Gd Loading in Water Mark Vagins University of California, Irvine Homestake Detector Fermilab October 12, 2007

Based on work we first did in 2002 here at Fermilab, John Beacom and I wrote the original GADZOOKS! (Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super!) paper in late It was published the following year: [Beacom and Vagins, Phys. Rev. Lett., 93:171101, 2004]

In a nutshell, we proposed a way to tag neutrons produced by the inverse beta process (from supernovae, reactors, etc.) in light water: e + p e + + n ( =~4cm,  =~20  s) At the 100’s of kton scale and beyond, the only way to see neutrons is a solute mixed into the water... Much beyond the kiloton scale, you can forget about liquid scintillator, 3 He counters, or heavy water! Water soluble GdCl 3 or Gd(NO 3 ) 3 should do the trick! They’re (recently) affordable, have low toxicity and reactivity, and once dissolved are quite transparent.

All of the events in the present SK low energy analyses are singles in time and space. And this rate is actually very low… just three events per cubic meter per year.

0.1% Gd gives >90% efficiency for n capture In Super-K this means ~100 tons of water soluble GdCl 3 or Gd(NO 3 ) 3 Gadolinium has 1500X the n capture cross section of Cl

But, um, didn’t you just say 100 tons? What’s that going to cost? In 1984: $4000/kg  $400,000,000 In 1993: $485/kg  $48,500,000 In 1999: $115/kg  $11,500,000 In 2007: $5/kg  $500,000

This positron/neutron capture coincidence technique is readily scalable to megaton class detectors at ~1% of their total construction cost, with one important caveat: In order to be both big and sensitive, ~40% photocathode coverage (or the equivalent in terms of photon collection) is required in at least part of the detector. Hyper-K UNO M3 MEMPHYS

As an example: adding 100 tons of soluble Gd to Super-K would provide at least two brand-new signals: 2) Discovery of the diffuse supernova neutrino background [DSNB], also known as the “relic” supernova neutrinos (~5 events per year) 1)Precision measurements of the neutrinos from all of Japan’s power reactors (~5,000 events per year) Will improve world average precision of  m 2 12 by 7X

Here’s what the coincident signals in Super-K-III with GdCl 3 or Gd(NO 3 ) 3 will look like (energy resolution is applied): Most modern DSNB range

In addition to our two guaranteed new signals, it is likely that adding gadolinium to SK-III will provide a variety of other interesting possibilities: Sensitivity to very late-time black hole formation Full de-convolution of a galactic supernova’s signals Early warning of an approaching SN burst (Free) proton decay background reduction New long-baseline flux normalization for T2K Matter- vs. antimatter-enhanced atmospheric samples(?)

How good a job can Super-K do - by itself - on the solar neutrino parameters? = ~3 years with gadolinium = 4.1 live years of data without gadolinium

KamLAND alone SK + SNO + KamLAND SK + SNO + Ga + Cl + KamLAND (all of the world’s data) ~3 years of GADZOOKS! (by itself)

Our proposal has definitely been getting some attention: At NNN05, before I had even given my talk, John Ellis suddenly stood up and demanded of the SK people in attendance: Why haven’t you guys put gadolinium in Super-K yet? As I told him, studies are under way…

…since we need to know the answers to the following questions: What does gadolinium do the Super-K tank materials? Will the resulting water transparency be acceptable? How will we filter the SK water but retain gadolinium?

Gadolinium R&D The total American R&D funding for this gadolinium-in-water project has reached $400,000, with additional support coming from Japan. So, can we make it work?

Over the last four years there have been a large number of GdCl 3 -related R&D studies carried out in the US and Japan:

What we really want is selective filtration. Adding nanofiltration (NF) to ultrafiltration (UF) and reverse osmosis (RO) could make this possible. }

UltrafilterNanofilter DI/RO Impurities to drain (RO Reject) Pure water (RO/DI product) plus GdCl 3 or Gd(NO 3 ) 3 back to detector Pure water plus GdCl 3 or Gd(NO 3 ) 3 from detector GdCl 3 or Gd(NO 3 ) 3 (NF Reject) Water “Band-pass Filter” [Undergoing testing at UCI] GdCl 3 or Gd(NO 3 ) 3 plus smaller impurities (UF Product) Impurities smaller than GdCl 3 or Gd(NO 3 ) 3 (NF Product) Impurities larger than GdCl 3 or Gd(NO 3 ) 3 (UF Reject)

On another R&D front, gadolinium has unusually strong magnetic properties – hence its widespread use as a contrasting agent in MRI scans: SubstanceMagnetic Susceptibility Gadolinium+185,000 Iron Chloride+14,750 Copper Chloride +2,370 Iron Sulfide+1,074 Copper Oxide-20

So - if funding allowed - it would be great to investigate using magnetic fields as a selective gadolinium filter. Method 1: Low Intensity Magnetic Separation

Method 2: High Gradient Magnetic Separation

6.5 m Laser Pointers/ N 2 Dye Laser Depth Normalized Light Intensity IS/PD Water with Gd(NO 3 ) 3 IS/PD IDEAL: Irvine Device Evaluating Attenuation Length This is an upgrade of a 1-meter long device successfully used for IMB [UCI High Bay Building]

Attenuation Curves Data taken September 2007 in pure water [plots by M. Smy]

Preliminary Measurement (Pure Water) [plot by M. Smy] Encouraging, but errors are yet to be determined. Will 7 meters of vertical pipe be enough? We’ll need to measure changes of less than 1% in very clear (~100 m  ~95 m absorption length) water.

A longer lever-arm would be nice…but where to do it? Hmmmmm… 40 m

That’s it for now…