGe0.30.00223804164828743
62RNGe0.310.00260452254421197
63RNGe0.310.00287251561053182
64RNGe0.310.0030847743792478
65RNGe0.320.00364353433071976
66RNGe0.320.00377944774660896
67RNGe0.330.0043408657779181
68RNGe0.340.00502676719160926
69RNGe0.350.00563738328135834
70RNGe0.360.00628738808546234
71RNGe0.370.00686342271354899
72RNGe0.390.00779875939479639
73RNGe0.40.00836998638844766
74RNGe0.420.00921748092040848
75RNGe0.440.0102841822185981
76RNGe0.470.0118534262126143
77RNGe0.490.0124813303614828
78RNGe0.520.0139605333285567
79RNGe0.560.0160074061872641
80RNGe0.590.0166745382209565
81RNGe0.630.0186960844902897
82RNGe0.680.0213195281887486
83RNGe0.720.0220546233470271
84RNGe0.780.0257736844389772
85RNGe0.830.0269552797941939
86RNGe0.890.0284120249967939
87RNGe0.960.0314296505534594
88RNGe1.030.0329531531465774
89RNGe1.110.0350481850198095
90RNGe1.20.0374002630586924
91RNGe1.290.0382949636463525
92RNGe1.40.0421508580065854
93RNGe1.510.0438115216286113
94RNGe1.630.0455127234777333
95RNGe1.760.0463916606952633
96RNGe1.90.0473442903819639
97RNGe2.050.0461838400552538
98RNGe2.220.0470472464137365
99RNGe2.40.0442985944040365
100RNGe2.640.0517477545626182
101RNGe2.890.0449188061444119
102RNGe3.090.0350087904744153
103RNGe3.340.0260608153224847
104RNGe3.610.017575034135677
105RNGe3.910.011597213591902
106RNGe4.230.00698651925454324
107RNGe4.580.00420001192901242
108RNGe4.960.00233112868277044
109RNGe5.370.00109626141275523
110RNGe5.830.000673015773965007
111PENe5.960.00442463347154718
112PENe5.560.00780350669639281
113PENe5.150.0128532253416846
114PENe4.740.0196122475138409
115PENe4.320.0277375767198909
116PENe3.910.0378725258909174
117PENe3.510.0483988063193173
118PENe3.120.0522114541706407
119PENe2.760.0443042555050492
120PENe4.030.227510362226532

The contents of this table can be downloaded as a .xlsx file here.

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