Cosmogenic  Ac,va,on  in  DM-­‐Ice  

Walter  C.  Pe9us  UW  –  Madison  

11  May  2011  

Uncertain  Dark  Ma9er  Status  

•  Annual  modula,on  by  DAMA  

•  Excess  of  low-­‐energy  events  by  CoGeNT  

•  Regions  excluded  by  XENON  and  CDMS  

11  May  2011   Walter  C.  Pe9us   2  

Eur. Phys. J. C (2008) 56: 333–355 337

Fig. 2 Model-independent residual rate of the single-hit scintillationevents, measured by the new DAMA/LIBRA experiment in the (2–4),(2–5) and (2–6) keV energy intervals as a function of the time. Theresiduals measured by DAMA/NaI and already published in Refs. [11,12] are also shown. The zero of the time scale is January 1st of thefirst year of data taking of the former DAMA/NaI experiment. Theexperimental points present the errors as vertical bars and the asso-ciated time bin width as horizontal bars. The superimposed curvesrepresent the cosinusoidal functions behaviors A cos!(t ! t0) with a

period T = 2"! = 1 yr, with a phase t0 = 152.5 day (June 2nd ) and

with modulation amplitudes, A, equal to the central values obtainedby best fit over the whole data, that is: (0.0215 ± 0.0026) cpd/kg/keV,(0.0176 ± 0.0020) cpd/kg/keV and (0.0129 ± 0.0016) cpd/kg/keV forthe (2–4) keV, for the (2–5) keV and for the (2–6) keV energy inter-vals, respectively. See text. The dashed vertical lines correspond to themaximum of the signal (June 2nd ), while the dotted vertical lines cor-respond to the minimum. The total exposure is 0.82 ton " yr

5

]2WIMP Mass [GeV/c6 7 8 910 20 30 40 50 100 200 300 400 1000

]2W

IMP-

Nuc

leon

Cro

ss S

ectio

n [c

m

-4510

-4410

-4310

-4210

-4110

-4010

-3910

]2WIMP Mass [GeV/c6 7 8 910 20 30 40 50 100 200 300 400 1000

]2W

IMP-

Nuc

leon

Cro

ss S

ectio

n [c

m

-4510

-4410

-4310

-4210

-4110

-4010

-3910

DAMA/I

DAMA/Na

CoGeNT

CDMS

EDELWEISS

XENON100 (2010)

XENON100 (2011) Buchmueller et al.

FIG. 5: Spin-independent elastic WIMP-nucleon cross-section

σ as function of WIMP mass mχ. The new XENON100 limit

at 90% CL, as derived with the Profile Likelihood method

taking into account all relevant systematic uncertainties, is

shown as the thick (blue) line together with the 1σ and 2σsensitivity of this run (shaded blue band). The limits from

XENON100 (2010) [7] (thin, black), EDELWEISS [6] (dotted,

orange), and CDMS [5] (dashed, orange, recalculated with

vesc = 544 km/s, v0 = 220 km/s) are also shown. Expecta-

tions from CMSSM are indicated at 68% and 95% CL (shaded

gray) [17], as well as the 90% CL areas favored by CoGeNT

(green) [18] and DAMA (light red, without channeling) [19].

and a density of ρχ = 0.3GeV/cm3. The S1 energy res-olution, governed by Poisson fluctuations, is taken intoaccount. Uncertainties in the energy scale as indicated inFig. 1 as well as uncertainties in vesc are profiled out andincorporated into the limit. The resulting 90% confidencelevel (CL) limit is shown in Fig. 5 and has a minimumσ = 7.0×10−45 cm2 at aWIMPmass ofmχ = 50GeV/c2.The impact of Leff data below 3 keVnr is negligible atmχ = 10GeV/c2. The sensitivity is the expected limit inabsence of a signal above background and is also shownin Fig. 5 as 1σ and 2σ region. Due to the presence oftwo events around 30 keVnr, the limit at higher mχ isweaker than expected. This limit is consistent with theone from the standard analysis, which calculates the limitbased only on events in the WIMP search region with anacceptance-corrected exposure, weighted with the spec-trum of a mχ = 100GeV/c2 WIMP, of 1471 kg × days.This result excludes a large fraction of previously unex-

plored WIMP parameter space, and cuts into the regionwhere supersymmetric WIMP dark matter is accessibleby the LHC [17]. Moreover, the new result challengesthe interpretation of the DAMA [19] and CoGeNT [18]results as being due to light mass WIMPs.

