Nucl ear I nst rument s and Methods in Physi cs Resear ch A 344 ( 1994) 243- 249 Nort h-Hol l and Lar ge cal ori met ri c devi ces f or doubl e bet a decay and dar k mat t er A. Al essandr el l o, C. Br of f er i o, D .V. Cam i n, C. Cat t adori , O . Cr emonesi , E. Fi or i ni , A. Gi ul i ani , M . Pavan, G. Pessi na, E. Pr evi t al i *, L. Zanot t i Depart ment of Physi cs, Uni ver si t y of M i l ano and I NFN M i l ano, Vi a Cel ori a 16, 20133 - M i l ano, I t al y The use of cr yogeni c t hermal par t i cl e det ect or s per m its t he r eal i zat i on of det ect or s of var i ous composi t i ons, var i ous si zes and ver y good ener gy r esol ut i on . In par t i cul ar t hese char act er i st i cs ar e ver y pr om i si ng f or t he r eal i zat i on of doubl e bet a decay and dar k mat t er sear ch experi ment s . Our gr oup is mai nl y i nt er est ed mt he st udy of doubl e bet a decay of 130Te and 116Cd . For t el l ur i umwe have r eal i zed var i ous det ect or s usi ng Te0 2 cr yst al s, t he f i nal one with a mas s of 334 g For cadm i uma CdW04 cr yst al of 58 g has been used in var i ous t est s . The doubl e bet a decay measur ement has been per f or med in t he Gr an Sasso Under gr ound Labor at or y . Measurement s on t he 334 g Te0 2 cr yst al have been per f or med f or 3000 h . Det ect or r esol ut i on is ar ound 10 keV FWHM and t he i nt er nal cont am i nat i on of 23s Uand 232Th in t he cr yst al is of t he or der of 10 - 13 g/ g . A l ower lim it on t he hal f - l i f e of neut r i nol ess doubl e bet a decay f or 130Te of 8 .2 X 10 21 yr ( 90% CL) is measur ed . The t est measurement s of CdW04 r each an ener gy r esol ut i on of about 5 keV FWHM with a ver y hi gh ef f i ci ency to gamma r ay det ect i on . A lim it on t he neut r i nol ess channel of 7 X10 19 yr ( 90% CL) is eval uat ed in 340 h . In t hi s t est an end poi nt ener gy of 318 . 8±1 . 4±5 keV and a hal f - l i f e of (9 . 3±0. 5±1) X 10 15 yr f or t he bet a decay of 113 Cd ar e al so measur ed . The l ast par t of t he paper is dedi cat ed to a br i ef di scussi on of our pr oposal f or t he sol ar neut r i no f l ux measur ement and f or t he sear ch of dar k mat t er usi ng cr yogeni c det ect or s . 1 . I nt r oduct i on The r eal i zat i on of cr yogeni c t hermal det ect or s was pr oposed in 1984 by di f f er ent aut hor s [ 1, 2] . The new i dea is ver y si mpl e and at t he s ame time per m its t he st udy and r eal i zat i on of a new ki nd of det ect or . In f act when a par t i cl e i nt er act s with a sol i d st at e mat eri al , it r el eases mos t of its ener gy as heat . St ar t i ng f r om t hi s poi nt it is cl ear t hat a det ect or t hat is abl e to measur e t he heat pr oduced by a par t i cl e i nt er act i on can r each ver y good per f or mance in ener gy r esol ut i on . In par t i cu- l ar a t hermal det ect or measur es t he ener gy car r i ed by t hermal phonons pr oduced by t he par t i cl e ener gy de- posi t ed i nsi de t he mat eri al . For a good ener gy r esol ut i on it is necessar y to eval uat e t he amount of ener gy necessar y to cr eat e an el ement ary ener gy car r i er event . In t he case of ger ma- ni um det ect or s t he ener gy needed to gener at e a hol e- el ect r on pai r is about 3 eV. The ener gy of t he t hermal phonons i nsi de a cr yst al is pr opor t i onal to kT ( wher e k is t he Bol t zmann const ant and T is t he t emper at ur e) . In or der to have a m i ni mum val ue of ener gy per phonon gener at i on it is necessar y to put t he det ect or s at ver y l ow t emper at ur e . Normal l y t he cr yogeni c t her - mal det ect or s ar e oper at ed at a t emper at ur e ar ound 10 mK, wher e kT is f ew t ent h of l t eV. * Cor r espondi ng aut hor . 0168- 9002/ 94/ $07. 00 C 1994 - El sevi er Sci ence B.V. Al l r i ght s r eser ved SSDI 0168- 9002( 93) E1080- H The t heor et i cal ener gy r esol ut i on of t hi s t ype of det ect or s is def i ned by t he t hermodi nam i cal r el at i on t1 E= ~( kT 2 C) 1 / 2 , wher e C is t he t hermal capaci t y of t he det ect or and ~ is a paramet er connect ed to t he t ype of t hermal sensor used . The t hermal capaci t ance f or a di el ect r i c and di amagnet i c cr yst al is descr i bed with t he Debye l aw: 3 C=1944T M ~T ° ) , NUCLEAR I NSTRUMENTS & METHODS IN PHYSI CS RESEARCH Sect i on A wher e mis t he mas s of t he cr yst al , m, is t he mol ecu- l ar wei ght and T o is t he Debye t emper at ur e . Fr om t hi s f ormul a it is cl ear t hat t he heat capaci t y decr eases with t he t hi r d power of t emper at ur e and it is di r ect l y pr o- por t i onal to t he mas s . For t hese r easons it is mor e si mpl e to r each ver y hi gh r esol ut i on usi ng a ver y smal l det ect or t han usi ng a l ar ge mas s det ect or . The best r esul t with a t hermal det ect or was obt ai ned with a ver y smal l si l i con cr yst al by t he NASA- W i nsconsi n col l abo- r at i on . Thi s devi ce pr esent s a r esol ut i on of 7 .3 eV exposed to X- r ays of " Fe [ 3] . Typi cal l y t he smal l si l i con det ect or has been r eal i zed in a monol i t hi c st r uc- t ur e . The si t uat i on of t he l ar ge devi ce is qui t e di f f er ent because, in gener al , t he r eal i zat i on of t he det ect or needs t he connect i on bet ween t he absor ber ( t he par t of t he det ect or in whi ch t he i nt er act i ng par t i cl e r e- l eases its ener gy) and t he sensor ( t he par t t hat conver t s VI I . UNDERGROUND DETECTORS