MINILENS - A Scalable Prototype Detector for LENS LONU-LENS: Mini-Workshop on Low-Energy Solar Neutrinos and LENS Blacksburg, VA, October Mark Pitt Virginia Tech

6 x 6 x 6 array of cubic cells, 12.5 cm on a side Optical foil segmentation cage InLS : 128 L PC Envelope (active shield) : 200 L Indium mass ~ 20 – 40 kg (8 – 16 % by weight) Read out with inch PMT’s (on three perpendicular faces; mirrors on other sides) MINILENS Final Test detector for LENS

MINILENS Final Test detector for LENS Goals for MINILENS Test detector technology  Medium Scale InLS production  Design and construction Test background suppression of In radiations by  Expect ~ 5 kHz In  -decay singles rate; adequate to test trigger design, DAQ, and background suppression schemes Demonstrate In solar signal detection in the presence of high background (via “proxy”) Direct blue print for full scale LENS

MINILENS Mark Pitt, Virginia Tech, October 2006 Cosmic Proton Secondaries CC -capture in 115 In to excited isomeric level in 115 Sn Excitation of the keV isomeric state via 115 In (p,n) from cosmic proton secondaries  can produce the same tag that mimics neutrino capture At 2000 mwe, this will be suppressed: BUT at surface this mechanism can be used as a PROXY for the solar neutrino events.

MINILENS Mark Pitt, Virginia Tech, October 2006 Indium  - -Background Topology – Space / Time coincidence Background Signal E( ) -114 keV 116 keV 497 keV 115 In 115 Sn e/    =4.76  s Background: Random time and space coincidence between two  -decays ( ); Extended shower ( ) can be created by: a)498 keV  from decay to excited state; b)Bremsstrahlungs  -rays created by  ; c)Random coincidence (~10 ns) of more  -decays; Or any combination of a), b) and c). Signal Signature: Prompt e - ( ) followed by low energy (e - /  ) ( ) and Compton-scattered  ( ) 115 In β 0 + n  (BS) (E max = 499 keV) 498 keV *Cattadori et al: 2003 β 1 (E max < 2 keV) (b = 1.2x10 -6 )* 115 Sn 

MINILENS Mark Pitt, Virginia Tech, October 2006 Proxy pp events in MINILENS from cosmogenic 115 In(p,n) 115 Sn isomers Pretagged via , p tracks Post tagged via 115 In(n,  ) and 230  s delay  Gold plated 100 keV events (proxy pp), Tagged by same cascade as In- events  Can measure detection efficiency of tag for our analysis cut scheme  Expect ~ 40 events of this type per year at the surface Proxy pp- events in MINILENS

MINILENS Mark Pitt, Virginia Tech, October In  -decay is a rare fourth forbidden unique type; current best measurements of it are from 1979 Bell Labs In-spectra with only ~ 100 g of In MINILENS will provide high statistics measurements of both the beta and bremsstrahlung spectra from 115In  -decay  needed to validate the input spectra currently being used in the Monte Carlo Recently there has been a claim of a rare < 2 keV endpoint energy beta branch in 115 In decay; these high statistics measurements could confirm its existence and measure its properties if it does exist (such a low endpoint energy case could be of interest to direct neutrino mass measurements) Physics from MINILENS

MINILENS Mark Pitt, Virginia Tech, October 2006 MINILENS: Scalable prototype LENS detector to test all the concepts and the technology developed so far & demonstrate Indium solar signal detection (via cosmic proton proxy) Summary ● Ongoing work on the optical foils Teflon identified as best material (nylon breaks down in the acidic PC) both single and double foil schemes being investigated Anti-reflection coating with SiO 2 nano-particles being investigated to minimize Fresnel losses Current work on MINILENS: Plan for MINILENS: First phase: Run at surface where we expect ~ 40 “proxy” events per year Second phase: Run at ~ 2000 mwe depth at the VT-NRL low background facility at the Kimballton mine