We gratefully acknowledge support from NSF, DOE,SNF, Volkswagen Foundation, FCT, Region des Pays dela Loire, STCSM, DFG, and Weizmann Institute of Sci-ence. We are grateful to LNGS for hosting and support-ing XENON.

∗Electronic address: rafael.lang@astro.columbia.edu

†Electronic address: marc.schumann@physik.uzh.ch

[1] G. Steigman and M. S. Turner, Nucl. Phys. B253, 375(1985); G. Jungman, M. Kamionkowski, and K. Griest,

Phys. Rept. 267, 195 (1996).

[2] N. Jarosik et al., Astrophys. J. Suppl. 192, 14 (2011);

K. Nakamura et al. (Particle Data Group), J. Phys. G37,075021 (2010).

[3] M. W. Goodman and E. Witten, Phys. Rev. D31, 3059(1985).

[4] J. D. Lewin and P. F. Smith, Astropart. Phys. 6, 87

(1996).

[5] Z. Ahmed et al. (CDMS), Science 327, 1619 (2010).

[6] E. Armengaud et al. (EDELWEISS) (2011),

arXiv:1103.4070.[7] E. Aprile et al. (XENON100), Phys. Rev. Lett. 105,

131302 (2010).

[8] E. Aprile et al. (XENON100) (2011), arXiv:1103.5831.[9] E. Aprile et al., Phys. Rev. C79, 045807 (2009).

[10] E. Aprile et al. (XENON100) (2011), accepted by PRD,

arXiv:1101.3866.[11] E. Aprile and T. Doke, Rev. Mod. Phys. 82, 2053 (2010).

[12] G. Plante et al. (2011), submitted to PRD and arXiv.

[13] F. Arneodo et al., Nucl. Instrum. Meth. A449, 147

(2000); D. Akimov et al., Phys. Lett. B524, 245 (2002);

R. Bernabei et al., Eur. Phys. J. direct C3, 11 (2001).

E. Aprile et al., Phys. Rev. D72, 072006 (2005). V. Che-

pel et al., Astropart. Phys. 26, 58 (2006). A. Manzur

et al., Phys. Rev. C81, 025808 (2010).

[14] E. Aprile et al., Phys. Rev. Lett. 97, 081302 (2006).

[15] E. Aprile et al. (XENON100) (2011), arXiv:1103.0303.[16] S. Yellin, Phys. Rev. D66, 032005 (2002).

[17] O. Buchmueller et al. (2011), arXiv:1102.4585.[18] C. E. Aalseth et al. (CoGeNT), Phys. Rev. Lett. 106,

131301 (2011).

[19] C. Savage et al., JCAP 0904, 010 (2009).

E.  Aprile  et  al.  arXiv:1104.2549v2  

R.  Bernabei  et  al.  J.  Phys.:  Conf.  Ser.  203  (2010)  012003  

DM-­‐Ice  Experiment  

11  May  2011   Walter  C.  Pe9us   3  

•  Expect  the  same  DM  signal  •  Opposite  muon  rate  –  Tagging  of  muons  by  IceCube/DeepCore  

•  Drilling  to  2500m  in  ice  established  –  No  temperature  fluctua,on  –  Ice  is  rela,vely  radiopure  •  No  radon  •  ppt  of  U/Th,  ppb  40K  

–  Ice  as  a  neutron  moderator  •  Infrastructure  at  Amundsen-­‐Sco9  South  Pole  Sta,on  

Cosmogenic  Ac,va,on  

•  Spalla,on  

•  Capture  

11  May  2011   Walter  C.  Pe9us   4  

€

ZA X n,γ( ) Z

A +1X

ZA X p,n( )Z +1

AY

ZA X µ−,ν( )Z −1AY

Produc,on  Rate  

11  May  2011   Walter  C.  Pe9us   5  

€

R ∝ dE φx E( )∫ σ E( )

! Rates presented in [2] are again compatible with our estimateswithin a factor "2, except for 58Co, with an enormous produc-tion much higher than in any other estimate.

From the comparison of production rates in Tables 3 and 4, theeffect of enrichment on activation can be studied. Only the enrich-ment percentage usual for DBD germanium detectors has been ta-ken into consideration. In general, production rates in enrichedcrystals are reduced to several tenths of the rates as in the naturalones. This is due to the suppression of the germanium isotopeshaving the lowest mass number and the highest productioncross-sections. However, according to our estimates, neither for60Co nor 63Ni production rates are reduced in enriched material;in [13] for these two isotopes the reduction of production ratesin enriched material is much lower than for the others. This behav-

ior for 60Co is corroborated by the available measured cross-sec-tions on individual germanium, as stated before.

One interesting point is to know which is the energy range ofnucleons giving the largest activation yields. Comparing the contri-butions to the production rates of HMS-ALICE below 150 MeV andYIELDX above 150 MeV in Tables 3 and 4, it is seen that for many ofthe induced nuclides high energy neutrons are the most relevantfor activation. But when considering natural germanium, this isnot true for 65Zn, and specially for 68Ge, for which"85% of the yieldcomes from neutrons below 150 MeV.

In the context of experiments searching for the neutrinolessDBD of 76Ge, the important production of 60Co and specially 68Gecould be a serious hazard. Fortunately, events entangled with theexpected signal in the region of interest are produced by variousenergy deposits and can be very efficiently rejected by means of

0.01

0.1

1

10

100

00001000100101 Energy (MeV)

Prod

uctio

n cr

oss

sect

ion

(mb)

Michel'86 Michel'97 Michel'95 Michel'89 Aleksandrov'90Aleksandrov'96 Greenwood'84 Mills'92 Grutter'82 MENDL(p)YIELDX MENDL(n) Kim'99(n)

Fig. 15. Comparison of excitation functions for 59Fe in natural copper by nucleons.

0.001

0.01

0.1

1

10

100

00001000100101 Energy (MeV)

Prod

uctio

n cr

oss

sect

ion

(mb)

Michel'95 Michel'89 Michel'97 Cumming'74 Orth'76Kozma'90 Mills'92 Greenwood'84 Yashima'03 Grutter'82MENDL(p) MENDL(n) YIELDX

Fig. 16. Comparison of excitation functions for 54Mn in natural copper by nucleons.

S. Cebrián et al. / Astroparticle Physics 33 (2010) 316–329 325

S  Cebrian  et  al.  Astropar,cle  Phys.  33  (2010)  316-­‐329.  

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

J.  Ziegler.  IBM  J.  of  R&D.  42  (1998)  117-­‐139  

Loca,on  and  Cosmic  Ray  Flux  

•  Contours  of  “geomagne,c  rigidity”:  

•  Flux  varia,on  with  rigidity:  

•  Up  to  a  factor  of  two  varia,on  in  flux  

11  May  2011   Walter  C.  Pe9us   6  

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

J.  Ziegler.  IBM  J.  of  R&D.  42  (1998)  117-­‐139  

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Al,tude  and  Cosmic  Ray  Flux  

•  Exponen,al  decay  of  nucleon  flux  with  atmospheric  depth:  

•  No  spectral  distor,on,  just  a9enua,on:  

11  May  2011   Walter  C.  Pe9us   7  

24. Cosmic rays 255

!

!"

!""

! !" !"" !"""#$%&'())*+%,-

!. "#$"!)*+%,

/ $01/) 2)2&3-

Figure 24.2: Di!erential spectrum of electrons plus positronsmultiplied by E3 (data from [15–22]) . The line shows theproton spectrum multiplied by 0.01.

p/p ratio also shows a strong dependence on the phase and polarityof the solar cycle [26] in the opposite sense to that of the positronfraction. There is at this time no evidence for a significant primarycomponent either of positrons or of antiprotons. No antihelium orantideuteron has been found in the cosmic radiation. The best currentmeasured upper limit on the ratio antihelium/helium is approximately7 ! 10!7 [27]. The upper limit on the flux of antideuterons around 1GeV/nucleon is approximately 2 ! 10!4 m2 s sr GeV/nucleon [28].

24.2. Cosmic rays in the atmosphere

Figure 24.3 shows the vertical fluxes of the major cosmic raycomponents in the atmosphere in the energy region where the particlesare most numerous (except for electrons, which are most numerousnear their critical energy, which is about 81 MeV in air). Except forprotons and electrons near the top of the atmosphere, all particles areproduced in interactions of the primary cosmic rays in the air. Muonsand neutrinos are products of the decay of charged mesons, whileelectrons and photons originate in decays of neutral mesons.

Most measurements are made at ground level or near the top of theatmosphere, but there are also measurements of muons and electronsfrom airplanes and balloons. Fig. 24.3 includes recent measurementsof negative muons [29–32]. Since µ+(µ!) are produced in associationwith !µ(!µ), the measurement of muons near the maximum of theintensity curve for the parent pions serves to calibrate the atmospheric!µ beam [33]. Because muons typically lose almost two GeV inpassing through the atmosphere, the comparison near the productionaltitude is important for the sub-GeV range of !µ(!µ) energies.

The flux of cosmic rays through the atmosphere is described bya set of coupled cascade equations with boundary conditions at thetop of the atmosphere to match the primary spectrum. Numerical orMonte Carlo calculations are needed to account accurately for decayand energy-loss processes, and for the energy-dependences of the crosssections and of the primary spectral index ". Approximate analyticsolutions are, however, useful in limited regions of energy [34,35]. Forexample, the vertical intensity of nucleons at depth X (g cm!2) in theatmosphere is given by

IN (E, X) " IN (E, 0) e!X/! , (24.3)

where " is the attenuation length of nucleons in air.The corresponding expression for the vertical intensity of charged

pions with energy E! # #! = 115 GeV is

I!(E!, X) " ZN!

$NIN (E!, 0) e!X/! X E!

#!. (24.4)

15 10 5 3 2 1 0

0 200 400 600 800 10000.01

0.1

1

10

100

1000

10000

Atmospheric depth [g cm–2]

Ver

tica

l flu

x [m

–2 s

–1 s

r–1 ]

Altitude (km)

µ+ + µ!

"+ + "!

e+ + e!

p + n

#µ + #µ_

Figure 24.3: Vertical fluxes of cosmic rays in the atmospherewith E > 1 GeV estimated from the nucleon flux of Eq. (24.2).The points show measurements of negative muons withEµ > 1 GeV [29–32].

This expression has a maximum at X = " "121±4 g cm!2 [36],which corresponds to an altitude of 15 kilometers. The quantityZN! is the spectrum-weighted moment of the inclusive distribution ofcharged pions in interactions of nucleons with nuclei of the atmosphere.The intensity of low-energy pions is much less than that of nucleonsbecause ZN! " 0.079 is small and because most pions with energymuch less than the critical energy #! decay rather than interact.

24.3. Cosmic rays at the surface

24.3.1. Muons : Muons are the most numerous charged particlesat sea level (see Fig. 24.3). Most muons are produced high in theatmosphere (typically 15 km) and lose about 2 GeV to ionizationbefore reaching the ground. Their energy and angular distributionreflect a convolution of production spectrum, energy loss in theatmosphere, and decay. For example, 2.4 GeV muons have a decaylength of 15 km, which is reduced to 8.7 km by energy loss. Themean energy of muons at the ground is " 4 GeV. For GeV muonsthere is also a solar activity and a latitude e!ect that results from thegeomagnetic e!ects. These two e!ects a!ect the GeV muon flux at the10% level. The energy spectrum is almost flat below 1 GeV, steepensgradually to reflect the primary spectrum in the 10–100 GeV range,and steepens further at higher energies because pions with E! > #!tend to interact in the atmosphere before they decay. Asymptotically(Eµ $ 1 TeV), the energy spectrum of atmospheric muons is onepower steeper than the primary spectrum. The integral intensity ofvertical muons above 1 GeV/c at sea level is " 70 m!2s!1sr!1 [37,38],with recent measurements [39–41] tending to give lower normalizationby 10-15%. Experimentalists are familiar with this number in theform I " 1 cm!2 min!1 for horizontal detectors.

T.  Gaisser  and  T.  Stanev.  PDG  

€

ʹ′ I = I e A − ʹ′ A ( ) /λ

GORDON et al.: MEASUREMENT OF THE FLUX AND ENERGY SPECTRUM OF COSMIC-RAY INDUCED NEUTRONS ON THE GROUND 3431

TABLE IDATA RELATING TO THE MEASUREMENT LOCATIONS

where is a normalization factor, and and depend on pres-sure (depth) and solar modulation. Values of these parametersfor solar minimum and maximum ( and ) were de-rived by BSY, and are given in the Appendix, along with a tableof values of for sea level and mid-value solar mod-ulation, normalized so . fits theobserved cutoff dependence and monthly-averaged solar modu-lation of the rates of many neutron monitors reasonably well forall the observed solar cycles except for the extremely low ratesbetween 1989 and 1991.

To compare our measurements at the different locations, fit(4) to them, and determine the best value for , we used theflux integrated above 10 MeV, because neutrons at lower ener-gies come partly from scatter in local materials which variedfrom site to site. The measured high-energy flux was divided by

at the cutoff and depth of each location. Our measure-ment with the most data, the one at Yorktown Heights, was doneat a time (November 2002) when neutron monitor count rateswere about 20% of the way from their typical minimum values,at , to their maximum values, at . Since we have pa-rameters from BSY only for and , we obtainedfor the time of the measurement by interpolating 20% of the wayfrom to .

Since the data from the 5 measurements presented herespanned a period of about 9 months, there was a slight changein the flux between measurements due to changes in solarmodulation. To compensate, the ratio of a neutron monitorcount rate at the time of each measurement relative to the timeof the Yorktown Heights measurement, , was used as ameasure of solar modulation, and this ratio was multiplied by

for the cutoff and depth of each measurement locationto obtain a solar modulation factor. This correction was 1% orless. Any neutron monitor could be used; we used data fromthe one in Newark, Delaware [30].

Table I shows data relating to each of the measurementlocations, including altitude, atmospheric depth, cutoff,

for November 2002, the solar modulation factor,and the value of resulting from a fit of (4) to thecorrected high-energy fluxes. The high energy flux data werecorrected by dividing by and the solar modulationfactor. The corrected data and the fit are shown in Fig. 5.

Fig. 5. Neutron flux above 10 MeV at 5 measurement locations as a function ofatmospheric depth (points). The data have been corrected for location-dependentgeomagnetic cutoff and variations in solar modulation as described in the textand fit with (4) (line).

Fig. 6. Measured neutron spectra for all five sites. Each spectrum has beenscaled to sea level at the cutoff of New York City and solar modulation forNovember 2002, as described in the text.

From the least-squares fit shown in Fig. 5, the neutron atten-uation length was determined to be . Thelargest fit residual occurred for the twodata points near sea level (Yorktown Heights and Houston) andamounted to 2.35%. If the measured flux had not been cor-rected for , the fitted attenuation length would have been135.0 and the fit to the data would not have been as good,with residuals of up to 4.2% and 4.9%.

To compare the shapes of the measured spectra at the 5 loca-tions, the spectra were scaled by applying the same correctionsused for the fit shown in Fig. 5 and then divided by foreach location (the last column of Table I). The resulting spectraare shown in Fig. 6. Above a few MeV, the spectra practicallylie on top of one another, justifying the assumption in (3) thatone spectral shape can be used at various locations, at leastfor the limited range of cutoffs covered by our measurements

M.  Gordon  et  al.  IEEE  Trans  Nuc.  Sci.  51  (2004)  3427-­‐3434.  

Flux  Adjustment  

•  Flux  scales  with  al,tude  (h),  rigidity  (Rc),  and  solar  cycle:  

–  Al,tude  dependence  (rela,ve  to  sea  level):  

•  Requires  conversion  from  al,tude  (H)  to  barometric  pressure  (h):  

–  Loca,on  dependence:  

•  Normaliza,on  factor  (N)  varies  with  solar  intensity  (I)  and  rigidity  (Rc)  

11  May  2011   Walter  C.  Pe9us   8  

€

h = 9.8025 ×10−4( ) 1033.7 − 0.03648( )H + 4.26 ×10−7( )H 2( )€

φ = φ0 *Falt (h) *FBSYD(Rc,h,I)

€

Falt = e hSL −h( ) /λ

€

FBSYD = N Rc,I( ) 1− exp −αRck

⎛

⎝ ⎜

⎞

⎠ ⎟

⎡

⎣ ⎢

⎤

⎦ ⎥

€

α = exp 1.89 + 0.12h − 0.14exp −5.6h( )[ ]k =1.36 − 0.53h + 0.21exp −9.2h( )

Ac,va,on  Targets  

•  125  kg  NaI(Tl)  –  23Na  and  127I  

•  850  kg  OFHC  Cu  –  63Cu  (69%),  65Cu  (31%)  

•  450  kg  SS  2205  –  67%  Fe  (54,  56,  57,  58)  –  22%  Cr  (50,  52,  53,  54)  –  5%  Ni  (58,  60,  61,  62,  64)  –  3.2%  Mo  (92,  94-­‐98,  100)  –  2%  Mn,  1%  Si,  0.18%  N,  0.030%  C,  0.030%  P,  0.015%  S  

11  May  2011   Walter  C.  Pe9us   9  

Table 3: Radioactive daughter isotopes of crystal elements

Isotope Half-Life Decay Mode Production Channel(s)

3H 12.31 y β− 23

Na(n,21Ne)

3H,

127I(n,

125Te)

3H

22Na 2.60 y β+

24Na 14.96 h β− 23

Na(n,γ)24Na,23Na(n,γ)24mNa

125I 59.40 d EC

129I 1.57x10

7y β−

Table 4: Comprehensive list of daughter isotopes

Isotope Half-Life Production Channel(s)

3H 12.31 y

23Na(n,

21Ne)

3H,

127I(n,

125Te)

3H

24Na 14.96 h

23Na(n,γ)24Na, 23

Na(n,γ)24mNa

46Sc 83.79 d Spallation

48V 15.9735 d Spallation

54Mn 312.12 d Spallation

56Co 77.27 d Spallation

57Co 271.79 d Spallation

58Co 70.82 d Spallation

59Fe 44.503 d Spallation

60Co 5.2714 y Spallation

65Zn 244.26 d

65Cu(p,n)

65Zn

7Be 53.2 d Spallation

54Mn 312.2 d

56Fe(n,p2n),

56Fe(µ−

,ν2n)58Co 70.9 d

60Ni(n,p2n),

60Ni(µ−

,ν2n), 58Ni(n,p)

56Co 77.236 d

58Ni(n,p2n),

58Ni(µ−

,ν2n)46Sc 83.8 d Spallation on Fe

48V 16.0 d

52Cr(n,p4n),

50Cr(n,p2n),

50Cr(µ−

,ν2n)51Cr 27.70 d

52Cr(n,2n),

50Cr(n,γ)

52Mn 5.59 d

56Fe(n,p4n),

54Fe(n,p2n)

56Ni 6.1 d

58Ni(n,3n)

95Nb 34.99 d

95Mo(n,p),

96−98Mo(n,p1-3n)

4

Es,ma,ng  Ac,va,on  

•  Obtain  reference  ac,va,on  rate  (/kg/day)  – Standard  is  sea  level,  New  York  City  

•  Scale  to  component  mass  

•  Scale  reference  rate  by  appropriate  al,tude,  loca,on  factors  

•  Scale  to  exposure  ,me  for  each  stage  

11  May  2011   Walter  C.  Pe9us   10  

€

R = Rref * Falt (h)Falt, ref (h)

* FBSYD(Rc,h,I)FBSYD, ref (Rc,h,I)

Height  Profile  

•  PSL,  Stoughton,  WI  –  30  days  of  tes,ng  (876  n)  

•  Shipment  to  Christchurch,  NZ  (high  flight)  –  20  +  10  hrs  (35,000  n)  

•  Christchurch,  NZ  –  30  days  processing  (123  n)  

•  Shipment  to  Pole  (low  flight)  –  10  hrs  (21,000  n)  

•  South  Pole,  Antarc,ca  –  30  days  tes,ng  (9,000  n)  

11  May  2011   Walter  C.  Pe9us   11  

Ac,va,on  Es,mate  

•  Ac,va,on  at  South  Pole  dominates  (>  50%)  followed  by  high  flight  (>25%)  

11  May  2011   Walter  C.  Pe9us   12  

Table 7: Total Activation for trip(atoms)

Isotope Stoughton, WI Christchurch South Pole High Flight Low Flight Total

7Be 7524282 5136528 57765200 31093993 6306526 107826529

46Sc 433911 296214 331213 1793133 363686 6218157

48V 1050765 717315 8066902 4342272 880705 15057959

51Cr 4518862 3084847 34692074 18674134 3787513 64757431

52Mn 570210 389260 4377599 2356385 477925 8171379

54Mn 4670366 3188273 35855199 19300224 3914497 66928560

56Co 536101 365975 4115737 2215429 449336 7682577

56Ni 132074 90162 1013958 545796 110699 1892690

57Co 2707149 1848063 20783247 11187257 2269014 38794730

58Co 2957021 2018641 22701559 12219851 2478447 42375519

59Fe 684307 467149 5253543 2827890 573556 9806446

60Co 3158341 2156074 24247121 13051799 2647184 45260518

in Physics Research Section B: Beam Interactions with Materials andAtoms, 251(1):115 – 120, 2006.

[3] R. Bernabei, P. Belli, A. Bussolotti, F. Cappella, R. Cerulli, C.J. Dai,

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6

Conclusions  &  Extensions  

•  Unshielded  storage  at  the  South  Pole  will  lead  to  a  dominant  contribu,on  to  cosmogenic  ac,va,on  of  the  detector  

•  Based  on  given  exposures,  expected  cosmogenic  background  decay  rate  is  ~68  Hz  

11  May  2011   Walter  C.  Pe9us   13  

Further  Work  

•  Ac,va,on  in  the  crystal  was  not  calculated  because  produc,on  rates  were  unavailable  – Only  24Na  and  3H  expected  

•  Consider  effect  of  shielding  the  detector  under  ice  at  the  South  Pole  – What  thickness  of  ice  would  be  needed?  

•  Produce  plots  of  ac,vity  vs  ,me  for  full  pre-­‐deployment  schedule  

11  May  2011   Walter  C.  Pe9us   14